EEVblog Electronics Community Forum
Electronics => Power/Renewable Energy/EV's => Topic started by: Seekonk on June 01, 2015, 01:35:29 pm
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Some may be feeling that they are missing the solar power bandwagon and wondering how they can do something actually useful without spending a lot of money. Batteries and grid tie make a system expensive with a long payback. Creating hot water is the most effective way to use a couple of PV solar panels since close to 100% of the power generated will be used. This assumes you are currently using a resistive hot water tank and not on demand as the rest of the civilized world. Never could get used to climbing into a shower with a 240V line.I have been heating hot water for years with excess PV for years at my camp. With as little as 800WH, we can both get a long hot shower at the end of the day. Just a couple panels totaling 400W can make a significant dent in electric use for heating. Under powering the heater assures 100% of the panels output is used. That is much greater than any battery application and much lower in cost than grid tie which isn't even allowed in some locations. Typical heat loss during the daylight hours of a well insulated tank is more than 1KWH. Solar makes up for that loss.
Most tanks have two heating elements. The top is the primary and only one operates at a time. That allows the lower resistive element to be used for solar and still have grid power backup. At 240V even a 5500W element is 10 ohms, a replacement 120V 2000W is about 7 ohms. That requires at least a 36V panel string tog et any useful power. One positive is that may keep the system classified as "low Voltage". Connecting a panel directly to a resistance will result in power losses of more than half. A simple PWM circuit keeps the panel voltage at the the power point. A small capacitor bank stores the panels power in the off cycle. A panels power point voltage is the same regardless of light level. It only varies with temperature. Attaching a couple of flat pack diode bridges to the back of the panel is an easy way to get a reference voltage tracks panel temperature. I use a $5 UNO to control everything and the 490Hz PWM makes driving a FET easy. Almost any switchmode chip would work just as well.
I'm not going to argue the economics of it. Watching solar work is just plain fun and panel prices are so cheap now. Everyone has some space they can stick a few panels on. It won't freeze and none of the plumbing issues of direct solar heating. I've built several versions with just junk box parts. I have more real world details if anyone is interested. This discussion is NOT open to direct solar heating
I think this form of hot water assist will be commonplace in another ten years. Here is a "commercial" unit that sells for $270. I believe it is a very poor design and do not recommend it. The explanation is sufficient that I don't have to duplicate it. http://techluck.com/ (http://techluck.com/)
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The voltage at the maximum power point also depends on radiation levels. It gets high at more radiation. This gets obvious if you include the point were open circuit voltage gets below the assumed optimum voltage. Also PWM at only 500 Hz needs rather large capacitors to get ripple down. The way to go would be a normal switched mode regulator. Another option might be switching a different number of heaters in parallel - so choose from 2 to 10 heaters in parallel, to get a useful power.
The downside of only using 36 V or so is that one needs relatively thick cables, not to loose to much in the cables. 400W peak power likely would not give enough for a shower - maybe not even compensate for the losses.
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This is the difference between thinking and knowing. The point of this discussion is that with as little as 400W of panels you can do something useful and that nearly all the power generated is used. If you were to have enough panels to supply all the hot water needs a lot of the energy would be wasted. I have a camp and 90% of the time we we can both have showers every day with about 600W of panels. I have a 10 and 20 gallon tank in series. When the first heats up power is diverted to the second. Many times after taking a shower the water is hotter than when I started.
A 36V string has a power point of around 50V and cable size is only #12. This year it will be a 48V as I reconfigure the charging system. Solar also run the fridge. Capacitor bank is about fifteen 330uF capacitors out of PC power supplies. PWM is generated 30 feet away and driver is an opto isolator. A good reason for slow and there is no FET heating. I monitor total power and 800WH gets me a shower, A little over a KWH a really hot shower.
You don't likely use a tank, but I have monitored heat loss during 12 hours of non use at night at 1600WH. While it seems absurd to use solar just to cover heat loss during the daylight hours, this is reality in the US. The controller is cheap (<$20) and easy to build. This is the most cost effective way to use a small solar system.
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Sorry, but if you want to heat water, best to heat it directly with a solar water heater.
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Sorry, but if you want to heat water, best to heat it directly with a solar water heater.
It could be if you only wanted hot water, but using the excess electricity from a rooftop solar stored as hot water is a cheap way for most PV solar installs to reduce their payback period.
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Sorry, but if you want to heat water, best to heat it directly with a solar water heater.
It could be if you only wanted hot water, but using the excess electricity from a rooftop solar stored as hot water is a cheap way for most PV solar installs to reduce their payback period.
I agree with Someone. I have a direct solar powered hot water system and it is great, but the idea suggested doesn't require any special installation apart from the PV cells which are installed for other purposes. Using excess PV capacity this way appears very sensible and economic.
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The topis is "Wanting to get into solar? Think HOT WATER", not "Want to use your current system more efficiently?".
I agree. If you have a solar system right now that is sitting idle some of the time, then divert the output to heating water if you can. Not all grid tied system are allowed to do that in all jurisdictions. So yes, divert your lost production to heating water or some other useful thing.
If you are "starting", then the best way to heat water is directly with a solar water heater.
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If you are "starting", then the best way to heat water is directly with a solar water heater.
If you had asked me this question a few years ago, I would have had the same response. That has been the conventional thinking for a long time. But the equation has changed recently with the extreme decrease in PV prices and also with the introduction of heat pump water heaters.
Direct solar hot water heating has a lot going for it. Simple and low tech. But - the plumbing is susceptible to corrosion issues and these systems are not maintenance free.
Using PV to heat hot water is starting to make more sense - both economically and practically. I considered adding a direct solar hot water system a few years ago. But looking into it I realized I could add more PV and a Nyle Geyser heat pump to my existing system for a lot less money and with less long term maintenance issues.
As far as using excess PV production to heat water (for those who can't sell excess to the grid) several people are using the programmable auxillary outputs from their MPPT charge controllers (eg the Midnite Classic) to drive SSRs which control power to resistive heating elements.
As far at the OP's idea - sounds reasonable but the link provided leads one to a web page promoting this simple board (http://www.ebay.com/sch/osan3156/m.html) selling for $275!!!! :wtf:
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Anything that has water in it is susceptible to corrosion. The other thing is that adding an electrical system to heat water is going to need permits and certified installers or an inspection afterward. I see your point about the dropping prices making PV production lower I still think that direct heating i the most economical and easiest way. Without hard numbers from a a properly conducted study, I am just going by experience. If you have a something with hard numbers I am very interested.
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I cannot wrap my head around using super low-efficiency PV to heat water. Trying to get it, but it seems so senseless.
I have been experimenting with a solar steam generator for fun. From my minimal knowledge, it seems that you need a LOT more PV surface area and complexity to heat water electrically.
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I cannot wrap my head around using super low-efficiency PV to heat water. Trying to get it, but it seems so senseless.
Watch some of the eevblog videos on Daves solar install, noting the tariffs paid for electricity. During periods of high PV solar generation the excess flows into the grid and those without artificially inflated feed in tariffs get paid a fraction of the price they buy electricity for, much less than the "off peak" discounted rate that some people heat their hot water from.
Assuming that:
a) the household needs a daily supply of hot water
b) the electricity from the solar panels is sold for much less than what you could buy the same energy for
c) the house already has a storage type water heater.
Using that excess cheap power to heat the water that would have been heated by some other energy source anyway is a quick way to improve the cost effectiveness of the system. You can assess the investment of a small solar system to do this against the cost of changing to a different hot water heater, direct solar hot water (most have boosters) or a heat pump, and the answer is different for different people. But as a typical case for most people adding some solar capacity or extending their solar system to the hot water storage is a very short payback.
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If you are "starting", then the best way to heat water is directly with a solar water heater.
For a completely greenfield install, solar heated thermal storage for both climate control and domestic hot water would be a strong contender but very few people get the chance to start from the ground up.
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I see your point about the dropping prices making PV production lower I still think that direct heating i the most economical and easiest way. Without hard numbers from a a properly conducted study, I am just going by experience. If you have a something with hard numbers I am very interested.
Lets do some numbers here.
http://users.tpg.com.au/users/robkemp/Power/HotWater.htm (http://users.tpg.com.au/users/robkemp/Power/HotWater.htm)
Daily losses of 2kW/h give or take.
http://reneweconomy.com.au/2013/graph-of-the-day-australian-retail-electricity-prices-in-2020-2020 (http://reneweconomy.com.au/2013/graph-of-the-day-australian-retail-electricity-prices-in-2020-2020)
A typical electricity price in Australia was 25 cents per kWh.
We can keep the estimates round at $200 per year, just to maintain hot water on standby (not counting the used hot water).
Delivering 2kW/h per day average from 500W of panels is typical, to smooth it out and ensure you can keep up the 2kWh through winter you might want to bump that up to a 1kW system. ***Insert your cost estimate here and divide by $200 per year***
http://www.sustainability.vic.gov.au/services-and-advice/households/energy-efficiency/at-home/hot-water-systems/hot-water-running-costs (http://www.sustainability.vic.gov.au/services-and-advice/households/energy-efficiency/at-home/hot-water-systems/hot-water-running-costs)
Looks like a winner to me, even more so when you count the offset energy consumption of the hot water used (which would be another 4-6kWh additional).
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The other thing is that adding an electrical system to heat water is going to need permits and certified installers or an inspection afterward.
In Australia (and I assume many other nations) the elegance is you can install a solar PV system and connect it to anything you like other than the power grid, without any need for licensed tradespeople or permits.
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This worked for me for camping:
http://www.amazon.com/Coleman-Sun-Shower%C2%AE-Portable-Shower/dp/B000NVC1JY (http://www.amazon.com/Coleman-Sun-Shower%C2%AE-Portable-Shower/dp/B000NVC1JY)
But if you want to actually drive a generator, well a sterling engine with a big parabolic mirror to boil the water to create the steam needed.
https://www.google.com/search?q=stirling+engine+solar&tbm=isch (https://www.google.com/search?q=stirling+engine+solar&tbm=isch)
But you need a sunny place, PV works on cloudy days, that wont.
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The other thing is that adding an electrical system to heat water is going to need permits and certified installers or an inspection afterward.
In Australia (and I assume many other nations) the elegance is you can install a solar PV system and connect it to anything you like other than the power grid, without any need for licensed tradespeople or permits.
I am not trying to be a naysayer. What I am trying to say is that if you already have a system hooked up to the grid, and wish to use it to also heat water, you now have to deal with the regulations of using the grid tie system to do other things. I am not saying you could not use a stand alone solar system to heat water, just that I am still not convinced it is more cost efficient than heating water directly with the sun.
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But if you want to actually drive a generator, well a sterling engine with a big parabolic mirror to boil the water to create the steam needed.
On a point of information, Stirling engines don't run off steam and don't need a boiler.
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The other thing is that adding an electrical system to heat water is going to need permits and certified installers or an inspection afterward.
In Australia (and I assume many other nations) the elegance is you can install a solar PV system and connect it to anything you like other than the power grid, without any need for licensed tradespeople or permits.
I am not trying to be a naysayer. What I am trying to say is that if you already have a system hooked up to the grid, and wish to use it to also heat water, you now have to deal with the regulations of using the grid tie system to do other things. I am not saying you could not use a stand alone solar system to heat water, just that I am still not convinced it is more cost efficient than heating water directly with the sun.
If you've already got a grid tie system (with net metering) then its simply modifying/building a plug in appliance, again not requiring any licensed tradespeople in the countries I am familiar with, you lose some efficiency going through the inverter but the implementation is cheaper than those solutions adding a DC heating circuit.
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Sorry I wasn't clear in my definition of "grid tie". Many people just have solar panels that push back to the grid, without any useful connection to their house. This is what I meant and is not really what should be called a "grid tie system". My error, sorry.
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But if you want to actually drive a generator, well a sterling engine with a big parabolic mirror to boil the water to create the steam needed.
On a point of information, Stirling engines don't run off steam and don't need a boiler.
I thought it was due to the expansion of a gas and usually they use water for it, I guess I have to read up on them.
I do understand they don't need a boiler but I thought it was steam powered but not in the conventional way.
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It seems like a more efficient way to heat water with a PV system would be to run the water under the panels, solar panels get less efficient as their temperature goes up, keeping them cool and pre-warming water on its way to your heater seems like a win-win situation. You get solar heating and solar electricity at the same time.
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I thought it was due to the expansion of a gas and usually they use water for it, I guess I have to read up on them.
