testing my panel's output

[solsauce]

Oooh here's another thing I've been wanting to do. So I have these 190w B modules, and I just want to see what I'm really getting out of them, next sunny day. If I just lay one of these out in the yard and use my volt meter on the connections that should tell me what my wattage out put is right? any idiot checks for folks like me?

[mike95490]

There are 2 tests to make on each panel.

1) set your DVM to VOLTS DC 25V range, or something a bit highter than the max output voltage listed on your panel.
Measure the panel voltage, and record it.

2) reconfigure your DVM to AMPS DC, usually involves moving a connector. Again set to a scale a little over the rated amps of the panel. Measure again, and maybe with a wooden clothes pin, clip the leads together, record the current, leave it all connected - wait a couple minutes, and then record the current again. The power from the short (DVM) you applied, will heat the panel up a bit, and you'll get a more real life reading.
The CURRENT / AMPS will vary depending on the angle to the sun, and the intensity.

Some like a 3rd test, where you connect a panel to a 12V battery, and measure the current, but the state of the battery becomes a questionable item, a small battery wont accept as much power as a larger battery would, and a fully charged battery wont accept as much either. But you can have fun, and maybe spill some battery acid doing it too.

[ edit - DON'T FORGET TO re-configure your DVM back to VOLTS after reading the AMPS,
or you will cook it if you forget and try to see how many amps are in your battery when
you thought you were measuring VOLTAGE. ]

[SolarCC]

different test ways to lead different results,the output power is a little different. If you source panel from some company(not famoous),you should be careful.

[Wayne from NS Cana]

Mike90045 hit the nail on the head. You need to make both of these tests. A panel with a high internal resistance, such as a bad solder joint, can still give a perfect voltage reading, but will show up when you do the current (amps) reading. Shorted cells for example, will pass full current and make the panel look OK on the current reading, but will show up in the voltage reading.
Wattage is normally determined by multiplying the Amps by the Voltage. HOWEVER, in the above test, doing that will give a greatly inflated value, because when under no load, the voltage will be much higher than in normal use. Likewise, during the current test, the panel is basically under short circuit conditions, so the amps output will also be higher than when in normal use.
Cheers
Wayne