For what it's worth I'll give my opinion and experience with solar on my Cal 39. My panels put out about 18+ volts in good mid day sun. I have a pwm controller, the TriStar 45 from Morningstar. I have 6 panels wired in parallel so there's no voltage increase because of the number of panels. Yes, an MPPT controller would put out a little more amps - when the sun was close to directly overhead. But except for less than 4 hours at mid day in La Paz, Mexico, the voltage was less than 15 and the MPPT wouldn't have helped at all, and at significantly more cost. I have since talked with a friend of mine, a PhD from MIT that works in the solar development field. She said that IF I wired the panels in series I'd get significantly greater voltage and a smaller amperage. Then I could have used smaller wire, significantly smaller, and an MPPT controller. But since the total round trip wire run was less than 20 feet the savings in wire cost wouldn't have come anywhere near the additional controller cost. Sailing in July in the Sea of Cortez, with radar running, computer-chart plotter running, VHF on standby, using the windlass to retrieve the anchor, making 20 gallons of water with an RO watermaker and a few other uses of electricity my 420 rated watts of solar panels ran it all and I ended the day with fully charged batteries. My opinion is that the additional cost of an MPPT controller and a higher voltage solar array isn't worth it.
Sailsam and Susie
1987 24' Travelmaster