For a while, I wanted to make one of these for day-time use, to measure cloud cover and maybe get daily/weekly averages. Then I realized that solar panels make

For a while, I wanted to make one of these for day-time use, to measure cloud cover and maybe get daily/weekly averages. Then I realized that solar panels make a great photo-diode for measuring light intensity. You just need a bit of math to account for ephemerides (sunrise/sunset in particular) and angle of exposure.