Batteries and inverters going off grid with solar.

[Simon]

I've always considered a home solar system. Due to the large expense of a professional system and political instabilities in solar I have shied away from a grid tied system where I sell back the power. The latest political move of our Conservative government to not only remove subsidies from renewables but to tax ecologically generated power has hardened my resolve to go off grid and do it my way rather than get tied in to the politics of the moment and what some company is offering me.

Panels are not a problem. My main thing is that is batteries and inverters. Most items in my house would probably work of DC so a modified sine wave inverter would not be a problem things like my computers and LED lights. I also seem to have separate upstairs and downstairs circuits for both lights and sockets so I can easily distribute the load over smaller inverters. The only thing I can think of for things like my fridge and perhaps microwave is to use a dedicated pure sine wave inverter. That way I spend the money just where it's needed and get a cheaper inverter for other stuff.

The next thing is batteries, these will probably be the first thing I need to buy and I am uncertain as to which voltage to work with. Below are the voltage the more batteries in parallel I will need or the larger single batteries will need to be. If I can work from say 100 V then even 110 amp leisure batteries would easily give me a 5 kW storage capacity.

I also need to give some consideration to wiring up, I cannot go completely off grid as I doubt I would be able to generate enough so I would need it ability to switch over. It ability to switch over automatically would be good unfortunately that would require running wires from the back of my house to the front and modifying my distribution box to put in switchover relays and perhaps devised some sort of under voltage mechanism for the batteries so that the inverters cut out before the batteries are damaged. I expect that to be relatively easy as all I need do is detect the voltage on the batteries and turn inverters off. If the inverters or the battery management are powering a relay relay could hold the system on and once released remain on the grid until I manually switch back over.

I think inverters are my main concern as they will drive the rest of the system but I need to forward plan as I will need to bite the batteries first.

I don't want to spend a fortune on inverters but I don't want to buy cheap rubbish.

[bookaboo]

I suggest getting a comfy chair and a marathon of Martin Lortons videos, he covers a lot of what you have asked. Good inverters will cost and I'd stick to pure sine for everything, I would however suggest sharing loads across a few different units, that way when one goes bang you still have some functionality.
I have a similar project in mind for a few years time, I'm going to research the feasibility of having a DC bus for lower loads... I think having an inverter drive a bunch of switchmode powersupplies (for example LED lights, TV, PC, Laptop, Chargers etc) is probably a bit wasteful and adds two levels of complexity. The efficiency of such will of course depend on distance from the battery array.

I wonder if the Tesla powerwall will be a feasible solution any time soon.

[Zero999]

Is it really worth it from an economic perspective?

How long will it take for you to see a return on your investment?

What battery life do you expect?

If the batteries need to be replaced before you've got the money you've spent on them back plus inflation, then it's not worth it and you would've been better  off putting the money in the bank. Of course thse calculation isn't easy, since you don't know what the price of energy will be in the future.

From an environmental perspective, you need to take into account the impact of the batteries being manufactured and recycled which is often not done in an environmentally friendly manner.

[johansen]

as far as solar goes.. i can buy a pallet of solar panels for about 75 cents a watt.. i do have to pay for shipping however, which means i would need to buy 4 to 10 grand worth of panels before its really worth it.

the problem being where i live, i would probably need 8 kw of panels to provide 8-16 kwh a day of electricity. not worth it at 10 cents a kilowatt hour.
if the panels last 27 years, they would pay for themselves.

in reality its probably worth it when i look at the electricity rates rising faster than inflation.

lead acid batteries will cost you a minimum of 25 to 50 cents per kilowatt hour. --so you'd better have a good sized hot water heater, and a heat pump connected to a 500 gallon tank of water as a thermal buffer.

the jury is out with regard to lithium iron phosphate being cheaper than lead acid.. it may very well be.


as far as inverter cost goes.. its not negligible but its close to zero as far as efficiency goes.
what is not zero is the no load cost. if your 6KW inverter sucks up 100 watts parasitic load thats probably unacceptable.
there are ways to get it well below that.

check the fieldlines.com forum for the recent thread on building your own inverter from relatively cheap power jack boards and winding your own toroidal transformer.

