Swansea has a strong solar resource for the UK. PVGIS, the European Commission’s free solar model, estimates 1,014 kWh per kWp a year for a south-facing roof at 35 degrees. That is just below London at 1,019 kWh per kWp, and about 14% above Aberdeen at 893 kWh per kWp.
Because Solar Yield is an independent estimator, not an installer, this page explains the Swansea figures and what to ask installers. It also sets out the local rules that apply.
What a typical Swansea system could produce
Annual output scales with system size. A 4 kWp system could generate about 4,056 kWh a year in Swansea, and a 4.5 kWp system about 4,563 kWh. Cardiff, at 1,042 kWh per kWp, does slightly better, with a gap of 28 kWh per kWp.
Ofgem’s medium household uses 2,500 kWh of electricity a year on a standard meter, according to its typical consumption values. A 4 kWp roof can therefore out-produce that over a year. However, you save most on the share you use as the panels generate it.
Best month and worst month
May is the strongest month in Swansea at 128.7 kWh per kWp. December is the weakest at 32.3 kWh per kWp, so the best month produces about 4 times the worst.
May, June and July together give 379.1 kWh per kWp. In contrast, November, December and January together give 110.5 kWh per kWp.
Tilt, direction and shade
PVGIS puts the optimal tilt for Swansea at 39 degrees, with 1,016 kWh per kWp a year. A 35 degree roof gives 1,014 kWh per kWp, which is almost the same.
Direction and shade matter more. Energy Saving Trust says east or west facing systems tend to produce 15% to 20% less than south facing ones. Our post on east-west solar panels explains when a split array still makes sense. Our guide to solar panel shading and optimisers covers the other common problem.
If your best roof faces north, our upcoming guide to north-facing solar panels will cover that case. Still, check the PVGIS figures first, because they show how much a poor direction costs.
Planning rules and the City and County of Swansea Council
Although Wales sets its own planning rules, the core limit matches England’s. According to the Welsh Government, roof solar on a single house is usually permitted development. Panels should project no more than 200 mm and must not go above the ridgeline. They also need siting to limit the effect on the building’s appearance.
However, listed buildings need planning permission and listed building consent. In conservation areas, panels on principal or side walls visible from the highway need permission. The City and County of Swansea Council is the planning authority, and local Article 4 directions can remove rights. Ask the council if you are unsure.
Grid connection under National Grid Electricity Distribution
Your network operator depends on your postcode. In Swansea it is usually National Grid Electricity Distribution. Under G98, a type-tested system up to 16 A per phase connects first. That is about 3.68 kW on a single-phase supply, and the installer tells the operator within 28 days.
Because larger systems fall under G99, the installer must apply and get approval before installing. The operator may limit export. MCS explains both routes on its notifying network operators page.
Cost and quotes
DESNZ puts the 2025 to 2026 median installed cost at about £1,595 per kW for systems up to 4 kW. A 4 kWp system therefore costs about £6,400, according to the DESNZ cost data. Quotes vary, so compare several.
We found no current Welsh Government grant for domestic solar, but that is not proof none exists. Check gov.wales and your council. Our pages on solar panel installation and solar battery storage explain how referrals work. For neighbouring cities, see the solar output figures for Cardiff and the Plymouth solar installation page.
Next steps
Start with the solar yield calculator and enter your roof direction and tilt. Then use get quotes to send one enquiry to MCS-certified installers. Solar Yield passes on your request and does not install anything itself.