Solar Diverters UK: iBoost, Eddi & Immersion Heaters Compared
A solar diverter sends your surplus solar electricity to your immersion heater instead of exporting it to the grid. Free hot water from energy you've already generated.
Quick Answer
A solar diverter (also called a solar immersion diverter) automatically diverts surplus solar electricity to your immersion heater, heating your hot water for free. The most popular models in the UK are the myenergi Eddi (£400–£600) and the Marlec iBoost+ (£300–£500). Most households save £100–£200 per year on hot water bills, with a typical payback of 3–5 years.
What Is a Solar Diverter?
A solar diverter is a device that automatically sends surplus solar electricity to your immersion heater (hot water tank) instead of exporting it back to the grid. It's a simple, low-cost way to use more of the solar energy your panels generate.
Without a diverter, any electricity your solar panels produce that you don't immediately use gets exported to the grid. Under the Smart Export Guarantee, you'll receive 3–15p per kWh for that exported power. But heating your own hot water with that same electricity saves you 24–30p per kWh (the cost of buying it from the grid). A diverter captures that difference.
Solar diverters are also known as solar immersion diverters, solar PV diverters, or surplus energy diverters. Popular brands include the myenergi Eddi and the Marlec iBoost+. They work with any standard immersion heater and any solar PV system.
How Does a Solar Diverter Work?
A solar diverter uses a CT (current transformer) clamp fitted around the meter tails to monitor the power flowing in and out of your home in real time. When it detects surplus solar generation being exported, it diverts that power to your immersion heater proportionally.
1. Monitor
CT clamp at the meter reads power flow every second. The diverter knows exactly how much surplus is available.
2. Detect Surplus
When generation exceeds household demand, the diverter identifies the excess power that would otherwise be exported.
3. Divert (PWM)
Uses pulse width modulation (PWM) to send precisely the right amount of power to the immersion heater — no more, no less.
4. Heat Water
Your immersion heater warms the hot water tank using free solar electricity. No gas or grid electricity needed.
The key technology is PWM (pulse width modulation), which allows the diverter to send a variable amount of power to the immersion heater. Unlike a simple on/off switch, PWM matches the diversion precisely to the available surplus, so you never import from the grid to heat water.
Best Solar Diverters Compared (2026)
We rank the top four solar diverters available in the UK based on features, reliability, app support, and value for money. All models listed below are widely available from MCS-certified solar installers and electricians.
myenergi Eddi
Best features overall
The most feature-rich solar diverter on the market. Dual load capability lets you divert to two devices (e.g. immersion heater and underfloor heating). Full app monitoring via the myenergi app. Works seamlessly with the Zappi EV charger for whole-home energy management. CT clamp included.
- Dual load output
- myenergi app monitoring
- Works with Zappi EV charger
- CT clamp included
- 3-year warranty
Marlec iBoost+
Most popular & reliable
The UK's best-selling solar diverter. Simple, reliable, and proven. Built-in LCD display shows real-time diversion and savings. Optional 'Buddy' wireless remote display for your kitchen. No app required — just fit and forget.
- LCD display built-in
- Buddy remote display (optional)
- Simple installation
- Proven reliability
- 2-year warranty
Solic 200
Best budget option
A straightforward, no-frills solar diverter at the lowest price point. No app or smart features — it simply diverts surplus solar to your immersion heater. Effective and reliable for those who want a basic solution.
- Lowest cost
- Simple operation
- Compact design
- LED status indicators
- 2-year warranty
Catch Power Relay
Best compact design
A well-designed solar diverter with a compact form factor. Good choice for smaller installations where space is limited. Reliable performance with a clean, modern interface.
- Compact form factor
- Clean interface
- Good for small systems
- Easy retrofit
- 2-year warranty
Solar Diverter vs Battery Storage
A solar diverter and a battery both help you use more of your solar generation, but they work differently and suit different budgets. Here's how they compare:
| Feature | Solar Diverter | Battery Storage |
|---|---|---|
| Cost | £300–£600 | £3,500–£6,000 |
| What it does | Heats hot water with surplus solar | Stores electricity for any use |
| Complexity | Simple — single electrical connection | More complex — inverter integration required |
| Payback period | 3–5 years | 8–12 years |
| Self-consumption boost | +20–30% | +30–60% |
| Evening use | Hot water only | Powers lights, appliances, heating |
| Lifespan | 15–20 years | 10–15 years |
Best combination: diverter + battery
For maximum self-consumption, install both. The diverter handles daytime hot water heating (the cheapest way to use surplus), while the battery stores remaining surplus for evening electricity use. This combination can push self-consumption above 80%.
How Much Can You Save with a Solar Diverter?
A solar diverter typically saves £100–£200 per year on hot water bills. Your actual savings depend on your solar system size, household hot water usage, and how much surplus you currently export.
£100–£200
Annual savings on hot water
3–5 years
Typical payback period
1,500–2,500 kWh
Annual diversion (4 kWp system)
The savings calculation is straightforward: every kWh diverted to your immersion heater saves you the difference between your import rate (around 24–30p/kWh) and your export rate (3–15p/kWh under the Smart Export Guarantee). That's a net saving of roughly 15–25p per diverted kWh.
