A bifacial module generates power from direct sunlight on its front and from sunlight diffusely reflected off the ground onto its rear. The rear gain depends on how much of the ground the back surface "sees" — its ground view factor — and how reflective that ground is (its albedo, ρ).
Front view factor to ground: F_f = (1 − cosβ) / 2
Rear view factor to ground: F_r,base = (1 + cosβ) / 2
Height correction: k(h) = 1 − e^(−h / 0.6)
Effective rear view factor: F_r = F_r,base · k(h)
Front irradiance: E_f = GHI · [cos θᵢ + ρ · F_f]
Rear irradiance: E_r = GHI · ρ · F_r
Rear power: P_r = φ · Pstc · (E_r / 1000)
Bifacial gain: BG = P_r / P_f × 100%
β is the panel tilt from horizontal (the view-factor pair above is the standard isotropic-sky formula used for ground-reflected diffuse irradiance). Raising the mounting height h reduces near-field shading and non-uniform reflection under the row, so the rear view factor approaches its ideal geometric value — captured here by the correction k(h). The bifaciality factor φ (typically 0.65–0.90) accounts for the rear cell's lower quantum efficiency relative to the front.
- Ground material — sets albedo ρ. Snow and light gravel reflect far more light than asphalt or grass.
- Mounting height — taller racking exposes more open ground to the rear side, raising F_r.
- Tilt angle — a steeper front tilts the rear surface more directly toward the ground below it.
- Sun elevation — sets the incidence angle θᵢ on the front face, changing how much direct beam is captured.
Real-world relevance: bifacial modules with elevated tracking racks are now standard in utility-scale solar farms, typically adding 5–20% annual energy yield over identical monofacial panels for the same footprint.