Bifacial Photovoltaic Power Modules

Bifacial photovoltaic (PV) power modules are advanced solar panels designed to capture sunlight from both their front and rear surfaces, significantly enhancing energy generation compared to conventional monofacial modules. By utilising reflected and diffused light from the ground and surroundings, bifacial modules improve efficiency, optimise land use, and reduce the levelised cost of electricity (LCOE). They have become a defining technology in the global transition toward sustainable and high-efficiency solar power generation.

Background and Development

The concept of bifacial solar technology dates back several decades, with early experimental designs emerging in the 1960s and 1970s. However, widespread commercial adoption began only in the 21st century, primarily due to advances in photovoltaic cell manufacturing, transparent encapsulation materials, and anti-reflective coatings. The demand for higher power output and better land-use efficiency in utility-scale solar farms accelerated research into bifacial systems.
As of recent years, bifacial modules have become a standard choice for large solar power plants worldwide, with installations across the United States, China, India, and the Middle East. Industry projections suggest that bifacial modules may dominate global PV capacity additions due to their superior energy yield and falling manufacturing costs.

Structure and Design

A bifacial PV module resembles a conventional monofacial module in its core design but differs in the material configuration that allows light absorption on both sides.
Key components include:

1. Solar Cells: Bifacial modules typically employ high-efficiency crystalline silicon cells, often PERC (Passivated Emitter and Rear Cell), PERT (Passivated Emitter Rear Totally Diffused), or Heterojunction (HJT) technologies. Unlike monofacial cells, their rear surfaces are not fully covered by opaque back sheets but instead are designed to be light-sensitive.
2. Encapsulation: Both the front and rear sides are encapsulated using transparent materials such as tempered glass or clear polymer backsheets, enabling the rear side to receive and convert reflected sunlight (albedo).
3. Frame and Mounting: The frames are often made of anodised aluminium, supporting elevated installations that maximise rear-side exposure. Some designs are frameless to further minimise shading and reflection losses.
4. Junction Box and Wiring: Electrical junctions are strategically placed to prevent shading on the back side. Split-junction box designs are common, enhancing current flow and reliability.

Working Principle

Bifacial modules generate electricity by converting both direct sunlight on the front side and reflected/diffused light on the rear side into electrical energy. The rear-side energy contribution depends on several factors:

• Albedo of the Surface: The reflectivity of the ground or nearby surfaces. High-albedo surfaces such as snow, white gravel, sand, or concrete increase the rear-side energy yield.
• Module Height and Tilt Angle: Elevated mounting allows more light to reach the rear side and optimises incident angles.
• Spacing Between Rows: Adequate inter-row spacing prevents mutual shading, improving overall performance.
• Bifaciality Factor: Defined as the ratio of rear-side to front-side efficiency, typically between 70–90%, depending on cell design and material properties.

Under ideal conditions, bifacial modules can produce 10–30% more energy than monofacial ones of the same rated capacity.

Technological Variants

There are several technological approaches in bifacial module manufacturing, including:

• n-Type Silicon Bifacial Modules: Using n-type wafers (such as n-PERT or HJT), these modules exhibit higher efficiency, better temperature coefficients, and reduced light-induced degradation (LID) compared to conventional p-type cells.
• Heterojunction (HJT) Modules: Combining crystalline silicon wafers with thin amorphous silicon layers on both sides, HJT modules naturally lend themselves to bifacial design and offer some of the highest bifaciality factors (>90%).
• IBC (Interdigitated Back Contact) Bifacial Modules: These integrate bifacial absorption with rear-contact cell architecture, improving current collection and efficiency.

Performance Characteristics

Several performance metrics define the behaviour of bifacial PV modules:

• Bifacial Gain: The percentage increase in total energy yield relative to monofacial modules, influenced by albedo, mounting configuration, and irradiance conditions.
• Energy Yield (kWh/kWp): Enhanced due to additional rear-side generation, particularly beneficial in high-reflectivity and open-field environments.
• Temperature Coefficient: Similar to or better than monofacial modules; lower operating temperatures are possible because of dual-sided heat dissipation.
• Durability: The use of dual-glass construction improves resistance to moisture, UV exposure, and mechanical stress, extending module lifespan to over 30 years.

Advantages

1. Higher Energy Output: The dual-sided absorption increases annual energy generation by 10–30% without requiring additional land or structural expansion.
2. Improved Efficiency in Diverse Conditions: Bifacial modules perform better in diffuse light, cloudy weather, or snowy conditions due to light capture from multiple directions.
3. Reduced Levelised Cost of Energy (LCOE): The higher yield per unit area leads to reduced overall energy costs over the lifetime of the installation.
4. Enhanced Durability: Dual-glass encapsulation improves resistance to potential-induced degradation (PID) and environmental wear.
5. Aesthetic and Architectural Versatility: Transparent modules can be integrated into building-integrated photovoltaics (BIPV) for canopies, facades, and skylights.

Limitations and Challenges

Despite their advantages, bifacial PV systems face certain challenges:

• Higher Initial Cost: Manufacturing and installation costs are slightly higher due to dual-glass construction and specialised mounting systems.
• Complex Modelling and Prediction: Estimating rear-side irradiance accurately requires advanced simulation tools, complicating energy yield forecasting.
• Dependence on Site Conditions: Performance gain is highly influenced by ground reflectivity and array layout, limiting uniform performance across regions.
• Soiling and Maintenance: Dust accumulation on both sides necessitates more frequent cleaning, particularly in arid environments.
• Inverter and System Integration: Power electronics must accommodate variable current generation from two active surfaces.

Applications

Bifacial photovoltaic technology is being increasingly adopted in:

• Utility-Scale Solar Farms: Maximising energy yield per unit of land area.
• Commercial Rooftop Installations: Particularly on light-coloured or reflective roofs.
• Agrivoltaic Systems: Dual-use agricultural and solar setups, where the reflective ground surface enhances rear illumination.
• Snowy and Desert Regions: Where high ground albedo naturally boosts performance.
• Floating Solar Plants: Water surfaces provide strong reflectivity, significantly enhancing bifacial energy gains.

Global Adoption and Market Trends

Bifacial modules have rapidly gained global market share. Countries such as China, the United States, India, Spain, and the UAE have integrated bifacial technology into their large solar projects. Falling production costs, improved energy yield, and compatibility with tracking systems have driven their deployment. When combined with single-axis or dual-axis trackers, bifacial modules achieve even greater efficiency, with yield gains surpassing 35% in optimal environments.
Industry forecasts indicate that bifacial PV capacity could account for more than 50% of new solar installations within the next decade, reflecting its position as a mainstream technology in the renewable energy landscape.

Future Prospects

Continuous innovation is driving further improvements in bifacial module performance and economics. Key research areas include:

• Development of ultra-high-efficiency n-type and perovskite-silicon tandem bifacial cells.
• Advanced optical coatings to maximise rear-side light capture.
• Integration with smart tracking systems and AI-based predictive modelling for energy optimisation.
• Use of recyclable materials to enhance environmental sustainability.

As solar energy becomes increasingly central to global energy systems, bifacial technology represents a major step toward maximising photovoltaic potential while reducing costs and environmental impact.