Author Topic: Looking at getting a home Solar system  (Read 6669 times)

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Offline Lightages

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Re: Looking at getting a home Solar system
« Reply #25 on: October 16, 2012, 03:15:55 pm »
First off: Unless you get grid tie payback, and/or tax rebates, then solar is still not cheaper than just using the grid in almost any part of the world.

So some some questions need to be answered first about what you want a solar system to do for you.

Is the solar system to be an experiment or education or practical offset of less environmentally friendly power or a total replacement for grid or grid tie payback system?

If this is a grid tie payback system, or a system to offset less environmentally friendly power, then you optimize the system to dump power back to the grid at peak payback/cost times. If it is to go off grid completely then you maximize power production all day. The two optimizations are not necessarily the same. It might be that peak power consumption is late afternoon so you optimize you panel orientation for that time of day. If you are maximizing power production it is sometimes beneficial to optimize the panel orientation for late morning before the panels start getting too hot and lose efficiency.

If you are going grid tie, you might also want to consider having a big enough battery bank to have some autonomy for a period of power outage from the grid.

If you are going off line, the biggest consideration in "making" energy is lowering your consumption first. Get rid of parasitic power use, buy a better fridge or freezer, more efficient anything! A watt saved here will lower your off grid system costs by a huge factor. Before you design any off grid system you NEED to measure your actual daily use of power so as to not find yourself in a deficit power condition.

Some useful tips:
1. DO NOT think that you can have a huge battery bank for long autonomy and then trickle charge them when power production is good. Lead acid batteries (they are by far the most commonly used) require a minimum % of their rated capacity in charge current or they will die an early death from plate sulphation. The minimum charge current is to ensure that the electrolyte gets moved and that not just that in contact with the lead plates is "locally" charged.

2. Count on destroying, or at least causing the early demise, your first battery bank. This happens to almost everyone the first time until they get a grasp on batteries and their quirks. They are not simple devices but rather a mixture of electronics and chemistry.

3. For the best bang for the buck used forklift batteries can be very useful especially as a first battery bank that might get trashed.

4. The most expensive but least problematic batteries are AGM types. They will withstand freezing, lower discharge and lower minimum charge rates. They are also safe for use inside the house without ventilation.

5. The most flexible inverter on the market, IMHO, is the Schneider/Xantrex range of grid tie inverters. They can manage a connection to the grid, a generator, and a huge battery bank all at once. If you connect this with their MPPT60-150 solar charger and some software and a cable, you can get full real time data from the system for a webpage and logging too. There is also a generator management controller. All of this connects together on their proprietary buss which is an adaption of CANBUS.

6. Solar panels are now so cheap that sun tracking is not worth it. The added expense and maintenance for the tracking system and mounting can gain you around 30% more energy harvest per day. Usually it is cheaper to add more panels to get that extra 30% at less cost and maintenance. Seasonal panel angle changes ARE worth considering.

7. If designing for total off grid, consider the number of days you might not have sun at a stretch and design the battery size to meet that length of time, and then the number of panels needed to charge the minimum rate required by the batteries.

8. Design for battery depletion of no more than down to 70% capacity for normal daily use, and for occasional 50%. Batteries do not like being discharged to less than 50% and should be recharged above 90% as soon as possible, better within two days always. Take a battery system down to less than 50% and their life will be shortened dramatically. Take them to 0% charge and kiss them goodbye.

9. If you plan on piece by piece expansion of a system then it should be noted that you cannot add more batteries into a bank after they have been cycled more than somewhere around 50 times. There will too much of an imbalance in the batteries that they will die quite fast from imbalance of charge/discharge. It is always better to have too much panel instead of too much battery as far as battery life goes. But on the other hand it is better to have the size of battery bank you need for proper autonomy time as it is not easy to add to the bank later.

10. For an off grid system, you need a generator. Don't cheap out. Get a good inverter output generator  and not one of the cheap Chinese simple generators. Their output waveform is usually atrocious and some inverters will probably reject them as power source or they can be dangerous for fridge motors for example. The good inverter output generators are also usually quieter and more fuel efficient.

