Bifacial Solar Gain Calculator
Bifacial solar panels capture sunlight on both their front and rear surfaces, generating extra energy from light reflected off the ground behind the array. This calculator takes your standard (monofacial-equivalent) annual output, the module bifaciality factor, and the ground surface albedo, then reports the bifacial energy gain percentage, the additional annual energy from the rear-side gain, and the total annual output with bifacial gain. To estimate the standard annual output figure, use our Solar Panel Output Calculator, and for the sunlight resource that drives it, see the Solar Irradiance Calculator.
Use the Solar Panel Output Calculator to estimate this figure for your system.
Modern bifacial modules typically have a bifaciality factor of 70-90%, representing the rear side's power output relative to the front side under identical illumination.
Selecting a surface auto-fills the Ground Albedo below (still editable).
Albedo measures how much light a surface reflects, from 0 (no reflection) to 1 (perfect reflection). Higher-albedo surfaces reflect more light to the panel rear side, increasing bifacial gain.
(bifaciality factor (%) ÷ 100) × ground albedo × 50
standard (monofacial-equivalent) annual output (kWh) × (bifacial energy gain (%) ÷ 100)
standard annual output (kWh) + additional annual energy from rear-side gain (kWh)
This is a simplified planning-level approximation. Real bifacial gain also depends on mounting height, row spacing, and tilt, and is typically modeled precisely using specialized software like PVsyst for actual project design.
Results update live as you type. For planning and field-check estimates — always verify against applicable standards and equipment ratings.
How we calculate this →Ground surface matters as much as panel technology for bifacial gain. The same 80%-bifaciality panel captures roughly 8% extra energy over standard grass or soil (0.20 albedo), but that gain more than doubles to around 20% over a white reflective membrane roof or fresh snow (0.55-0.80 albedo). For ground-mount installations, some developers now specifically install white gravel or reflective ground cover beneath bifacial arrays specifically to capture this extra yield -- a genuine engineering lever that requires no additional panels.
How bifacial solar gain is calculated
This calculator estimates the bifacial energy gain, the additional annual energy from the rear-side gain, and the total annual output with bifacial gain, tying three inputs together: the standard (monofacial-equivalent) annual output, the bifaciality factor, and the ground albedo. Three quantities tie the calculation together.
Bifacial Energy Gain (%) = (Bifaciality Factor (%) ÷ 100) × Ground Albedo × 50. The bifaciality factor expresses the rear side's power output relative to the front side under identical illumination -- modern bifacial modules typically land in the 70-90% range. Ground albedo measures how much incident light the surface beneath the array reflects back up, on a scale of 0 (no reflection) to 1 (perfect reflection): grass or soil is roughly 0.20, concrete about 0.30, white membrane roofing about 0.55, and fresh snow about 0.80. The 50 multiplier is a representative planning-level coefficient that converts the product of bifaciality and albedo into an expected percentage energy gain over the monofacial-equivalent output. At the defaults (80% bifaciality, 0.20 albedo), that is (80 ÷ 100) × 0.20 × 50 = 0.80 × 0.20 × 50 = 8.0%.
Additional Annual Energy from Rear-Side Gain (kWh) = Standard (Monofacial-Equivalent) Annual Output (kWh) × (Bifacial Energy Gain (%) ÷ 100). The bifacial gain percentage is applied to the standard annual output the array would produce as a monofacial system, giving the extra kilowatt-hours the rear side adds. At the defaults (12,000 kWh, 8.0% gain), that is 12,000 × (8.0 ÷ 100) = 12,000 × 0.08 = 960 kWh.
Total Annual Output with Bifacial Gain (kWh) = Standard Annual Output (kWh) + Additional Annual Energy from Rear-Side Gain (kWh). Adding the rear-side energy to the standard front-side output gives the array's total expected annual production. At the defaults (12,000 kWh, 960 kWh), that is 12,000 + 960 = 12,960 kWh.
Two notes on the model. First, this is a simplified planning-level approximation -- the 50 multiplier is a representative coefficient, and real bifacial gain also depends on mounting height, row spacing, tilt, and the diffuse/direct radiation split, all of which are typically modeled precisely using specialized software like PVsyst for actual project design. Second, the ground albedo is the single most site-controllable lever in the calculation: a reflective ground cover (white gravel, membrane roofing, or seasonal snow) can more than double the gain versus grass or soil, which is why some ground-mount developers intentionally install reflective surfaces beneath bifacial arrays. Data sources: Bifacial panel technology and bifaciality factor ranges from IEC 60904-1-2 and manufacturer specifications; ground albedo values for grass, concrete, white roofing, and snow from solar irradiance measurement standards and PVsyst documentation; bifacial energy gain calculation methodology from bifacial photovoltaic research literature and PVsyst modeling; mounting height and row spacing effects on bifacial gain from bifacial PV research and field performance studies; cost-benefit analysis of bifacial vs. monofacial panels from solar project economics literature. Verification: with defaults (12,000 kWh, 80% bifaciality, Grass/Soil/0.20 albedo), Bifacial Energy Gain = 8.0%, Additional Annual Energy from Rear-Side Gain = 960 kWh, Total Annual Output with Bifacial Gain = 12,960 kWh.