Bifacial Gain

Quick Facts

What is Bifacial Gain?

Bifacial PV modules have photovoltaic cells exposed on both sides. The rear side captures reflected and diffuse light, producing additional energy beyond the front-side contribution.

Bifaciality factor

Modern modules:

• PERC bifacial: 60–75% bifaciality (older).
• TOPCon bifacial: 70–85%.
• HJT bifacial: 85–95%.

Bifaciality factor × rear-side POA × area = rear-side energy contribution.

Drivers of Bifacial Gain

Ground albedo

Reflectance of the surface beneath the modules:

• Snow: 0.70–0.85
• White gravel: 0.25–0.35
• Concrete: 0.20–0.30
• Sand: 0.25–0.40
• Vegetation: 0.15–0.25
• Dark asphalt: 0.05–0.10

Ground clearance

Higher mounting → more rear-side light. Optimal: ≥1 m for fixed tilt, ≥1.5 m for tracker. Hitting that reveal height consistently across a site is a foundation-design problem as much as a racking one — see our pile foundation design guide for solar ground-mount for embedment depth and pile-reveal tolerances.

GCR (Ground Coverage Ratio)

Lower GCR = wider rows = less self-shading = more rear-side gain. Bifacial typically uses GCR 0.35–0.45 vs. monofacial 0.40–0.55. On single-axis trackers, the backtracking algorithm manages this same self-shading trade-off dynamically through the day, rather than relying on fixed row spacing alone.

Module tilt

Higher tilt → more rear-side ground illumination. Effect strongest for fixed-tilt.

Diffuse fraction

Climates with more diffuse irradiance (cloudy) gain less from bifacial because diffuse already reaches front. Sunny climates gain more.

Bifacial Modeling in PVsyst

PVsyst’s “Bifacial systems” module:

1. 2D unlimited-row ray tracing.
2. User inputs: ground albedo (monthly), module height, row spacing (GCR), tracker geometry.
3. Computes rear-side POA hourly.
4. Combines with front-side POA × bifaciality factor.
5. Outputs total energy with bifacial contribution separated in the loss diagram.

For a full walkthrough of setting this up on a tracker plant — shading scene, row geometry, and bifacial parameters together — see our PVsyst tracker yield study methodology.

Worked Example

100 MW tracker plant, Rajasthan India:

• Module: 545 W bifacial TOPCon, 80% bifaciality.
• Ground albedo: 0.35 (sand).
• GCR: 0.42.
• Ground clearance: 1.8 m at tracker rest.
• Annual front-side POA: 2,200 kWh/m²/yr.
• Estimated rear-side POA: 320 kWh/m²/yr (15% of front).
• Effective rear contribution: 320 × 0.80 = 256 kWh/m²/yr (12% of front).

Bifacial gain: ~12%.

Annual energy: monofacial baseline 1,560 kWh/kWp × 1.12 = 1,748 kWh/kWp.

Design Considerations

• Avoid mounting structure shadowing. Tracker torque tubes and rails reduce rear gain. Choose low-profile racking.
• Inverter sizing. Rear-side gain increases Imp. Verify per-MPPT current limit.
• Verify bifaciality on .PAN file. Some manufacturers overstate; cross-check with IEC 60904 testing.
• Account for monthly albedo variation. Snow cover, vegetation growth, dust.
• Bifacial premium ROI. Typically positive in 1–2 years — isolating that uplift in a full project cash flow is easier with a dedicated model, such as SurgePV’s generation financial tool.

US & India Adoption

• US utility-scale: ~80% of new builds bifacial (2024).
• India utility-scale: ~70% bifacial.
• US commercial rooftop: ~40% bifacial.
• Residential: rare due to limited benefit on rooftops.

Common Mistakes

1. Ignoring bifacial gain in design calculations.
2. Using STC bifaciality without considering field conditions.
3. Not increasing per-MPPT current limit margin for Imp uplift.
4. Optimizing GCR for monofacial logic on bifacial designs.
5. Wrong albedo assumption (using vegetation default for desert sites).

Best Practices

• Run PVsyst bifacial model on every utility-scale project.
• Use site-measured albedo from a portable albedometer.
• Reduce GCR by 5–10% vs. monofacial for optimal rear gain.
• Pair bifacial with trackers for synergy (10–15% combined gain).
• Maintain ground clearance ≥ 1.5 m for tracker projects.

Comparison Tables

Bifacial Gain by Application

Standards & Certifications

• IEC TS 60904-1-2 — Bifacial PV measurement.
• IEC 61853-2 — Bifacial energy rating.
• IEC TS 61724-1 Annex — Bifacial PR measurement.

Key Takeaways

• Bifacial gain adds 5–25% energy above monofacial baseline.
• Driven by ground albedo, GCR, ground clearance, tilt, and bifaciality factor.
• Best for ground-mount and tracker projects with reflective ground (sand, concrete, gravel).
• PVsyst’s bifacial model is the bankable industry standard.
• Account for Imp uplift in inverter and per-MPPT current limit selection.

Related Reading

The rear-side geometry that drives bifacial gain is easiest to reason about alongside how trackers actually move. Our overview of auto solar tracking systems explains the tracking types and expected gains that compound with bifacial modules on tracker plants, while the PVsyst 3D near shading scene builder walkthrough shows how to build the row-pitch and torque-tube geometry that feeds the rear-side irradiance calculation described above. Since the bifacial module premium is only worth paying if it pays back on schedule, QuickEstimate’s solar financial modeling software guide is a useful reference for isolating that uplift within a project’s cash flow.