Battery Size

[mrtim]

I recently purchased a solar system kit from Northern tool so I could get some power out to a shed that I have in the back of the yard. one thing I didn't know much about was what to buy for a battery that goes with the system and Northern tool didn't provide any sizing information. the manufacturer of the system is now telling me that I need 100ah for my 110 watt system and I think I have learned that it's bad for solar batteries that continually drop down to less than 50% rated capacity. I think I have ruined the first battery I bought that had a 36ah as it no longer appears to take a charge.

Advice?

[SunEagle]

I recently purchased a solar system kit from Northern tool so I could get some power out to a shed that I have in the back of the yard. one thing I didn't know much about was what to buy for a battery that goes with the system and Northern tool didn't provide any sizing information. the manufacturer of the system is now telling me that I need 100ah for my 110 watt system and I think I have learned that it's bad for solar batteries that continually drop down to less than 50% rated capacity. I think I have ruined the first battery I bought that had a 36ah as it no longer appears to take a charge.

Advice?

Hello mrtim and welcome to Solar Panel Talk

If you are using a FLA type battery you will need to have about 1/10 the Ah rating in charging amps. So my guess is that your 110 watt panel system is about 6 amps so a 60Ah battery will work for you. But depending on your loads and need for your shed you may need a bigger battery and more panel wattage to charge it.

Have you determined you daily watt hour needs? That is the beginning step to size a solar/battery system.

[mrtim]

yes about 20

[SunEagle]

yes about 20

Then a 60Ah battery should safely get you about 30 watt hours a day (60Ah x 12V x .2)/5 = 28.8 wh. That formula is using a 20% discharge rate and 5 days of no sun. You will get more watt hours if you get more usable sunlight or if you discharge below 80% SOC. Hopefully that works for you. But your battery life may be less due to a higher discharge. The number of cycles and discharge amount should be listed by the battery manufacturer.