11. If you do not want to go totally off grid then maybe a good design is to have your solar system take care of specific items you wish to have working during a power outage. A fridge, wireless telephones, cable modem, a couple of lights and a laptop are usual targets for this approach. That way you still have the food safe, and some light consumption conveniences.


If this is to be an experimental/play system then there are so many options in the low range it is hard to recommend anything specific. The most important thing is to not bother with anything other than sine wave output inverters as the "modified sine wave" ones are useful for some things but absolutely useless for other equipment. DO NOT use car batteries for energy storage. They are not designed for this and will die within months from this kind of use. Deep cycle marine batteries are still not suitable as they are designed with slightly thicker plates and can take a slight deeper discharge for a slightly longer period of time but they are not designed for long term discharge. A good start for small systems are wheel chair batteries in either AGM or GEL cell types.

« Last Edit: October 16, 2012, 05:00:06 pm by Lightages »
 

Offline johnnyfp

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Re: Looking at getting a home Solar system
« Reply #26 on: October 17, 2012, 04:03:16 am »
If money was no object, what about LiFEPO4 cell's? They seem to have better cycling capabilities then Pb.
 

Offline NiHaoMike

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Re: Looking at getting a home Solar system
« Reply #27 on: October 17, 2012, 04:28:11 am »
If you're looking to make an independent power system (on board a RV, for example), it's much more cost effective to try to use the energy as it's being generated. For example, you could have the refrigerator automatically set itself to a lower setpoint when there is a lot of sunlight, resorting to batteries only if it really needs to. (Add more thermal mass to the fridge in the form of water in order to make it work more effectively. It works really well if the water can freeze, since phase change is a really good way to store energy.)
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Online EEVblog

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Re: Looking at getting a home Solar system
« Reply #28 on: October 17, 2012, 05:28:48 am »
If you pay for wind power electricity how do you know that the electricity being delivered was from a wind generator and not a coal powered unit.

You don't know where your actual electrons comes from, it's called the grid for a reason.
The whole idea is that you pay extra to buy available capacity on a wind farm, or solar, or gas, or whatever.
In Australia it is a government audited program and publicly available info, and there are various levels from 10% to 100%, and 100% "new" which means new infrastructure put in place after a certain date.
It is very important who you sign up with and what plan to know exactly what you buying.
When we first signed up we did our own auditing of the whole thing, and it was all above board and added up.

Dave.
 

Offline Strada916

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Re: Looking at getting a home Solar system
« Reply #29 on: October 17, 2012, 05:40:43 am »
Had a 3kw panel array in stalled. With a sma Sunnyboy 4000tl. Its been runn oi ng for a yesr now. In that year it has made 4500kWh. Thats about 13kwh a day that we are not billed. On average synergy snd WA gov pays us about $25 a month in feedin.Sma have Bluetooth connectivity and you can use sunny explorer so read data remotely within the house.
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Offline G7PSK

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Re: Looking at getting a home Solar system
« Reply #30 on: October 17, 2012, 12:47:43 pm »
If you pay for wind power electricity how do you know that the electricity being delivered was from a wind generator and not a coal powered unit.

You don't know where your actual electrons comes from, it's called the grid for a reason.
The whole idea is that you pay extra to buy available capacity on a wind farm, or solar, or gas, or whatever.
In Australia it is a government audited program and publicly available info, and there are various levels from 10% to 100%, and 100% "new" which means new infrastructure put in place after a certain date.
It is very important who you sign up with and what plan to know exactly what you buying.
When we first signed up we did our own auditing of the whole thing, and it was all above board and added up.

Dave.

Here in the UK due to the EU regulation we pay a levy on all the power used if I then went for so calld green power I then get charged extra on top having already paid the levy used to subsidize wind power, and all this government regulated.Also if I buy green power I still get to pay the carbon emmisions tax.
 


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