A solar power diverter is a neat idea: instead of sending your spare solar electricity to the grid for a low export rate, it quietly heats your hot water tank with it for free. If you have solar panels, a hot water cylinder and you export a fair amount, a diverter can turn wasted export into free hot water. If you already earn a good export rate or you have no cylinder, the case is much weaker. Here is how to tell which you are.
The problem it solves
As the solar basics guide explains, the electricity you use yourself is worth far more than the electricity you export. On a sunny day your panels often produce more than the house is using, and that surplus flows out to the grid for the export rate, which is usually a fraction of what you pay to buy electricity back. A diverter spots that surplus in real time and, instead of letting it leave, sends it to the immersion element in your hot water cylinder. You get a tank of hot water heated with electricity you would otherwise have almost given away.
How it works
The diverter sits by your consumer unit and watches the flow of power at the meter. The moment you are about to export, it ramps the immersion heater up by exactly that amount, so you heat water with the surplus and nothing spills to the grid. As soon as the house needs the power, or a cloud passes, it backs off. The two common units are the myenergi eddi and the Solar iBoost. Both do the same core job. It only works if you have a traditional hot water cylinder with an immersion heater. A combi boiler with no tank has nothing to divert into, so a diverter is not an option there.
What it costs and what it saves
A diverter is roughly £250 to £350 for the unit, plus fitting by an electrician, so call it £400 to £600 installed. The saving is the gas or electricity you no longer spend heating water, because the sun does it instead. For a household that uses a cylinder of hot water a day and exports plenty of surplus, that can be a large slice of the water-heating bill through the sunny half of the year. Heating a cylinder with off-peak or grid electricity is not cheap at 26.11p per kWh, the current Ofgem cap for July to September 2026, so replacing even part of that with free solar adds up over spring and summer.
The catch: your export rate changes the sums
Here is what the sales pages skip. A diverter is only sending you free water because your export is worth so little. If you are on a generous Smart Export Guarantee rate, the electricity you would divert is actually worth a decent amount sold to the grid, and heating water with it saves less than the headline suggests. Do the comparison: the value of the hot water you make versus the export payment you give up to make it. On a low export rate the diverter wins easily. On a high one, exporting and paying for hot water separately can be the better deal. It also does nothing in winter, when there is little surplus to divert, so treat it as a spring-to-autumn saver.
Diverter, battery, or neither?
A diverter and a home battery both use up your surplus instead of exporting it, but they are not the same bet. A battery stores surplus as electricity you can use for anything later, and costs thousands. A diverter turns surplus into hot water only, and costs hundreds. If your main evening draw is general electricity, a battery does more. If you use a lot of hot water and want the cheapest way to stop wasting export, a diverter is far better value for that one job. Get the free efficiency basics done first, as with the panels themselves in is solar worth it, then add a diverter if you have a cylinder, a low export rate and real hot water demand. For cutting the hot water bill without any of this kit, start with hot water savings.