[TheElectricChicken]

All solar is brilliant, just go for it. Start with one panel. Start saving right away. By the time you move along from one panel you'll learn a lot and be expert at big systems.

You don't need batteries in the daytime. That is that part of your bill taking a hit. You can eventually set things up so that there are different tariffs on your own home grid. So that storage gets filled, lights get priority and off peak things like a stone polishing tumbler or http://articles.latimes.com/2011/mar/10/food/la-fo-grinding-grain-20110310 get done later when there is too much sunlight.

Don't worry about generators yet unless you have a factory near your house where they throw out wood.  Then you can get one of these or and also can drive but it helps you when there is cloudy weather for a week or you want to have a welding party.

[Simon]

Is it really worth it from an economic perspective?

How long will it take for you to see a return on your investment?

What battery life do you expect?

If the batteries need to be replaced before you've got the money you've spent on them back plus inflation, then it's not worth it and you would've been better  off putting the money in the bank. Of course thse calculation isn't easy, since you don't know what the price of energy will be in the future.

From an environmental perspective, you need to take into account the impact of the batteries being manufactured and recycled which is often not done in an environmentally friendly manner.

Economically I'm not sure. But I have a very strong desire to stick two fingers up to the government and the energy companies, whilst also being very well aware that prices are likely to rise. Let's face it just listen to the news, Centrica are making I believe 2000 people redundant despite doubling their profits over the last year the excuse is that they gave Joe public a 5% price reduction which was a partial passing on of their own wholesale costs going down. With this sort of attitude from our private and often foreign energy companies I'm willing to bet the money that energy prices will go up and they will come a time when they will start to go up quite quickly.

As for battery lifetime I hear that well treated lead acid batteries can last 20 years. That is why I am only expecting 500 W capacity from a 110 amp battery and if I had 10 batteries that would be 5 kW. I believe the batteries are around £80 although I might get a good deal on 10. Of course the battery configuration is also driven by the inverters.

Panels are cheap now it's actually a case of the fixings and wiring could be the thing that turns out to be more expensive than expected. I have a section of ground which would be ideal for a frame to hold a substantial amount panels of course the frame will cost money but my house roof does not point South so it's pretty pointless putting them up there.

[TheElectricChicken]

Dont forget to remove the largest electrical loads that you have too. Like get solar hot water, because electric hot water sucks up the juice.

[TheElectricChicken]

As for battery lifetime I hear that well treated lead acid batteries can last 20 years. [.....] I believe the batteries are around £80 although I might get a good deal on 10.

Simon, the best way to get cheap BIG batteries is to work out where in your nearest city all the I.T. people are. That area is the best place to go door to door and ask about old Uninterruptible Power Supplies. Many I.T. firms don't even bother to change the batteries, they just throw out and buy new U.P.S.s every 12 months like clockwork because they are IT experts not battery experts and it's a negligible irrelevant cost on paper for big companies. Often places will just give them to you, but you can buy them at auction online for nothing. I usually set a limit of at least 2kva and less than $50. Yes you get the UPS as well as the batteries to test. End up with more batteries than you know what to do with. good ones too.

[nowlan]

Going off grid will never be worth it, if you have access to the grid.

Get solar, but size it to your day time needs. Even if your not home during the day, switch loads like washing to peak solar times.

If you do want to pursue batteries, look at the what the EV guys are using.

[ralphd]

In the last 5 years wholesale electricity rates have not gone up, they've gone down.  The average in NA now is ~3c/kWh.
http://iso-ne.com/

[ralphd]

Grid-tie inverters cost ~30c/W, and are getting cheaper faster than the panels.
https://www.littleboxchallenge.com/

[Simon]

In the last 5 years wholesale electricity rates have not gone up, they've gone down.  The average in NA now is ~3c/kWh.
http://iso-ne.com/

wholesale yes

[johansen]

In the last 5 years wholesale electricity rates have not gone up, they've gone down.  The average in NA now is ~3c/kWh.
http://iso-ne.com/

for small residential houses, by the time you add the monthly minimum fee, you're past 20 cents per kilowatt hour.

for these folks, solar is absolutely worth it, particularly in California where some folks are allegedly already paying 25 cents a kilowatt hour plus monthly fees.

