Solar Panel Hot Water Diverters: Are They Worth It in NI?

A solar PV diverter is one of the simplest and most cost-effective additions you can make to a solar panel system. Instead of exporting surplus solar electricity to the grid for a few pence per kWh, a diverter routes it to your immersion heater, giving you free hot water. For NI homeowners with a hot water cylinder, it is a compelling proposition.

This guide covers how PV diverters work, the most popular models available in Northern Ireland, who benefits most, and how they compare to battery storage.

How a PV diverter works

The principle is straightforward. When your solar panels generate more electricity than your home is using, the surplus has to go somewhere. Without a diverter or battery, it flows to the grid. Your Smart Export Guarantee payment for this exported electricity is typically 4 to 8p per kWh.

A PV diverter monitors your electricity flow in real time. The moment it detects surplus generation, it diverts that electricity to your immersion heater element. The heater warms the water in your hot water cylinder, effectively storing solar energy as heat.

The diverter adjusts continuously. If a cloud passes and your generation drops, it reduces the power going to the immersion heater instantly. If you switch on the kettle and your home’s demand increases, the diverter reduces hot water heating to ensure your home’s needs come first. Surplus solar always goes to the immersion heater; it never takes electricity you need for other purposes.

Popular PV diverters in NI

myenergi eddi (£400 to £500 installed)

The myenergi eddi is the most popular PV diverter in the UK, and for good reason. It offers smart features, a good app, and reliable performance.

Key features:

• Diverts surplus solar to one or two heating loads (immersion heater, underfloor heating, or other resistive loads)
• Integrates with myenergi ecosystem (pairs with the zappi EV charger and libbi battery)
• App-based monitoring shows exactly how much free energy has been diverted
• Boost function lets you manually heat water on demand
• Compatible with any solar inverter

Why it is the most popular: The combination of smart features, reliable hardware, and the ability to see your savings in the app makes it the default recommendation from most NI installers. If you also have a myenergi zappi EV charger, the two devices coordinate automatically to prioritise solar usage.

iBoost+ (£300 to £400 installed)

The Marlec iBoost+ is the simpler, more affordable option. It does one thing well: diverts surplus solar to your immersion heater.

Key features:

• Straightforward installation and operation
• Wireless sender clips onto your meter tails (no complex wiring)
• LCD display shows diverted energy and hot water status
• Manual boost button for topping up water on demand
• No app (display unit only)

Why choose it: If you want a no-fuss diverter at the lowest cost and do not need app-based monitoring, the iBoost+ is a solid choice. It has been on the market for years and has a proven track record.

SolarEdge immersion controller

If your solar system uses a SolarEdge inverter, the SolarEdge immersion controller integrates directly into the SolarEdge ecosystem. It monitors surplus generation through the inverter itself rather than using a separate CT clamp.

Key features:

• Seamless integration with SolarEdge systems
• Managed through the SolarEdge monitoring portal
• No additional CT clamp or wireless sender required

Why choose it: Only relevant if you already have (or are installing) a SolarEdge inverter. The integrated approach is neater, but it limits you to the SolarEdge ecosystem.

How much can a diverter save?

The savings depend on how much surplus solar you generate and how much hot water you use. Here is a realistic estimate for a typical NI home.

Factor	Typical Value
Annual surplus solar available for diversion	1,000 - 2,000 kWh
Hot water electricity equivalent	1,500 - 2,500 kWh per year
Diverted energy (realistic)	800 - 1,500 kWh per year
Saving at 28-32p per kWh (replacing grid electricity)	£225 - £480 per year
Saving at oil equivalent cost	£100 - £250 per year
Net saving (accounting for lost SEG income)	£100 - £200 per year

The “net saving” accounts for the fact that diverted electricity would otherwise have earned you a small SEG payment. Since the SEG pays 4 to 8p per kWh and using the electricity for hot water offsets grid purchases at 28-32p per kWh, the net benefit is strongly positive.

At £400 to £500 for a myenergi eddi, payback is typically 2 to 4 years. For the iBoost+ at £300 to £400, payback can be under 2 years. These are some of the fastest payback periods of any solar accessory.

Who benefits most?

Homes with a hot water cylinder

This is the essential requirement. A PV diverter heats water using an immersion heater element inside a hot water cylinder. If your home has a combi boiler (which heats water on demand and has no cylinder), a diverter will not work without installing a separate hot water cylinder, which adds significant cost and complexity.

Most NI homes with oil heating have a hot water cylinder as standard, making them ideal candidates for a PV diverter.

Oil-heated homes

This is where diverters are particularly valuable in Northern Ireland. A large proportion of NI homes rely on oil for heating and hot water. Oil prices fluctuate, and heating water with oil is expensive. A PV diverter lets you heat your water for free using surplus solar during the warmer months (April to September), when solar generation is highest and you need oil heating least.

During summer, many NI homeowners find they can switch off their oil boiler entirely for hot water, relying solely on the diverter. That is several months of zero oil usage for hot water, which translates to meaningful savings and extends the life of your boiler.

Homes without battery storage

If you do not have a battery, a PV diverter is the most affordable way to use more of your solar generation rather than exporting it. It does not replace a battery (it only heats water, not power appliances), but at a fraction of the cost, it captures value from surplus electricity that would otherwise earn just a few pence on the SEG.

Large solar systems with significant surplus

The more surplus solar you generate, the more a diverter can capture. Homes with 5 kW+ systems and moderate daytime electricity usage will produce plenty of surplus for hot water diversion, particularly from March to October.

Who should skip it?

Combi boiler homes (no cylinder)

Without a hot water cylinder and immersion heater, there is nowhere for the diverter to send electricity. Installing a cylinder specifically for a diverter is usually not cost-effective.

Homes with large battery systems

If you already have a large battery (10 kWh+), most of your surplus solar is being stored for evening use. There may not be enough consistent surplus left over to justify a diverter. That said, during peak summer months, even large batteries can be full by midday, and a diverter can capture the afternoon surplus.

Diverter vs battery: how do they compare?

This is one of the most common questions from NI homeowners. The two technologies serve different purposes, and many homes benefit from having both.

Feature	PV Diverter	Battery Storage
Cost (installed)	£300 - £500	£3,500 - £10,000
What it does	Heats water with surplus solar	Stores electricity for any use
Payback period	2-4 years	8-12 years
Flexibility	Hot water only	Powers any appliance
Complexity	Simple	More complex
Maintenance	Minimal	Minimal

A diverter is not a substitute for a battery. A battery stores electricity for lighting, cooking, entertainment, and EV charging during the evening. A diverter heats water and nothing else. But a diverter is dramatically cheaper, pays for itself faster, and works alongside a battery perfectly well.

Many NI installers recommend installing a diverter from day one and adding battery storage later when budgets allow or when battery prices come down further. This gives you immediate use of surplus solar without the larger battery investment.

For a detailed look at battery options, see our battery storage guide.

Installation and compatibility

PV diverter installation is straightforward and typically takes one to two hours. The installer fits a current transformer (CT) clamp to your meter tails to monitor electricity flow, wires the diverter unit near your consumer unit or hot water cylinder, and connects it to your immersion heater circuit.

Diverters are compatible with any solar panel system and any inverter brand. They do not interfere with your battery, export meter, or any other component of your solar setup.

Most NI solar installers can fit a diverter during your initial solar installation or as a retrofit at any time after. If you are getting solar quotes, ask your installer to include a diverter in the package for the most cost-effective installation.