Solar battery run time question

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Small Cabin Forum / Off-Grid Living / Solar battery run time question


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thetick Member	# Posted: 11 Mar 2015 19:09 Reply here is the setup; (8) 225 ah AGM 6 volt batterys, wire series/parallel @ 24 volts. If I have a pretty constant 40 amp load, how long should I be able to run? Assuming a DOC down to 0% just to make things simple...

MtnDon Member	# Posted: 11 Mar 2015 19:51 Reply Quoting: thetick (8) 225 ah AGM 6 volt batterys, wire series/parallel @ 24 volts. Which is 450 AH at 24 VDC The amp hour capacity is calculated on the discharge period of 20 hours. Over 20 hours theory states that you would be able to withdraw at the rate of 450 AH / 20 hours = 22.5 amperes (taking it down to zero. But you want to draw at the rate of 40 amperes. Plain math calculates that to be 450 / 40 = 11.25 hours. Here's where theory falls apart. Withdrawing at a higher rate basically means the time will be reduced. That difference is due to the Peukert Effect. There are online Peukert calculators. The big question is what is the correct value to use for the batteries you have. This can vary. Instead of that 11.25 hours it might only take 7 hours. That's a guess. As the batteries age the available energy will fall; Peukert value goes up.