I do understand they don't need a boiler but I thought it was steam powered but not in the conventional way.
Stirling engines usually use air as the working fluid. Here's a very nice one that someone built. It uses heat from a wood burning stove to circulate warm air around the room:
https://youtu.be/XzE7pkIknmQ
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Sorry I wasn't clear in my definition of "grid tie". Many people just have solar panels that push back to the grid, without any useful connection to their house. This is what I meant and is not really what should be called a "grid tie system". My error, sorry.
It all depends on the metering scheme, net metered you can use the power from the grid tied system as you wish. Its the gross metering systems where you have no control and always pay full tariff, removing any incentive to time shift loads.
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Anything that has water in it is susceptible to corrosion. The other thing is that adding an electrical system to heat water is going to need permits and certified installers or an inspection afterward. I see your point about the dropping prices making PV production lower I still think that direct heating i the most economical and easiest way. Without hard numbers from a a properly conducted study, I am just going by experience. If you have a something with hard numbers I am very interested.
I can't give you "hard numbers from a properly conducted study". I can give a quick analysis of what it looks like for me. I installed a Nyle Geyser heat pump water heater (http://water.nyle.com/residential/) and the measured power it uses to keep our home (2 adults and 2 small kids) in hot water is 2 to 3 kWh per day with normal use. Obviously the amount of PV needed to provide this will depend on the solar insolation but of course so would the area of direct solar water heating panel needed.
For my location, 1,000 watts of PV can produce this on most days. Since i already have a PV system, the cost of adding the additional PV is about $1/watt (I paid $0.72/watt for my panels). The Nyle Geyser cost me about $700 IIRC. So about $1700 total (I did my own install). BTW Permit fee here in WA state for this is less than $100 and in my case I was already expanding my system so no extra cost.
To get the equivalent with direct solar hot water heating, i would have to install a 40 sq ft closed loop system (it freezes here) for about $4000 (assuming i could install it myself which is questionable!).
Also since i have grid tied PV system (with battery back up), i can sell any excess PV back to the grid on sunny days.
I realize my situatuon is different from someone who doesn't already have a PV system in place and i'm not arguing that using PV to heat water always makes more sense than direct solar water heating. It's just that the previously held common wisdom that heating water with PV never makes sense is no longer true given the low cost of PV now.
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What I would like to see is an open hardware inverter specifically designed to drive a common split phase refrigeration or A/C compressor direct off solar to make a heat pump. It could fall back to resistive when there's not enough power to operate the compressor.
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I live in the middle of nowhere in the desert and have a gravity hot water system with a non-pressurized solar hot water system. It gets down to -15C at night in the winter. My system is a 200L tank with double wall glass tubes with a vacuum that heat the water. I have to keep the water trickling when the temp gets below zero to keep things from freezing in the pipes to the house but that is because I haven't taken the steps to keep it from freezing in the pipes. The tank and tubes have no problem with below freezing. I have enough water for two people with this system. The systems cost me $500 plus plumbing. Hard to beat that for cost!
So it depends on what you expect and/or need from a system. There is no way I could do a proper hot water heating system with PV energy for under $4000 here. I just happen to have a 3kW soar system with a big battery bank that is charge before 2pm so yes I could also heat water with an electric heater but my system cost much more than $10000.
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http://www.immersun.co.uk/ (http://www.immersun.co.uk/)
I saw these guys at New Electronics last month. I know its UK based, but its a system where energy its can't dump into your gird, it dumps into an immersion heater.
They did let us take the top of one of their units and poke around though!
Rather than hot water: guy i work with had seen an idea where the energy not used powers a compressor and stores it as compressed air...then use the compressed air to run a turbine generator, as and when.
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I really can't understand the logic of using a PV panel to power a resistive heater and letting all that potential heat gain go to waste and all that electricity for powering other essentials in the evening go to waste, ok if your offgrid batteries are fully topped off and there is nothing else to do with them but a basic thermal collector is the kind of thing I was discovering when I was filling a paddling pool with a hosepipe at about six years of age. Even in the UK it worked, but then again we had endless summers decades ago.
I've installed and used PV panels in some very remote locations, but they have all been tiny panels, no arrays, 10 - 30W mainly with a few at around 100W. Washing in hot water powered by the PV wasn't ever a design requirement or even something that would be tagged on as a desirable.
If I really wanted hot water for a shower in the middle of nowhere and had a roof at a suitable angle and orientation, by choice I'd always heat the water directly with a panel, maybe made of corrugated sheet covered by a glass panel. Trickling water using a circulating pump powered with a small PV panel or as they have done in the south of Italy and in Greece for many decades, big pipes, a large header tank and a thermosyphon.
Of course with the way some grid connected PV is metered (or not), in the assumptions made on the level of export (such as 50% of PV Generated), or in the payments from that export, all that you can use locally often benefits you to a greater extent than extra income (if any)
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Compressed air is a rather low efficiency way of storing energy. Normal compressors and air powered tools combined give about 10% efficiency. With a better turbine you might end at 2-3 times that, still far from efficient. Batteries are much more efficient.
Having PV to supply electricity as a main function and only spend excess energy to make hot water is a different thing. Then on usually already makes 50/60 Hz AC from it. So one can use standard AC water heaters as well, and PV voltage is more in the 600 V range.
Having a local isolated grid just for your home is a rare case.
Depending on how much you get paid for electricity this might be economic, though rates are subject to change. At least in much of Europe this may mean you save a little in summer, but have an expensive way of making hot water for the rest of the year, when the sun is not enough. You also might need a sizable buffer, as there will not be excess electricity every day or even every week.
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It is a common misconception that panel voltage varies with light intensity. Panels are a current source. The power point voltage of a panel for all practical purposes only varies with temperature. Tracking panel temperature is an effective way of creating a MPPT controller. Even having a fixed power point is effective enough if adjustment is made by season.
I just finished a test in May with a single 100W solar panel connected to my water heater. This is at location 39N latitude and should be fairly typical for many people. For a 23 day period, the average power created per day was 252WH. Lowest daily power was 126WH and the highest was 413WH. An interesting aspect of temperature was evident. Highest power create3d was 88.6W on a day with only 162WH
created for the day. Clouds kept the panel cool till that burst of sunshine came through. On the best day, 413WH was created but 57.7W was the maximum power. This is the reason "12V" panels have a 18V power point at 25C. A temperature they will only see in winter. 1KWH is a good estimate for 400W of panels.
Life isn't always simple. At my camp none of my solar panels are actually on my property. It can be difficult to find a place close to put solar, adding plumbing makes it even harder. Antifreeze, heat exchangers and pumps add a lot of cost. Throwing a couple hundred feet of garden hose on the roof isn't a solution. I don't think the title of the thread should change.
It is a simple idea. If electric is used to heat water, replace some of that with solar PV. Hardware wise this is a minimal solution if you only have a few hundred to spend. If you don't use a power point controlling solution, half the power will be wasted.
This is the same technology used in linear current boosting for remote pumping systems without batteries. You would think someone in the entire world would have some question about hardware or software. To paraphrase a famous astrophysicist when asked what aliens from another planet would think of us. They would think of us as chickens, something to eat.
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I really can't understand the logic of using a PV panel to power a resistive heater and letting all that potential heat gain go to waste and all that electricity for powering other essentials in the evening go to waste, ok if your offgrid batteries are fully topped off and there is nothing else to do with them but a basic thermal collector is the kind of thing I was discovering when I was filling a paddling pool with a hosepipe at about six years of age. Even in the UK it worked, but then again we had endless summers decades ago.
I've installed and used PV panels in some very remote locations, but they have all been tiny panels, no arrays, 10 - 30W mainly with a few at around 100W. Washing in hot water powered by the PV wasn't ever a design requirement or even something that would be tagged on as a desirable.
If I really wanted hot water for a shower in the middle of nowhere and had a roof at a suitable angle and orientation, by choice I'd always heat the water directly with a panel, maybe made of corrugated sheet covered by a glass panel. Trickling water using a circulating pump powered with a small PV panel or as they have done in the south of Italy and in Greece for many decades, big pipes, a large header tank and a thermosyphon.
Of course with the way some grid connected PV is metered (or not), in the assumptions made on the level of export (such as 50% of PV Generated), or in the payments from that export, all that you can use locally often benefits you to a greater extent than extra income (if any)
Same.
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Compressed air is a rather low efficiency way of storing energy.
Regardless of that they are now being installed for UPS/standby power installations in electricity substations in the UK, replacing 48v and 110v battery banks. Large capacity external compressors are already used on site for the switchgear.
http://www.flowbattery.co.uk/case-studies/national-grid-case-study (http://www.flowbattery.co.uk/case-studies/national-grid-case-study)
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Isn't that compressed air just to run the sub station, it is 24kWhrs total, also remember compressed air makes a pretty dangerous device having seen an oxygen cylinder 'torpedo' across the room having had its regulator accidentally knocked off. Maintenance would be significant, rust on the inside is a significant issue in the long term.
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Isn't that compressed air just to run the sub station, it is 24kWhrs total, also remember compressed air makes a pretty dangerous device having seen an oxygen cylinder 'torpedo' across the room having had its regulator accidentally knocked off. Maintenance would be significant, rust on the inside is a significant issue in the long term.
I am not specifically familiar with that system. In general, the cylinders have a large margin of safety, safety valves, and they are all tied together. The compressors filter and dry the air so that water does not end up in the tank. Common practice for life supporting systems like SCUBA. Industrial cylinders have a very long maintenance free life. They are supposed to be tested periodically, but not as often as 3000psi SCUBA tanks.
I would totally believe that the maintenance would be low when used as standby only. It only appears to backup the logic of the operation. It is a LOT of bulk to make that much power. A traditional generator and on-site propane tank would be my choice.
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I really can't understand the logic of using a PV panel to power a resistive heater and letting all that potential heat gain go to waste and all that electricity for powering other essentials in the evening go to waste, ok if your offgrid batteries are fully topped off and there is nothing else to do with them but a basic thermal collector is the kind of thing I was discovering when I was filling a paddling pool with a hosepipe at about six years of age. Even in the UK it worked, but then again we had endless summers decades ago.
I've installed and used PV panels in some very remote locations, but they have all been tiny panels, no arrays, 10 - 30W mainly with a few at around 100W. Washing in hot water powered by the PV wasn't ever a design requirement or even something that would be tagged on as a desirable.
If I really wanted hot water for a shower in the middle of nowhere and had a roof at a suitable angle and orientation, by choice I'd always heat the water directly with a panel, maybe made of corrugated sheet covered by a glass panel. Trickling water using a circulating pump powered with a small PV panel or as they have done in the south of Italy and in Greece for many decades, big pipes, a large header tank and a thermosyphon.
Of course with the way some grid connected PV is metered (or not), in the assumptions made on the level of export (such as 50% of PV Generated), or in the payments from that export, all that you can use locally often benefits you to a greater extent than extra income (if any)
You get there in the end, its about the specific economic situation that most residential solar installations are in. Also note that installing an electricity storage system (battery, flywheel, etc) is both expensive and usually requires permits/licensing which storage as heat in hot water gets around.
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Installing PV solar just for hot water doesn't make much sense to me. Installing PV solar for hot water as a stepping stone to something else might make sense to me, but my first panels before I do a real installation are probably going to power my servers and network gear and a battery backup.
Using excess power from a PV installation to heat hot water makes perfect sense to me, particularly given how cheap panels are these days. If you are already grid tied, and have the space, it seems like the simplest thing would just be adding an extra electric tank water heater upstream of your existing water heater and powering that with the excess power.
I was thinking it might be fun to use excess power to refine aluminum, but that isn't too amenable to intermittent power. I guess there is always electrolysis.
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Isn't that compressed air just to run the sub station, it is 24kWhrs total, also remember compressed air makes a pretty dangerous device having seen an oxygen cylinder 'torpedo' across the room having had its regulator accidentally knocked off. Maintenance would be significant, rust on the inside is a significant issue in the long term.
The compressed air primarily has just operated the switchgear, and normally there would be a pair of 48v and 110v lead acid batteries for protection, tripping and SCADA equipment. It's replacing, at least for now, one of the pair of batteries. The compressed air needs to be of a high quality in terms of moisture and oil for the switchgear (it's the insulant as well as one of the means of extinguishing the arc) so it's already put through dessicant stacks and refrigerant driers. The claim is a 40 year asset life, there are fixed air receivers older than that right across the UK that are still servicable and insurable.
