any way to measure the wattage of a solar panel

[Viva Las Vegas JDR]

Hello all,

I recently purchased a 120 watt solar panel and was doing some research to learn more about solar and looked up the brand they had installed which, written on the controller, is a Go-Power model from Carmanah (Canadian made). Looking at their website, they only offer a 50, 80, and 110 watt system, no 120 watt system as is written on my paperwork from the installer. Also, in comparing the panel I have to the picture on their website, it exactly matches the 80 watt panel, not the 110 watt. When I measured it though, it didn't match the dimensions of either panel. This leaves me to wonder if they installed a different brand panel than what the brand is of the controller or did they simply install an 80 watt panel hoping I wouldn't be any wiser.


My question is... is there any way to measure the wattage of a panel to see if it really is an 80 watt or 110/120 watt?? I was unable to find any writing on the panel itself and I really don't want to remove it from the roof to look under it to see if the writing is there as the mounts are all nicely sealed to the rubber roof.

I appreciate any help I can get. Thanks!

[NewellCrazy]

Testing the true output of a solar panel is almost impossible. It would require an absolutely clear day at the equator, your solar panel being exactly perpendicular to the sun's rays, and a very low resistance load shunting an ammeter, and an accurate voltmeter. In short, it's not practical, and the difference between a 110 and 120 is only about 9%. That said, if the dimensions and design aren't even close, you have no way of knowing what they installed.