Solar panels in Cardiff: output, grid and Welsh planning

Planning in Wales

Wales sets its own planning rules, so England’s August 2026 changes do not apply. The Welsh Government’s page on planning permission for solar panels sets two simple tests. Panels on a roof or wall should project no more than 200mm from the surface. They should also stay below the ridgeline.

However, extra rules apply in some places. The same page says listed buildings need planning permission and probably listed building consent. In conservation areas and World Heritage Sites, panels on principal or side walls visible from the highway need planning consent.

Your planning authority is Cardiff Council. Because we have not checked local maps, we cannot say which streets sit in a conservation area. Ask the council about your address before you sign anything. A short email now can save a redesign later, and it costs nothing.

Our post on planning permission for solar panels compares England, Scotland and Wales, including flats and conservation areas. It is a useful check before you speak to the council. Flats often add another step, because a landlord or freeholder may need to agree.

What a roof can make

The European Commission’s PVGIS model gives about 1,042 kWh a year for each kWp in Cardiff. That is for a south-facing roof at 35 degrees, with default losses of 14%. At the best tilt, 39 degrees, it rises to about 1,044 kWh per kWp.

For example, a 3.6 kWp system would make around 3.6 x 1,042, or about 3,751 kWh a year. Think of that as a modelled estimate. Weather, kit and shading will all change what your meter shows.

Direction and shade matter most. A south roof does best, whereas east and west roofs make less overall but spread power across the day. Trees and nearby walls can cut output sharply, even if they touch only part of the array.

Tilt matters least, since the gap between 35 and 39 degrees is tiny. If your roof is far flatter or steeper than that, ask the installer to model your exact pitch.

Panels need care once they are on the roof, too. Our post on solar panel maintenance and cleaning covers monitoring, inspections, warranties and bird proofing.

Value is worth checking as well. Ofgem’s price cap from October to December 2026 averages 26.32p per kWh for electricity, though your region and tariff may differ. Each unit you use from your own roof is a unit you do not buy. Meanwhile, exported power earns whatever your supplier’s export tariff pays.

Joining the grid

For South Wales, our data names National Grid Electricity Distribution. The operator must be told about your system, and under MCS rules your installer does that.

The route depends on size. MIS 3002 says installs up to and including 16 A per phase follow G98, and larger ones follow G99. The limit adds up all generators. As a result, a battery alongside panels may push you into G99.

For G98, a National Grid page describes telling the operator within 28 days of commissioning. G99 takes more steps, so ask your installer for a timeline in writing.

Finding a reliable installer

Look for MCS certification, the UK quality mark for small-scale renewables. GOV.UK says you need it to claim Smart Export Guarantee payments. The MCS site lets you check a business.

Then ask about the Renewable Energy Consumer Code. RECC members must insure deposits, stage payments and workmanship warranties. That cover matters if a firm stops trading.

On funding, the Welsh Government says Nest can recommend a package that could include solar panels. Nest advisers check eligibility, so ask them first.

Expect a roof check too. MIS 3002 says a suitably competent person must check that the roof structure can carry the load. Ask to see that check in writing.

Get at least three quotes, because prices and designs vary. Compare kWp, equipment, warranty and who handles the paperwork. Our solar panel installation guide lists what a full quote covers. Our solar panel costs guide shows what government data says about price.

Nearby, our page on solar panels in Swansea runs through the same checks for another South Wales city. When you are ready, ask for quotes. With your consent, we will pass your enquiry to an MCS-certified installer.