Why does Edinburgh have more daylight but less output?

More daylight hours (17.6hrs) but lower sun angle and more cloud cover. Net result: Edinburgh generates 15-20% less on the solstice than London despite having nearly 1 hour more daylight.

Summer Solstice: Peak Output

By Home Solar Guide Team|Updated 20 March 2026|educational

Independently written | Plain-English guide

Summer solstice solar — June 21: 16+ daylight hours. 25-30 kWh from a 4kW system.

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Find the right system size for your roof

Panel count depends on your electricity use, roof space and direction — not on a rule of thumb. Get a recommended size and what it should cost.

Size My System

How much solar do you get on the longest day?

Solar output on June 21 (longest day) for a 4kW south-facing system: LONDON: 16hr 38min daylight. Peak: ~3.8kW at noon. Total (clear day): 28-32 kWh. Total (typical): 18-24 kWh. MANCHESTER: 16hr 57min daylight. Total (clear): 25-30 kWh. Typical: 16-22 kWh. EDINBURGH: 17hr 36min daylight. Total (clear): 24-28 kWh. Typical: 15-20 kWh. INTERESTING FACT: June 21 isn't always the highest-output day. Clear days in late May or early July often beat it — the solstice has the most daylight but June weather in the UK can be cloudier than May. RECORD OUTPUT: A well-positioned 4kW UK system can produce 30-35 kWh on a perfect clear June day — enough to power the average home for 4 days. UK TOTAL: On a sunny June day, UK solar fleet (~16GW) generates enough for 3-4 million homes. Sources: PVGIS hourly data, National Grid ESO solar generation data, Met Office.