Solar Diverters in Ireland: Free Hot Water from Spare Solar, and When a Timer Is Better
A solar diverter is a small box that watches the electricity leaving your home. When your panels make more than the house is using, it sends that spare power to the immersion heater instead of the grid, so you end up with a tank of hot water instead of a small export payment. It is one of the cheapest add-ons to a solar system, but whether it pays depends on how you heat water now and whether you have a battery and a night-rate tariff. This guide gives the Irish prices, works out the savings from today's rates, and explains when a simple immersion timer does the job better.
Quick Answer
A solar diverter (also called a PV diverter or immersion diverter) sends solar electricity you would otherwise export to your immersion heater, so spare daytime solar heats your hot water. In Ireland the myenergi Eddi costs €535 and the Solar iBoost+ about €447, plus an electrician to fit it. Each diverted kWh saves the price of the electricity or fuel it replaces, minus the 19c export payment you give up: about 18c if you would otherwise heat water at the day rate, but only about 7c if you already heat it on a night rate. With a battery and a night-rate tariff, a €75 smart immersion timer is often the better buy.
How a solar diverter works
A sensor clamped around the main electricity cable tells the diverter, second by second, whether your home is importing from or exporting to the grid. When it sees power going out, it switches that amount into the immersion element instead. Most diverters, including the Eddi and iBoost+, vary the power they send, so even a few hundred watts of surplus goes into the tank rather than the element waiting for a full 3 kW.
SEAI's homeowner guide to solar PV lists a hot water diverter as one of two optional extras, alongside a battery, and describes it as a cost-effective way to make the most of what your panels produce. Your hot water tank effectively becomes a cheap thermal battery.
What a diverter can and cannot do
- It only uses power you would otherwise export. It never draws from the grid to divert.
- It stops once the tank reaches the immersion thermostat temperature.
- In winter there is little surplus, so it does most of its work from April to September.
- With a battery, the battery normally charges first and the diverter gets what is left, so it diverts less.
- Most models have a boost timer so the immersion can still run on a schedule.
Solar diverter prices in Ireland
| Product | Price | Key details |
|---|---|---|
| myenergi Eddi | €535 | Single phase, up to 3.68 kW (16A) heater load, two heater outputs used in turn, built-in boost timers, app control, 3-year warranty |
| myenergi Eddi+ | €977 | Three-phase version, for homes with a three-phase supply |
| myenergi harvi | €82 | Wireless sensor, needed when the Eddi cannot be wired to the clamp at the meter |
| Marlec Solar iBoost+ | about €447 | Wireless sender at the meter, boost button (15-minute steps up to 2 hours), 2-year warranty |
Prices are the unit only, checked 4 November 2026 at myenergi's Irish shop and Irish retailer Solar Boss. Fitting is extra: it needs an electrician to wire it between the fuse board and the immersion. Fitted at the same time as your panels it is a small add-on to the job; fitted later it is a separate call-out, so ask for a fixed price. See the myenergi review for the Eddi alongside the zappi charger and libbi battery.
How much does a solar diverter save?
Diverted solar is not quite free. Every kWh that goes into the tank is a kWh you no longer export, and exports pay about 19c per kWh (see export rates by supplier). So the saving per kWh is the cost of whatever would otherwise heat the water, minus that 19c:
| You would otherwise heat water with | Cost per kWh | Saving per diverted kWh |
|---|---|---|
| Immersion on a 24-hour or day rate | about 37c | about 18c |
| Immersion on a night rate | about 26c | about 7c |
| Gas or oil boiler | Check your fuel price per kWh | Small, and can be close to zero |
How many kWh a diverter moves depends on how much you export and how much hot water you use. A typical 4.4 kWp system without a battery exports around 2,000 kWh a year, but a diverter only takes as much as the tank can hold, and mostly in summer. Your inverter app shows your yearly export, which is the upper limit.
| kWh diverted a year | Saving vs day-rate immersion | Saving vs night-rate immersion |
|---|---|---|
| 300 kWh | €54 a year | €21 a year |
| 600 kWh | €108 a year | €42 a year |
| 1,000 kWh | €180 a year | €70 a year |
Based on a 37c day rate, 26c night rate and 19c export rate, the averages used across this site. Your own tariff will shift the figures.
Diverter vs immersion timer vs battery
On a smart or night-rate tariff, a plain immersion timer that heats the tank overnight saves about 11c on every kWh compared with heating it at the day rate, all year round, including winter when a diverter has nothing to divert. A WiFi timer switch costs around €75 and a basic 24-hour mechanical timer about €58, plus fitting.
| Solar diverter | Immersion timer on night rate | Battery | |
|---|---|---|---|
| Unit price | €447 to €535 | €58 to €75 | €4,200–€8,000 installed |
| Works in winter | Barely | Yes | Yes, charging on the night rate |
| Saving per kWh | 18c vs day rate, 7c vs night rate | 11c vs day rate | Covers all evening use, not just hot water |
| Needs a smart meter tariff | No | Yes | For night charging, yes |
| SEAI grant | No | No | €600 for 5 kWh or more (details) |
Many homes end up with both: a timer that heats the tank on the night rate as a backstop, and a diverter that tops it up for free on sunny days. If your tank is already hot from the night rate, though, there is less room left for the diverter to fill, which is why its saving against a night-rate setup is so small. See night rate electricity and what size battery.
