Rob R. wrote:So what kind of battery bank is needed to meet that demand?
A battery bank that is huge! Assuming that as a rule you only ever want to discharge a deep cycle battery bank to 50% of full charge, and using a midrange one day demand for the coldest day of the year of 8,000 Watts required (8 KWH), and assuming a 24V inverter I get:
8,000 Watts / 0.5 (for 50% discharge) = 16,000 Watts worth of batteries
16,000 Watts / 24 Volts = 667 amps worth of batteries. Multiply times 1.1 for the typical 90% inverter efficiency and you get 734 amps.
3 parallel wired banks of 245 amp rated 6 volt deep cycle batteries, each bank leg with 4 batteries (since 6V x 4 = 24V) would do it. The 3 banks in parallel would deliver the required 734 amps (3 x 245 = 735 amps). 12 batteries total. For average winter days this should provide up to
4 full days of boiler operation on batteries alone, but on the coldest single day in the past 10 years it would only (perhaps) provide 1 full day of heat.
The first battery seen on this website would come close. http://www.altestore.com/store/Deep-Cyc ... Acid/c435/
12 x $200 = $2,400 for the batteries.