Every solar array needs a charge controller between the panels and the battery bank, and the choice comes down to two technologies: PWM (pulse width modulation) and MPPT (maximum power point tracking). They do the same basic job, regulating charge to the battery, but they get there very differently, and the difference in real-world output on a boat is often larger than owners expect.
This guide compares them on the points that actually affect a marine installation: output, wiring flexibility, cost, and which situations still suit the simpler PWM technology.
A PWM controller connects the panel directly to the battery and switches that connection on and off rapidly to control charge current, which means the panel is effectively forced to operate at close to battery voltage, whatever the panel's own optimal voltage might be at that light level and temperature.
An MPPT controller instead constantly hunts for the panel's maximum power point, the voltage and current combination producing the most watts at that moment, and then converts that power to whatever voltage the battery needs, similar in principle to a DC-DC converter. This lets the panel run at its own best voltage rather than being clamped to the battery's.
In good direct sunlight with a panel closely matched to battery voltage, PWM and MPPT can perform similarly. As soon as conditions move away from that ideal, cooler or hazy light, partial shading, a panel voltage significantly higher than the battery voltage, or cold mornings when panel voltage rises, MPPT recovers meaningfully more energy, commonly quoted in the region of 20-30% more depending on conditions, though the exact figure varies with installation.
On a boat, where panels are frequently partially shaded by rigging, booms or radar arches and rarely sit at an ideal fixed angle, these are exactly the conditions where MPPT's advantage shows up most, which is why it has become the default choice for most new marine solar installations.
Because a PWM controller needs the panel voltage close to battery voltage, arrays are generally wired in parallel at 12V or 24V nominal, using thicker cable to carry the resulting higher current over what can be a long run from a coachroof or gantry to the controller.
MPPT controllers accept a wider input voltage range, so panels can be wired in series to raise voltage and lower current for the same power, allowing thinner cable over long runs and, in many cases, a wider choice of panel arrangement given the boat's actual shading and mounting constraints.
PWM controllers are meaningfully cheaper than MPPT for the same current rating, and for a small array, a single panel keeping a start battery topped up, or a modest panel on a boat used mainly on shore power, the extra cost of MPPT may not be recovered in any meaningful sense.
Whichever technology you choose, the controller needs a charge profile suited to the battery chemistry on board, lead-acid, AGM, gel and LiFePO4 all want different absorption and float behaviour, and a controller left on the wrong profile will chronically undercharge or gradually damage the bank. On a networked system such as Victron, an MPPT that joins the network also reports into the same monitoring and lets the rest of the system see solar contribution alongside other charge sources, which a stand-alone PWM controller cannot do.
For most boats with more than a token panel, yes, because shading, angle and temperature conditions on a boat rarely match the ideal PWM prefers. For a small maintenance-only panel, PWM can still be perfectly adequate.
Often yes if the array is already wired appropriately, though series-wired arrays designed around MPPT's wider input range may need reconfiguring if you started with a PWM parallel layout.
Most modern MPPT controllers support lead-acid, AGM, gel and LiFePO4 profiles, but the correct profile has to be selected, it is not automatic on every unit.
It improves the outcome but cannot fully overcome heavy shading. Array layout and separating badly shaded panels onto their own controller often matters as much as the controller technology itself.
The controller's rated input voltage and current both need headroom over the array's actual output under worst-case conditions such as cold, bright mornings when panel voltage peaks, not just its nameplate rating.
We assess your array, shading and battery chemistry, then specify a controller sized correctly rather than defaulting to the biggest one available.