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A Reader wrote to us: Hi!

I intend to use a solar system, but don’t seem to get proper advice on storage batteries.

I was advised to use Trojan 105 (6 volt) golf cart batteries x 2 for my six 22 Watt solar panels. Apparently there’s also a 12 volt type golf cart battery available, instead of the two 6 v. batteries. We have daily good sunshine of app. 8 hours and PV output app.12 amp @ app.. 16.8 (Voc).

Now, I don’t know if above are **wet cell** types, giving of gasses or whether they are sealed types. And moreover, should their electrolyte be topped up etc. The main point is: I would like to keep my batteries inside the house, due to excessive heat in our area, but with vapours it would be very corrosive indoors. On the other hand I would prefer “deep cycle” batteries for longest lifespan, that would be the most cost effective.

I would greatly appreciate it if you could advise on these matters.

Kind regards, Hans Henrico

STEVE SPENCE replies

I need to know more about his loads, and where he’s located, but I’ll give some rules of thumb.

6 x 22 watts = 132 watts

A nice day in California might have 6 “full sun” hours. This is different than hours of daylight. Here in NY, we get on average 3 “full sun” hours.

I’ll use NY as the example.

132 watts x 3 “Full Sun Hours” = 396 watt hours (wh)

Trojan T105 6v deep cycle batteries (superior to 12vdc golf cart
batteries) can contain 225 ah each, and need two in series for 12vdc.
Two in series gives you a 225ah, 12vdc pack. You should only discharge to 50% maximum, so you really have 110 ah or so available. 110ah x 12vdc = 1320 wh, so it would take 3 days of no load to fully charge these batteries from 50% discharge. You will therefore want to keep your daily loads less than 396 wh’s (396/12= 33ah’s). An example would be 10amps (at 12vdc) for 3 hours would be 30 ah’s.

Trojan t105’s are wet cell lead acids, and should be in a sealed battery box indoors, with a vent to the outdoors. distilled water should be added monthly if needed.

Batteries are rated at the 20 hour rate, so 225ah (110ah usable) over a 20 hour period, is a maximum of 11.25 amps per hour, for 9.7 hours (109.125ah). If consumed faster, then less than 110ah is available. Keep in mind you only have 33 ah’s per day for recharging, given my NY example of 3 full sun hours. California, at 6 Full Sun Hours would give you 66ah’s a day for recharging. Tell me where you live, and I can give better numbers.

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