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# Thread: How many batteries with a 160 watt solar system?

1. ## How many batteries with a 160 watt solar system?

I have enough solar panels to equal 160 actual watts of output in fairly bright sunlight. I also have a Xantrex controlled that can handle up to 60 amps of input current.

How many deep cell batteries can I charge with this setup based on a very light load?

2. Depends on your location. If you live up north only around a 75 AH battery at 12 volts, up to 150 AH if you live in Arizona.

What do you mean by a tight load? Systems are designed around the amount of power you use in a day and your location.

3. I was hoping you would say 5-6 deep cycle batteries lol. I live in the high desert of California. Lots of sun. What I mean by light load is that I will not put any draw on the batteries at all for weeks at a time.

4. Originally Posted by tundrawolf
I was hoping you would say 5-6 deep cycle batteries lol. I live in the high desert of California. Lots of sun. What I mean by light load is that I will not put any draw on the batteries at all for weeks at a time.
Sorry to disappoint you but it is a simple physics problem.

You say high desert but that does not answer the question of your solar insolation. But for argument sake let's say you get a 4 Sun Hour Day. The most power your 160 watt solar panel array generate in a day with a battery system is 160 watts x 4 hours x 66% efficiency factor = 422 watt hours at best.

Ok to size the battery properly you select a size based on 20% discharge per day. So with 422 wh we can multiply by 5, so 422 wh x 5 = 2110 wh capacity. Now to find the battery amp hours all you have to do is divide by the battery voltage so 2110 wh / 12 volts = 175 Amp Hours.

So as you can see from the example you design based on your daily power requirement and location, not buy something and pray it works.

5. Looking at it another way, 160W of panels, gives you 130W of power (after de-rateing) at 14V, (standard charging voltage) thats only 9.2 amps. That would maintain 9, 100ah batteries, but if a battery is discharged, you would not have enough power to recharge it before it begins to sulphate, and degrade, from not being charged. Might take 4 or more days to "top off" the battery bank, and damage is done after 24 hours.

2 batteries would be rechaged in 2 days, preventing damage. After a year of weekends, you could have 5 dead batteries, or 2 working ones.

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