Albedo
The fraction of incoming solar radiation that a surface reflects, from 0 (absorbs everything) to 1 (reflects everything).
Albedo (ρ) is a dimensionless reflectance coefficient. In solar engineering it determines how much light the ground sends back onto tilted modules and, above all, onto the rear side of bifacial modules. In climate science it governs how much sunlight the Earth surface absorbs; the planetary average is about 0.30.
Typical broadband albedo values:
- Open water (high sun): 0.05–0.10
- Asphalt: 0.05–0.12
- Green grass, crops: 0.15–0.25
- Dry sand, desert: 0.30–0.40
- Concrete, light gravel: 0.25–0.35
- White roofing membrane: 0.60–0.85
- Fresh snow: 0.80–0.90
Under the isotropic sky assumption, ground-reflected irradiance on a surface tilted at angle β is:
For a standard 30° tilt this term is small (a few percent of plane-of-array irradiance), but for vertical facades and bifacial rear sides it is substantial. Simulation tools often default to 0.2, which can underestimate output over sand or snow. Some utility plants deliberately lay white gravel or reflective geotextile beneath trackers to boost bifacial gain, a measure that pays off only when the extra energy outweighs the material and maintenance cost. Albedo also changes seasonally with vegetation, moisture and snow cover.
Related terms
All terms →- Bifacial module
A PV module that collects light on both its front and rear faces, using a transparent back sheet or glass to harvest ground-reflected and diffuse light.
- Irradiance
The instantaneous solar power received per unit area, measured in watts per square metre (W/m²).
- GHI (Global Horizontal Irradiance)
Total shortwave solar radiation received on a horizontal surface, the sum of direct beam and diffuse sky components.
- DHI (Diffuse Horizontal Irradiance)
Solar radiation reaching a horizontal surface after being scattered by molecules, aerosols and clouds, excluding the direct beam from the sun disc.
- Floating solar
PV arrays mounted on buoyant platforms on reservoirs, lakes, ponds or sheltered coastal waters instead of on land or roofs.