The first bifacial photovoltaic cells were created in the laboratory several decades ago. The first company that commercialized them was the Spanish company Isofoton (1981), based on the studies of Antonio Luque at the Institute of Solar Energy in Madrid.
Today’s bifacial solar modules are a simplified double-sided version, they are designed to produce energy by the light incident on the front and back of the panel, but they are not made with double cells.
In fact, they are very similar to standard products but transparent to light from the backside.
What does a bifacial cell and module look like?
Using bifacial cells, bifacial modules can be made in two versions:
Double glazing: The white polymer back sheet of a conventional module is replaced by the glass with white stripes in the spaces between cells. The advantages are greater resistance to hot climates with high humidity, easier cleaning, greater robustness, and hardness.
Transparent backsheet: The white polymer backsheet of a conventional module is replaced by a transparent polymer sheet. The advantages are lower weight and cost.
How can I generate more power with a bifacial module?
The front side of the photovoltaic module receives direct solar radiation, while the backside receives solar radiation reflected from the ground and other surfaces (albedo).
By taking advantage of the back radiation, we make the module more productive compared to monofacial panels. The backside of the bifacial module can generate up to 30% additional power depending on the reflectivity of the surfaces.
A bifacial module receives energy from 3 different sources:
1- Sun: direct solar radiation.
2- Diffuse light: projected by elements of the landscape such as clouds.
3- Ground albedo: solar radiation reflected from surfaces.
The secret is albedo.
What is albedo?
It is the percentage of radiation reflected by a given surface. The average albedo reflected by the Earth is about 35%, but it all depends on the type of surface. Thus, light-colored, shiny surfaces, for example, a white surface, have a much higher albedo, exceeding 60%.
A value is much higher than that of dark-colored, matte surfaces (e.g. gravel), which are usually around 30%. Higher reflected radiation will cause the back of the panel to produce more energy and therefore the module will perform better.
How to install bifacial modules to get the most out of them?
To take advantage of the characteristics of the bifacial panel and obtain the maximum gain we must follow these recommendations:
Fixing Structure: The structure must allow the light to reach the back in the most homogeneous way without creating shadows. Avoid shading the backside of the module by the support tack
Height: The height at which the panels are installed with respect to the rear surface influences seriously on the reflection capture. Although in co-planar assemblies much more reflected energy can be captured than it seems if we separate the modules from that surface a significant increase in albedo is achieved. Also, it is possible to capture the most of albedo by installing the modules on poles or turrets, that way it can boost the bifacial gain and capture even more diffuse reflected light from the ground.
Spacing: It is very important to measure well the distance between one panel and another because if they are separated, you can take more advantage of the reflected solar radiation.
Surface: The choice of the correct surface on the backside is the most important key to the performance of the panel. The best choice is the use of white surfaces. On other surfaces, there are also significant gains such as on tiles or cement.
What are the major advantages of bifacial panels?