24/12/4 10:27 AM I made a Desmos graph that calculates the percentage of reserve power you will build up relative to a factory's power consumption over the course of a day when using solar panels in Factorio. I actually used calculus for once to make this! I hope my math is right!
The variable p determines how much power you generate compared to how much you consume per second, at max production during the day. For example, setting it to 2 (i.e. 200%) would mean that the during the day you generate 2 watts for every 1 you consume, leaving you with a surplus of 1.
10/7, or about 143%, is just enough to break even for a net change of 0% per day, although requires a bit of reserve power already built up to not go negative.