[Simon]

My heater is gas, I'd need the pure sine wave inverter for the electrics. Although considering it has a mains powered mechanical timer clock and it has its own wiring back to the main switchboard I might as well leave it connected to the mains.

[TheElectricChicken]

My heater is gas, I'd need the pure sine wave inverter for the electrics. Although considering it has a mains powered mechanical timer clock and it has its own wiring back to the main switchboard I might as well leave it connected to the mains.

Can't change the mechanical clock for you, but I do know that the output from UPS inverters is much better than the mains.

[ralphd]

In the last 5 years wholesale electricity rates have not gone up, they've gone down.  The average in NA now is ~3c/kWh.
http://iso-ne.com/

for small residential houses, by the time you add the monthly minimum fee, you're past 20 cents per kilowatt hour.

for these folks, solar is absolutely worth it, particularly in California where some folks are allegedly already paying 25 cents a kilowatt hour plus monthly fees.

Even 25c/kWh is cheaper than what it'll cost to go off-grid.  For grid-tie, the economies of scale kick in around 8-10kW, but your average residential suburban home in CA doesn't have enough south-ish facing roof for 8-10kW.

[johansen]

Even 25c/kWh is cheaper than what it'll cost to go off-grid.  For grid-tie, the economies of scale kick in around 8-10kW, but your average residential suburban home in CA doesn't have enough south-ish facing roof for 8-10kW.

perhaps, but if my folks were paying 25 cents/kwh i would buy solar panels where i live now, i think i could pull it off.
payback should be in 8 years if you're off grid completely.

that said most people can't. and the reason why is because the only thing they know is:
professional installation: 1 dollar per watt.
grid tie inverter: 1 dollar per watt.

letting the utility buy your own power for less than half the residential rate? priceless.

but once you add up all the inscentives and government cash, yes it is very profitable if you can sell the utility power at 46 cents a kilowatt hour.

the key thing to do is shift all your power to onpeak hours.
cook food with gas, heat your hot water with a heat pump during peak hours. (yes this does work and a few people have built their own systems using just regular propane as a heat fluid, you don't need no titanium turbines and co2)

put your washing machine on a timer to wash your cloths while you're at work, etc, etc.

once you do all these things and half a dozen others your battery load is minimal.. and then you can afford to experiment with lipho4 cells which should be cheaper than lead acid on a lifecycle basis (but no one has proved it yet)

[Simon]

Seems the highest input voltage you can get for an non grid tie inverter is 48V, and they are not bad either on ebay although I'm wary, 100 quid can get you a KW

[Aodhan145]

If you think of going on-grid. (Battery technology today is not good enough yet. This might be your best option) You can get a Sunny Home Manager for a SMA Inverter. It can turn off and on loads in your house. So when you are generating enough electricity you can use it for things like your washing machine, heat pump,  . This will get the most money out of the electricity you generate instead of selling most of it back out to the grid. The only problem is the Sunny Home Manager does not have UK sockets/plugs. So you need a Plugwise Stretch with its socket, it communicates with the Home Manager and the Home Manager communicates with the inverter. The Plugwise Stretch also has a feature to turn off appliances when they have been on standby for a long time.

[Simon]

If you think of going on-grid. (Battery technology today is not good enough yet. This might be your best option) You can get a Sunny Home Manager for a SMA Inverter. It can turn off and on loads in your house. So when you are generating enough electricity you can use it for things like your washing machine, heat pump,  . This will get the most money out of the electricity you generate instead of selling most of it back out to the grid. The only problem is the Sunny Home Manager does not have UK sockets/plugs. So you need a Plugwise Stretch with its socket, it communicates with the Home Manager and the Home Manager communicates with the inverter. The Plugwise Stretch also has a feature to turn off appliances when they have been on standby for a long time.

