nofossil said:
You could get an idea from reading your meter at the start and end of your 16 hour period for a few days. That will give you your consumption in kWh. A deep cycle battery is good for about 1 kwh, and you'd have to subtract for inverter losses. Might be good to get an idea of how many cycles a battery is good for - I don't know. There may be some issues relating to discharge rate and the extent of discharge that might affect battery life. Somebody out there knows, but it's not me.
Follow nofossil's suggestion to get a profile of usage, then go through and figure out how to cut some of that usage, remember every watt saved is watt you do not have to buy. Next do you want to add solar or wind some day? OK, now you have a target number of kwh's needed, now double that. That is the min size battery bank you will need assuming you will be able to charge the next day.
Why double the size? 1st) you can not total discharge a battery bank with out distroying it. 2nd) you need some measure of reserve capacity just because you do not know what will happen.
DO NOT I repeat DO NOT use standard automotive or marine batteries. Of Course you can and when come back to whine about what a short life that pack had I will be first in line to tell you I told you so.
What to use then? Batteries designed for this type of service vendors like: Concorde
http://www.sunxtender.com/ , Surrette Rolls;
http://www.surrette.com/ With these vendors you will have a much longer battery life.
You will also need a inverter/charger system, I only know of two vendors Xantrex
http://www.xantrex.com/xw/ and Outback Power; (broken link removed) . Both offer automatic generator start when the battery pack gets low.
Both Xantrex and Outback offer battery backup offgrid and ongrid systems. If you have grid available why not sell back and get credit. I would NOT recommend selling off of your generator or from battery those are NOT cost effective for a variety of reasons.
Choice of solar panels there are many depends whats on best offer from your local dealer. Wind power you can roll your own see;
http://www.otherpower.com/ there are various commerical wind power systems on offer BE AWARE that most wind vendors inflate the amount of power they produce. Stay away from eBay. One vendor I like
http://www.skystreamenergy.com/skystream/ this model seems to be honest and it has built in grid tie. In the installation manual is a connection diagram to allow this unit to work with Outback Power inverter system to act as battery charger offgrid/ongrid, a very neat and interesting system.
Reading; start with the bible of the offgrid community
http://www.homepower.com . They also have an annual wind power survey in this months issue Jan/Feb-08 (barnes & noble). Homepower is the only magazine that I read the advertisments before the articles, just to see what is new.
This should get you started.
-- Brandy
