Work out whether a solar diverter will save you money by heating your hot water with surplus solar.
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A solar diverter (also called an immersion diverter or solar relay) monitors how much surplus electricity your panels are exporting to the grid and redirects it to heat your hot water cylinder instead — at no extra cost.
Panels generate surplus power
When your panels are producing more than your home is consuming — typical on a sunny weekday afternoon — the surplus would normally flow to the grid at your SEG rate.
The diverter intercepts the surplus
The diverter device (fitted near your consumer unit or immersion heater) detects this export signal and switches on the immersion element in your hot water cylinder.
Hot water heated for free
Your cylinder heats up using power you were giving away cheaply. In summer, a diverter can provide most of your hot water from solar alone.
Falls back to your boiler or immersion
On cloudy days or high-demand periods, the diverter backs off and your normal heating takes over — so you're never without hot water.
iBoost / Solar iBoost+
~£200–£280 installed. Simple, reliable, wireless sender unit monitors consumption at the meter. Most popular in the UK.
myenergi eddi
~£350–£500 installed. Works with Zappi EV charger and Libbi battery as an integrated system. CT clamp monitoring. App-connected.
Marlec Solar iBoost
~£200–£300 installed. UK-made. WiFi connected with app control and scheduling. Good for gas-only homes wanting to maximise solar use.
Solic 200
~£250–£350 installed. Proportional control (not just on/off) for smoother operation. Less common but well-reviewed.
No SEG tariff or very low rate
If you're getting 0p or under 10p for exports, diverting to hot water is almost always better — especially if your hot water costs 20p+ per kWh (electric immersion).
Electric immersion heater heating
Electric hot water at 26p/kWh is the most expensive heating method. A diverter replaces that with free solar. The saving per kWh is large.
No battery (or installing solar fresh)
A diverter costs £200–£350 installed. If you're not getting a battery, it's the cheapest way to reduce exported surplus. Often worth adding at initial installation for minimal extra cost.
Good SEG rate + gas hot water
If you earn 15p+ on SEG and your gas costs less than 10p/kWh effective (6.28p ÷ boiler efficiency), exporting earns more than diverting saves. Don't fit a diverter in this scenario.
Already have a battery
If your battery captures most surplus, there's little left for a diverter to work with. The combined payback is unlikely to justify adding both.
Hot water cylinder with an immersion heater
You need a cylinder with an immersion element (usually 3 kW). Combi boilers have no storage cylinder and cannot use a diverter. A thermal store or unvented cylinder is required.
Existing solar PV system
Any grid-connected solar system works. The diverter fits separately from the inverter — brand doesn't matter. No changes to the solar system are needed.
Access for installation
Typically a half-day job for an electrician. The diverter unit goes near the consumer unit. A CT clamp sensor fits around the main supply cable — non-invasive, no meter changes needed.
Combi boiler? There's still an option
If you have a combi boiler with no hot water cylinder, you can't use a standard diverter — but you can install a separate small thermal store (100–150 litre cylinder) with an immersion heater specifically for solar diversion. It's a bigger job but some homes find it worthwhile, especially in larger properties with high hot water use.
Read our full guides on costs, battery storage, and the Smart Export Guarantee before you get quotes.