The problem is I have one of those inconvenient things called a job. So I would not be at home to use electricity during most of the time it is been made available. It is very clear to me between government policy and the attitude of the energy companies that I would never be able to sell electricity back for any money. And in case it was not obvious from my initial post this is not so much about saving on my electricity but sticking two fingers up to the government and the energy companies. In time my investment may well pay off particularly if the cost of energy does go up.

[KD0CAC John]

How come nobody looks at return on money with just paying your electric bill monthly ?
The only issue I see is the upfront cost of building a system for hole house .
In the US there are a lot of companies installing a system and you pay them , this is for profit , so the idea that it does not pay for its self is off .
I have been doing solar for decades and watched prices for panels fall from as high as b.s. / rip off $25 per watt , and now as low as $00.26 per watt .
As for inverter prices falling , that only seems to be happening with non home use portable cheep inverters .
Good inverters for hole home use are still high .
As for batteries , buying right , flooded lead acid is still the cost per- performance , especially if you find surplus commercial , fork lift , telecom etc.
My last battery bank was 4 x Trojan 6v L16  and lasted 12+ yrs. before I moved did use and froze one winter .
Nickel Iron batteries can last 50 + yrs. and almost hard to kill .   

[TheElectricChicken]

Seems the highest input voltage you can get for an non grid tie inverter is 48V, and they are not bad either on ebay although I'm wary, 100 quid can get you a KW

I'm not sure anyone would want one, however there are UPS's which use battery strings of 90v or so. I have one, I can find out exactly the number of 12v batteries that it has in series if anyone has an interest (actually is it 10?)

Making a home made charger for that string of batteries wouldn't be too hard. I have not tried as I do not like high voltage DC myself. Some people can deal with it though and have probably done it.

[Aodhan145]

If you think of going on-grid. (Battery technology today is not good enough yet. This might be your best option) You can get a Sunny Home Manager for a SMA Inverter. It can turn off and on loads in your house. So when you are generating enough electricity you can use it for things like your washing machine, heat pump,  . This will get the most money out of the electricity you generate instead of selling most of it back out to the grid. The only problem is the Sunny Home Manager does not have UK sockets/plugs. So you need a Plugwise Stretch with its socket, it communicates with the Home Manager and the Home Manager communicates with the inverter. The Plugwise Stretch also has a feature to turn off appliances when they have been on standby for a long time.

The problem is I have one of those inconvenient things called a job. So I would not be at home to use electricity during most of the time it is been made available. It is very clear to me between government policy and the attitude of the energy companies that I would never be able to sell electricity back for any money. And in case it was not obvious from my initial post this is not so much about saving on my electricity but sticking two fingers up to the government and the energy companies. In time my investment may well pay off particularly if the cost of energy does go up.

It works for when you are at work. You can throw your dirty clothes in a washing machine, then when you are at work it washes the clothes or if you use a heat pump / immersion heater you can store the hot water in a tank for when you are back from work. There is lots of other applications of this. Nobody is really at their house when they are generating the most electricity (most people have those things called jobs).

[ralphd]

As for inverter prices falling , that only seems to be happening with non home use portable cheep inverters .
Good inverters for hole home use are still high .

CAD $1700 == USD $1300 for a 6kW inverter is 22c/W:
http://dnmsolar.com/product.php?product=126

[TheElectricChicken]

CAD $1700 == USD $1300 for a 6kW inverter is 22c/W:

Strange, smaller ones are much cheaper

$120 1.5kw

http://www.ebay.com.au/itm/1-5-kW-Solar-Grid-Inverter-Brand-New-in-Sealed-Box-/141743406192

$100 1.5kw

http://www.ebay.com.au/itm/Sunna-1500TL-1-5-kw-Grid-Tie-Connected-Solar-Inverter-/221847655429

$200 2kw

http://www.ebay.com.au/itm/Sunnyroo-SR2000TL-2-kw-Grid-Tie-Connected-Solar-Inverter-/321820768035

they are for 220v though...