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Battery for Off Grid Solar - How to Calculate Battery Amp Hours

Battery for Off Grid Solar - How to Calculate Battery Amp Hours

Every day we get asked what battery should be used for off grid solar?  The answer is always different because every customer has a different situation...  Here are the questions we ask

What is the size of load you are looking to power?  What is the sum total of watt hours.?  Google Watt Hours, it is easy to calculate.

Are you putting the batteries inside or outside?

Do you have a lot of space for big 2 volt or 4 volt batteries?

Do you have a forklift to move big 4 volt or 2 volt batteries?  400 lbs ea

Design to Never Exceed Three Strings of Batteries

Here is an example of a job were asked to quote

The customer wants about 2000 amp hours using a 48 Volt inverter
Should he buy 6 volt, 4 volt or 2 volt?

Watts = Volts x Amps and Batteries for Solar Power

A) Forty Eight  Trojan L16RE-2V  2 Volt 1110 Amp Hour (ah)  119 lbs 11.67" x 6.95" x 17.56" $259 ea

48v * 1110 a = 53280 watts  (24 x 2v =48 volt)

Two banks of twenty four 2 v bank connected in series then parallel = 48 v 2220 ah bank

approx battery cost $ 12432

Expected life, with properly size pv array, good hydration, not excessive hot climate, 40-50% DOD , ten years

 Trojan L16RE-2V

or

B) Twenty Four Trojan L16P  6 Volt 420 Amp Hour (ah)  114 lbs 11.67" x 6.95" x 16-74" $260 ea

One String = 48v * 420 ah = 20160 watts  (8 x 6v =48 volt)

Eight 6 v batteries connected in series, then connect the three stings in parallel (3 * 420ah) = 48 v 1260 ah bank (not enough power)

approx battery cost for twenty four L16P$ 6240

Expected life, with properly size pv array, good hydration, not excessive hot climate, 40-50% DOD , six years

Trojan L16P

or

C) Twelve Trojan Ind29-4V  4 Volt 1618 Amp Hour (ah)  465 lbs 27.10" x 10.35" x 23.81" $1200 ea

One String Twelve Batteries = 48v * 1618 ah = 77664 watts  (12 x 4v =48 volt)

Twelve 4 v batteries connected in series but only one string = 48 v 1618 ah bank (not enough power but closer)

approx battery cost for twelve Ind29-4V $ 14,400

Expected life, with properly size pv array, good hydration, not excessive hot climate, 40-50% DOD , Twelve years

 IND29-4V

or

D) Twenty four Crown 2CRP3000 2 Volt 2050 Amp Hour (ah)  259 lbs 10.56" x 6.56" x 29" $1200 ea

One String Twenty four Batteries = 48v * 2050 ah = 98400 watts  (24 x 2v =48 volt) 

Twenty four 2 v batteries connected in series but only one string = 48 v  2050 ah bank (hit the mark with only one string!)

approx battery cost for twenty four 2CRP3000 2 Volt $ 28,800

Expected life, with properly size pv array, good hydration, not excessive hot climate, 40-50% DOD , Fifteen+ years