- Asked 3/10
- 2072 Chaitra
- 2069 Chaitra · 3 marks
- 2071 Shrawan · 2 marks
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Solar constant, insolation, irradiance, peak sun
Short answer
Solar constant is about 1367 W/m2, the solar energy per unit time on a perpendicular surface at mean earth-sun distance outside the atmosphere. Insolation is solar energy received per area over time, irradiance is instantaneous W/m2, and global irradiation is beam plus diffuse on a horizontal surface. Peak sun hours equals daily insolation in kWh/m2 divided by 1 kW/m2; sunshine hours are bright direct sunshine hours.
Define solar constant, extraterrestrial radiation, insolation, irradiance, global irradiation, peak sun and sunshine hour.
| Term | Definition |
|---|---|
| Solar constant (Gsc) | Energy from the sun per unit time received on a unit area of surface perpendicular to the rays, at the mean earth–sun distance, just outside the atmosphere. Value: about 1367 W/m² (the modern value is about 1361 W/m²). |
| Extraterrestrial radiation | Solar radiation received on a surface outside the earth's atmosphere, before any absorption or scattering. It varies slightly through the year (±3.3%) with earth–sun distance. |
| Insolation | Solar radiation energy received on a given surface area over a given time (INcoming SOLar radiATION). Usually in kWh/m²/day. |
| Irradiance (G) | Rate at which radiant energy falls on a unit area at an instant, in W/m². (Power per unit area.) |
| Global irradiation / radiation | Total solar radiation on a horizontal surface at the earth's surface, i.e. beam plus diffuse radiation. |
| Irradiation (energy) | Irradiance integrated over time (hour or day), in kWh/m² or MJ/m². (Called hourly or daily irradiation.) |
| Peak sun hours | Number of hours per day for which the solar irradiance would be 1000 W/m² to give the same daily energy. Example: 5 kWh/m²/day = 5 peak sun hours. Kathmandu typically has about 4.5–5.5 peak sun hours. |
| Sunshine hour | Number of hours in a day when the direct sunshine is bright enough to burn a mark on a recorder (Campbell–Stokes), i.e. direct radiation above about 120 W/m². |
Relation: peak sun hours (h) = daily insolation (kWh/m²/day) ÷ 1 kW/m².
✓ Answer checked by Claude Opus 5.5 (high effort)
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