Adding solar panels to a summer house: the electrical work involved

Why the existing consumer unit usually needs replacing

Older summer houses often have a small fuse box with two or three circuits and no earth leakage protection to speak of. Solar installations need a unit that can take a dedicated circuit breaker for the inverter, a surge protection device, and proper RCD coverage throughout. Fitting a modern inverter onto an old porcelain fuse board is rarely realistic.

In practice this means the consumer unit gets replaced as part of the project, not as an afterthought. It is worth pricing this in from the start rather than discovering it once an installer has already been round with a quote for panels alone.

We do consumer unit replacements from 350 € per job, which includes fitting a board sized and specified for what the property will actually carry, solar included.

What wiring stays and what needs adding

The existing circuits inside the house, sockets, lighting, the odd immersion heater, generally stay as they are if they are in reasonable condition and correctly rated. Solar does not mean rewiring the whole building.

What gets added is new cabling between the panels and the inverter, and between the inverter and the consumer unit, sized correctly for the current involved and routed so it is protected from weather and rodents alike. A dedicated isolator switch near the inverter is standard, so the system can be shut down safely for maintenance.

Where the summer house has an older two-core supply with no proper earth conductor, that becomes a problem at this stage, since inverters and modern protective devices assume a correct earth. This sometimes means a partial rewire from the meter or supply point onward, even if the rest of the house is left alone.

Adding a battery makes the system more complex

A grid-tied system with no battery is comparatively simple: panels, inverter, consumer unit, done. A battery brings charge controllers, additional wiring rated for the battery's output, and often a separate small enclosure with its own ventilation and temperature considerations, since batteries do not like extreme heat or cold.

For a summer house used mainly from May to September, a battery makes sense if the goal is to run lights and a fridge on days without much sun, or to have power at all when the place is off-grid. For a property already connected to the network, a battery is an extra layer of cost and complexity that is not always needed.

The wiring for a battery also needs to cope with the property standing empty and unheated for months over winter, which affects where cable runs and enclosures are sited.

When the network operator or a permit gets involved

Connecting a solar installation that feeds power into the grid, even a small one, usually needs to be reported to the network operator before it goes live, so they know generation is happening on that connection. This is separate from any building permit question.

Whether a building notice or permit is needed depends on the size and type of installation and sometimes on whether the summer house sits in a protected area or has restrictions from its planning conditions. This is worth checking with the local government or the building register before work starts, rather than after.

None of this is a reason to avoid solar, but it is a reason to budget time for paperwork alongside the physical installation, particularly if the connection capacity needs increasing at the same time.

• Check the existing connection capacity with the network operator before ordering equipment
• Ask whether the installation needs reporting or a formal agreement before switch-on
• Confirm with the local government whether a building notice applies to your property
• Keep documentation of the installation for the consumer unit's next inspection

What is the electrician's job, not the owner's

Sizing the consumer unit, choosing breaker and RCD ratings, connecting the inverter to the supply, and signing off that the installation meets the required standard is electrician's work, done by a qualified electrician rather than the property owner, however capable that owner is with tools.

An owner can reasonably handle mounting the panels themselves, choosing a supplier, and deciding on battery capacity based on how the house is used. The connection into the electrical system itself is where a professional needs to take over.

Our electrical work starts from 49 € per hour, with the consumer unit itself quoted as a fixed job once we know what the property needs. A short site visit before ordering any equipment usually saves money later, since it catches wiring problems before panels are on the roof.