From Cornwall's 1,600+ annual peak sun hours to Scotland's 1,200, discover what peak sun hours really mean for your solar panel kWh output across the UK.
What are "sun hours"?
When solar installers talk about "sun hours" they don't mean the total number of daylight hours. They mean peak sun hours — the equivalent number of hours per day that your location receives solar irradiance at a standard intensity of 1,000 watts per square metre (1 kW/m²).
This matters because it's the figure used to estimate how much energy your solar panels will generate. A 4 kWp solar system in a location with 3 peak sun hours per day will theoretically produce around 12 kWh on an average day.
UK regions: peak sun hours
The UK is often assumed to be a poor choice for solar panels. In fact, the south of England receives solar resource comparable to parts of northern Germany — one of Europe's biggest solar markets.
Here's a rough guide to annual peak sun hours by UK region:
| Region | Annual peak sun hours | Daily average |
|---|---|---|
| Cornwall / South West | 1,550–1,650 | 4.2–4.5 hrs |
| South East England | 1,400–1,500 | 3.8–4.1 hrs |
| East Anglia | 1,350–1,430 | 3.7–3.9 hrs |
| Midlands | 1,250–1,350 | 3.4–3.7 hrs |
| Wales | 1,200–1,350 | 3.3–3.7 hrs |
| North West England | 1,150–1,280 | 3.2–3.5 hrs |
| Yorkshire / Humber | 1,200–1,300 | 3.3–3.6 hrs |
| Scotland (Central) | 1,100–1,200 | 3.0–3.3 hrs |
| Scotland (Highlands) | 950–1,100 | 2.6–3.0 hrs |
Data based on Open-Meteo historical irradiance and NASA POWER satellite records.
How sun hours vary through the year
The UK's solar resource is heavily seasonal. In June, a south-facing location in England might see 6–7 peak sun hours per day. In December, that drops to under 1 hour.
This seasonal variation is why a single annual figure can be misleading. The Sun Hours app shows you month-by-month and day-by-day data so you can see exactly when your panels are working hardest — and plan your energy usage accordingly.
Converting sun hours to kWh
The basic formula is:
Daily kWh = System capacity (kWp) × Peak sun hours × System efficiency
A typical system efficiency of 75–80% accounts for inverter losses, temperature effects, wiring losses and shading.
So a 4 kWp system in Cornwall (4.3 average daily sun hours) produces:
4 × 4.3 × 0.78 = 13.4 kWh per day on average
In Scotland (3.1 average daily sun hours):
4 × 3.1 × 0.78 = 9.7 kWh per day on average
How Sun Hours simplifies this
Rather than ask you to know your system's kWp or efficiency rating, the Sun Hours app takes a different approach. You provide your best-ever single-day output — the peak kWh your panels have actually produced. That real-world number already bakes in all the efficiency factors for your specific installation.
From there, Sun Hours compares upcoming weather conditions to your location's historical solar patterns and gives you a practical 7-day forecast scaled to your real system performance.
No spreadsheets. No engineering calculations. Just your forecast.
Try Sun Hours free — Android now, iOS coming soon
Enter your postcode, your best solar day, and get a 7-day forecast in under a minute.
Get it on Google Play →