Your Questions About Solar Power Panels

Your Questions About Solar Power Panels

How many watt solar panel do I need to charge a 12v battery that wont be using much electricity?

1. The 12v battery will only be turning a small 12v motor that will be turning very slowly yet possibly or a long time.
2. 1-2 hours max per day it will be running
3. I want it to be fully sufficient on solar power once the energy in the battery runs out.

What specifications for my panel do you think I will need. However, i have limited space so the smaller the better as long as it can do the job

You need to do some calculations. First, what is the “small” motor’s actual rating in current drawn. Second, what is the size of the battery.

“fully sufficient on solar power once the energy in the battery runs out” is not possible, as the sun will set when night comes.

If the motor is 1 amp, and it runs 2 hours, that is 2 amp-hours of capacity you need.

If the battery is 10 amp-hours, it will operate the motor for 5 hours if fully charged.

If you have a 0.5 amp solar panel (at 15 volts), which is 7.5 watts, if will charge the battery in 10 amp-hours/0.5 amp = 20 hours. The question is how many hours of sun do you get daily? if you get 7 hours, the battery will be charged in 3 days. But panels do not put out full power much of the time, and there are losses in the battery, so you should count on 5 days.

Are those numbers OK to meet your expectations? (which you really don’t list) If so, then you need a 15 volt 7.5 watt panel. The 15 volts is because you need that voltage to charge a 12 volt battery. If you expect a lot of days without much sun, I’d bump that to 20 volts.


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