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John is right about the 50% thing even 25% will get the full 10 or so years out of AGMs. When I was working out the battery bank you did some simple maths.
Add up all the draw in watts eg
Lighting 6x3watt 12 volt globesx10 hours =180 watt hours.
Add up everything and it might come to 1 to 2 kwh
Then multiply by 50% discharge and then cloudy days say 3
So 1.5 kwh x 2 x 3 = 9kwh.
Divide by battery voltage to get amp hours
9000/12 = 750ah of battery bank needed to run for 3 days and only discharge at 50% not including inverter loss etc.
So 4x 12 volt 220ah in series should get this.
Or you can go a compleatly different way and have a good auto start genset in the system buy an underrated battery bank and hammer the batterys and get only 4 years out of them but burn more fuel with the genset.
Fuel is a lot cheaper than batteies and if you upgrade a smaller bank every 4-5 years in the long run it may be cheaper and also technology changeover every 4-5 years is better than 10-11 years.
Then only thing is most households use up to 10kwh which needs a huge battery bank.
Hope this all makes sense.
Cheers
Andy
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