Plain explanation
The datasheet range (JinkoSolar: 'Module power increases 5-25% generally') depends on how much light reaches the back, so it is a range, not a promise. The IEA PVPS Task 13 report sums up field data: bifacial modules on single-axis trackers over typical natural ground (albedo 0.2 to 0.3) generally see bifacial gains under 10%, and much more when the ground is covered with snow. One measured example in the same report is NREL's field in Golden, Colorado: single-axis trackers, 1.5 m high, ground coverage ratio 0.35, mowed grass with 26% albedo, average module bifaciality 73%. It made 8.9% more energy (1-minute data, June 2019 to April 2020). The gain rises with albedo, diffuse light, mounting height, row spacing and gaps between modules. Those field numbers are for elevated trackers. A module sitting close to a dark pitched roof gets much less light on the back, so expect less there; the report gives no single rooftop number. Bifacial arrays also run at higher DC current, so wires, fuses and inverter input need to be sized for it.
Steps from the source
- Compare modules on front-side STC power; treat the bifacial gain as a bonus, not as rated watts
- Model the back side with your real site: ground albedo, mounting height, row spacing (ask for a kWh simulation, not a %)
- Light gravel, white membrane or snow help; dark roofs and low mounting help little
- Size string cables, fuses and inverter DC input for the higher bifacial current
"Bifacial modules on single-axis tracker fields over typical natural ground covers (albedo = 0.2 to 0.3) generally see bifacial gains less than 10%. These values increase significantly when the ground is covered with snow."
Word for word from the source.
Source
Where installers ask this
- Is Bifacial Solar Panel claimed wattage meaningful for rooftop mounting? (r/solar)
- reddit.com/r/solar/comments/1ruk094/bifacial_panels_on_rooftops_and_other_issues/
General guidance based on the manufacturer's manual or the named source. Always follow the current manual for your exact model and your national code. DC and AC electrical work is for qualified installers only. Not affiliated with or endorsed by any brand named; trademarks belong to their owners.