Testing solar panel output?

[ZMAN]

When determining solar panel output (input for that matter), do you need to have a load plugged into it? Or just raw power into volt meter will give accurate reading?

 

[smritte]

Best way to test is loaded. I test amperage and voltage where it connects to the battery. You can test voltage unloaded but its not really a true test.
You can test amperage at the inverter input but it wont show you the loss from the inverter itself.
If you do the math, you may be disappointed with what they really put out.

Here's my panels pointed at the sun, through the same inverter.
120 watt fixed. math says 10 amp. Reality 7amp
180 watt flex. math says 15 amp. Reality 10 amp
180 watt folding. math says 15 amp. Reality 9 amp.
All three panels are high quality. If its not pointing right at the sun, drops the power pretty quick. My flex panel is mounted on my trailer roof so, it gets less then what I posted because its not pointing at the sun.