Watts law and solar controllers

[Horseshoe]

Before I install my 20 amp controller, I want to make sure I understand Watts law correctly. I will be installing a 160 panel on the roof, so if Watts/voltage=amps, then 160/12=13.3, so a 20A controller should be sufficient? And if I wanted to add capacity to add an additional 80 W portable, 240/12=20, so I should still be okay? Or is there a factor I am missing?

 

[MarkBC]

Yes, that's how I've figured it.

Actually, the voltage will be higher than the nominal "12 volts", so the calculation of amps is more favorable than what you've shown.

 

[photohc]

You need to look at the detail specs of the controller. Usually, there is a solar panel current rating and a load rating. If you don't plan to connect your load via the controller and only through the battery, then you only need concern yourself with the panel current rating. Look at the amperage specs for the panel and they will tell you the maximum current rating. As noted by MarkBC, usually the nominal voltage of the panel is higher than 12 volts, so using the 12v to compute the possible amps is being conservative.

In general, a 20 amp controller should not have any problems handling the two panels you want to use.

 

[Horseshoe]

Awesome. Thank you both!