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We got a few solar panels for hot water and supporting the central heating (oil) and it really helps to reduce the oil consumption. Based on the sunshine the central heating runs from autumn to late spring only. The hot water is stored in a split tank (hot water and heating) of about 1000l. I think, in the summer the system could provide hot water for two or three houses easily, just would require some piping to the neighbours and more tanks :)
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Compressed air directly from the compressor contains quite some water, unless you live in a very dry dessert environment. If you don't want the water, this needs an extra dryer with extra costs, energy consumption and maintenance. If you just want hot water, the compressor still might work, as for 1 kW in, you get slightly more than 1 kW of heat and the compressed air in addition.
There are a few tests using large scale compressed air to store excess energy (e.g. solar or wind), but usually they don't use the air to directly drive a turbine, but to combine it with natural gas, to get something like a gas turbine with decoupled air compression. So the compressed air is used to get a very high efficiency gas turbine when needed. Something like half (or more) of the energy still comes from the burned gas. Even with this trick efficiency is not that great.
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Creating hot water is the most effective way to use a couple of PV solar panels since close to 100% of the power generated will be used.
Nope, PV solar panels have very low efficiency and it is loosing huge amount of energy so STE is the way to go with good ROI http://en.wikipedia.org/wiki/Solar_thermal_energy, (http://en.wikipedia.org/wiki/Solar_thermal_energy,) so you need store solar energy directly as a heat without any conversions to battery, etc
(http://www.folkecenter.net/mediafiles/folkecenter/rd/solar/Solar_thermal_collector.jpg)
So, you might need 3m parabolic mirror ot create decent CSP system and using additional sun tracker software position dish directly into the sun and have w few kW of thermal energy stored as a heat ready to use with high efficiency ;)
Future is now - 500 suns concentrated in vacum insulated absorber at 3m parabolic dish focus >:D
https://www.youtube.com/watch?v=6JL4q02gX7g (https://www.youtube.com/watch?v=6JL4q02gX7g)
This is free energy, look at those numbers in this video below description:
The new 15ft (4.5m) diameter SolarBeam is capable of providing 13kW (44,000 btu's) of thermal heat per hour. Unlike solar flat plate panels or evacuated tubes that lose efficiency with higher operating temperatures, the SolarBeam maintains a continuous 82% efficiency.
https://www.youtube.com/watch?v=o-eFwiraVv8 (https://www.youtube.com/watch?v=o-eFwiraVv8)
There are also other patents like this below-I like beter this idea of mounting such huge dish (10m), but its Fresnel lens probably costs a lot so much lower ROI than in the case of classic parabolic mirror, I guess :popcorn:
https://www.youtube.com/watch?v=3oN1nh-XWVo (https://www.youtube.com/watch?v=3oN1nh-XWVo)
Now you see, why I'm interested in 3m dish-because do not need so much power, but could easy cut mirrors into 5m diameter parabolic dish if wanted more :phew:
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SUN is: 2015-06-3.897 21:30:59 UTC (2457177.397 JD) lat: 50.***N lon: -20.***E Sun hour azimuth: -14.876 Sun (geo) azimuth: 194.876 Sun elevation: -16.230 Sun CSP power: 0.0 W Day of the year: 154
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Nope, PV solar panels have very low efficiency and it is loosing huge amount of energy so STE is the way to go with good ROI
PV efficiency is essentially irrelevant unless you are going to argue that sunlight is a limiting resource. PV efficiency only comes into play if you have a very limited area to place panels.
Efficiency of converting the power produced by PV into heat is a different issue and is not "very low", in fact depending on how you use that electricity to heat water it can be very good.
As I stated earlier, direct solar hot water heating is often the right solution but not always. Using PV to heat water can be both efficient and economically rational in some cases.
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There are also other patents like this below-I like beter this idea of mounting such huge dish (10m), but its Fresnel lens probably costs a lot so much lower ROI than in the case of classic parabolic mirror, I guess :popcorn:
https://www.youtube.com/watch?v=3oN1nh-XWVo (https://www.youtube.com/watch?v=3oN1nh-XWVo)
:o Jesus that's the biggest lenses I've seen! bet that's a bugger to clean, or worse, replace!
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In my first post I said I didn't want to discuss the economics or direct solar heating. There were certainly enough technical issues to discuss. Some have reasons other than economic for going into solar. In a prior post my experiments indicated 400W of solar would produce on average 1KWH a day. That investment of $500 would yield about 8% ROI with moderate electric rates and no government rebates.
The government energy star website indicates that an 11CF refrigerator uses 920WH a day. This is comparable with my water heating example. One person who is trying to save the world www.solar-trap.com (http://www.solar-trap.com) proposes operating your refrigerator with solar. This solution requires solar panels, charge controller, batteries, inverter, and
of course his custom board. I estimate the total outlay for this would be about $2,500 and the batteries would likely have to be replaced in six years. Small scale water heating is appealing for low cost and minimal hardware for the same KWH savings. As I am moving in four days, I don't have the time for further discussions.
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Nope, PV solar panels have very low efficiency and it is loosing huge amount of energy so STE is the way to go with good ROI
PV efficiency is essentially irrelevant unless you are going to argue that sunlight is a limiting resource. PV efficiency only comes into play if you have a very limited area to place panels.
Efficiency of converting the power produced by PV into heat is a different issue and is not "very low", in fact depending on how you use that electricity to heat water it can be very good.
As I stated earlier, direct solar hot water heating is often the right solution but not always. Using PV to heat water can be both efficient and economically rational in some cases.
Completely agree. Unless you only have access to very limited roof, this is a very good argument in the PV water heater. Making a small scale water heating system looks like is not economic anymore, and as the OP revealed, the heating system can be stripped down to the very basics, reaching higher efficiency than generating a mains electricity, lower cost and and overall more flexible system. It takes a certain size where a system is viable and by the looks of it, cheap PV is the best for small scale. Thank for sharing this, I can only hope others will understand that efficiency is not everything.
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If you use the electricity only to directly heat water, you can not compare the value to electricity rates. There are often cheaper sources of heat than direct electricity to a tank. Even if you use electricity this may be a only on demand system, so you have less loss. Anyway the buffer can be smaller in an electric system.
With very small systems the PV way may still be cheaper than direct thermal, as the wire is cheaper and easier to route than tubings. But due to lower efficiency you need something like 2-5 times the area.
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:o Jesus that's the biggest lenses I've seen! bet that's a bugger to clean, or worse, replace!
While polution might be obvious issue with such thermal solar CSP system, I've optomized my parabolic mirror dish to be able cover mirrors side and this way protect mirrors and let clean everything just using high presure water karcher.
Additionaly, its shape reminds everybody who see this first time... UFO on house roof, while 3m dish focus is choosen to have the same height from diameter circle center to bottom mirror and to vacum absorber-simple math and solving equation for parabola parameter A, whereL y=A*X^2, allows us find this perfect focus, which for 3m dish is ~1.1m ;)
This way even strong wind will create very small aerodynamic drag when we move our dish in horizontal position, so no worry about flying roofs :-DD
BTW: Putting many square meters of solar PV pannels at 15%max efficiency is like those solar roads :bullshit: with hopeless ROI, additionaly overall it destroys roof architecture design since those black PV pannels looks bad on nice red roofs, so I prefere to have 3m in diameter and 1m high UFO thermal solar and let neighbours and pedestrian guess what it might be :popcorn:
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BTW: Putting many square meters of solar PV pannels at 15%max efficiency is like those solar roads :bullshit: with hopeless ROI..
I think that's backwards.
No offense intended, but I think you and many others are misunderstanding Seekonk's concept and/or goals. (maybe I am?)
PV panels might not be as efficient as thermal systems, but that's not the point.
The goal isn't to power your house from hot water or maximize power output from a given area of land. Motives are purely financial. i.e. To find the best cost per watt solution, to hasten ROI and minimize initial capital investment that could be making money itself.
His apparent intention is to minimize cost per watt by eliminating the most expensive parts.. the inverter, grid tie solution, batteries and professional labor.
He is not suggesting a traditional PV install, but a much much cheaper version with the same panels. He is suggesting a system with a ROI measured in months, not years like a traditional PV installation or a TES.
It is also scalable from a smaller size, unlike thermal systems and traditional PV installations.
The initial investment would be one or two orders of magnitude less than those thermal systems you linked!
ALTHOUGH, I will say that this concept is only as scalable as the home's demand for hot water. Beyond that, it falls apart. .... unless you have another need for a poorly regulated intermittent power source.
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That is a pretty good summation. For the rest........
I can't believe it. You're trying to convince me to take the ugliest girl in town to the dance. You don't see it because she is your sister and all you can say is she is smart and has a good personality. I didn't take the prettiest girl, but she was easy.
If my neighbor told me he was installing direct solar I would tell him he is totally out of his mind. In some scale applications and climates it works. For the majority it doesn't work. Do any of you heat water with it? I didn't think so. In theory you focus on a small slice of the technology pie and ignore the rest of the system. One home program quoted $10,000 for a system. I've seen these home built systems on roofs and a few years later they are gone. I worked with a guy that had one. A few years later he couldn't keep it from leaking.
You are correct, my post promotes a small system. It only works if it is kept small and everything produced can be put into heating. The voltage remains low keeping it under the radar of many building codes. It can't produce that much heat so no plumbing is needed to install a tempering valve. Only a few panels are needed, enough to cover a garden shed. A system that is actually useful. A couple panels,
small controller and some wire. It could be put in a box and sold at Home Depot as a weekend project. It is like the brick they came around with to put in the toilet to reduce water consumption. With tens of thousands of homes doing it it makes a big difference. Two panels on every house would be a lot of energy.
This thread wasn't to encourage people to go out and buy panels. There are plenty of people who want to buy them just to play with solar. Just like all those who have a $1,000 digital scope who have no reason for more than an old Heathkit. I thought it would be a venue to discuss importance of operating panels at power point, power point tracking methods and circuit designs. So far it has been a waste of bandwidth with nothing but senseless dribble. I think we need a delete thread button.
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If you use the electricity only to directly heat water, you can not compare the value to electricity rates. There are often cheaper sources of heat than direct electricity to a tank. Even if you use electricity this may be a only on demand system, so you have less loss. Anyway the buffer can be smaller in an electric system.
With very small systems the PV way may still be cheaper than direct thermal, as the wire is cheaper and easier to route than tubings. But due to lower efficiency you need something like 2-5 times the area.
Due to their higher conversion efficiency,the direct solar hot water systems common in Australia have a very much smaller footprint than Solar panels for Electricity generation of similar capacity.
Boosters are useful on Solar HWS,but not essential in places with a reasonable amount of sunshine.
The maintenance comments are a "red herring",as the system proposed by the OP would need similar levels of maintenance.
After all,the storage tank doesn't know where the hot water came from,& needs most of the same facilities.
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The maintenance comments are a "red herring",as the system proposed by the OP would need similar levels of maintenance.
After all,the storage tank doesn't know where the hot water came from,& needs most of the same facilities.
The system proposed by the OP uses your existing electric hot water tank, adds a couple solar panels, some wire and a cheap circuit board. It's as simple as mounting a couple solar panels to the shed with some 2x4 treated lumber, running a wire and having a cool beverage.
The system proposed by the OP..
- Does not add pipes, tanks, PTC valves, check valves, directional control valves, elaborate insulation, closed loop 'refrigerants', mixing valves, expansion tanks, heat exchangers, pumps, electronic controllers, temp sensors or even a single additional joint.
- It does not use an inverter, grid tie solution, or batteries.
- There are no massive temperature fluctuations in the pipes/fittings causing expansion/contraction stresses.
- There is no worry of extra cold days causing freeze induced leaks, excessively hot days causing scaling, vapor lock, absorber fade, etc.
- There is no worry of equipment failure causing massive water/refrigerant leaking damage.
- There's no need to replace glazing, or refrigerants, recaulk seals, de-scale/drain the lines, or inspect for corrosion.
Maintenance of the OP's proposed system amounts to keeping snow off the panel.
Actually, in the spirit of this concept, you shouldn't even do that.. because it would unnecessarily push out the ROI. :D
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The maintenance comments are a "red herring",as the system proposed by the OP would need similar levels of maintenance.
After all,the storage tank doesn't know where the hot water came from,& needs most of the same facilities.
