Summer Solstice: Peak Output

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.