How can I find the wattage of my panels

[jackedo]

Hi All

I was given 12 Solarex panels and they don't have any part or type # I can find. I've used two on my RV with a charge controller that came with the panels (old) no readouts. These two seem to keep batteries charged okay. The others I would like to set up for the house with a GTI of some wattage. I think it maybr necessary to know the wattage of the panels to size the GTI needed. These panels are 20" x 43 1/2 ". They have 36 4 3/8 by 4 3/8 inch solar cells that can be setup as either 6 or 12 volts. In the direct sun light, the output voltage is 20v about. I think these are polycrystaline cells. Thats all the info I have. Can anyone help?

Thanks Jack

[Sunking]

Only thing you can do is measure Voc and Imp, but that will not give you the the power rating but you should be able to guestimate. The Vmp should should be around 77% of Voc, and Imp around 80% of Imp.

[jackedo]

Panel wattage

Only thing you can do is measure Voc and Imp, but that will not give you the the power rating but you should be able to guestimate. The Vmp should should be around 77% of Voc, and Imp around 80% of Imp.

Thanks for the reply, but I don't understand how to use the info. I though someone would tell me what resistive load I should use to recourd the voltage and current to compute the panel wattage.

Jack S.

[Mike90250]

You make 2 meter measurements (read the meter manual to make the connections properly)

1) V open circuit. Simply measure the voltage of the panel with the meter.

2) Isc (current/amps short circuit) Configure meter for AMPS. and measure AMPS from the + & - leads of the panel (don't forget to set the meter configuration back to volts)

Then as Sunking says

The Vmp should should be around 77% of Voc, and Imp around 80% of Isc.

(typo corrected)

Then, taking those 2 numbers, it's now simply Volt x Amps = watts

[Sunking]

Thanks for the reply, but I don't understand how to use the info. I though someone would tell me what resistive load I should use to recourd the voltage and current to compute the panel wattage.

Jack S.

There is no resistor. It is either short circuit or open circuit. Maximum power point is a moving target which you cannot hit as it changes every second.

Voc is measured at noon on a clear bright day with the panel facing directly into the sun with only the volt meter connected to the output of the panel. That is open circuit, infinite resistance.

Isc is taken at the same time with the meter configured in the current measuring mode with ZERO resistance, or the leads of the panels shorted together.

From those two measurement you can get a ball park idea of what Pmax is. To actually measure Pmax you need a lab and a few million dollars of test equipment.

[jackedo]

I think I get it now!

Thanks for the instructions. I think I get the process now.

Later Jack S.