The radiation reflected back from the ground depends on the reflectivity of the ground $\rho_\text{A}$ (Albedo, the “Whiteness” – not Wisdom:) – of the ground) and the geometric conditions.
In most models, the radiation reflected from the ground to the module level is calculated as follows:
$ RTI = GHI \cdot \rho_\text{A} \cdot \frac {1}{2}\left(1- \cos \left(\gamma_M \right)\right) $
| Surfaces | Albedo $\rho_\text{A}$ in % |
|---|---|
| Water surfaces | |
| Water in low sunlight | 50 – 80 |
| Water surface (angle of inclination > 10°) | 22 |
| Water surface (angle of inclination > 20°) | 12 |
| Water surface (angle of inclination > 30°) | 8 |
| Water surface (angle of inclination > 45°) | 5 |
| Rivers and lakes | 5-10 |
| Sea | 3-8 |
| Ice and snow | |
| Fresh snow | 80 – 90 |
| Old snow | 45 – 90 |
| Glaciers | 20 – 45 |
| Sea ice | 30 – 40 |
| Rock and sand | |
| Sandy ground | 20 - 40 |
| Dry sand and dunes | 25 - 35 |
| Rock (cliffs) | 10 - 40 |
| Vegetation | |
| Veldt | 20 - 30 |
| Broadleaf and mixed forest of temperate latitudes | 10 - 20 |
| Tropical rain forest | 10 - 20 |
| Coniferous forest | 5 - 12 |
| Dark soil (e.g. brown earth) | 5 - 10 |
| Settlement and farming | |
| Grassland, agricultural crops | 15 - 30 |
| Uncultivated fields | 26 |
| Lawn | 18 - 23 |
| Residential areas | 15 - 20 |
| Cropland | 5 - 20 |
| Asphalt | 15 |