Now that Chinese are dumping high quality panels, it's a good time to convert my 300L solar hot water heater to a few panels.
Choices are:
4x Trina Vertex S+ 440W - (44-55Voc) in parallel --> 36V element (1200W, 33A, 1.08ohm) heater element. Trina specs say Pmax is 44V, but it will end up being 37V in the hot weather. This 1200W solution is a bit slow, because each one-person shower is 2kwh. However, it's also likely to deliver 40V in winter (1450W). And if it doesn't I can add another panel.
5x Trina 440W (ditto) in parallel --> 48V element (1500W, 31A, 1.5ohm). The panels probably wont make it to 48V, even lightly loaded. Probably 40V -> Yield 1248W
4x Trina 440W in a 2x2 configuration, into a Victron MPPT 150/45 or 150/70 --> 48V element (31A)
Plasmatronics PLW, which is specially designed for 48V, but costs $1400
There are also dangerous HVDC methods, like 4 in series (Pmax 160V). This into 240V 3600W element would yield 1500-1800W. Would also go into MPPT 250/70 for house battery. Rural fire brigades don't like 200VDC.
A complication in Australia is that amateurs are not supposed to work above 60VDC, option 1 - 36V element looks good, even if I'm overloading it a bit.
I can't find a 48V MPPT with a 40A load, because Victron has monopolized DC MPPT, but has no LOAD on any of the controllers. I suspect that if you output directly to a linear element, the impedance mismatch at low voltage may put extra burden on the MPPT, and also the MPPT may get confused with low voltages, since it expects a battery. But on the other hand, it may work, and only cost $200. I also want to use the 4-5 panels for cloudy weather charging my house battery.
