80 3 X 6 cells two panels battery requirement

[knoxgi]

I am planning to build two panels with 36 3 X6 cells for each panel, what battery I should choose? this will be for an off grid power. thanks!

[Jason]

Hello and welcome to Solar Panel Talk!

I moved your post to a separate thread. Thanks for joining! Someone should be with you shortly.

[Mike90250]

Battery sizing.

First, determine your loads. Then you only want the nightly load to deplete 20% of your battery. So that gives you a size.

Then you want your solar to be able to recharge the battery from 50% dead to full, in one day, running all the normal loads too.

And the charger needs to be able to supply about 10% of the battery's capacity rating, to insure a well agitated electrolyte.

Then you must assume that your will get only 80% of the spec output of the cells.

Now you can order the cells and build your panel.

[Jason]

moving this thread to "Building Homemade Solar Panels" forum

[Clean energy seeker]

Battery sizing.

First, determine your loads. Then you only want the nightly load to deplete 20% of your battery. So that gives you a size.

Then you want your solar to be able to recharge the battery from 50% dead to full, in one day, running all the normal loads too.

And the charger needs to be able to supply about 10% of the battery's capacity rating, to insure a well agitated electrolyte.

Then you must assume that your will get only 80% of the spec output of the cells.



Now you can order the cells and build your panel.

Mike that was very helpful. I try to not discharge my battery no more than 15% ( somewhere around 12.5v) because it takes too long to recharge it back to full. It seems like the deeper the discharge, the slower the rate of recharge too.

I assume when you say dead battery, you mean discharged 20%.

[Mike90250]

Then you want your solar to be able to recharge the battery from 50% dead to full, in one day, running all the normal loads too.

I'm allowing for 20% discharge from full, daily. If you have 2 cloudy days, you are now down 40 or 50% from full. When you go below 50%, it really begins to impact the lifetime of the batteries, so you don't want to plan on regular 50% drawdowns.

[Clean energy seeker]

I'm allowing for 20% discharge from full, daily. If you have 2 cloudy days, you are now down 40 or 50% from full. When you go below 50%, it really begins to impact the lifetime of the batteries, so you don't want to plan on regular 50% drawdowns.

My charge controller shuts me off at 11v loaded, so if the battery were measured in unloaded voltage, it would probably be, 20% discharge and off it goes. Good feature.

The advise on the 10% match of the battery to solar panel amperage output sounds good. So I guess if I had a 100ah battery, I would need at least 10a coming in from the panels to get the battery solution boiling good enough to keep the battery in good shape.