How Much More Power Does an MPPT Controller Harvest Than PWM, and When Does the Gap Close?
Summary
In Victron's worked example, a 100 W, 36-cell panel charging a 12 V battery at 25°C cell temperature yields 81 W through a PWM controller, 19% less than through MPPT. At 75°C the gap nearly disappears, 77.5 W against 77 W. The same paper calls PWM a good low-cost choice only for small systems whose cells run moderate to hot, between 45°C and 75°C.
A switch versus a converter
A PWM controller is essentially a switch between array and battery. When it closes, the panel's voltage is pulled down to near the battery's, and no DC-to-DC conversion takes place. An MPPT controller is a DC-to-DC converter that turns higher-voltage power into lower-voltage power, decoupling the array voltage from the battery voltage.
The test panel's maximum power point is 18 V at 5.56 A. Through MPPT, those 100 W reach a 13 V battery as about 7.7 A. Through PWM, the panel is held at 13.5 V and delivers 6 A, and 13.5 V times 6 A is 81 W.
Heat narrows the difference
| Cell temperature | MPPT | PWM |
|---|---|---|
| 25°C | 100 W | 81 W |
| 75°C | 77.5 W | 77 W |
Output power and voltage both fall by about 4.5% for every 10°C rise, per the paper, and with cells between 45°C and 75°C and a charge voltage of 13 V to 15 V, PWM stays within 10% of MPPT. Victron's 100/30 data sheet advertises up to 30% more harvest than PWM, while the technical paper's own example moves from 19% to under 1% on the same panel as temperature changes.
Where the paper draws the line
The paper lists the cases for MPPT: array power above a few hundred watts on a 12 V battery, cells that often run below 45°C or above 75°C, systems where a higher array voltage would cut cabling cost, and setups where low-light output or partial shading matters. For panels, it pairs 36 cells with 12 V PWM, and 72 cells (a 24 V array) or more with MPPT charging a 12 V battery. The paper is dated January 20, 2020.
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Sources
- Victron Energy — Which solar charge controller: PWM or MPPT? (20 January 2020)
- Victron Energy — SmartSolar charge controller MPPT 100/30 & 100/50 datasheet
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