Peak Sun Hours explained
Peak sun hours (PSH) is a standardised way to express the total daily solar energy available at a location. It's defined as the number of hours during which solar irradiance averages 1,000 W/m² (the benchmark intensity used for panel ratings).
For example: if a location receives 4 kWh/m² of solar energy in a day, that's equivalent to 4 peak sun hours — even if the sun shone for 12 hours at varying intensities.
Average peak sun hours by location:
- UK (south): 2.5–3.5 PSH/day (annual average, including cloudy days)
- UK (Scotland): 2.0–2.5 PSH/day
- Germany: 2.5–3.2 PSH/day
- Spain: 4.5–6.0 PSH/day
- Florida, USA: 4.5–5.5 PSH/day
- Arizona, USA: 5.5–7.0 PSH/day
To estimate annual system output: multiply system size (kW) × PSH × 365. A 4 kW system in southern England at 3 PSH gives roughly 4 × 3 × 365 = 4,380 kWh/year (before losses). Real-world losses from temperature, wiring, and inverter efficiency typically reduce this by 15–25%.
PSH values are based on long-term averages and vary significantly by season — UK summer days deliver 4–5 PSH while winter days might deliver only 0.5–1.5 PSH.