Peak sun hours
Daily solar irradiation expressed as the equivalent number of hours at 1,000 W/m²; numerically equal to kWh/m² per day.
Peak sun hours (PSH) compress a whole day of varying sunlight into an equivalent number of hours at the standard irradiance of 1,000 W/m². A location receiving 5 kWh/m² on a given day has 5 peak sun hours, regardless of whether the sun was above the horizon for 10 or 14 hours.
Because module ratings are given at 1,000 W/m² (STC), PSH lets installers make a quick estimate: a 6 kWp array with 4.5 PSH and a performance ratio of 0.8 yields about 21.6 kWh per day.
Typical annual averages on an optimally tilted plane:
- UK, Netherlands, northern Germany: about 2.8–3.2
- Northern Italy, central US: 3.8–4.5
- Southern Spain, Southwest US, northern India: 5–6
- Atacama, Sahara, Arabian Peninsula: 6–7.5
Seasonal swings matter more than the annual mean for off-grid and battery sizing: at 52° N, December PSH can be below 1 while June exceeds 5. For off-grid systems the design month is usually the worst one.
Related terms
All terms →- Irradiation (insolation)
Solar energy received per unit area over a period, usually expressed in kWh/m² per day or per year; the time integral of irradiance.
- GHI (Global Horizontal Irradiance)
Total shortwave solar radiation received on a horizontal surface, the sum of direct beam and diffuse sky components.
- Performance ratio
Ratio of actual AC energy output to the theoretical output implied by plane-of-array irradiation and nameplate capacity; a location-independent quality metric for PV plants.
- Specific yield
Annual energy produced per unit of installed PV capacity, expressed in kWh/kWp per year; combines solar resource and system performance.
- Kilowatt-peak (kWp)
The DC power rating of a PV module or array under Standard Test Conditions; the conventional unit of installed solar capacity.