by | Jul 15, 2021 | Blog

A double bifacial solar module array in the mountains

Summary

  • Unlike standard monofacial modules, bifacial solar modules enable light to enter from both the front and the back. Bifacial systems can generate up to 30% more energy due to both the direct and reflected light being converted into electricity.
  • As with most solar panels, bifacial modules have a power rating between 250 and 400 watts. This rating represents their expected power yield during ideal weather conditions but it only takes the power generated by the front face into consideration. For this reason, bifacial modules have a second rating for the energy generated from the reverse face, referred to as the ‘bifaciality’ factor.
  • The ways in which bifacial modules are mounted depend on the types of systems that are used. Framed bifacial panels tend to be considered easier to install than frameless ones, as the traditional mounting and racking systems are made for framed models. The frameless options often come with rubber guards to protect the glass. Extra care is needed when installing them as the glass can be damaged when the bolts are over-tightened.
  • There are many ways energy production can be increased when it comes to bifacial modules. The two major factors to consider when predicting the bifacial module energy yield are the panel mounting height and the albedo (i.e. the reflection power from the ground).
  • The implementation of bifacial modules can have an impact on PV system designs and equipment in some substantial ways. In some cases, an existing racking system may get in the way of two-sided power generation. In others, additional power oututs may require cable and overcurrent protection.

Introduction

When you think of solar panels, you’re most likely picturing a photovoltaic (PV) monofacial system (i.e. a one-sided structure). However, there is another type worth learning about – bifacial solar panels. Unlike PV solar systems that use standard monofacial modules, the alternative bifacial modules enable light to enter from both the panel’s front and back sides. Compared to a monofacial system, bifacial systems can generate up to 30% more energy due to both direct and reflected light being converted into electricity. The amount of energy produced by the solar PV system will depend on how the system is installed.
Although bifacial module technology has been around since the 1970s (when the Russian space program first deployed it), it has not been embraced commercially due to the associated expenses. However, now that it costs a lot less to manufacture solar panels, the renewable energy industry is giving bifacial panels a second look. So let’s explore why these bifacial solar modules have gotten solar experts so excited.

The Technology Behind Bifacial Solar Modules

Since standard power ratings only consider the front side of the solar panel, the bifacial module has a secondary rating for the energy generated from its reverse face.

Bifacial modules can be created using monocrystalline or polycrystalline wafers. Monocrystalline bifacial panels have a single silicon crystal in each solar cell, whereas polycrystalline bifacial panels are made of silicon fragments that have been melted together. Generally, monocrystalline wafers are more expensive to produce than their polycrystalline counterparts. However, by giving the electrons that generate electricity flow more space to move, the polycrystalline panels are more efficient.

As is the case with all solar panels, bifacial modules have a power rating that is typically between 250 and 400 watts. This rating represents their expected power yield during ideal weather conditions. Since standard power ratings only consider the front side of the solar panel, the bifacial module has a secondary rating for the energy generated from its reverse face. This is known as the ‘bifaciality’ factor. The ratio compares the power produced by the solar panel’s reverse side to the power generated by the front. This rating is measured during standard test conditions (STC).

Although the bifacial ratio does have its value, it is not the best indicator of the true performance of a bifacial PV system. There are many aspects to consider, from the time of day to the geographic location. The bifacial solar modules can also be optimised to boost efficiency and yield. For example, bifacial module arrays can be installed above bright surfaces that reflect as much light as possible. They can also be lifted and tilted to collect more reflected light and avoid shading the reverse face. It is helpful to note that ‘albedo’ is the official term used to describe the fraction of light reflected by the surface.

Solar tracking systems have also helped maximise electricity production by rotating the bifacial modules to follow the sun throughout the day – optimising the angle at which the panels are receiving the solar radiation. The tracking systems can also be adjusted for bifacial solar panels to reduce the amount of backtracking or to adjust mid-day positions.

How Are Bifacial Solar Modules Installed?

Infographic depicting different types of bifacial solar module installations

There are several different bifacial solar module setups available, and the installation methods vary as a result. Framed bifacial panels tend to be considered easier to install than frameless ones simply because the traditional mounting and racking systems are already tailored for framed models. The majority of bifacial panels come with their own clamps to mount to specific brands, so there are few installation complications. The frameless options tend to feature rubber guards to protect the glass. Often, the installation stage requires special caution, as over-tightening the bolts can damage the panels.

When it comes to determining the height of the panels used in bifacial modules, there is a simple rule: the higher they are tilted, the more power they can produce. If a bifacial module is mounted flush to a rooftop, any reflected light will be blocked from reaching the cells on its reverse face. Commercial rooftops and ground-mounted arrays tend to be a better option for bifacial modules for this reason. It is best to have as much room as possible so that bouncing rays of reflected light can reach the rear of the panels.

Aside from the height of the panels, the mounting system itself can influence the performance of the bifacial modules. For example, the back rows of the bifacial cells can become shaded by the standard support rails found on conventional racking systems. These rails usually cover the monofacial module’s back sheet for support.

