> if the sun is always directly overhead everywhere [...] Apply whatever multiplication factors you like about what percentage of the year a given real solar ce

> if the sun is always directly overhead everywhere [...] Apply whatever multiplication factors you like about what percentage of the year a given real solar cell will generate power A simple but useful back-of-the-envelope estimate would be 25%. Half of the day, there's no sun, so you have 50%; the other half, it increases gradually until the middle of the day, then decreases gradually until the sun sets. Simplifying this to a linear increase and decrease, if you plot it into a graph you'd have a pair of isosceles right triangles, which cover half of the area, so you have another 50% over that first 50%, and the end result is 25%. (IIRC, the real result for the single-axis trackers you'd find on grid-scale power plants is something like 30%, showing how good that simple back-of-the-envelope estimate is.)