Bifacial Gain

Bifacial Gain refers to the additional energy produced by a bifacial solar module due to sunlight captured on the back side of the panel. Unlike monofacial panels, which only convert light hitting the front surface, bifacial panels generate power from both sides—resulting in a measurable performance boost that increases total energy yield.

This gain is influenced by ground reflectivity (albedo), mounting height, row spacing, tilt angles, tracking systems, and shading conditions. Bifacial Gain is a critical parameter in commercial and utility-scale solar design, especially when conducting performance simulations, financial modeling, or energy yield assessments within platforms like Solar Designing.

Key Takeaways

Bifacial Gain measures additional energy production from a module’s rear side.
Gain varies significantly depending on albedo, mounting height, spacing, and shading.
Proper modeling requires accurate POA rear irradiance and 3D shading analysis.
Understanding bifacial gain is critical for performance forecasting and financial modeling.
Bifacial technology is now standard in many utility-scale and C&I solar projects.

What Is a Bifacial Solar Panel?

A bifacial solar panel is a PV module that has active solar cells exposed on both sides. The front side functions like a conventional solar panel, while the rear side captures additional irradiance bouncing from:

Soil
Concrete
Sand
Snow
White rooftops
Reflective ground coverings

This additional energy capture leads to bifacial gain, typically ranging from 5% to 30%, depending on site conditions.

Bifacial modules are often used in:

Utility-scale solar farms
Commercial rooftops
Carports and canopies
Tracker-based systems

Foundational related concepts include Albedo, Solar Irradiance, and Solar Tracker.

How Bifacial Solar Panels Work

1. Front-Side Generation

The front side absorbs direct sunlight and operates similarly to standard monocrystalline modules.

2. Rear-Side Generation

The rear side collects reflected irradiance and diffuse sky radiation.

Rear-side production depends on:

Surface reflectivity (albedo)
Mounting height
Tilt and orientation
Row spacing
Tracker configuration

See POA Irradiance for how irradiance is calculated on both sides of a module.

3. Electrical Integration

Both sides feed into a single electrical circuit within the module.

The module's performance is determined by the total combined irradiance.

4. System Optimization

Bifacial panels are modeled with specialized simulation tools to capture rear-side behavior.

Designers often use Solar Layout Optimization to place modules at heights and angles that maximize bifacial gain.

Types / Variants of Bifacial Solar Panels

1. Glass-Glass Bifacial Modules

Glass on both sides for durability, transparency, and improved rear exposure.

2. Glass-Backsheet Bifacial Modules

More flexible and lighter but slightly lower rear-side transmission.

3. Monocrystalline Bifacial Modules

Most common type; high efficiency and stability.

4. Heterojunction (HJT) Bifacial Modules

Deliver exceptional bifacial efficiency, often exceeding 90% bifaciality.

How Bifacial Panels Are Measured

1. Bifaciality Percentage

Indicates how efficient the rear side is compared to the front side.

Bifaciality (%) = Rear-Side Efficiency / Front-Side Efficiency × 100

Typical values: 70–90%.

2. Bifacial Gain

Additional energy produced due to rear-side irradiation.

Typical gain: 5%–30%, depending on albedo.

3. POA (Plane of Array) Irradiance

Measured separately for front and back sides.

See POA Irradiance.

4. Height Above Ground

Higher mounting = more rear irradiance capture.

5. Inter-Row Spacing

Wider spacing reduces shading on the rear side.

Typical Values / Ranges

Practical Guidance for Solar Designers & Installers

1. Choose surfaces with high albedo

Rear-side performance improves significantly on reflective surfaces.

See Albedo.

2. Increase ground clearance

12–24 inches minimum; utility systems may use 1–1.5 meters.

3. Model shading and rear irradiance

Use tools like Shadow Analysis for realistic shading impact.

4. Optimize row spacing

Reduce row-to-row shading to improve total output.

5. Pair with trackers

Single-axis trackers increase bifacial yield significantly.

See Solar Tracker.

6. Use accurate design tools

Platforms like Solar Designing help evaluate rear-side POA, layout, spacing, and stringing.

7. Consider structural load

Glass-glass modules weigh more and may require engineering validation.

See Mounting Structure.

Real-World Examples

1. Utility-Scale Bifacial Tracker Farm

A 150 MW project uses single-axis trackers with bifacial modules elevated 1.2 meters above ground, achieving a 12% energy gain over monofacial systems.

2. Commercial Flat Roof

A 500 kW rooftop uses raised racking and reflective roof coating, delivering 18% bifacial gain.

3. Solar Carport System

A bifacial canopy installation leverages concrete ground reflectance and angled canopy design for 15% rear-side production.