Example: a 4 kWp solar system that diverts 1,800 kWh per year at a net saving of 12p/kWh saves £216 annually. With an iBoost+ costing £400 installed, that's a payback of under 2 years in the best case.
Do You Need a Solar Diverter?
A solar diverter is worth considering if you tick most of these boxes:
You have an immersion heater
A diverter needs a standard immersion heater in a hot water cylinder. If you only have a combi boiler (no tank), a diverter won't work.
You export surplus solar
If your solar panels regularly generate more than you use during the day, that surplus is being exported. A diverter captures it.
You use hot water daily
The more hot water your household uses, the more a diverter saves. Families with higher hot water demand benefit most.
You want a quick payback
At £300–£600, a diverter pays for itself in 3–5 years — much faster than a battery.
You don't have a battery (yet)
If a £4,000+ battery isn't in the budget, a diverter is the cheapest way to boost self-consumption immediately.
You heat water with gas or electricity
Replacing gas or electric hot water heating with free solar is one of the simplest energy savings you can make.
A diverter is not suitable if you only have a combi boiler with no hot water cylinder, or if your solar system is very small (under 2 kWp) and you already use most of your generation during the day.
Solar Diverter Installation
Installing a solar diverter is a straightforward job for a qualified electrician. There are no plumbing changes required — it's purely an electrical connection.
What's involved
- CT clamp fitted around meter tails
- Diverter unit wired to immersion heater
- Unit mounted near consumer unit or hot water tank
- Configuration and testing
Key facts
- Installation time: 1–2 hours
- No plumbing changes needed
- Works with any existing immersion heater
- Compatible with all solar PV systems
- Can be retrofitted to existing installations
Most solar installers will offer a diverter as an add-on when installing your solar panels. If you already have solar, any qualified electrician can retrofit a diverter. The installation is covered under Part P of the Building Regulations.
Frequently Asked Questions About Solar Diverters
What is the best solar diverter in the UK?
The myenergi Eddi is the best solar diverter for features, with dual load capability, app monitoring, and Zappi EV charger integration. The Marlec iBoost+ is the most popular choice for its simplicity and reliability. Both are excellent — the Eddi suits tech-savvy users, while the iBoost+ is best for a fit-and-forget solution.
Is a solar diverter worth it?
Yes, for most homes with solar panels and a hot water cylinder. At \u00a3300\u2013\u00a3600 installed, a diverter typically saves \u00a3100\u2013\u00a3200 per year on hot water bills, giving a payback of 3\u20135 years. It\u2019s one of the cheapest ways to increase your solar self-consumption.
Can I use a solar diverter with a combi boiler?
No. A solar diverter requires a hot water cylinder with an immersion heater. Combi boilers heat water on demand and have no storage tank, so there\u2019s nothing for the diverter to heat. If you have a combi boiler, a battery is a better option for using surplus solar.
What is the difference between the myenergi Eddi and iBoost?
The myenergi Eddi (\u00a3400\u2013\u00a3600) offers dual load output, app monitoring, and integration with the Zappi EV charger. The Marlec iBoost+ (\u00a3300\u2013\u00a3500) is simpler with a built-in LCD display and optional Buddy remote. The Eddi has more features; the iBoost+ is more straightforward.
Does a solar diverter work in winter?
Yes, but with reduced output. Solar panels still generate electricity in winter (around 10\u201320% of their summer output), and a diverter will use any surplus to heat water. In winter months, you\u2019ll likely need your boiler or immersion to top up. The main savings come from March to October.
Can I have a solar diverter and a battery?
Yes, and it\u2019s an excellent combination. The diverter handles surplus hot water heating first (cheapest use of surplus), then remaining excess charges the battery for evening use. Most systems can be configured to prioritise the diverter or battery as needed.
How much does it cost to install a solar diverter?
A solar diverter costs \u00a3300\u2013\u00a3800 fully installed, depending on the model and installation complexity. The unit itself costs \u00a3250\u2013\u00a3600, with installation adding \u00a3100\u2013\u00a3200 for a qualified electrician (1\u20132 hours of work).
Do I need planning permission for a solar diverter?
No. A solar diverter is a small electrical device installed inside your home, connected to your existing immersion heater. No planning permission, building regulations approval, or MCS certification is required for the diverter itself.
Related Guides
Sources
- Energy Saving Trust — Solar Panels — energysavingtrust.org.uk
- myenergi — Eddi Solar Diverter — myenergi.com
- Marlec — iBoost+ Solar Immersion Controller — marlec.co.uk
- Ofgem — Smart Export Guarantee — ofgem.gov.uk
- MCS — Microgeneration Certification Scheme — mcscertified.com
Last updated: March 2026
Fact-checked by John Rooney, Solar Energy Editor. Editorial policy
John Rooney is the founder of Solar Info and has been covering the UK solar energy market since 2023. He fact-checks all content against official MCS and Ofgem data and maintains relationships with MCS-certified installers across the UK.
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