My 65W DIY solar panel testing

One year ago I built my first bigger DIY solar panel which should ideally deliver 65W. Today I cleaned it up and hooked up it up with car battery trough solar controller cmtp02 and put volt-ampere meter between controller and panel.

Panel itself is actually not finished yet and very robust build (old window frame with glass). It has 36 cells and each cell should be 1.8W. So overall rating should be 36 cells * 1.8 W = 64.8W (~65W)

Some results measured on this DIY solar panel

Here are the results with pictures.

Time and place

  • Location: Europe, Estonia, Lat: 58.3216 Lng: 25.7577
  • Latitude: 58.323162158° 19′ 23.38” N
  • Longitude: 25.762687225° 45′ 45.67” E
  • Time of the day: around 14:00 local time

With cloud covering

When cloud moved over sky- readings were following.

  • Volts: 12.7
  • Amps: 0.57
  • Watts: 7.24

As expected, output decreased drastically, but still this “ambient” light produces some electricity. With one panel in array it’s close to nothing.

diy solar panel testing with cloudy sky

diy solar panel testing with cloudy sky

Clear sky

Nice clean direct sun results. Results are much better.

  • Volts: 13.7
  • Amps: 3.35
  • Watts: 45.9
diy solar panel testing with clear-sky

diy solar panel testing with clear sky

Rainy, grey clouds

Another day month later. Almost rainy grey clouds that cover all the sky. Started rain after I made this test.

  • Volts: 12.4
  • Amps: 0.64
  • Watts: 7.94
diy solar panel testing with cloudy sky

Rain clouds test




Overall- it produces 20W less power than “rated”. But I am not sure- is charging the battery the right load for this test. Maybe I’ll find something better in future to carry out this testing. But I’am pretty OK with these results also.



  1. By Richard


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