Definition: A solar diverter (power diverter) is a device that sends surplus electricity from your solar panels to your hot water cylinder’s immersion heater instead of exporting it to the grid — turning spare generation into hot water.
How it works
A CT clamp watches for export at your meter; the diverter then feeds exactly that surplus into the immersion heater, so nothing extra is drawn from the grid. The best-known UK unit, myenergi’s eddi, modulates from a 100 W minimum up to a 3.68 kW heater load and idles at about 3 W (myenergi, checked July 2026).
You need a hot water cylinder for a diverter to make sense — combi-boiler homes without one cannot use it. If you also have a battery, the battery normally takes priority, with the diverter mopping up whatever still spills to the grid.
Does diverting actually pay?
It depends what the spare energy would otherwise earn or replace. Diverted electricity that displaces gas-heated water saves only about 8.9p per kWh of heat (gas at the October–December 2026 cap rate of 7.97p/kWh through a 90%-efficient boiler) — so if your Smart Export Guarantee rate is higher than that (SEG rates typically run 4–15p/kWh), exporting can pay better than diverting. The strongest cases are homes heating water on peak-rate electricity at 26.32p/kWh, or stuck on a low SEG rate. Our guide to solar diverters and free hot water works through the sums for typical solar panel systems.
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