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The £30 question that affects every watt you harvest.
Both manage charging your battery from the panel; they differ in how much of the panel's output they actually capture.
PWM (pulse width modulation) is the simple, cheap option (£15–30). It effectively drags the panel's voltage down to the battery's voltage, wasting whatever headroom the panel had. Fine for very small systems (≤50W) where total harvest barely matters.
MPPT (maximum power point tracking) constantly finds the panel's most productive operating point and converts the excess voltage into extra charging current. In UK conditions — low sun angles, cloud, winter — that's typically 20–30% more energy from the same panel, and even more on cold bright days.
The verdict for almost everyone: spend £40–90 on a quality MPPT (Victron and EPEver are the names you'll see recommended). It usually pays for itself versus buying a bigger panel, and it lets you use higher-voltage panels with long, thin cable runs.
From EcoPowerful — plain-English DIY solar & wind guidance for UK homes, with a free instant system plan builder. Guidance is general; 230V fixed wiring always needs a qualified electrician. Last updated 2026-06-13.