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Old 06-09-2020, 06:34 PM   #1
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Battery Bank for Solar Panels

How many batteries and Amp Hours did you decide to go with? Trying to decide how many batteries and Amp hours, I want to go with. Your system?!?!

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Old 06-09-2020, 07:35 PM   #2
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You need an energy budget and figure how many days of autonomy (DOA), that is, days of less than favorable solar conditions, you need. In my case I figured 3 days. Then you need to know the maximum discharge allowed for the battery type. In the case of AGM and Gel, it’s 50%, so I doubled the 3 DOA and in my case it was just a little more than 400Ah, so I got 400 Ah and if I start running down, I’ll stop blasting the stereo.
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Old 06-09-2020, 07:39 PM   #3
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An energy budget is a calculation in Watt-hours. So if you have 8 3 watt LED puck Lights and you figure you’ll run them 5 hours a day you’d have

8 x 3 x 5 = 120 watt-hours

Do that for everything, add them up, and that’s your budget.
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Old 06-09-2020, 09:39 PM   #4
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I have a 450 amp-hour 12 volt battery bank. Made up of 4, 6-volt golf cart batteries in a box down under.

Nowadays people do it differently. Of course, size the capacity for your load conditions, but what battery bank voltage? What kind of battery? How much money you got? How much experience doing electrical work?

Without the money, or electrical experience, but some common sense, you should do a 12 volt battery bank. Pairs of 6-volt golf cart batteries, depending on your load. My battery box can hold 3 pair, which would be about 675 amp-hours at 12 volts. The golf cart batteries are flooded lead-acid, which means there're heavy and filled with acid.

If I were doing it over I'd do a 48-volt lithium-ion (of some kind), or an absorbed mat lead acid, battery bank. The higher voltage battery bank is about solar controller (and inverter) efficiency.

There's a low voltage thing in the NEC, and I thought it was for under 24 volts. Looser reguation. Regardless, although none of us ever get any kind of electrical inspection on our bus, it behooves this community that we follow the Code as closely as possible.
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Old 06-09-2020, 09:57 PM   #5
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Quote:
Originally Posted by Stoshtan View Post
How many batteries and Amp Hours did you decide to go with? Trying to decide how many batteries and Amp hours, I want to go with. Your system?!?!
We went with 6 6V golf cart batteries. 12V system at 700AH. No complaints, we've been able to live full time without really needing to ration our energy. We've got a generator, but we've only used it a few times. The 1100w of solar keep the batteries topped up. We rarely go below 80%.
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Old 06-09-2020, 10:49 PM   #6
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How many batteries and Amp Hours did you decide to go with? Trying to decide how many batteries and Amp hours, I want to go with. Your system?!?!
How will you charge your batteries? If it's from solar, the generally-accepted wisdom among the cognoscenti on RE forums such as Northern Arizona Wind & Sun is to charge FLA batteries at between 5 and 13 percent (of their 20-hour rating). Anything less than 5% runs the risk of long-term deficit charging that will kill the batteries long before their natural lifespan, and anything over 13% could either boil the batteries, or in the worst case cause a thermal runaway if your charger isn't temperature-corrected.

Batteries are just one part of the overall electrical system, and they must be sized not only to supply your needs but also to be charged correctly by whatever means you'll use. Everything's got to stay balanced!

John
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Old 06-10-2020, 02:17 AM   #7
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Originally Posted by Iceni John View Post
Batteries are just one part of the overall electrical system, and they must be sized not only to supply your needs but also to be charged correctly by whatever means you'll use. Everything's got to stay balanced!

Well said!
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