Quick answer: MPPT harvests noticeably more power from your panels across a full day of changing sun, while PWM costs less and is fine when your panel voltage closely matches your battery bank. For 12V boat systems with a single panel, either works; for larger banks or 24V systems, MPPT usually pays for the difference.
What a PWM Controller Does
PWM (pulse width modulation) acts like a switch between panel and battery, pulling the panel voltage down to the battery voltage. It is simple, reliable and inexpensive. The trade-off: the panel operates at battery voltage, so any voltage headroom above the battery's charging voltage is wasted as heat in the panel rather than harvested as power.
What an MPPT Controller Does
MPPT (maximum power point tracking) continuously finds the panel's optimal operating voltage and converts the excess voltage into extra charging current. In cool weather, early morning, or when panel voltage sits well above battery voltage, the gain is real - commonly in the 15-30% range over PWM for the same panel, though exact figures depend on conditions.
Side-by-Side Comparison
| PWM | MPPT | |
|---|---|---|
| Cost | Lower | Higher |
| Harvest in mixed sun | Baseline | Typically 15-30% more |
| Best fit | Panel voltage close to battery voltage, small banks | Larger panels, 24V banks, cool climates |
| Wiring flexibility | Panel must match bank voltage | Panels can be wired in series |
Matching a Controller to Your Innospo Setup
- 10A 12V MPPT (SAE) - compact charging for a single 12V battery and portable panel.
- 10A/20A 12V-24V MPPT - covers larger banks and 24V trolling architectures.
- 10A/20A Smart MPPT (Bluetooth) - adds app monitoring of charge state.
- 30A 12V-24V PWM (Bluetooth) - a budget-friendly option for matched panels and big banks.
See all ratings in the solar charge controllers collection.
FAQ
Can I use a 24V panel on a 12V battery?
With MPPT, yes - the controller converts the surplus voltage into charging current. With PWM, no: the panel needs to match the battery's charging voltage.
Does MPPT help on cloudy days?
It helps most when panel voltage sits well above battery voltage - cool, overcast and low-sun conditions are where MPPT pulls further ahead of PWM.
What size controller for a 100W panel on a 12V battery?
A 10A controller covers a 100W panel with headroom; step up to 20A if you plan to add a second panel. 12V vs 24V vs 48V explains how bank voltage changes the math.
Related Guides
- Marine Power System Buying Guide - the hub that connects propulsion, battery and charging.
- 50Ah vs 100Ah vs 200Ah LiFePO4 Marine Battery - size the bank your controller feeds.