Solar Panel Output UK: How Much Electricity Will Your System Generate?

Understanding solar panel output in the UK is the first step to sizing a system correctly, estimating your savings and deciding whether solar is worth the investment. The short answer: a well-installed system on a south-facing roof will generate roughly 850–1,000 kilowatt-hours (kWh) for every kilowatt-peak (kWp) of capacity each year, though the figure varies meaningfully by where you live and how your roof faces. This guide breaks that down into system-size tables, a regional comparison, a seasonal breakdown and the factors that push real-world output above or below the textbook figures.

What does kWp mean — and why does it matter?

kWp stands for kilowatt-peak — the rated power of a solar panel array under standard test conditions (1,000 W/m² irradiance, 25 °C cell temperature). It is the unit installers quote when sizing a system, and it is the denominator for the all-important yield figure: kWh output per kWp per year. Multiply that yield by your system's kWp rating to get expected annual generation. A 4 kWp system generating 900 kWh/kWp would produce around 3,600 kWh per year — roughly equal to the average UK household electricity consumption of around 3,300–3,500 kWh per year, according to Ofgem's typical domestic consumption values.

UK solar yield: the national picture

The UK national average yield is approximately 900 kWh/kWp/year for a south-facing roof at a 30–35° pitch. This figure is derived from the European Commission's PVGIS (Photovoltaic Geographical Information System) satellite irradiance dataset, which forms the basis of the MCS (Microgeneration Certification Scheme) irradiance tables used by accredited UK installers. The BRE (Building Research Establishment) standard design reference similarly cites a range of 850–1,000 kWh/kWp for England and Wales. To run a site-specific estimate yourself, read our guide on how to use PVGIS to estimate your output.

Regional variation across the UK

Solar yield can vary by around 30% between the sunniest and least sunny parts of the UK, according to PVGIS satellite data. The table below shows indicative annual yields for a south-facing roof at approximately 35° pitch:

Region	Indicative yield (kWh/kWp/year)
Cornwall / Devon / Dorset	1,000–1,050
South-East England (Kent, Sussex)	950–1,000
London / South Midlands	900–950
North-West England / Yorkshire	850–900
Northern Ireland	800–850
Central Scotland	800–850
Highlands and Islands	750–800

These figures are based on PVGIS irradiance data collated by Solar Info UK's regional solar map and are consistent with MCS irradiance zone tables used by certified installers across England, Scotland, Wales and Northern Ireland.

Annual output by system size

Most UK homes install systems between 3.5 kWp and 10 kWp. The table below uses a mid-range yield of 900 kWh/kWp (central England, south-facing, ~35° pitch) as the baseline. Adjust up by roughly 10–15% for the south coast, or down by 10–15% for Scotland.

System size	Typical panels	Est. annual output (central England)	Est. annual output (south coast)	Est. annual output (Scotland)
3.5 kWp	8–9 × 400 W	~3,150 kWh	~3,500 kWh	~2,800 kWh
4 kWp	10 × 400 W	~3,600 kWh	~4,000 kWh	~3,200 kWh
6 kWp	15 × 400 W	~5,400 kWh	~6,000 kWh	~4,800 kWh
10 kWp	25 × 400 W	~9,000 kWh	~10,000 kWh	~8,000 kWh

To work out how many solar panels you need for your specific consumption, divide your annual electricity usage by the expected yield per kWp for your region. These figures align with typical outputs cited by Sunsave Energy and the Renewable Energy Hub for south-facing UK installations.

Seasonal output: summer vs winter

Solar output is highly seasonal. UK panels generate roughly 65–70% of their annual electricity between April and September, with May and June typically being the peak months. December and January produce the least — around 25–30 kWh per kWp, compared to around 110–120 kWh per kWp in May. That is broadly a 4:1 ratio between peak summer and midwinter output, according to real-world monitoring data from Solar by Postcode covering thousands of UK installations.

For a 4 kWp system in central England, the monthly pattern looks roughly like this:

January / December: ~80–100 kWh/month (the system)
February / November: ~120–150 kWh/month
March / October: ~250–280 kWh/month
April / September: ~380–420 kWh/month
May / August: ~440–480 kWh/month
June / July: ~450–510 kWh/month (peak)

Importantly, cold weather does not reduce output — panels actually operate more efficiently at lower temperatures. It is the shorter days and lower sun angle that drive winter's lower numbers. For a detailed look at winter performance, see our article on whether solar panels work in winter in the UK.

Factors that affect real-world output

Roof orientation and tilt

A south-facing roof at 30–40° delivers maximum output. East- or west-facing roofs typically yield around 15–20% less than a comparable south-facing installation. A flat roof (0°) loses around 10–15% compared to the optimum tilt. MCS installers calculate orientation and tilt losses using standard irradiance tables from the PVGIS dataset. For tips on panel placement, see our guide to solar panel dimensions and roof layout.

Shading

Even partial shading significantly reduces output. A chimney stack, dormer window or overhanging tree casting shadow on even one panel in a traditional string-inverter system can drag down the output of the entire string. The MCS installation standard MIS 3002 requires installers to assess shading from surrounding structures and nearby obstructions. Microinverters or DC optimisers mitigate string shading losses by letting each panel operate independently.

Panel efficiency and technology

Modern monocrystalline panels typically achieve 20–22% cell efficiency, while older polycrystalline panels sit around 15–17%. Higher-efficiency panels generate the same output from a smaller area — useful when roof space is limited. For a deep dive into how efficiency varies by technology, see our guide to solar panel efficiency explained.

Soiling and maintenance

Dirt, pollen, moss and bird droppings reduce output by 1–3% on average in the UK, according to industry data from installers. UK rainfall keeps most panels reasonably clean, but panels in coastal areas exposed to salt spray or sites with heavy tree cover may need periodic cleaning. Annual professional inspection is standard under MCS maintenance recommendations.

System degradation

All solar panels degrade gradually over time. Most quality panels lose around 0.3–0.5% of output per year, meaning a system will typically produce around 80–85% of its original output after 25 years — within the range of manufacturer performance warranties. This is a relatively modest loss; the figures above are for a new system and should be discounted slightly when projecting long-run generation.

What does a kWh of solar power actually cover?

A single kWh runs a washing machine cycle, boils a kettle roughly 6–8 times, or keeps a large TV running for 3–4 hours. Put another way, a 4 kWp system in central England generating ~3,600 kWh per year covers the electricity needs of an average UK home (around 3,300–3,500 kWh/year, per Ofgem) almost entirely during the months when you are generating most. Surpluses can be exported to the grid under the Smart Export Guarantee (SEG), earning between 3p and 24p per kWh depending on your tariff. For a full breakdown of costs and financial return, see our guide to solar panel cost and savings.

Key takeaways

The UK average solar yield is approximately 900 kWh/kWp/year for a south-facing roof (PVGIS / MCS data).
Regional variation spans from ~750 kWh/kWp (Highlands) to ~1,050 kWh/kWp (Cornwall).
A typical 4 kWp system in central England generates around 3,600 kWh per year — roughly matching average household consumption.
Output in May–June is roughly 4× higher than in December–January.
Shading, orientation, panel efficiency and annual degradation all affect actual yield — an MCS-accredited installer will model these for your specific site.