Solar Diverter UK 2026 — Free Hot Water From Your Solar Panels

If you have solar panels and a hot water tank, you are almost certainly exporting surplus electricity to the grid for 12–15p per unit. Your immersion heater, if you ran it on grid electricity, would cost you 24.67p per unit. A solar diverter plugs that gap. Instead of sending cheap exports to your energy supplier, the diverter sends them to your hot water tank. Same electricity, free hot water.

What Is a Solar Diverter?

A solar diverter is a device that sits between your solar system and your hot water tank. It monitors your solar generation and your home’s electricity consumption in real time using a current transformer (CT) clamp clamped around your electricity supply cable.

When generation exceeds consumption — meaning electricity would otherwise be exported to the grid — the diverter detects this surplus and ramps up the power flowing to your immersion heater. It does this continuously and proportionally: if you have 800W of surplus generation, it sends 800W to the tank. If that drops to 300W, it adjusts accordingly. The tank temperature rises until it hits its thermostat limit, then the diverter stops.

The result is that much of the electricity you would have exported for a small SEG payment instead heats your water at no cost. The immersion heater does the same job it always does — the only difference is the electricity driving it comes from your roof rather than the grid.

Why Bother? The SEG Export Maths

The Smart Export Guarantee (SEG) pays you for electricity you export to the grid. Rates vary by supplier, but most standard SEG tariffs pay between 12p and 15p per kWh. That sounds reasonable until you compare it to what you pay for grid electricity: 24.67p/kWh on the current energy price cap.

Here is the real cost of exporting instead of diverting:

• You export 1 kWh → you earn ~12p from your supplier.
• You then run the immersion heater on grid electricity → you spend 24.67p.
• Net position: you have spent 12.67p to heat water you could have heated for free.

A solar diverter turns that equation around. For every unit diverted rather than exported:

• You save 24.67p (grid electricity not consumed).
• You “lose” 12p in SEG income you no longer earn.
• Net benefit: ~12–13p per unit diverted, on top of the 12p SEG you were already getting.

In practice, most households with a diverter simply shift from “exporting cheaply, buying expensively” to “using their own generation efficiently.” It is one of the highest-return accessories you can add to an existing solar system.

The myenergi Eddi: UK’s Most Popular Diverter

The myenergi Eddi dominates the UK solar diverter market. It is well-designed, widely supported, and integrates with the broader myenergi ecosystem (including the Zappi EV charger). There are two versions:

• Eddi (single-phase): Maximum 2.4kW diversion. Suitable for the vast majority of UK homes, which are single-phase. Works with standard 3kW immersion heaters at reduced power or up to 2.4kW elements at full power.
• Eddi+ (three-phase): Up to 9kW diversion across three phases. For commercial premises or larger properties with three-phase supply.

The Eddi connects to your home WiFi and comes with an app that shows you how much energy has been diverted, how much hot water you have, and what your system is doing in real time. It also integrates with the myenergi hub, allowing the Eddi and Zappi to share solar intelligently — for example, prioritising the car charge in the morning and switching to water heating in the afternoon.

Unit cost for the single-phase Eddi is currently around £300–£400. Installation by a qualified electrician adds £100–£200, giving an all-in installed cost of £400–£600 for most UK homes.

How Much Does It Save?

Let’s use real numbers. A typical UK household uses 1,200–1,800 kWh per year on domestic hot water heating. A south-facing 5kWp solar system in Buckinghamshire generates around 4,250–4,750 kWh/yr and typically exports 1,500–2,500 kWh/yr depending on how much the household uses during daylight hours.

In practice, not all of that export goes to the hot water tank. The tank has a thermostat and gets hot quickly in summer. You also run the tank on a timer overnight via the cheaper Octopus Go or Agile rate. Realistically, a diverter captures 500–800 kWh/yr of surplus solar that would otherwise have been exported.

Savings calculation:

• 500–800 kWh diverted × 24.67p/kWh (grid electricity avoided) = £123–£197/yr
• Minus the SEG income you no longer earn on that electricity: 500–800 kWh × 12p = £60–£96/yr
• Net saving: £63–£137/yr (conservative view)

Many homeowners report the simpler figure: they no longer need the immersion heater on the grid tariff for most of the year, cutting their water heating electricity costs by £125–£200/yr. Whether you net off the lost SEG income depends on whether you were actively claiming SEG payments before — many households are not.

Payback Period

With an installed cost of £400–£600 and annual savings of £125–£200, the payback maths are straightforward:

• £400 installed ÷ £200/yr saving = 2 years payback
• £600 installed ÷ £125/yr saving = 4.8 years payback

In practice, most installations land somewhere in the 2–4 year range. The Eddi itself has no moving parts and no degradation — it should last the life of your solar system (25+ years). After payback, it is pure saving.

Compare this to battery storage at £4,500–£6,000 with a 7–12 year payback. The diverter does not replace a battery, but as a stand-alone accessory for hot water, it is exceptional value.

Solar Diverter vs Battery Storage

These are two different products solving different problems. Here is the direct comparison:

Feature	Solar Diverter	Battery Storage
Installed cost	£400–£600	£4,500–£6,000
What it powers	Hot water only	All household appliances
Payback period	2–4 years	7–12 years
Battery degradation	None	~2% per year
Powers home overnight?	No	Yes
Complexity	Simple, reliable	More complex system

The verdict: a diverter is not a replacement for a battery, but it is a sensible first step if budget is a constraint. Many households install both: the diverter handles hot water cheaply from day one, and the battery handles general electricity demand. The two do not conflict — the battery charges first (as it charges from grid tariff off-peak too), and the diverter captures any remaining surplus the battery cannot take.

See our battery storage page for details on home battery options, and our solar installation service if you are still to go solar.

Installation: What You Need

To fit an Eddi solar diverter, you need:

1. An existing solar PV system. The diverter has nothing to divert without generation. It works with any solar inverter brand.
2. A hot water cylinder with an immersion heater. The cylinder must be in reasonable condition. Old tanks with failing thermostats or corroded elements should be checked first.
3. A qualified electrician. The Eddi wires into your consumer unit and immersion heater circuit. This is notifiable electrical work in England and Wales and must be done by a Part P registered electrician or an MCS-certified installer.
4. A WiFi connection. The app works over WiFi. The device functions without it, but you lose remote monitoring.

The installation itself typically takes 2–3 hours. There is minimal disruption. The electrician clamps a CT sensor around your incoming supply cable, wires the Eddi unit into the immersion heater circuit, and configures the app.

Depth of Light installs myenergi Eddi units across Milton Keynes, Buckinghamshire, and the surrounding area. We also install the myenergi Zappi if you want to combine solar EV charging with hot water diversion on one system. Call us on 07516 762540 or get a free quote online.

Frequently Asked Questions