With all these factors to consider when installing bifacial solar modules, it is worth comparing different system types to understand how the installation processes may vary. Here are some of the main types of bifacial solar systems:
 

  • Ground-Based Systems – It is common practice for bifacial solar arrays to be installed on the ground. Ground-based arrays can take advantage of any reflections on the floor when installed over a surface with high albedo or reflectance. An excellent choice to help maximise reflection is to use white tile, white sand, or brightly coloured gravel. When units are installed on top of soil, grass, or rocks, the sunlight reflection will be minimised and the solar panels may be less efficient.
     
    Ground-based arrays are exceptionally efficient in snowy areas. This is due to snow having a high albedo. If the ground beneath the solar panels is covered in snow, the bifacial modules will capture the brilliant sunlight. This can make up for the reduced daylight hours during the winter months.
     
    The key to installing bifacial solar panels on the ground is to minimise any prospective shadows and shading. Bifacial manufacturers often provide special mounting clamps to complement solar panels from specific brands. The mounting brackets and clamps tend to be thinner than those for monofacial panels, as they are designed to reduce shadows.
     
    Just like monofacial solar panels, the bifacial panels need to be tilted correctly to get the maximum power output from the solar array. The angle of the tilt differs depending on the latitude, so panels must be tilted in a way that is optimal for the location.
  • Roof-Mounted Systems – As with ground-based systems, it is best if the surface beneath is reflective in some way. White or highly reflective roofs that lack any significant slopes are superb for bifacial panels as they have the highest albedo. It is not ideal to install solar panels flush with the roof as it defeats the point of having two sides to capture sunlight.
     
    Roof-mounted bifacial solar panels should be tilted at an angle that corresponds to the latitude. Most of the same rules for ground-based systems correlate with rooftop systems. However, it is important to note that bifacial solar panels are much heavier than monofacial ones. As a result, it’s vital to check if the roof is capable of supporting the additional weight.
  • Vertical Bifacial Systems – Vertically installed bifacial solar modules tend to be installed from east to west. This enables the panels to capture electricity both in the early morning and late afternoon. In addition, during the midday period, the panels can capture sunlight reflected off the ground and surrounding areas.
  • Horizontal Bifacial Systems – Horizontal bifacial setups can be a good option for the sides of homes or buildings, especially since the solar panels can add to the aesthetics and provide partial shade for the people underneath. Horizontal systems can obtain energy directly from the sun during the day and still accumulate reflected light from the ground. They have added benefits when installed in snowy locations, over swimming pools, or near decking areas. They can also work well as a transparent roof on a pergola or open walkway.

Ways To Increase Bifacial Module Energy Production

The most notable factors to consider when predicting the bifacial module yield are the panel mounting height and albedo.

As we explored above, there are many ways that energy production can be maximised for the use of bifacial modules. However, the most notable factors to consider when predicting the bifacial module yield are the panel mounting height and albedo. Let’s have a look into why these two factors play such a crucial role in bifacial power efficiency:
 

  • Module Mounting Height – The higher the bifacial PV arrays are off the ground or rooftop, the more easily the reflective light can reach the back of the array. However, a significant boost can be achieved in bifacial energy with even a modest height increase. In one test reported by SolarPro, they confirmed that after around 20 inches, the curve of increased energy flattened out, and the additional energy gains were negligible. This data from SolarPro indicates that bifacial modules are suitable for most ground-mounted applications as long as the leading edge of the array is between 18 and 36 inches above the ground.
  • Albedo – The annual energy production increase of 5% to 10% is standard for bifacial modules. For most of the bifacial solar areas, there is the need for imported groundcover to push the increase over 10%. It is debatable whether it pays off to bring in light-coloured gravel or roofing materials to boost albedo. The answer tends to be based on both location and the project itself. Cost evaluations are also helpful.

Impacts Of Bifacial Modules On PV System Equipment

To optimise energy generation in bifacial PV systems, designers need to discover ways to avoid or minimise elements that produce shade on the rear side of the modules.

The implementation of bifacial modules can have an impact on PV system equipment and design in some substantial ways. Traditional racking systems used for monofacial modules include rails that cross the reverse sides of these panels. To optimise energy generation in bifacial PV systems, designers need to discover ways to avoid or minimise elements that cast shade on the rear of the modules. In addition, the rails and other structural components can sometimes cover the cells, which can cause hot spots that might damage the modules.

To prevent these potential issues, bifacial PV panels tend to require special mounting systems. Optimised bifacial applications have thinner mounting rails in their racking and tracker structures. Strategically placing the vertical supports will also help minimise shading. Equally, the junction box on most monofacial modules is located directly at the back of one or more PV cells. Most bifacial modules also tend to have a smaller and more discreet junction box positioned on the back or at the perimeter.

