I built 5, 60w solar panels. Checked voltage before & after mounting on roof. Each produced 18.5v or more. Since i live at 41 degrees N. lat. I mounted them facing due south and at 41 degrees. They only produced about 14v at noon. I played with the angle and found 13 degrees worked best. They've been in service 6 wks now and I've noticed that they charge best from 7:00 to 10:00 am. And here is the wierd thing. On sunny days, they can barely charge 4, 35ah batteries to capacity. But on cloudy days it charges like it's on steroids. This has happened every cloudy day since they've been in use. Anyone have any ideas about this?