The system proposed by the OP uses your existing electric hot water tank, adds a couple solar panels, some wire and a cheap circuit board. It's as simple as mounting a couple solar panels to the shed with some 2x4 treated lumber, running a wire and having a cool beverage.
The system proposed by the OP..
- Does not add pipes, tanks, PTC valves, check valves, directional control valves, elaborate insulation, closed loop 'refrigerants', mixing valves, expansion tanks, heat exchangers, pumps, electronic controllers, temp sensors or even a single additional joint.
- It does not use an inverter, grid tie solution, or batteries.
- There are no massive temperature fluctuations in the pipes/fittings causing expansion/contraction stresses.
- There is no worry of extra cold days causing freeze induced leaks, excessively hot days causing scaling, vapor lock, absorber fade, etc.
- There is no worry of equipment failure causing massive water/refrigerant leaking damage.
- There's no need to replace glazing, or refrigerants, recaulk seals, de-scale/drain the lines, or inspect for corrosion.
Maintenance of the OP's proposed system amounts to keeping snow off the panel.
Actually, in the spirit of this concept, you shouldn't even do that.. because it would unnecessarily push out the ROI. :D
A solar HWS as used in temperate climates doesn't have much more than any storage HWS --the only largish addition is the solar absorber.
It doesn't use refrigerants of any kind,the electric wiring is only for the booster,which you can do without in a temperate climate.
In Australia,solar HWS operate with minimal maintenance for upwards of 20 years.
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I think this form of hot water assist will be commonplace in another ten years. Here is a "commercial" unit that sells for $270. I believe it is a very poor design and do not recommend it. The explanation is sufficient that I don't have to duplicate it. http://techluck.com/ (http://techluck.com/)
Seekonk- can you post more details and/or a schematic of your system?
I agree this type of system has merit but the link you provided has few technicial details and much of what it does say is just bogus - along the lines of "solar roadways" type nonsense.
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A solar HWS as used in temperate climates doesn't have much more than any storage HWS --the only largish addition is the solar absorber.
It doesn't use refrigerants of any kind,the electric wiring is only for the booster,which you can do without in a temperate climate.
In Australia,solar HWS operate with minimal maintenance for upwards of 20 years.
The system proposed by the OP is not a hot water storage system, so that's apples to oranges. The concept does not add additional hot water tanks and plumbing. It simply adds a couple solar panels to the existing electric water tank.
A solar HWS is an elaborate system ADDED to a home's existing water system. They involve most of what was already listed. i.e. pipes, tanks, valves, etc
Solar HWS systems without refrigerants/antifreeze are called open loop systems and require additional maintenance and equipment to avoid scale buildup and/or legionnaires disease, freezing pipes, etc. Systems that last twenty years are more likely closed loop and are like cars that last twenty years. i.e They were not the cheapest model and were regularly maintained.
The OP's concept is simple. A few solar panels can operate one of the two hot water tank heating elements directly, no inverter. Nearly all of the solar panel's energy (notice I didn't say nearly all of the SUN'S energy) is subtracted from how much electricity you would otherwise consume. The hot water tank already cuts off power at a given temperature.
The board linked by the OP is mostly BS. It simply toggles polarity at 50Hz to prevent the hot water tank's thermal switch contacts from welding shut. That's all you need though. No inverter, no grid tie, no plumbing just solar panels, wire and a cheap circuit board. MPPT would be nice, but meh.
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You don't even need to reverse polarity - just chopping the current is enough. And at that point, adding MPPT is so easy you might as well put it in, even if it's as simple as an opamp integrator controlling the duty cycle of the 555 or whatever based on input voltage.
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A solar HWS as used in temperate climates doesn't have much more than any storage HWS --the only largish addition is the solar absorber.
It doesn't use refrigerants of any kind,the electric wiring is only for the booster,which you can do without in a temperate climate.
In Australia,solar HWS operate with minimal maintenance for upwards of 20 years.
The system proposed by the OP is not a hot water storage system, so that's apples to oranges. The concept does not add additional hot water tanks and plumbing. It simply adds a couple solar panels to the existing electric water tank.
A solar HWS is an elaborate system ADDED to a home's existing water system. They involve most of what was already listed. i.e. pipes, tanks, valves, etc
Solar HWS systems without refrigerants/antifreeze are called open loop systems and require additional maintenance and equipment to avoid scale buildup and/or legionnaires disease, freezing pipes, etc. Systems that last twenty years are more likely closed loop and are like cars that last twenty years. i.e They were not the cheapest model and were regularly maintained.
The OP's concept is simple. A few solar panels can operate one of the two hot water tank heating elements directly, no inverter. Nearly all of the solar panel's energy (notice I didn't say nearly all of the SUN'S energy) is subtracted from how much electricity you would otherwise consume. The hot water tank already cuts off power at a given temperature.
The board linked by the OP is mostly BS. It simply toggles polarity at 50Hz to prevent the hot water tank's thermal switch contacts from welding shut. That's all you need though. No inverter, no grid tie, no plumbing just solar panels, wire and a cheap circuit board. MPPT would be nice, but meh.
Solar HWS replace the existing HWS in its entirety,& apart from the solar absorber have no parts that other systems don't have.
Their cost is competitive with other forms of HWS.
I've had one which lasted around 23 years,with minimal maintenance until I had to replace it,
The replacement will probably see me out.
Gas & Electrical storage HWS have all of the same potential problems of scale build up,etc.
OK.if you already have all the panels & are producing more energy than you need,the OP's idea is reasonable,but,if you live in a sub-Arctic climate where all the other stuff you mention would be needed for a direct Solar HWS,how much excess energy are your Solar panels going to produce in the first place? ;D
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People talk of solar systems in Australia and Florida, that is pretty low hanging fruit. Dealing with-20F has a whole different set of issues. Every site has different engineering solution. I find problems are technical and solutions are political. This PV solution is elegant with the infrastructure found in many homes. The greatest interest has been from people who have their water heater on a timer to get reduced night time electric rates. As far back as the 70's this was done in Vermont and oddly enough today in Ontario. I thought of that as the land of cheap hydro. For them adding solar has nothing but upside.
The control structure is fairly simple. My camp uses a UNO. I became acquainted with these a few years ago when I had to do a store animation project. Now I use $3 328 mini's for about everything. I haven't used a 555 since 1975 and don't intend to start. I have helped people with 555 problems as they are prone to doing unexpected things. Generally a switch mode chip like the TL494 will do a better job because it has a stable voltage reference and op amp built in. I'll explain the functional code because those are the systems I have running.
Your eye is log and a solar panel is linear. Get a little wisp of a cloud and it is still a nice day to you. The solar panel, however, takes a real hit in power power. Match up a heating element resistance to a solar panel array and you have great power transfer for an hour and a half in ideal sun. The fixed resistance is a real killer when the light levels drop a little or are off axis. A power point controller can increase the power output by five times or more compared to a direct connection at low light levels. At moderate light levels the numbers are about double. Some claim they do just fine with direct connect and anyway panels are cheap. Fact is you can get away with 30% fewer panels by building a $20 controller.
Nothing magical about the $276 controller I linked to. It uses an IGBT that saturates to about 2V. That wastes a little potential heat and there is a little warning that it may need an additional heat sink. The capacitors on that board will not last a long time because they can't handle the surge currents. As those fail, it will likely keep operating but will not put out as much power. The functionality is the same, the claims a little exaggerated. To be energy independent it takes a lot of panels and that means some of that time the panels will be cut off and not produce anything. They use the water heaters thermal switch to open the circuit. The most efficient use of panels is when they are sized to cover heat loss. If more panels are desired a tempering valve needs to be installed that blends cold with the hot and produces water that is 120 degrees as required in many new codes. That would allow you to set the upper tank limit to 150F and effectively increase water capacity.
Better have an expansion tank with wild temperature swings.
Higher voltage is the key to using existing tank heaters. They sell 12V elements and they are expensive, but the currents are so high a signifigant amount of power is lost in the wiring. 2000W 120V elements can be found in many big box retailers for about $10 if stuck using a 36V array. The power point voltage for a 36V array is a little over 50V. A 48V array should work well with 240V heaters.
How do you track? Solar panels are just big diodes, their power point voltage varies with temperature not light level. They are current sources, the current varies with light level. Very effective tracking can be done with just temperature. Is tracking that important? Not really. At peak power times (about two hours a day) it will likely be a direct connection. In lower light the major gain is from getting the set point anywhere near the power point. A seasonal adjustment could be sufficient if going for simplicity. Whether digital or analog, a couple of flat pack bridge rectifiers have a lot of surface area to couple thermally with a panel. The four diodes in series give a nice 2.5V reference (about midway for an A/D converter. Have a pot in the voltage divider from the panels, compare that with the reference, and adjust the pot for maximum power. Tracking made easy.
What about calculating MPPT and shading? You can do that and no current sense is required. Heating element is a fixed resistance, current is a function of PWM number. Shading is another issue. If there is 50V coming in and a 12V battery is being charged, you can follow that voltage down to hell. Drop the voltage on a heater and you have already lost it. A single large MPPT controller is sooooooooo yesterday. Yup, like everything else by the time you figured it out the world has moved on.
More later.
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The initial investment would be one or two orders of magnitude less than those thermal systems you linked!
Thermal systems I've linked are given as example of existing ones to make visual teardown and get best solutions of them and make yourself something cheaper, while people have some hobbies, so afterwork are interested in many things and a with alittle bit effort and help of CNC machines easy available nowadays which cut easy aluminium and steel plates, someone can make something similar or even with better electronics inside at his garage.
Yes, it require some workhours, but... to buy solar PV panels and this control stuff you have to go to work to earn some money too and if this thing fail (usually close to its warranty period) you are done and... have to work again to buy another PV system.
For solar thermal we need a huge insulated water tanks (better a few smaller to fully heat each one) unless we are on deserts, while at sunny nice day like today in some nothern Europe climates when we have perfect sky than having CSP thermal solar system with decent thermal capacity we can catch sun energy which can be used a few days later, eg, when we do not have such perfect conditions for thermal solar.
So, 3m dish with 7 square meters area now get according to Bird Clear Sky model close to 1000W/m2 in Central Europe, which means close to 7kW is reflected from this CSP, and a lot of thermal energy taken from the sun, while this CSP system tracks the sun and sun is 60 degs above horizon on perfect blue sky right now 8)
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SUN is: 2015-06-7.404 09:42:18 UTC (2457180.904 JD) lat: 5*.***N lon: -2*.***E Sun hour azimuth: 24.623 Sun (geo) azimuth: 155.377 Sun elevation: 60.690 Sun CSP power: 1006.4 W/m2 Day of the year: 158
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What about calculating MPPT and shading? You can do that and no current sense is required. Heating element is a fixed resistance, current is a function of PWM number. Shading is another issue. If there is 50V coming in and a 12V battery is being charged, you can follow that voltage down to hell. Drop the voltage on a heater and you have already lost it. A single large MPPT controller is sooooooooo yesterday. Yup, like everything else by the time you figured it out the world has moved on.
More later.
Thanks for the additional details. I'd be interested in more details on your $20 controller. specifically the PWM control loop.
BTW, direct PV water heating has been around for decades. (for example see this (http://fire.nist.gov/bfrlpubs/build02/PDF/b02012.pdf)). It's only rcently with the drop in panel prices that it makes economic sense. I've seen several proposed ways of doing it and a few fly by night commercial products (usually making wildly unrealistic claims like the one you linked).
The most successful method I've seen, which I know of a few people using, is in off grid PV systems that use the PWM output from the programmable auxillary port on a Midnite CC to control a SSR. This is used as an opportunity load once their batteries have been topped off early on a sunny day.
The most efficient (but more expensive and NOT direct heating) way that I know of using PV to heat water is via a heat pump water heater.
But I realize these kind of add ons to an existing PV system is not what you are talking about. I get the basic premise, but am interested in the specifics. I have several spare PV panels sitting around and may even try it myself.
Cheap atmel mcu PWM output controlling power mosfet, got it. But I'm not sure i understand the control loop you're using to control current with varried solar insolation.
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The simplest method is to use a fixed set point. The A/D value is compared with that and the PWMcount is adjusted up or down. A dead band is needed to prevent continuous adjustment. When a major change is detected an additional change to the count is made to speed the transition. The upper and lower limits of the countare constrained. Narrow pulses at each extreme only result in heating of the switching device and are prevented. Delay reading A/D at least 100ms after PWM is changed to allow system to respond. For a fish pond pump, the code is the same except the upper PWM limit would be about 170. This can also be used as a diversion controller on a MPPT charge controller without diversion control. A second A/D would monitor the battery and allow diversion at power point when the battery is over 13.8V. Code has been made intentionally simple for clarity.
