How Much Extra Energy Does a Bifacial Panel Really Add?
Summary
The gain comes from how the array is installed, not from the label on the module. IEA PVPS reports that bifacial modules on single-axis trackers over typical natural ground, with an albedo of 0.2 to 0.3, generally see gains below 10%. Snow cover on the ground pushes that number up significantly.
The back side converts light less efficiently
More than 75% of modules manufactured in 2024 were bifacial, up from about 50% in 2023, according to IEA PVPS. Many buyers now end up with a bifacial panel without asking for one.
NLR's System Advisor Model (SAM) handles the rear side in three steps. It calculates the irradiance reaching the back, multiplies it by the module's bifaciality, and adds the result to the front-side irradiance. Bifaciality is rear-side efficiency divided by front-side efficiency, and SAM describes typical datasheet values as 0.65 to 0.9. A panel rated 0.7 turns rear-side light into electricity at 70% of the front-side rate.
What sends light to the rear
IEA PVPS lists albedo, diffuse fraction, array height, row spacing, and the space between modules as the factors that raise bifacial gain. SAM names ground albedo, row-to-row spacing, and ground clearance height as the primary drivers of rear irradiance. Sandia's modeling group adds that rear irradiance varies a lot with position and with nearby objects such as combiner boxes and racking.
| Condition | Effect on bifacial gain |
|---|---|
| Higher ground or roof albedo, including snow | Larger gain |
| Higher mounting above the surface | Larger gain |
| Wider row spacing and gaps between modules | Larger gain |
| More diffuse light | Larger gain |
| Racking and equipment close behind the module | Patchier rear irradiance |
IEA PVPS gives elevated parking structures, fixed-tilt arrays on flat white roofs, and vertical sound barriers as settings that make good use of the rear face. A dark roof with the modules mounted close to the surface sits at the low end of the first two rows in that table. Uneven rear light also causes electrical mismatch inside each module, which IEA PVPS counts as a loss.
Sources
- NLR System Advisor Model — Module (bifacial inputs)
- IEA PVPS — Bifacial Photovoltaic: Two Sides are Better than One (webinar, June 10, 2021, presenting the Task 13 report)
- IEA PVPS — Trends in Photovoltaic Applications 2025
- Sandia PVPMC — Bifacial PV Performance Models
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