Solar & battery
Solar Battery Capacity Calculator
Convert between amp hours and kilowatt hours, and see what is usable at a given depth.
Result
Depth of discharge is how much of the nameplate you may actually use. Lithium iron phosphate tolerates 80% to 90%; lead acid should not go past 50% if you want it to last. Round-trip efficiency then takes another 5% to 15% on the way in and out. Amp hours mean nothing without a voltage: 200 Ah at 12 V is 2.4 kWh, and the same 200 Ah at 48 V is 9.6 kWh. Comparing banks on amp hours alone is the classic mistake.
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About this calculator
Why is amp hours a bad way to compare batteries?
Because it ignores voltage. Energy is amp hours times volts, so a 100 Ah 48 V battery holds four times the energy of a 100 Ah 12 V one.
What voltage should a system use?
Higher is better for anything sizeable: 48 V systems carry a quarter the current of 12 V for the same power, so the cabling is far smaller and the losses far lower.
The formula
kWh = amp hours x volts / 1000
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