Bifacial reference yield

The bifacial reference yield extends the concept of reference yield to account for rear-side irradiance collection in bifacial PV systems. It represents the number of equivalent hours at reference irradiance (1000 W/m²) when both front and rear-side irradiation are considered, with the rear-side contribution weighted by the module’s bifaciality coefficient. This provides a more accurate baseline for evaluating bifacial system performance than the front-only reference yield.

Output name

Bifacial reference yield

Symbol

Y_r,bifi

Units

kWh⋅kWp^-1

Formula

$$\frac{H_{POA,f}+\phi \cdot H_{POA,r}}{G_{i,\text{ref}}}$$

Where:

• $H_{POA,f}$ is the front-side plane-of-array irradiation in kWh/m²
• $H_{POA,r}$ is the rear-side plane-of-array irradiation in kWh/m²
• $\phi$ is the module bifaciality coefficient (typically 0.70 to 0.85)
• $G_{i,\text{ref}}$ is the reference irradiance (1000 W/m²)

The bifaciality coefficient weights the rear irradiation according to the module’s rear-side performance. For example, with a bifaciality coefficient of 0.7 and a rear irradiation of 100 kWh/m², the rear contributes 70 kWh/m² to the total reference irradiation.

Usage

Bifacial reference yield is used in bifacial-specific performance metrics:

• Bifacial performance ratio: $P{R}_{bifi}=\frac{E_{out}\mathrm{/}{P}_0}{Y_{r,\text{bifi}}}$
• Bifacial array capture loss: $L_{c,bifi}=Y_{r,\text{bifi}}-Y_A$

Version history

In SunSolve versions prior to 7.30.1 (December 2025), the bifaciality coefficient was not applied to the rear-side irradiance in this calculation. The equation was:

$Y_{r,\text{bifi}}=\frac{H_{POA,f}+H_{POA,r}}{G_{i,\text{ref}}}$

This has been updated to correctly weight the rear-side contribution using the module’s bifaciality coefficient, in line with the IEC definition.

Previously, the equation matched PVsyst’s implementation at the time (without bifaciality weighting). PVsyst has since revised its calculation to include the bifaciality coefficient.