I have some installed and I noticed that out of 4X225w panels,I'm only getting around 315w and 95w, give or take. The person that installed them said to test each one with a voltmeter,but I'm not familiar with panels. They are DC,so can i hook up meter leads any way? also,if they are hooked up in series, is it possible to block the sun on a panel,one at a time, to see if the power drops or stays the same? I am using a 77w Sunny Boy inverter. Thanks