When a solar diverter is worth it
Usually worth it
- You heat water with the immersion on a 24-hour or day rate
- You have no battery, so you export a lot in summer
- You are not on a smart tariff with a cheap night rate
- It is fitted at the same time as the panels
Often not worth it
- You have a battery that soaks up most of your surplus
- You already heat water on a cheap night or EV rate
- Your hot water comes from gas, oil or a heat pump
- You have a small system that rarely exports
As a check: a €535 Eddi saving €108 a year (600 kWh against day-rate heating) pays for the unit in about 5 years before fitting. Against night-rate heating the same 600 kWh saves only €42 a year, and the unit takes well over a decade to pay back.
Is there an SEAI grant for a solar diverter?
No. There is no separate grant for a diverter. The SEAI solar PV grant is worked out from the size of your panels in kWp, so adding a diverter to the quote does not change it, and the €600 battery grant only covers batteries. SEAI does list the diverter as an optional extra and tells homeowners to check whether quotes include one. If a quote does, make sure it is itemised so you can compare like with like. See SEAI grants.
Installing a solar diverter
- Who fits it: a registered electrician, as it is wired into the immersion circuit. Your solar installer can fit it on the day.
- Sensor: a current clamp goes on the incoming supply cable at the meter. If the immersion is far from the meter, a wireless sender (iBoost+) or harvi (Eddi) avoids running a cable.
- Immersion size: the Eddi handles elements from 100 W up to 3.68 kW, which covers a standard 3 kW immersion. It can feed two elements in turn, such as a top and bottom element.
- With a battery: ask your installer to set the priority so the battery charges first, or the diverter can heat water while the battery still has room.
- Existing timer: keep a timer or the diverter's own boost schedule for days with no sun, so you always have hot water.
Solar diverter FAQ
What is a solar diverter?
A solar diverter, also called a PV diverter, immersion diverter or power diverter, sends solar electricity you would otherwise export to the grid into your immersion heater, so spare solar heats your hot water. The best-known models in Ireland are the myenergi Eddi and the Marlec Solar iBoost+.
How much does a solar diverter cost in Ireland?
The myenergi Eddi is €535 from myenergi's Irish shop (€977 for the three-phase Eddi+), and the Solar iBoost+ is about €447 from Irish retailers. An electrician's fitting cost is on top, and is lowest if it goes in with the panels.
How much does a solar diverter save?
Each diverted kWh saves what it replaces minus the 19c export payment you give up: about 18c if you would otherwise heat water at the day rate, or about 7c on a night rate. Diverting 600 kWh a year saves about €108 against day-rate heating, or €42 against night-rate heating.
Is a solar diverter better than an immersion timer?
Not if you have a smart tariff with a cheap night rate. A timer that heats the tank overnight saves about 11c per kWh against the day rate all year, for €58 to €75. A diverter wins when you heat water at the day rate and export a lot in summer.
Do I need a diverter if I have a solar battery?
Usually not. A battery uses most of your daytime surplus, so the diverter only gets what is left once the battery is full, mostly on long summer days. With a battery and a night-rate tariff, an immersion timer is normally the better value.
Is there an SEAI grant for a solar diverter?
No. The SEAI solar PV grant is based on panel size in kWp and the battery grant only covers batteries, so a diverter is not grant-funded. SEAI lists it as an optional extra.
Does a solar diverter work in winter?
Very little. Irish solar panels make a fraction of their summer output in winter, and the house uses most of it, so there is rarely surplus to divert. Most of a diverter's saving comes from April to September.
Can a diverter heat water with a heat pump or gas boiler?
A diverter only drives an electric immersion element. If your tank has an immersion as well as a boiler or heat pump coil, it can top the tank up, but the saving is small because gas, oil and heat pumps already heat water cheaply per kWh.
Related Guides
Night Rate Electricity
Night rate hours, every supplier's night rate, and the break-even against a flat plan.
What Size Solar Battery?
Sizing a home battery by evening use and home profile.
Battery Storage
Solar battery costs, sizing, popular models, and payback analysis.
Export Payments
Sell surplus electricity at 15–32c/kWh.
Sources
- SEAI: A Homeowner's Guide to Solar PV, seai.ie
- myenergi Ireland: eddi product page (3-year warranty), myenergi.com
- myenergi Ireland shop: eddi, eddi+ and harvi prices, myenergi.com
- myenergi eddi datasheet (heater load, outputs, boost timers), portal.segen.co.uk
- Solar Boss: Solar iBoost+ listing, solarboss.ie
- Marlec: Solar iBoost downloads and manuals, marlec.co.uk
- Dwyers: Timeguard WiFi fused spur, dwyers.ie
- Willoughbys: Suevia IMM24F 24-hour immersion timer, willoughbys.ie
Prices and specifications checked on 4 November 2026.
Fact-checked by John Rooney, Solar Energy Editor. Editorial policy
John Rooney is the editor of Solar Info and has been covering the Irish solar energy market since 2023. He fact-checks all content against official SEAI data and maintains relationships with SEAI-registered installers across Ireland.
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