Bifacial modules
A bifacial module captures light on its rear side: light reflected by the ground and the surroundings. Radiaris adds that gain to the front irradiance as an equivalent irradiance.
Model
The rear irradiance is calculated with the infinite sheds model (Mikofski et al., 2019), the same one used by the pvlib/PVsyst community. It depends on:
- the tilt of the modules,
- the height of the rows above the ground,
- the ground coverage ratio (GCR): ratio between the sloped length of the module and the row spacing,
- the ground albedo.
The equivalent irradiance added to the front side is:
G_eq = G_front + φ · G_rear · (1 − structure_shading) · (1 − mismatch)
| Term | Value | Meaning |
|---|---|---|
| φ | From the datasheet; 0.70 if missing | Bifaciality: rear / front side at STC |
| Structure shading | 2 % | pvlib default value |
| Rear mismatch | 10 % | The rear irradiance is not uniform |
When it applies
- Only if the module is bifacial and the modules are raised (there is row spacing and height above the ground).
- Modules flush with the roof: the rear side faces the roof a few centimetres away, so no rear gain is counted (this stays on the safe side).
What matters most
| Factor | Effect |
|---|---|
| Albedo | The most important: a white membrane (0.65) or snow (0.80) give a lot of gain; grass (0.25) little |
| Height above the ground | More height, more and more uniform rear light |
| Row spacing | More spacing, less shade on the ground under the modules |
| Tilt | Steeper angles capture more reflection from the surroundings |
How to configure it
- Choose a bifacial module in the catalogue (or upload it with its .PAN and φ).
- Set the albedo of the surroundings in Horizon and albedo.
- Raise the modules in Placement: tilt, row spacing and height of the lower edge.
The rear gain is added to the effective irradiation on the plane, so it is included from that level of the loss waterfall onwards.
Is something missing or wrong? Write to us at hola@radiaris.com. Last reviewed: 26 October 2026.