Bifacial photovoltaic panels represent a major innovation in solar energy. Capable of capturing and converting sunlight on both sides, unlike traditional panels which do so only on their front side, they offer increased energy production, generally by 10 to 30%. Bifacial panels also perform better in low-light or partially shaded conditions, as the rear side continues to generate electricity even when the front side is partially shaded. In addition, bifacial panels offer greater durability and resistance to extreme environmental conditions, thanks to their reinforced structure and encapsulation between two layers of glass or composite materials.
The promise of bifacial solar panels
Bifacial solar panels are photovoltaic panels with the unique ability to capture and convert sunlight on both sides of the cell, unlike traditional solar panels which are only sensitive to light on their front side. This ability to use sunlight reflected from the back of the panel significantly increases energy production.
Bifacial solar panels offer several advantages over traditional solar panels. Firstly, they offer higher energy production, typically 10-30% higher, thanks to the use of incident sunlight on the back of the panel. This increase in energy production reduces the surface area required to install solar panels and optimizes the use of available space.
Secondly, bifacial solar panels perform better in low-light or partially shaded conditions, as the rear face of the panel continues to generate electricity even when the front face is partially shaded.
Finally, bifacial panels offer greater durability and resistance to extreme environmental conditions, thanks to their reinforced structure and encapsulation between two layers of glass or composite materials.
The design of bifacial solar panels
The structure of bifacial solar panels is similar to that of traditional solar panels, with photovoltaic cells encapsulated between two layers of transparent glass or a mixture of glass and transparent composite materials. The transparency of the back layer is essential to allow sunlight penetration and maximize energy production. Since bifacial solar panels are often encapsulated between two layers of glass or composite materials, they are generally more resistant to mechanical stress and extreme environmental conditions than conventional photovoltaic panels.
Their design brings with it a number of specific challenges:
- Unlike conventional photovoltaic panels, bifacial panels require transparent materials for the back layer and encapsulation. Designers need to choose materials that allow optimum light transmission, while ensuring adequate protection of the cells against environmental conditions.
- Bifacial solar panels are exposed to sunlight from both sides, which can lead to an increase in cell temperature. Effective thermal management is crucial to maintaining high efficiency and preventing premature material degradation. Designers need to consider ventilation, material selection and cell layout to minimize thermal impact.
- Bifacial solar panels can be more expensive to produce than conventional photovoltaic panels due to the complexity of materials and design. Designers need to strike a balance between production costs and profitability, taking into account the advantages in terms of energy production and sustainability offered by bifacial panels.
The importance of installation
However, it’s important to note that the installation and design of bifacial solar systems must be carefully planned to maximize their potential. Light reflection on the rear surface of the panel depends on the nature of the soil or supporting material, and sufficient space must be provided between the panels and the ground to allow access to light.
Installation is even more crucial for bifacial panels than for monofacial ones. Not just one exposure, but two! Indeed, the performance of bifacial panels depends largely on the reflection of light on the rear surface. Designers need to take into account the nature of the ground or support material, and allow sufficient space between the panels and the ground to allow for light reflection. Solutions such as the installation of reflective surfaces under the panels can also be considered to improve light reflection.
The tilt angle and orientation of bifacial solar panels can have a significant impact on their energy production. Designers need to analyze the sunlight and shading conditions specific to the installation site to determine the optimal orientation and tilt angle that maximize energy production.
Compatibility with other technical innovations
The photovoltaic cells used in bifacial panels are generally based on monocrystalline or polycrystalline silicon, although other semiconductor materials can also be used. Heterojunction cells and PERC (Passivated Emitter and Rear Cell) cells are particularly well suited to bifacial solar panels, thanks to their improved defect management and higher energy efficiency.
Bifacial solar panel technology can be combined with a variety of other technologies to further improve efficiency and performance. Here’s an overview of the compatibility of bifacial panels with half-cells, Tiling Ribbon Technology and PERC cells:
- Half-cells: Bifacial panels can be manufactured using half-cells instead of whole photovoltaic cells. Dividing the cells in half reduces internal resistance and shading losses, improving overall panel efficiency. Half-cell bifacial panels can therefore offer higher efficiency and better shade tolerance than full-cell bifacial panels.
- Tiling Ribbon Technology: This technology uses flat, solderless conductive ribbons to connect photovoltaic cells together. Tiling Ribbon Technology reduces efficiency losses due to soldering and increases the active surface area of the cells. Bifacial panels incorporating this technology can benefit from increased efficiency and improved aesthetics due to the absence of visible soldering.
- PERC (Passivated Emitter Rear Contact)cells: PERC cells are an improvement on traditional solar cells, offering higher efficiency thanks to a passivating layer on the back of the cell that reflects unabsorbed photons back to the cell for another chance at absorption. Bifacial panels equipped with PERC cells can thus benefit from improved overall efficiency and increased energy production.
Compatibility with different cell technologies
While bifaciality may offer advantages for some photovoltaic cell technologies, it is not necessarily applicable or beneficial for all existing cell technologies.
Bifacial solar panels are compatible with crystalline silicon cells, including monocrystalline and polycrystalline cells. Heterojunction cells and PERC cells are particularly well suited to bifacial panels, thanks to their improved defect management and higher energy efficiency.
In contrast, for thin-film and multi-junction cells, bifaciality may not be as advantageous due to differences in the structure and manufacture of these cells. Thin-film cells, for example, have more uniform light absorption across their entire surface, making the bifacial effect less beneficial. As for multi-junction cells, they are generally used in very high-efficiency applications, such as aerospace, where bifaciality is not a priority.
Why is the advertised yield of bifacial panels often the same as that of monofacials?
Advertised yields do not necessarily reflect the actual performance of solar panels under real installation and use conditions. Bifacial panels have superior energy production potential, especially when installation and lighting conditions are optimized to take full advantage of their double-sided design. Nevertheless, they can be presented as having equivalent, or even lower, performance due to standardized test conditions.
Indeed, solar panel manufacturers use standardized test conditions (STC) to measure and compare the performance of their products. STCs are based on a solar irradiance of 1,000 W/m², a cell temperature of 25°C and an AM 1.5 solar spectrum. These conditions do not take into account the additional energy generated by the rear side of bifacial panels, which may explain why the claimed efficiencies are identical for both panel types.
Moreover, this is what happens if the panel is incorrectly installed and the bifaciality factor (the portion of light captured by the rear face) is 0.