The picture is a test bed I used to gather data from a single 12V panel. The 150 boost converter on the topis connected directly to the panel and was used to create 35V. This would not be needed with more than one panel in series. The UNO kept the panel at the power point. The pot was adjusted for highest power on the meter. Two 5V gate FETs were driven directly through 100 ohm resistors. Sufficient at these levels. Prefer
driving with opto isolators which will protect the controller and provide a level shift. Nothing more complicated is needed at these speeds.
// A resistive voltage divider produces about 2V-3V at pin A0
// to give A/D count of about 500
// READ ANALOG VALUE AT PIN A0
panel = analogRead(0);
// A/D values go from 0 to 1023
// ADJUST PWM COUNT
// FAST RECOVER from high panel voltage at startup
if (panel > setpoint + 25) PWMcount = PWMcount + 1;
// FAST RECOVER from low panel voltage
if (panel < setpoint - -25) PWMcount = PWMcount - 1;
// NORMAL HIGH VOLTAGE RAMP UP
if (panel > setpoint + 2) PWMcount = PWMcount + 1;
// voltage is over setpoint
// NORMAL LOW VOLTAGE RAMP DOWN
if (panel > setpoint - 2) PWMcount = PWMcount - 1;
// voltage is under setpoint
// CHECK PWM LIMITS
// is count too high?
if (PWMcount >= 255) PWMcount = 255;
// is count too low?
if (PWMcount <= 0) PWMcount = 0;
// Set count to output?
PWM3 = PWMcount;
// PREVENT NARROW DRIVE PULSES
// is count too high?
if (PWM3 >= 245) PWM3 = 255;
// is count too low?
if (PWM3 <= 4) PWM3 = 0;
// PWM FET DRIVER OUTPUT PIN #3
analogWrite(3,PWM3);
// PWM values are between 0 and 255
a delay or additional program is needed
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Is tracking that important? Not really. At peak power times (about two hours a day) it will likely be a direct connection.
In the case of PV where you have very bad efficiency, 30% more energy due to tracking by pointing into the sun maybe is not worth it, but in the case of thermal solar even at 50% efficiency no tracking means lost a lot of sun energy, so much worse ROI without sun tracker.
There is also something else-there are days when there are sunny days, but after dinner 14 o'clock in Europe thunder storms comes, so without sun tracker you miss sun maximum elevation due to after dinner rain, while using sun tracker from the morning to dinner you have enougth energy and can easy give up with any attempts to catch sun after dinner ;)
Forget about peak power times, while thunder storms after dinner will show you quickly that nature rules needed solar system design and tracking the sun can be sometimes much more than 30% of energy, while without sun tracker you will have to watch sometimes instead of peak power times.... cloudy skies with huge lighting :-DD
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The simplest method is to use a fixed set point. The A/D value is compared with that and the PWMcount is adjusted up or down....
Thanks for more details. Correct me if I'm wrong, but it seems what you are doing is essentially simplified MPPT tracking. Since there is no battery involved there is no need to buck down the voltage and no need to worry about charging stages, etc.
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Not that kind of tracking of the arc of the sun. It is always a mistake when I expect people to get it out of context. I once advised someone to use a "15-47K resistor". They put in a 33 ohm just to be safe they said and it went up in smoke.
Yes it is simplified. Power tracking can often be skipped because the PWM often goes to 100% during peak hours if the load doesn't have low enough resistance and it is just a 36V string. A seasonal camp wouldn't see much difference. Big difference between winter and summer and at low light levels there isn't that much to capture. I wanted to show that code because it is applicable to linear current booster for a pond pump. It is an easy place to start and thermal tracking can be added later. This year I will have the opportunity to try some power tracking when I go to 48V strings at the camp.
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Not that kind of tracking of the arc of the sun.
??? No, no of course. MPPT is not same as mechanical array tracking of the path of the sun in the sky. But as Maximum Power Point Tracking - it is optimizing power output under different levels of solar insolation - which can vary with cloud cover, fog, shading and yes, position of sun in the sky relative to the panels. This is essentially what you are attempting to do with your Arduino , no?
BTW, there are several examples of DIY Arduino MPPT solar charge controllers out their (Tim Nolan's was the first I believe). But what you are doing is different since you are not trying to charge a battery.
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Not that kind of tracking of the arc of the sun.
??? No, no of course. MPPT is not same as mechanical array tracking of the path of the sun in the sky.
Yep, now at the morning sun has 42 deg elevation, but decent CSP estimated power available from the sun is... ~940W. There is nice sunny day, so this is input power to thermal solar when dish tracks the sun.
If someone has PV panel fixed and pointed to south to hit into a few hours only peak power at sun maximum elevation, than... he has much lower input power to PV system now.
Additionaly bad neews for PV today in my area-thunder storms comes and at peak hours might be cloudy and rain soon, so no time to waste any sun energy right now ;)
(http://s28.postimg.org/z8xrq3wz1/sat_clouds.png)
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SUN is: 2015-06-9.299 07:10:30 UTC (2457182.799 JD) lat: 5*.***N lon: -2*.***E Sun hour azimuth: 74.430 Sun (geo) azimuth: 105.570 Sun elevation: 42.148 Sun CSP power: 943.8 W/m2 Day of the year: 160
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Saving the world one shower at a time. Pope might even put me up for sainthood. I am now at my camp for the summer. It has been a week of rain and clouds, still get a shower every day and still runs my fridge + more. Brought a new panel with me and now the hot water is 900W, 3S3P 36V configuration. Was going to make it 48V but now all these panels are identical and this keeps me "low voltage." Wanted to try perturbing software but that will never work here. I have a 50V buss that is fed from both ends with multiple devices pulling from it. Each device has an assigned power point voltage. A slightly lower power point device has priority and is served first. I will implement temperature tracking this year sometime. At a 50V potential a 20C panel temperature change only changes the power point 3V. Plop that in the middle and the loss is quite small when adjusted seasonally. The internet is filled with R&C people (Rob & Copy). They can't design or program their way out of a paper bag. Even with all the details spelled out they struggle to make a project work. The simplified code I have shown might give them a chance to have organic capability.
I had wondered why there wasn't a solar corner here. Clearly there is no interest. I want to thank even the detractors for giving this thread a long enough life to give it visibility to such a large number.
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Brought a new panel with me and now the hot water is 900W, 3S3P 36V configuration.
Which is total area of those panels? How many square meters of PV solar? Do you have some kind of pyrometers to estimate available input solar power, than integrate and get daily averages? ;)
For example for 1kWp I've found such "made in China" PV panels: 142 Wp/m2 14% Dimension: 1473*670*35mm ~0.987 m2 ~1m2, I'd need seven (7) like those below and do not want invest more than that 1kWp solar PV.
(http://s9.postimg.org/d1tal9dob/com_shutten_solar_pv.jpg) (http://postimg.org/image/d1tal9dob/)
BTW: Do you know what this magic: AM 1.5 means close to: Standard Test Conditions: AM 1.5, 1000W/m2, 25*C at the bottom of the above specs? ::)
Update: Never mind-I've found it there: http://www.amsolar.com/home/amr/page_164 (http://www.amsolar.com/home/amr/page_164) it is airmass defined to test PV panels at varying degrees of latitude and altitude .
Idea is put a few solar PV panels around 3m thermal solar CSP dish, so I could have ~4m in diameter hybrid solar CSP 5kWp & 1kWp PV system, with sun tracking MPU software of course :popcorn:
Note: At the botom, with exclemation mark (!) they says that those given Wp are at those perfect conditions 25*C and 1000W/m2 sun input power, so efficiency is <15% of course in the case of those solar PV.
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last month we instaled here a solar heat system for water , way to go mate , very noticeable reduction on eletric bill , way to go if you eletric bil is salty like mine and have plenty of sun to use :0)
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I'm jumping in at the end of the thread without reading all posting, so forgive me if I'm repeating what others have said. Broadly speaking, I agree that using PV to make hot water can make a lot of sense. A few years ago I decided to get a grid-connected domestic PV system, and conventional solar hot water. I got the PV system first, and left an area on the roof for the hot water solar collector. The I started thinking. A decent solar hot system that can provide 100% hot water needs is quite expensive, and also complex with pipework and circulation pump. If you size it big enough to provide all your HW needs in winter, then it will be way oversized and under-utilized in summer, possibly have boiling problems in summer as a result, and in my climate you have additional complexity to prevent freezing in winter. Fortunately I saw the light before installing the solar HW. Just in raw economic terms, I was better off just to add 1.5 kW or so of panels to my PV system, and get a bigger inverter, which is reason enough to go that way. However, when you think of all the other advantages of the PV approach, I would need to have had rocks in my head to proceed with the solar HW. No messy plumbing to the roof, no circulation pump, no boiling or freezing issues, but there are even more advantages. Most of the time, the solar HW would have had excess capacity, that is wasted. With the PV, when there is excess capacity, you can use it for other useful things, or sell it back to the utility company, to be usefully used by someone else, both saving you even more money, not to mention being environmentally desirable.
There is much talk about using batteries on domestic PV systems, to better match PV production to demand, but PV hot water storage systems can do much the same thing at very low cost, if cleverly controlled, yet another advantage. I am about to build a controller that only diverts my PV output to the HW system when there is excess PV power available. For example, in the early morning and late afternoon, all my PV output is available for my domestic use, minimizing or eliminating my drain on the grid at the precise time when community demand is high, and PV generation (all PV generation, not just mine) is low. In the middle of the day, when the panels are really pumping out the kW far in excess of my needs, then the excess power is used to heat the hot water. Quite literally, I'm using the stored energy of the hot water as if it was an electrical battery, with the storage capacity of a large, expensive battery, but without the cost and dubious environmental credentials of a battery, when the limited life and large quantity of materials that go into making the battery are considered. If everyone had a smart PV HWS like me, this would have a profoundly beneficial effect on the power grid, flattening out the PV production over the day. I know that our electricity utility is quite worried about the problems that large numbers of PV installations would cause, with fluctuating PV production, and smart domestic HW systems could be of great benefit here, at essentially no cost. A decent controller must be capable of proportionally controlling the amount of electrical power made available to the HW system, for example using triac phase control, or time-proportioning. In this way, for example, if there is only 1kW of excess PV power available from a 5kW system, then exactly and precisely that 1kW will be made available for water heating. PV water heating with smart control has a very big future, I would predict. The system can respond fast to changing environmental conditions. Even if a cloud blows over for a few minutes, the (reduced) PV output will be removed or wound back from the HW system, then made available again when the cloud has passed. Thus is not academic. Our utility company is studying methods of measuring the moving clouds over tthe city, so they know in advance that an entire suburb(s) are about to have their PV generation become reduced, so they can quickly switch in additional power to compensate. Smart PV HW systems would be a Godsend.
With the low cost of PV panels, direct-solar HW systems are obsolete technology as far as I am concerned. Circumstances vary, but in many situations, mine included, you really would need to have rocks in your head to even consider installing a solar HW system.
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Sorry, but you can't simply say that solar HW is economically nonsense per se. It depends on the situation and enviroment. We got a solar HW system supporting the central heating system for hot water and heating (oil). From late spring to early autumn the central heating barely runs. The HW also helps in spring, autumn and on sunny winter days to reduce the oil consumption. No issues with freezing. On the long run the HW system incl. maintenance is less expensive than the oil we would have to buy instead.
We've also thought about a parallel PV system. But back then PV modules were quite expensive, though you would have gotten a fixed payment per kWh for feeding the power into the grid (law to support green energy). The payment was higher then buying a kWh and the break-even was about 15-17 years for most small private PV systems. Meanwhile the modules are cheaper but the fixed payment dropped also dramatically. Nowadays a small PV system just for feeding the grid and collecting the money isn't economical anymore. But using your own PV power becomes economically interesting, because we pay much more for a kWh (about +40% vs. 10 years ago).
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Sorry, but you can't simply say that solar HW is economically nonsense per se. It depends on the situation and enviroment. We got a solar HW system supporting the central heating system for hot water and heating (oil). From late spring to early autumn the central heating barely runs. The HW also helps in spring, autumn and on sunny winter days to reduce the oil consumption. No issues with freezing. On the long run the HW system incl. maintenance is less expensive than the oil we would have to buy instead.
