Nice weather today, just a bit overcast and high 50Fs. So I decided to get my backup PV regulator board put together. I did that, and bench tested it.
It's a low side linear regulator that takes an analog optical isolator input of 0-5 ma for 0-15 amps charge current. The battery bank controller computes that signal via micropower analog op amp math. The PV linear regulator is powered by 7 ma of nominal +24V from the lowest 24V panel in the 5 panel string. It was designed for a nominal 120V (220V peak no load) PV array but now that I've changed to 500V linear mosfets, it could do a 230VDC system at half the current. Mosfets as linear devices are pretty sweet compared to power Darlington Bipolars, there is no base current (called gate for Mosfets) to control them, just gate voltage of around 4 to 10 volts. Each transistor carries 1/7th of the total demanded current.
The PV regulator is a tight squeeze on the experimenter's bargain board size at ExpressPCB. On the back you see the solid 14 gauge "jumpers" for power distribution. For the new build I updated the two quad operational amplifiers to some newer ultra low offset bias, rail to rail input and output types. The analog world just keeps getting better. To use MOSFETs as linear devices in parallel, you must use an op amp for each MOSFET, just as for Darlington transistors. A 0.1 ohm, 3W shunt resistor for each transistor's output allows current sensing for each. The op amp drives the gate voltage just enough to get the desired current at the shunt resistor. The world runs on OP amps.
This board gets mounted on a 36"x12"x 5 inch deep finned aluminum heat sink as I don't care for fan motors.
I do miss out on about 17% power gain of very cold mornings; the linear regulator must piss away the excess voltage on very cold days, unlike a switching buck converter. It's not all loss, it does help warm up the closed up battery bank shed in the winter.
I am not seriously tempted to do a low frequency, low EMI buck converter version just yet, but I have thought about that design after my success with the inverter project.
Linear is simple, and I like that.