The easy way to do it it with a TL494, these are like 10 for $1. It has all the features you need. Just operates the inverse of what it is usually used for, turning off at a low voltage and on when it gets high. A resistor and capacitor for the oscillator. Voltage divider pot to turn PV voltage to about 5V. 4 resistors to drive the two FET. Two fet as the output switchers. These FET will be in parallel and you use two to get the resistance down so there is no heating. If you buy a 100A FET, don't use it at over 10A. Two get you 20A easily. They are cheap and no reason to use big heat sinks. Litle perf boards are 5 for $1. There are also thru hole TL494 driver boards cheap that a couple of traces could be cut on.Then a resistor and zener are needed to supply 12-15V.
This is one I built for a famous youtuber that gets millions of views. He just had to make the capacitor bank, that is the boxy thing. So ugly I couldn't figure out what it even was. He got this far and never bothered to hook it up. It uses one of those cheap China driver boards. I'm closing the camp, packing up and leaving today. I won't have time for about a week.