We've also thought about a parallel PV system. But back then PV modules were quite expensive, though you would have gotten a fixed payment per kWh for feeding the power into the grid (law to support green energy). The payment was higher then buying a kWh and the break-even was about 15-17 years for most small private PV systems. Meanwhile the modules are cheaper but the fixed payment dropped also dramatically. Nowadays a small PV system just for feeding the grid and collecting the money isn't economical anymore. But using your own PV power becomes economically interesting, because we pay much more for a kWh (about +40% vs. 10 years ago).
All agreed, and I did say that circumstances vary. I was being deliberately provocative to get people thinking about PV HW. Traditionally, making hot water from electricity is regarded as the ultimate environmental crime, especially here in Australia where most electricity is generated from coal, and electric HW is banned by law. However, the ridiculously low cost of PV panels has changed the game, but legislation and attitudes have yet to catch up.
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Using Solar power to heat water is one option. However, it sounds like you have over sized your panels vs your needs.
Would be a waste in summer, but at least you can export your power in that case.
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Using Solar power to heat water is one option. However, it sounds like you have over sized your panels vs your needs.
Would be a waste in summer, but at least you can export your power in that case.
But thats the point, its not oversized when the cost of moving the hot water to a solar collector would be more. For a lot of people adding solar PV capacity is the cheapest way to create hot water.
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With the low cost of PV panels, direct-solar HW systems are obsolete technology as far as I am concerned. Circumstances vary, but in many situations, mine included, you really would need to have rocks in your head to even consider installing a solar HW system.
You need to provide some figures for this, and I think you will find that in the majority of cases the payback time for solar hot water is quicker than the system you are proposing.
Try Sydney, family of four, no current PV, and 15sqm of usable roof space.
a) initially with gas powered stored hot water.
b) initially with electrical powered stored hot water.
My opinion you would need rocks in your head not to at least consider a solar HW system.
My personal experience is I put a indirect passive solar HW system on my roof, did the plumbing myself into the existing instantaneous gas HW system. Save $450 a year on gas. and it paid it self back in about 4.5 years not accounting for my labour. Maybe 6? years considering labour.
It has been great but the main drawback is that it is a bit ugly. Looks good in summer when it is letting of steam.
I agree that we will and should be moving toward getting PV to work with domestic HW and smart metering/load control.
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With the low cost of PV panels, direct-solar HW systems are obsolete technology as far as I am concerned. Circumstances vary, but in many situations, mine included, you really would need to have rocks in your head to even consider installing a solar HW system.
You need to provide some figures for this, and I think you will find that in the majority of cases the payback time for solar hot water is quicker than the system you are proposing.
Try Sydney, family of four, no current PV, and 15sqm of usable roof space.
a) initially with gas powered stored hot water.
b) initially with electrical powered stored hot water.
My opinion you would need rocks in your head not to at least consider a solar HW system.
My personal experience is I put a indirect passive solar HW system on my roof, did the plumbing myself into the existing instantaneous gas HW system. Save $450 a year on gas. and it paid it self back in about 4.5 years not accounting for my labour. Maybe 6? years considering labour.
It has been great but the main drawback is that it is a bit ugly. Looks good in summer when it is letting of steam.
I agree that we will and should be moving toward getting PV to work with domestic HW and smart metering/load control.
Circumstances vary. With only 15 sqm of roof space, no existing PV, and an existing gas HW system for backup, then your solar HWS makes sense. I have 100 sqm of useable roof and was installing PV anyway, so in my case installing a solar HW in addition made no sense at all. I forgot to mention another advantage of going the ‘one-big-PV-installation’ way. With a reverse-cycle aircon installed, you can use the power to heat your house in winter, and cool it in summer – can’t do that with the excess capacity of a solar HWS.
The issue of backup is very important from an environmental (and possibly economic as well) perspective. In reality, it turns out that solar HW backed up with mains-grid electricity is one of the worst possible options for producing HW in Australia from an environmental perspective, where coal-produced-electricity is used in a criminally inefficient way to provide electric-heater backup. If you already have gas HW like you did then of course you use that for your backup. If you don't have gas HW installed already, but have gas available, then it becomes a mighty expensive solar HW system when the cost of installing the gas backup is accounted for. The alternative is to grossly oversize the solar HW so that backup is very rarely required, and that costs extra, and then you can have over-capacity issues in the middle of summer. If you install a small number of PV panels dedicated solely to making HW, then most of the same issues apply.
However, if you have 30 sqm or more of roof area and wish to install PV anyway, then the game changes completely. In that case, just add another 2kW or so of panels and inverter capacity over and above your intended PV generation system, and for relatively little marginal extra cost you get all the benefits described in my first posting, plus you probably won’t need any backup at all as you can draw on the overall capacity of the PV system when needed. An obvious partner with PV systems is reverse-cycle HW, which reduces the electrical power requirement for the HW by a factor of x3 or so, but panels are so cheap that if roof area is not an issue, then the capital cost and finite lifetime of the reverse cycle unit may mean you are better off without it.
Beauty is in the eye of the beholder. I would probably find your solar HWS an object of great beauty. :) But I’m so glad that I did not install one in my situation.
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Some other of advantages of Solar HW over PV hot water.
solar efficiency, probably 2 to 3 times pv per unit area.
works better than many PV systems when subject to partial shading.
doesn't need planar alignment with other solar catchers.
far less regulatory and safety issues/requirements/costs.
less safety issues/requirements.
Don't get me wrong I am all for PV and I just got my ticket for it, but all options should be considered.
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With the low cost of PV panels, direct-solar HW systems are obsolete technology as far as I am concerned. Circumstances vary, but in many situations, mine included, you really would need to have rocks in your head to even consider installing a solar HW system.
You need to provide some figures for this, and I think you will find that in the majority of cases the payback time for solar hot water is quicker than the system you are proposing.
Page 1 of this thread already has the numbers for electricity. Even using the inflated costs of a "professional installer" to setup the PV to hot water link its still very competitive:
https://www.ecoelectric.com.au/solar-hot-water-or-solar-pv/ (https://www.ecoelectric.com.au/solar-hot-water-or-solar-pv/)
Some other of advantages of Solar HW over PV hot water.
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far less regulatory and safety issues/requirements/costs.
less safety issues/requirements.
I'd much rather work on a sealed electric hot water system and fiddle with its electricals than do plumbing on a pressurised steam system. And oh wait, working on the hot water system requires a licensed plumber while swapping the electricals on a plug in appliance (such as a hot water system) requires no license or permit. So the PV attachment to hot water is actually much easier and requires no licenses while plumbing does, the safety aspect is debatable and down to personal assessment.
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Sorry I didn't realise there were already some figures in this thread. Though as they are coming from a PV installer I doubt they are objective.
Even using these figures you should still consider it. Solar HW doesn't preclude a PV installation. If you have a look at the photo on https://www.ecoelectric.com.au/solar-hot-water-or-solar-pv/ (https://www.ecoelectric.com.au/solar-hot-water-or-solar-pv/) you can see a combined installation. Notice the separate plane you can install the solar PV on. You might have a small section of roof no good for PV that you can use as a preheater for your HW.
I'd much rather work on a sealed electric hot water system and fiddle with its electricals than do plumbing on a pressurised steam system. And oh wait, working on the hot water system requires a licensed plumber while swapping the electricals on a plug in appliance (such as a hot water system) requires no license or permit. So the PV attachment to hot water is actually much easier and requires no licenses while plumbing does, the safety aspect is debatable and down to personal assessment.
I suppose if you keep the PV below 120V in you can do the wiring yourself, but most people in Australia have the grid connect system, so it is highly regulated. Those monetary figures are probably only valid for a CEC approved installation which is highly regulated, to the point of barcoding each solar panel and sending the details to the CEC.
It's not really more pressurised and not really a steam system. I like the indirect (heat exchange) versions where the HW tank is only barely above 1 atmosphere.
Another advantage of the heat exchange storage systems is that you don't have to worry about Legionnaires disease.
Actually after saying all that I should mention I am quite wary of the Solar HW system on my roof. I don't even go up there if it is boiling. 250l of boiling water is a bit scary.
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Some other of advantages of Solar HW over PV hot water.
solar efficiency, probably 2 to 3 times pv per unit area.
True, though irrelevant unless roof area is scarce, as in your case.
works better than many PV systems when subject to partial shading.
Yes. PV systems need to sized to account for that, or in severe shading cases one must accept that PV is not suitable.
doesn't need planar alignment with other solar catchers.
This could be argued either way. With PV, it’s real easy to have two banks in different locations, connected to separate inputs on the inverter. That’s not a practical option with solar HW collector(s), as you really don’t want long, insulated hot water pipes running from here to there and back again – messy,expensive and thermally lossy. Electrical wires have got it all over fluid-carrying-pipes as a method of getting energy from one place to another, and wires don’t boil or freeze, either, and nor do they need a separate pump. Chalk and cheese. Electricity is the most high-quality, flexible, multi-use, easily transported source of energy available – nothing else even comes close.
far less regulatory and safety issues/requirements/costs.
less safety issues/requirements.
Sometimes, but often not. Some people have described very simple, safe low voltage PV HW DIY systems that are not mains connected at all, though in this case the overall utilization of the PV panels is poor. If you have or are getting a PV system anyway, then the regulatory and PV wiring stuff will be done anyway, and thus given that the 240V power will be there anyway, it’s much easier to install an electric HWS than a solar one. The DIY experimenter can make the electric HWS into an appliance by connecting a 3-pin plug lead (subject to the heater wattage being low enough) and simply plugging the HWS into a power point, a 15A power point if necessary. With this approach, the DIY experimenter can also build his own controller box for the electric HWS. The controller box plugs into a power point, and the HWS plugs into the control box.
Don't get me wrong I am all for PV and I just got my ticket for it, but all options should be considered.
Agreed.
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Sorry I didn't realise there were already some figures in this thread. Though as they are coming from a PV installer I doubt they are objective.
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It's not really more pressurised and not really a steam system. I like the indirect (heat exchange) versions where the HW tank is only barely above 1 atmosphere.
Another advantage of the heat exchange storage systems is that you don't have to worry about Legionnaires disease.
The numbers on the first page of the thread are my easy calculation for rate of return, each person can determine the costs of the parts for themselves (as they very wildly) but as we keep going over a low voltage install is a great DIY project and can pay for its self in short order if you already have an electric hot water system. Given the lower upfront cost for supply/install of an electric storage system compared to a solar hot water system it becomes very hard to see how the direct solar hot water could be cheaper over its life.
Dual circuit systems are a great option, they could be useful in Australia for heating too if a energy dump exchanger were installed through the floor of living areas.
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The website in the link seems a bit ridiculous. Just get a standard MPPT controller and be done with it, if you already use an electric water heater tank obviously you should also hook your solar system up to it. Where is the question? I wasn't even aware this was a revolutionary idea. I will say that I find it completely unexciting to just buy a couple panels to hook up to your water heater, advantage of PV is you can use that power for anything. If you only care about smoking up the shower there are a hundred ways to do it for pennies. If you really want to pinch pennies buy an electric kettle and take a bath in a bucket. :scared:
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I have recently built a ‘PV Power Diverter’, which diverts my excess PV power to a 250 liter electric storage heater with 3.6kW element, that provides my entire hot water needs.
For those not familiar with PV diverters, a current xformer is used to monitor the net power flowing into the grid, and a triac is used to regulate the amount of power fed to the hot water (HW) heater such that only excess PV power is fed to the heater. In my case, using excess PV power in this way cost me nothing, because my feed in tariff pays me for every kWh of power generated, regardless of how it is used. More commonly, the feed in tariff is almost negligibly small, so it makes good economic sense to usefully use excess PV power for hot water, that would otherwise need to be paid for at a higher rate.
I live in Canberra, Australia, where the winters are moderately harsh, typically zero to -6 DegC overnight, though we do often get a run of clear days with daytime max of around 12 DegC. My PV installation has moderately severe shading issues in winter, but a lot of panels, so performance is probably equivalent to a 6kW system with little shading. The hot water serves 2 adults.
So how well does this PV hot water system perform? How often do I need to boost, and how does it perform compare to an evacuated tube system in the same city?
