Solar Panels for a Granny Flat in Ireland: What to Know

A granny flat can have solar panels, and the roof of a garden annexe is often the best unshaded surface on the property. The practical questions are how the panels connect to the main house, whether the SEAI grant can be claimed separately, and how the new planning exemption for granny flats affects the answer. In most cases the system is wired into the main house supply, the grant is claimed once for the property, checked against the MPRN, and a self-contained unit with its own meter is the exception rather than the rule.

Can You Put Solar Panels on a Granny Flat?

Yes. Panels can go on the annexe roof, the main house roof, or both, and the choice is a design question rather than a permission question in most cases.

• An annexe roof that faces south or east to west and is clear of trees is often the best site on the property.
• A north-facing or heavily shaded annexe roof is usually not worth using.
• The panels can be wired back to the main house inverter and consumer unit, subject to cable size and voltage drop.
• A long cable run may make a separate inverter or a hybrid unit in the annexe the better option.

The technical constraint is the same as any outbuilding: the cable between the annexe and the main board has to carry the generation safely, and that is a job for the installer's survey.

Does the SEAI Grant Cover a Granny Flat?

This is where most of the confusion sits. The SEAI solar PV grant is per home and is checked against the MPRN, the meter point reference number.

• If the granny flat shares the main house MPRN, it is part of the same home for grant purposes, so the grant is claimed once for the property.
• If the annexe has its own MPRN and was built and occupied before 2025, it may be eligible for its own grant, provided there has been no previous solar PV funding at that MPRN. SEAI decides whether the unit counts as a separate home, so an MPRN is the test it applies, not an automatic yes.
• If the main house has already claimed the solar grant, a shared annexe cannot claim it again.
• The battery grant of €600 follows the same logic and is also limited to one per eligible home.

At the time of writing November 2026, the solar grant is €700 per kWp up to 2 kWp, then €200 for each additional kWp up to 4 kWp, capped at €1,800. The battery grant is €600 for a system of 5 kWh or more, and 0% VAT applies when the battery is installed with solar.

*Rules correct as of November 2026. Confirm the MPRN position with SEAI before applying.*

How Do You Connect an Annexe System?

There are two workable designs, and the survey decides between them.

• A single system on the main house, with the annexe treated as another load. This is simplest and cheapest if the main roof has space.
• A system on the annexe roof wired back to the main inverter. This works when the cable run is short and the main roof is full or shaded.
• A separate system in the annexe with its own inverter. This suits a long run or a unit that is metered separately.

The choice affects the grant, the inverter warranty and the way the system is monitored. It also affects the battery: a battery in the annexe can serve the annexe loads, but it will not automatically cover the main house unless the wiring is designed for it.

What About Planning Permission?

The planning position changed in 2026. A new exemption allows a detached auxiliary habitable dwelling of 32 to 45 square metres in a back garden without planning permission, and it came into effect on 27 July 2026. The conditions include a height limit of 4 metres with a tiled or slated pitched roof, at least 25 square metres of private open space kept for the main house, a build date before the end of 2030, and no separate utility connection to the main house.

That last condition matters here. An exempt granny flat must not have separate utility connections, and electricity is normally treated as a utility, so in practice it shares the main MPRN and the grant is claimed once for the property. A unit with its own MPRN is usually one that was built with planning permission rather than under this exemption, and that is the case where a separate grant may be possible.

The dwelling exemption says nothing about the panels, which are a separate planning question. Rooftop solar on a house is exempt development, provided panels sit at least 50cm from the roof edge and comply with the other conditions. For a detached annexe, the position can depend on how the unit is classified, so it is worth confirming with the planning authority before ordering, particularly in a conservation area or a protected structure.

The safe sequence is to settle the annexe planning first, then the solar design, then the grant application.

What Size System Makes Sense?

The annexe load is usually smaller than the main house, so a large array on the annexe roof rarely pays on its own.

• An annexe used by one or two people typically needs 2 to 4 kWp, or roughly 5 to 10 panels.
• A 4 kWp system generates about 3,700 kWh a year in Ireland, which is more than most annexes use.
• The surplus can be exported, but export pays about 18 to 20 cent per unit against about €0.35 for a unit used at home.
• If the main house is also electrified, a 5 to 6 kWp system on the best roof, with the annexe as a load, is usually the better design.

A battery is worth considering if the annexe is occupied in the evening and the main house is not, or if the property has a night-rate tariff and the battery can arbitrage it.

What Should You Check Before You Install?

A granny flat installation has a few extra checks.

• Confirm the MPRN position before applying for any grant, because it decides the whole funding structure.
• Measure the cable route from the annexe to the main board, including any duct, and check voltage drop.
• Check the annexe roof structure, since garden units often use lighter construction than a house.
• Confirm the planning position for the unit and for the panels.
• Decide whether the battery serves the annexe, the house or both.
• Ask for a post-works BER if the unit is self-contained, because a separate BER may be needed if it is sold or let.

WattCharger's solar panel service covers the survey, the grant application and the ESB Networks notification, and our guide to solar for garden offices and outbuildings explains the cabling and sizing questions in more detail.

Final Thoughts

Solar on a granny flat is usually a good idea, but it is a design and paperwork question more than a technology one. The panels can go on the annexe roof, the grant is normally claimed once for the property, checked against the MPRN, and a self-contained unit with its own meter is the case worth checking carefully. Settle the MPRN and planning position first, then size the system around the whole property rather than the annexe alone.

Ready to Plan Solar for an Annexe?

WattCharger will check the meter position, survey both roofs and quote a system that covers the house and the granny flat without wasting grant eligibility. Book a free consultation and we will confirm what is possible before you commit. Start with our solar panel page or read our SEAI grants guide for the amounts.