In the calculators on the web that I've seen used to compute the number of batteries needed in a battery bank, all calculations seem to be based on the capacity of the PV array, not the daily electrical usage.
Example: 1500 W array (the example from the Alt-E bb calculator)
5 day supply = 1500 X 5 = 7500 W-days = C
( C X T ) / D = (7500 X 1.02) / 0.50 = 15,300
where T=temperature multiplier for 75 degs. (1.02)
D=deep cycle multiplier (50% = 0.50)
15,300 / voltage of battery = amp-hrs required
therefore, 15,300 / 12 = 1275 amp-hrs
required amp-hr / amp-hr of selected battery
= # of batteries (rounded up to nearest even integer.)
1275 / 344 = 4 batteries
However, this implies that the array in the days leading up to the cloud period would only collect 1500 watts per day. That doesn't seem correct to me. I would have expected a 1500 W array to produce 1500 Watts per hour of full sun for each day before the cloudy period.
Am I missing something here ?
Any thoughts would be greatly appreciated.
Ed