I have had it running now for around 3 weeks, in the middle of winter, and it’s very good indeed. On clear sunny winter days we run a 2.4kW (input), 7.2kW (heating) reverse cycle aircon all day to heat the 45 sqm living area, and there is still enough excess PV power to do the hot water without boosting, though only just. On cloudy/raining days we don’t use the R/C, and on most such days the cloud-shine and occasional appearance of sun also provides enough excess PV for the hot water. Without any PV input at all, the 250L tank, with setpoint at 80 DegC, will last for about 3 days. So far, we have not needed to boost, and I estimate boosting may be necessary around 4 days per year on average. I can ‘boost’ by choosing to draw power from the grid, or by using gas, but would choose gas because it’s cheaper and environmentally better than using grid power, though for a few days per year either is fine. It’s free hot water, for an initial capital cost of ~AUD$1000 for the 250L, stainless steel storage tank, plus my time and ~$100 of parts to build the diverter.
So how does this compare with an evacuated tube (ET) system? Turns out I have a good mate in Canberra with an ET system, and we know exactly how well his system performs, and how often it needs boosting, because his Resol solar HW controller logs all the key temperatures, and even plots them over a 30 day period on a web page. He started out with a 30 tube system, and it was pathetic, requiring very frequent gas boosting over winter. As he uses gas only for HW boosting, and the fixed costs of providing gas are $300 PA, he really wanted to eliminate the need for gas boosting and terminate his gas supply altogether, so he applied a ‘big hammer’ to the problem, and installed another 30 tubes, optimally pointed and angled for maximum winter performance. He has separate pumps for each bank of tubes, and his Resol controller is able to control both banks independently. That’s a 60 tube system, and optimally set up, at that! In summer he has to put black plastic over one bank, or the system will boil its brains out.
Even to my own surprise, the comparison is chalk and cheese. It’s been an unusually wet and cloudy winter here in Canberra, and when we get 2 or more days with heavy cloud and rain, the ET system just isn’t up to the task, even with 60 tubes, and gas boosting becomes necessary. Physics cannot be cheated. Even with 60 tubes, the collection area is still relatively small, and on days with little sunlight, the ET system can capture little heat energy, at best. But it is worse than that, because to prevent freezing at night, the tank water needs to be pumped through the collectors, destroying much of what little energy was collected. Also, the collection efficiency is very poor on cold, cloudy days, because on such days, the collector heat loss during the day is very significant compared to the amount of heat being collected. In contrast, PV panels don’t need defrost heating, and efficiency does not drop off under conditions of low temperature and low solar insolation, and nor does the efficiency drop off when producing water at high temperatures.
The practical result is that my PV hot water system leaves this 60-tube ET system for dead under all conditions. In summer, both systems have more than enough capacity, except of course that the excess PV power can be sold, or used for air conditioning or whatever. In the depths of a Canberra winter though, my PV system pumps out wonderfully hot water under nearly all conditions, when the 60-tube ET system has collapsed and needs significant boosting. I have had a lot of fun watching the day-by-day data plots of the water temperatures in this 60-tube ET system, and comparing with my PV system, and am quite surprised by just how much better the PV system performs. If you have the roof area, and are thinking about installing a PV system, then don’t waste your time with a traditional solar-collector HW system, with all of it’s additional complexity, freezing, boiling, and inferior performance that demands significant backup. Just add a few more kW of panels to your PV system, build or buy a PV power diverter, and take the PV hot water route. I’m laughing all the way to the bank. Hot showers never felt so good.
In warmer climates, or where roof area is scarce, or where you don’t have or want a PV system in the first place, the optimum choice may be different. Also, while for practical purposes I never need boost backup, that is with only 2 people. With a family of 4 or more, then my experience indicates that you will need some sort of boost backup with pretty much any solar HWS setup, at least in Canberra.
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To add some balance, I should point out that my mate’s 60 evacuated tube HW system works well by most measures. When averaged out over a full year, then it probably provides 80% to 90% of his total hot water energy needs, which on environmental or economic grounds makes it pretty good, but it does need significant boost backup in winter, while for practical purposes my PV HWS system does not, which was the point being made. His circumstances were unusual, in that he wanted to get off the gas completely, but couldn’t because his hot water storage tank has no provision for an electric heater, and he found to his cost that no practical number of tubes would remove the need for boosting over winter. His long term solution is to maintain his solar collector system, and replace the gas-boosted tank with an electric-boosted one. It’s been an expensive exercise, with first adding another 30 tubes, and then replacing the storage tank, but his final result should work well.
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If you have the roof area, and are thinking about installing a PV system, then don’t waste your time with a traditional solar-collector HW system, with all of it’s additional complexity, freezing, boiling, and inferior performance that demands significant backup. Just add a few more kW of panels to your PV system, build or buy a PV power diverter, and take the PV hot water route. I’m laughing all the way to the bank. Hot showers never felt so good.
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This echos what I was saying early in this thread. With PV prices so low, the equation has changed.
Sounds like you have a great system in place. :-+
You might want to consider a heat pump hot water heater when your current one goes. I think you'll then find that even in winter, you'll never need to "boost" with grid power.
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Some thoughts re the importance of how a solar HWS is backed up. In Australia, where most of our power is generated from coal, producing hot water from grid power is environmentally very undesirable indeed, and this has interesting consequences for the overall environmental credentials of competing HW systems. In order of ‘environmental badness’, HW systems can be ranked as :-
Conventional Electric Storage HWS (worst by a long shot)
Direct Solar, with grid-sourced electric backup
Natural Gas
Direct Solar, with gas backup
DirectSolar, with diverted PV electric backup (equal best)
Solar PV, using 100% diverted PV power (equal best)
It might be thought that a Solar HWS is an excellent environmental choice, ‘obviously’ better than burning gas, but actually this is often not true. The second worse choice, on environmental grounds, is a Solar HWS backed up by coal-fired, grid-sourced electricity. The reason is that, as per previous discussions, unless you install a monster sized solar HW system, then significant boosting will be required in many climates, ruining the environmental credentials if the boosting is provided by coal-fired electricity. Generally speaking, 100% gas-fired HW systems are environmentally better than electrically-backed solar systems.
Solar with gas backup is an excellent environmental choice, but the initial capital cost is expensive. The gas backup is done with an instantaneous style gas heater, adding considerable cost over and above the solar HW installation.
The two equal-best options, from an environmental perspective, are Direct Solar with PV backup, and Solar PV, assuming in both cases that the PV system is large enough to provide all the electrical power needs, at all times of the year.
I haven’t ranked heat-pump systems, because I’m not sure exactly where they fit, but are generally ‘good’, and arguably best of all if the power is PV sourced.
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This echos what I was saying early in this thread. With PV prices so low, the equation has changed.
Sounds like you have a great system in place. :-+ (It works for me ....)
You might want to consider a heat pump hot water heater when your current one goes. I think you'll then find that even in winter, you'll never need to "boost" with grid power.
Yes. With a heat pump, the electrical power required is about 1/3 compared to direct resistive heating, so without doubt I would never, ever need to boost, given that I hardly ever need to boost now.
Heat pumps can be wonderful, but in this case I decided that on balance I would prefer not. On straight economic grounds, I would be much worse off with the heat pump in my particular case, because already I have enough free excess power to provide all my water using resistive heating. So for me the operating cost would be the same, but the initial capital cost of the heat pump is much higher. On top of that, heat pumps are complex devices that are not always reliable, and have a definite lifetime, probably not more than 10 years at best. In contrast, my simple, low-tech stainless-steel electric hot water tank cost a modest AUD$1000, has no maintenance or reliability issues, and is expected to last at least 20 years. As it is, for practical purposes I never need to boost with my resistively-heated tank, so in my particular case there was no reason to get a heat pump, and many reasons not to. I do swear by my reverse-cycle aircon though, that heats my house for free on most winter days using PV power, and still leaves enough PV power left over to heat the hot water. Way to go. :)
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Why heat hot water?
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has no maintenance or reliability issues
FYI Hot water tanks are not completely reliable nor maintenance free. Especially if your water is hard. The tempering valves do fail. The elements and thermostats also fail.
Obviously these issues affect both Direct HW and PV hot water though.
I don't see how you can claim your system is lower maintenance when much of the stuff is the same.
I have done very little maintenance on my Solar HW system and it has been running a long time.
Also about your economics, and as it may apply to other people. If you use your house as an example you should include some of the cost of your solar system which seems to be huge. (?10kw)
Freezing and boiling are not issues for me either. I have a 20 or 30 tube system, i bought it long ago so I cant remember.
These all point to the fact that so much depends on specific circumstances, so you should do a proper analysis before you design or choose your system.
When designing, often the difference between say 85% and 95% solar power is not worth the extra up front cost if you have effective backup.
Also if you DIY then be aware of the regulatory issues and how it could possibly effect your insurance.
In Australia only electricians should be wiring systems above 120V DC.
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I was thinking Zeranin that you should use your Hot water for Hydronic heating so you dont use the straight electric Heaters at night.
Just an idea.
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has no maintenance or reliability issues
FYI Hot water tanks are not completely reliable nor maintenance free. Especially if your water is hard. The tempering valves do fail. The elements and thermostats also fail.
Obviously these issues affect both Direct HW and PV hot water though.
I don't see how you can claim your system is lower maintenance when much of the stuff is the same.
Except the direct solar systems have the same storage and pressure valves, and then a whole bunch of extra bits to go wrong that don't exist on the simple electric storage tank. The same with a heat pump, its replacing a resistive immersion heater (cheap and readily available) with a thermal engine that includes pressurised gas and heat exchangers. Its is entirely reasonable to say that the simple solution will be more reliable since it has fewer parts to fail and those parts are almost completely included with the alternatives.
In Australia only electricians should be wiring systems above 120V DC.
You've been shown to be wrong time and time again on Australian regulations. If its not hard wired into the grid or connecting a generating source to the grid you can do what you like, no electricians required. I've no exclusions in my insurance policy for building appliances or systems on my property or in my dwelling. The examples being suggested here as implemented as plug in appliances, or standalone DC systems.
You have direct solar hot water, thats fine. It was probably the most cost effective solution when you installed it. But times have changed and using PV to power hot water storage is now more cost effective, its less complex, and can be done as a DIY modification to existing equipment.
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You've been shown to be wrong time and time again on Australian regulations.
Ok you have made the statement, now point out where I was wrong time and time again.
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Some other of advantages of Solar HW over PV hot water.
far less regulatory and safety issues/requirements/costs.
less safety issues/requirements.
I suppose if you keep the PV below 120V in you can do the wiring yourself, but most people in Australia have the grid connect system, so it is highly regulated.
In Australia only electricians should be wiring systems above 120V DC.
All wrong. We are talking about modifying or controlling the hot water system, nothing to do with grid inverters, and no fixed mains wiring. This requires no regulatory oversight for a DIY project, no licenses, nothing. Stop perpetuating these messages, or show the regulations/legislation to which they would need to meet.
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has no maintenance or reliability issues
FYI Hot water tanks are not completely reliable nor maintenance free. Especially if your water is hard. The tempering valves do fail. The elements and thermostats also fail.
Obviously these issues affect both Direct HW and PV hot water though.
I don't see how you can claim your system is lower maintenance when much of the stuff is the same.
I have done very little maintenance on my Solar HW system and it has been running a long time.
Also about your economics, and as it may apply to other people. If you use your house as an example you should include some of the cost of your solar system which seems to be huge. (?10kw)
Freezing and boiling are not issues for me either. I have a 20 or 30 tube system, i bought it long ago so I cant remember.
These all point to the fact that so much depends on specific circumstances, so you should do a proper analysis before you design or choose your system.
When designing, often the difference between say 85% and 95% solar power is not worth the extra up front cost if you have effective backup.
Also if you DIY then be aware of the regulatory issues and how it could possibly effect your insurance.
In Australia only electricians should be wiring systems above 120V DC.
Yes, HW tank issues issues affect Direct and PV hot water equally. However, you are quoting me out of context, for I was comparing my PV resistively-heated water with heat-pump hot water, and I think we would both agree that a stainless steel tank with $30 replaceable element will be a lot more reliable and long-lived than a heat pump. I surfed various forums to gauge people’s experience with heat pump reliability, and concluded that they are often an infinite problem source and money sink.
As to comparing complexity and reliability of Direct and PV hot water systems, they probably come in about the same, if you compare a Direct system with a mains voltage inverter/PV system that is dedicated entirely to producing hot water, but that will almost never be the case. In practice, the homeowner will already have or decide to have a grid-tied PV system, for all of the financial and environmental benefits that it provides in it’s own right. Then, the choice is between building a separate solar HW system, with collectors, pumps, plumbing, controller, backup etc, or adding a simple diverter module to send excess PV power to an electric storage tank. There simply is no argument about which is simpler and will be more reliable, and these days it is likely that the PV HW solution (added to a PV system that you have or plan to have anyway) will be cheaper as well. But if roof area is scarce, that could change everything.
