How to Calculate the Gain in Bifacial Modules
In many cases, in the new solar parks with bifacial modules that Greensolver is starting to manages, we have noticed that the gain in irradiation from albedo is not being taken into account. As a result, the Performance Ratios of these assets are much higher than expected.
Here, we explain how to account for this gain and how to improve albedo to achieve greater system efficiency:
Bifacial Gain
The Bifacial Gains (BG) is the additional energy yield obtained from the rear side of the bifacial module compared to a monofacial module. It is expressed as a percentage increase in energy generation. The calculation involves measuring the energy contributions from both the front and rear sides.
Where:
- Grear = Rear-side irradiance (W/m²)
- Gfront = Front-side irradiance (W/m²)
- ηrear = Rear-side efficiency (typically 70%-90% of front-side efficiency)
- ηfront = Front-side efficiency (from STC ratings)
pyranometers to measure rear-side irradiation
Factors Affecting Bifacial Gain Calculation
Several factors impact the bifacial gain, including:
Albedo (Ground Reflectivity)
- Higher albedo (e.g., white concrete, snow) increases rear-side irradiance.
- Albedo values typically range from 0.1 (dark soil) to 0.6 (fresh snow).
Module Height and Tilt Angle
- Higher mounting height allows more reflected light to reach the rear side.
- Optimized tilt angles improve overall energy yield.
Row Spacing and Shading
- Increasing spacing between module rows reduces shading on the rear side.
Bifaciality Factor (BFBFBF)
- Defined as the ratio of rear-side efficiency to front-side efficiency:
- Typically ranges from 0.7 to 0.9 depending on module technology.
Conclusion
Bifacial gain is a crucial metric for evaluating the benefits of bifacial PV technology. By optimizing system design (albedo, elevation, spacing), the bifacial gain can be 10%-30% or more, significantly improving solar plant efficiency.
Written by Alberto Ruiz