Module bifaciality

The bifaciality coefficient (φ) is a dimensionless parameter that characterizes the relative electrical performance of the rear side of a bifacial PV module compared to its front side. In SunSolve it is defined as the ratio between the rear-side and front-side maximum power measured under standard test conditions (STC). A bifaciality of 0.70 means the rear side generates 70% of the front side’s output under identical illumination conditions.

Output name

Module bifaciality

Symbol

φ

Units

-

Formula

$$\frac{P_{max,rear}}{P_{max,front}}$$

Where:

• $P_{max,rear}$ is the maximum power of the rear side at STC
• $P_{max,front}$ is the maximum power of the front side at STC

Usage in SunSolve

The module bifaciality is shown in the module summary so users can verify the STC-derived value.

The bifaciality coefficient scales the rear-side contribution in irradiance-based system metrics, including the bifacial reference yield and the bifacial performance ratio.

It is not used in the actual yield solving. Module output is determined by ray tracing, module quantum efficiency, irradiance spectral content, and the electrical model. This differs from tools like PVsyst, which typically apply the bifaciality to increase the front-side irradiance.

Actual module bifaciality can vary with spectrum and illumination intensity, especially for emerging technologies such as tandem cells.