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Bifacial Solar Panels: a technical overview

Bifacial solar panels are panels that generate energy from both sides of the photovoltaic cell. Discover how they work, their advantages and costs.

Bifacial solar panels, as the name suggests, harness solar radiation through a double layer of glass positioned on the back of the photovoltaic cell.

This ability to absorb sunlight from both sides is made possible by the so-called Albedo coefficient, a parameter that measures the reflective capacity of an object.

The Albedo value of the surface directly impacts the efficiency of bifacial solar panels, as their increased productivity depends on the ability to also utilize the reflected light. Besides this key factor, it is essential that the structure on which the panel is installed allows the reflected light to reach the back of the module, minimizing shading caused by the support system.

To better understand the incident solar radiation at a specific point, in addition to referring to astronomical and environmental data on direct or diffuse radiation, we recommend using a solar design software that enables you to input albedo values into the analysis of photovoltaic panel performance.

What are bifacial solar panels

Bifacial solar panels are a type of panels that capture solar energy and thus produce electricity on both the front and back sides of the photovoltaic cell.

In the past, they were mainly used in niche applications due to higher costs compared to traditional modules. However, with technological advancements and production standardization, costs have decreased, and bifacial panels are emerging as a competitive choice even for more widespread applications.

From a construction perspective, these panels do not differ significantly from monofacial ones, except for a fundamental element: the absence of the plastic layer that usually blocks light passage on the lower surface. In this case, the photovoltaic cell is enclosed between two glasses that allow light to penetrate from both sides.

Bifacial solar panels: how do they work

The operation of a bifacial photovoltaic system is based on the concept of the Albedo Factor of the surface where the modules are installed.

Albedo measures the reflective capacity of light radiation from a surface or object and is defined as the ratio between incident solar radiation and radiation reflected by a surface. It depends on the characteristics of the surface itself (e.g., color) and the wavelength of the radiation considered.

Radiation-reflection

Radiation-reflection

In essence, albedo is the reflective power of a surface and is expressed as a percentage or a pure number.

Considering solar radiation, albedo can range from:

  • 0 = minimum value, perfectly black surface (non-existent in nature) that absorbs all solar radiation (thus reflecting no light);
  • 1 = maximum value, corresponding to a perfectly white surface (non-existent in nature) that reflects all solar radiation.

Therefore, an albedo factor of the ground at 10% means that if the solar irradiance received by the ground is 1 kilowatt, the reflected amount is 100 Watts.

For example:

  • dark building surfaces have a low albedo, not exceeding 0.27;
  • light surfaces can reach values up to 0.6;
  • ice and snow, instead, have an albedo of about 0.75.

As the albedo of a surface increases, the amount of reflected light also increases. Consequently, this results in higher energy production by bifacial solar panels.

Bifacial solar panels: installation

The performance of a photovoltaic system depends not only on the reflective capacity of the surface but also on other factors related to the installation of bifacial modules. To fully unleash the module’s potential, certain conditions must be met.

Optimal energy production from the rear side of the bifacial cell will occur under the following conditions:

  • the surface where the module is installed is reflective;
  • the tilt angle or the height above the surface is greater;
  • absence of shading on the back of the photovoltaic generator, caused, for example, by structural components like mounting rails.

Ideal surfaces for installing a bifacial photovoltaic system include light-colored concrete, white membrane, or gravel-coated surfaces that can reflect up to 80% of incident light. However, even when installed on non-optimal surfaces like grass or corrugated metal, a bifacial module still ensures superior performance compared to a standard module with similar characteristics.

In general, the greater the distance between the module and the ground, the better the bifacial yield. Therefore, it is advisable to avoid surface-flush installations, such as roofs or grounds, as this can limit light reflection.

To maximize performance, simply raise the module from the ground or roof or increase its tilt angle to allow better light reflection. Optimal applications for installing a bifacial photovoltaic system include flat roofs, grounds, or canopies.

Pros and cons of bifacial solar panels

One of the main benefits of these panels is the ability to harness reflected light from the rear, allowing for an increase in energy production ranging from 10% to 25% more than monofacial modules.

This feature is particularly advantageous for large ground-mounted installations, which still have long return periods on investment. Therefore, it becomes essential to install bifacial components capable of ensuring high performance and reliable production.

According to a study conducted by the IEA in 2020, during the year of the pandemic and construction bonuses, there was a significant increase in bifacial module installations. This increase represented 12% of the market, and a further 30% increase is expected by 2030. Some estimates indicate that by 2025, bifacial modules could cover up to 40% of the market.

Another advantage is their extreme versatility. This type of system can be installed on large flat roofs with reflective surfaces, agrovoltaic installations, photovoltaic canopies for electric vehicle charging, floating photovoltaic systems, or integrated into building facades.

There are no specific limitations except those related to the necessary technical requirements to exploit the physical principle underlying the operation of bifacial photovoltaic systems.

Requirements to leverage the advantages

Fully exploiting the potential of bifacial solar panels is a consideration to be made from the design phase onwards. It depends on the amount of light that reaches the lower surface of the panel. In cases of installation on roofs, it is essential to have clear coverings that reflect light as much as possible.

If the panels are placed on dark surfaces, such as dark metal sheets, the advantage derived from using bifacial panels is practically nullified. In common residential installations, such as those on tiles, a productivity increase can still be achieved, albeit minimal.

Today, it is crucial to plan for the use of clear insulating coverings in commercial and industrial building renovations. This not only allows for full utilization of bifacial module potential but also helps minimize overheating due to solar irradiation, reducing the need for summer building cooling.

Bifacial photovoltaic systems and plant revamping

The power increase achieved with bifacial modules translates into higher electricity production. This aspect, particularly relevant in industrial installations, requires careful design of every component of the photovoltaic system, with special attention to inverters to avoid potential operational issues.

Therefore, attention must also be paid in cases of revamping or repowering interventions. In these situations, involving the upgrade of an existing photovoltaic system to enhance efficiency, the use of bifacial modules is certainly an advantageous choice.

How much does bifacial photovoltaics cost?

Until recently, installing bifacial solar panels entailed a 50% increase compared to traditional panels. However, this difference has significantly decreased in recent times, almost disappearing entirely, thanks to increased large-scale production promising further cost reductions in the future.

Moreover, regarding installation, no special precautions or components are required for systems with bifacial panels, and generally, the same installation standards as traditional setups are followed, with few exceptions.

Next-generation bifacial photovoltaic system: HJT type

The bifacial photovoltaic system has been around for several years and has seen a true technological revolution. Among the various innovations, HJT panels stand out.

The acronym HJT (Hetero Junction Technology) stands for heterojunction solar cells, and as the term implies, production occurs using a technology of amorphous and crystalline silicon hetero-junction.

The HJT technology combines the best advantages of N-type crystalline silicon and thin-film, enabling:

  • cell efficiency exceeding 24% and panel efficiency exceeding 22%;
  • lower temperature coefficient (only -0.24%);
  • very low annual degradation rate (only 0.4%);
  • absence of LID (light-induced degradation) and PID (potential-induced degradation) effects.

 

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