In December 2018, the US Department of Energy supported a white paper called ‘Bifacial vs Silicon Modules on Genius Tracker.’ It took a deep dive into tackling the optimal mounting configurations for bifacial panels. The paper suggests that mounting doubled-up modules in a landscape layout helps to reduce degradation. Interestingly, modules that are mounted in a portrait configuration may produce better results from an economic perspective. However, the actual field results may vary depending on the broader system elements.

Along with these factors, there are multiple other aspects that should be considered during the design stages. For example, some bifacial modules are designed with a central gap between cells with the goal of minimising cell shading. Modelling efforts should focus on whether more spacious layouts are required.

Due to the increased power output generated by the bifacial modules, considerations should be made for the cable and overcurrent protection, along with the electrical equipment ratings. Cables and equipment will need to be measured to ensure they can handle the maximum currents listed in the PV module datasheets. Higher currents can increase the balance of system (BOS) costs and equipment sizes. Elevated energy output can also have the ability to influence the lifespan of PV inverters. System designers and inverter manufacturers need to work together to help make sure the extra direct current (DC) power generated by bifacial modules does not surpass the ratings of the inverter components or recommended DC/AC ratios. This is a common variable in PV design.

Further considerations also need to be accounted for when estimating operation and maintenance expenditures. For example, routine maintenance budgets must factor in the costs of keeping the rear sides of bifacial modules clean. In addition, the maintenance of the surrounding vegetation and direct site may need to be more frequent to ensure that the albedo is at its finest.

Are Bifacial Solar Panels The Future?

The bifacial panels take a significant stride towards the ultimate goal of lowering the levelized cost of energy (LCOE).

Bifacial solar modules offer many advantages over traditional PV systems. The potential performance gains achieved with the additional light collection is just the start. Bifacial modules also have lower balance of system (BOS) costs due to the fact that the individual modules tend to generate more power than their monofacial counterparts. Bifacial systems also require a smaller array footprint which is often better for the local environment. In many cases, bifacial panels are also more durable since both sides are UV-resistant and any potential induced degradation (PID) risks are reduced.

Overall, the energy gains and enhanced durability associated with bifacial solar panels result in improved electricity generation and performance in the long term. The bifacial panels take a significant stride towards the ultimate goal of lowering the levelized cost of energy (LCOE). The LCOE analysis for bifacial modules is still in the early stages, and the development of uniform measurement standards is still being figured out.

Closing Thoughts

Although bifacial solar panels are already in existence, their benefit-cost ratio is yet to be determined. They are currently considered by many as a costly luxury, but others believe the price is well worth it. It can’t be ignored that they have twice the surface area of standard monofacial modules. They also pick up the residual reflected light that single-sided panels can’t use, which gives bifacial systems an edge on efficiency.

There is a need for more bifacial module installations and real-world data to determine how bright this technology will be in the future. Further advancements are necessary to confirm the benefits and justify the additional costs of bifacial systems through LCOE analysis. On the upside, this should be achievable in the relatively near future. Once the bifacial solar module standards are tightened (and LCOE estimates are quantified and proven), it is expected that these panels will become the norm for utility-scale installations.

Frequently Asked Questions (FAQs)

When were bifacial solar modules invented?

The first demonstrations of bifacial solar cells and panels were carried out in Russia as part of the Soviet Space Program in the Salyut 3 (1974) and Salyut 5 (1976) LEO military space stations. The bifacial solar cells were developed and manufactured by Bordina et al. at the VNIIT (All-Union Scientific Research Institute of Energy Sources) in Moscow. In 1975, this facility became the Russian solar cell manufacturer KVANT.

 

Are bifacial systems more expensive than monofacial systems?

Bifacial solar panels are more expensive than conventional monofacial panels; however, they generate more energy. According to a 2019 study by NREL, the cost discrepancy between monofacial and bifacial panels ranges from $0.01 to $0.05 per watt for large utility-scale projects.

 

Can bifacial solar panels go on rooftops?

Yes, bifacial solar modules can go on roofs. However, the roof needs to be flat and lack any steep slopes. The roof will also benefit from being painted white or some other reflective colour. It is not sensible to install the solar panels directly onto the roof lying flat. This is because it defeats the point of having a two-sided solar panel. Bifacial solar panels are also much heavier than their monofacial counterparts. The structural integrity of the roof needs to be examined before any installations are made.

 

What is the main difference between monofacial and bifacial solar panels?

The key difference between monofacial and bifacial technology is that bifacial modules produce solar power from both sides, whereas conventional monofacial panels only generate energy from the front.

 

Are bifacial panels better than monofacial panels?

Monofacial modules tend to be more cost-effective at latitudes below 40 degrees for low albedo. Bifacial modules, however, are more cost-effective at latitudes beyond 40 degrees. Bifacial PV systems generate up to 12% more energy at latitudes below 65 degrees and up to 71% above 65 degrees.

 

Westbridge Energy Corporation

Subscribe To Email Updates

.

Join our mailing list to receive the latest news and updates from Westbridge Energy Corp.

You have successfully subscribed to the Westbridge email list.