From the Land of Magic! a high tech solar panel load controller, built for son Pete. You can see that the latest components and construction methods are employed.
There’s a differential amp that drives an Ebay PWM speed controller ($11) to load the panels to their max power voltage, regardless of the insolaton* level. A sample of the panel voltage is compared to a Zener reference to generate the control signal to the PWM unit.The load is a 4500W water heater element in a tank in front of his regular water heater. There are three 235W panels with 29.4 V max power voltage.
I had a great talk with a dealer recently. It seems that PV power is now cheaper than heating water directly with wet panels. Cheaper panels and good inverters seem to have made a big difference.
insolation* – No that’s not a mispillin’ Insolation‘ is the solar radiation (power/Unit Area) that reaches the earth’s surface, which average high sun is close to 1KW/square meter.