I have been-there-done-that. When I first planned the PV system, I dutifully set aside an additional area of roof for my solar HW system. The fortunately I saw the light and realized that I would be bonkers to build two separate systems, and instead opted for a few more PV panels so that the PV system could do both. I have never looked back. My good mate with his 60 evacuated tubes would not go down that path if he had his time again. That system has cost him a small fortune, and all it can do is produce hot water, and it doesn’t even do that as well as my PV HW system. He is now a complete convert to PV diverted hot water, and is an engineer in an Australian company that is is building and selling PV diverters. I have no connection with the company BTW :) The writing is on the wall. Sales of direct solar HW systems have stagnated, while the popularity of PV HW is increasing. The times, they are a changin …
FYI, my PV system has a 6kW inverter, but about 10kW of panels, to compensate for severe shading in winter. The net result is that the performance in winter is about the same as an unshaded 6kW system. So it’s a respectable sized system, but certainly not huge. You can buy a 6kW system these days surprising cheaply and, as I have demonstrated, you can do a lot of useful things with that power – power your house, reverse-cycle heat and cool your house in the daytime, make hot water, and sell what is left over.
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I was thinking Zeranin that you should use your Hot water for Hydronic heating so you dont use the straight electric Heaters at night.
Just an idea.
Actualy a bad idea in my particular case. At night I use natural gas heating. My hot water production in winter using excess PV power just nicely matches my HW usage, with 2 adults in the house, so there is none left over for heating the house at night. It is much more efficient (x3 better) to use my excess PV power during the day to heat the house using reverse cycle, so that's what I do. It's true that I have excess PV power coming out of my ears in summer, even with the hot water production, which I use for cooling the house on very hot days, and the rest gets squirted out onto the grid so others may use it. I get paid handsomely for every kWh that the panels produce, so financially it makes no difference to me whether I use the PV power, or push it onto the grid, so it makes financial sense that I usefully use as much as possible to reduce my power and gas bills. Such ridiculously generous gross feed in tariff schemes are no longer available.
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This legislation is done on a state by state basis.
each state has a definition of what is 'electrical work'.
https://www.legislation.qld.gov.au/LEGISLTN/CURRENT/E/ElectricalSA02.pdf (https://www.legislation.qld.gov.au/LEGISLTN/CURRENT/E/ElectricalSA02.pdf)
from about page 24. sorry its so long but I'm sure someone (lower case) ;) would complain if I cut part of it out.
18
Meaning of
electrical work
(1)
Electrical work
means—
(a)
connecting electricity s
upply wiring to electrical
equipment or disconnecting
electricity supply wiring
from electrical
equipment; or
(b)
manufacturing, constructing, installing, removing,
adding, testing, replacing,
repairing, altering or
maintaining electrical equi
pment or an electrical
installation.
Examples of electrical work—
•
installing low voltage electrical wiring in a building
•
installing electrical equipment into an installation coupler or
interconnecter
•
replacing a low voltage electrical
component of a washing machine
•
maintaining an electri
city entity’s overhead
distribution system
(2)
Electrical work
does not include the following—
[s 18]
Electrical Safety Act 2002
Part 1 Preliminary
Current as at 8 April 2016
Page 25
Authorised by the Parliamentary Counsel
(a)
work that involves connecti
ng electrical equipment to an
electricity supply by means of
a flexible cord plug and
socket outlet;
(b)
work on a non-electrical
component of electrical
equipment, if the person carr
ying out the work is not
exposed to an electrical hazard;
Examples for paragraph (b)—
•
painting electrical equipment covers
•
repairing hydraulic
components of an electrical motor
•
replacing a drive be
lt on a washing machine
(c)
replacing electrical equipment or a component of
electrical equipment if
that task can be safely performed
by a person who does not have
expertise in carrying out
electrical work;
Examples for paragraph (c)—
•
replacing a fuse
•
replacing a light bulb in a light fitting
(d)
assembling, making, modify
ing or repairing electrical
equipment in a workplace under the
Work Health and
Safety Act 2011
that is prescribed under a regulation for
this paragraph, if that is
the principal manufacturing
process at the workplace, and
arrangements are in place,
and are detailed in written form, for ensuring that—
(i)
the work is done safely and competently; and
(ii) the equipment is tested to ensure compliance with
relevant standards;
(e)
building or repairi
ng ducts, conduits or troughs
(channels) where electrical wiri
ng will be or is installed,
if—
(i)
the channels are not intended to be earthed; and
(ii) wiring installed in the channels is not energised;
and
(iii) the work is done under
the supervision of a person
licensed to perform electrical installation work;
[s 18]
Electrical Safety Act 2002
Part 1 Preliminary
Page 26
Current as at 8 April 2016
Authorised by the Parliamentary Counsel
(f)
locating or mounting elect
rical equipment, or fixing
electrical equipment in plac
e, if this task is not
performed in relation to th
e connection of electrical
equipment to an electricity supply;
(g)
assisting a licensed electrical worker to carry out
electrical work, on
electrical equipmen
t under the direct
supervision of the electrical
worker, if the assistance
does not involve physical co
ntact with any energised
electrical equipment;
(h)
carrying out electrical
work, other than work on
energised electrical equi
pment, in order to meet
eligibility requirements in
relation to becoming a
licensed electrical worker
and only if the work is
prescribed under a regulation for this paragraph;
(i)
building, under the supervis
ion of an elect
ricity entity,
an overhead electric line
on structures that do not
already carry an energised overhead electric line;
(j)
laying, cutting or sealing
underground cables that are
part of the works of an electri
city entity before the initial
connection of the cables to an electricity source;
(k)
recovering underground cables th
at are part of the works
of an electricity entity
after disconnection from an
electricity source;
(l)
altering, repairing, main
taining or recovering an
overhead electric line that
is part of the works of an
electricity entity, if the work is performed under the
entity's supervision and—
(i)
if the line is not on
supports supporting another
electric line—the line h
as been isolated from an
electricity source so that
the closure of a switch can
not energise the section of the line where work is
being done; or
(ii) if the line is on supports
supporting another electric
line—both lines have been isolated from an
electricity source so that
the closure of a switch can
not energise the section of
the line where the work
[s 19]
Electrical Safety Act 2002
Part 1 Preliminary
Current as at 8 April 2016
Page 27
Authorised by the Parliamentary Counsel
is being done or an adj
acent section of the other
line;
(m) erecting structures for
the support of electrical
equipment;
Examples of structures—
•
electric poles and towers
(n)
locating, mounting or fi
xing in place electrical
equipment, other than—
(i)
making or terminating elec
trical connections to the
equipment; or
(ii) installing supply conducto
rs that will connect the
equipment to a supply of electricity;
(o)
maintaining the structural pa
rts of the electrical traction
system on a railway, other than overhead electric lines,
that forms part of the works of
an electrical entity, if the
work is structural work
performed under a safe system
of work.
19
Types of electrical work for this Act
(1)
Electrical installation work
is electrical work associated with
an electrical installation, but
does not include the following
electrical work—
(a)
testing, repairing or mainta
ining electrical equipment
included in the electrical installation;
(b)
electric line work associ
ated with the electrical
installation.
Examples of electrical installation work—
•
installing or altering wiring or fixed appliances in a building
•
installing or altering a switchboard
(2)
Electric line work
is electrical work
associated with an
electric line.
[s 20]
Electrical Safety Act 2002
Part 1 Preliminary
Page 28
Current as at 8 April 2016
Authorised by the Parliamentary Counsel
Examples of el
ectric line work—
•
erecting an aerial conductor that
is part of the works of an
electricity entity or of
an electrical installation
•
installing or maintaining street lighting circuits
•
testing an overhead electrical
line to ensure it is correctly
connected
(3)
Electrical equipment work
is electrical work other than
electrical installation work
or electric line work.
Examples of electrical equipment work—
•
repairing substation
electrical equipment
•
repairing an electric range, whether
or not it is part of an electrical
installation
•
installing, jointing or terminating covered cables
http://www.fairtrading.nsw.gov.au/ftw/Tradespeople/Home_building_licensing/Licence_classes_and_qualifications/Electrical.page (http://www.fairtrading.nsw.gov.au/ftw/Tradespeople/Home_building_licensing/Licence_classes_and_qualifications/Electrical.page)
Tasmania
4. Meaning of "electrical work"
(1) Electrical work is any one or more of the following:
(a) work on the installation, repair, alteration or removal of an electrical circuit or associated fittings, equipment or accessories;
(b) work on an electrical installation;
(c) work on the installation, repair, alteration or removal of electrical infrastructure including lines and wires for the generation, transmission or distribution of electricity and also including supporting and protective structures relating to any such equipment, lines or wires;
(d) work that has been determined by the Regulator, as defined in the Electricity Supply Industry Act 1995, to be regarded as specialist work.
(2) Despite subregulation (1), electrical work does not include –
(a) electrical work performed under an electrical safety management scheme approved under Part 8 of the Electricity Industry Safety and Administration Act 1997; or
(b) any low voltage electrical work on telecommunications equipment that is carried out by technical workers trained in the telecommunications industry; or
(c) any extra low voltage electrical work if the electrical work is not in a hazardous area as defined by AS 3000; or
(d) the insertion of a plug into a socket outlet through which electricity is, or is to be, supplied in order to connect an electrical article or an extension cord to an electricity supply; or
(e) repair work on an electrical article that is, or is to be, operated at a nominal electrical voltage of 250 volts or less with reference to earth and that electrical article, when manufactured, was to be connected to an electricity supply with a plug and cord; or
(f) the affixing of a plug or socket to an extension cord through which electricity is, or is to be, supplied at a nominal electrical voltage of 250 volts or less with reference to earth.
The exceptions are important but I didn't see any that apply to this case.
Pretty sure you cant in QLD and TAS but not sure about NSW.
AFAIK (and I'm not a lawyer) my statements were correct on the regulations anyway.
ps. I dont agree with this level of restriction either.
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Planning on getting solar PV grid connect myself soon, but I will have to move/change the Evac tubes to fit it on.
-
Pretty sure you cant in QLD and TAS but not sure about NSW.
NSW are unequivocal on the matter:
http://www.austlii.edu.au/au/legis/nsw/consol_act/esa2004309/s3.html (http://www.austlii.edu.au/au/legis/nsw/consol_act/esa2004309/s3.html)
Does not include plug in appliances.
VIC only regulate the supply (sale) of certain electrical appliances:
http://www.austlii.edu.au/au/legis/vic/consol_act/esa1998209/s57.html (http://www.austlii.edu.au/au/legis/vic/consol_act/esa1998209/s57.html)
You are free to build your own if you do not sell it.
QLD:
http://www.austlii.edu.au/au/legis/qld/consol_act/esa2002169/s18.html (http://www.austlii.edu.au/au/legis/qld/consol_act/esa2002169/s18.html)
Cant do anything requiring skill without a license.
SA:
http://www.austlii.edu.au/au/legis/sa/consol_act/ea1996139/s4.html#electrical_installation (http://www.austlii.edu.au/au/legis/sa/consol_act/ea1996139/s4.html#electrical_installation)
No worries
WA:
http://www.austlii.edu.au/au/legis/wa/consol_reg/er1991331/s4a.html' (http://www.austlii.edu.au/au/legis/wa/consol_reg/er1991331/s4a.html')
Though there are exemptions, appliances are considered electrical work.
TAS:
http://www.austlii.edu.au/au/legis/tas/consol_reg/olwr2008472/ (http://www.austlii.edu.au/au/legis/tas/consol_reg/olwr2008472/)
http://www.austlii.edu.au/au/legis/tas/consol_act/ola2005222/ (http://www.austlii.edu.au/au/legis/tas/consol_act/ola2005222/)
A mess with inconsistent terminology, hard to determine if private DIY work is controlled.
So QLD and WA are restrictive, possibly TAS while the majority of Australia is sensible and allows anyone to make their own appliances. People from other countries think its ridiculous that we cant do the wiring or plumbing in our own houses, Australia is the exception rather than the norm. So the current roundup of Australian states is that two of them are prohibiting hobbyists (or even professionals) from making equipment powered by low voltage (mains).