Buy the MPPT controller. Then understand that most of what you paid for arrives only if your array voltage stays well above your battery voltage, and that on a hot panel wired the usual way, it does not.
The numbers come from Victron’s own white paper, dated January 20, 2020 and read August 12, 2026. It works one example all the way through: a 100W, 36 cell monocrystalline panel with a maximum power point of 18V and 5.56A.
At 25C (77F) cell temperature, the MPPT sits the panel at its maximum power point and takes 100W, which becomes 7.7A into a 13V battery. The PWM cannot do that. It is a switch, so it drags the panel down to battery voltage plus about 0.5V of cable and controller loss. The panel ends up at 13.5V and 6A, which is 81W. Victron’s words: “which is 19% less than the 100W harvested with the MPPT controller.”
Heat closes the gap
Panel voltage falls as the cells warm. Current barely moves. So the maximum power point slides left, toward battery voltage, and the advantage the MPPT was exploiting shrinks.
At 75C (167F) cell temperature, the same panel’s rated output drops to 77.5W using its -0.45 percent per degree coefficient. The MPPT gets 77.5W. The PWM gets 77W. The paper’s caption reads “MPPT performance advantage: nil.”
At 100C (212F) it gets worse for both. The maximum power point voltage falls to 11.7V, below the battery. An MPPT controller cannot step voltage up, so it stops being an MPPT and behaves like a switch, and the charge current collapses to 4A. That is the whole controller, doing nothing for you.
The fix is array voltage, not a better controller
Victron’s answer is to put more cells in series. Replace the one 12V 100W panel with two 12V 50W panels wired in series, and at that same 100C cell temperature the MPPT harvests 66W, or 5.1A at 13V, instead of 4A. Same panels, same controller, different wiring.
Their sizing rule for keeping the maximum power point above the battery: 72 cells or more for a 12V battery, 108 for 24V, 216 for 48V. A single 36 cell “12V” panel into an MPPT is the configuration that gives up the most in heat.
There is a second reason to do it. Double the array voltage and you halve the current, and cable loss goes with current squared, so the paper notes the cable cross section can drop by a factor of four for the same loss. On a van roof that is a real cost and a real weight.
What we would tell you
This is a manufacturer document from a company that sells MPPT controllers, and one panel model at one battery voltage. Take it with that in mind. It is also a document in which the manufacturer reports that its expensive product gains you nothing at 75C, which is not the kind of thing marketing writes.
The honest summary is Victron’s own line: MPPT outperforms PWM “in a cold to temperate climate, while both controllers will show approximately the same performance in a subtropical to tropical climate.” If you camp Arizona in July with one flat 36 cell panel, the controller upgrade is close to a rounding error. Wire two panels in series and it stops being one.
To size the array itself, run your loads through the RV solar calculator, then read how much solar you actually need. More on charging and battery sizing sits on the RV power hub.