We are living through an information revolution where technology is quickly and constantly adapting to new innovations. In the solar industry, this is reflected through the improvement of solar cell design and efficiency. One of the most notable among these improvements is the development and commercialization of bifacial modules, which can capture energy from both the front and rear sides of the panel. As with their monofacial counterparts, the performance of bifacial modules depends on system design choices, installation methods, and environmental conditions &#; all of which are explored in this article.
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How Do Bifacial Solar Panels Work?
The core idea behind bifacial modules is simple &#; instead of just using one side, why not use both? In practice, however, there is a multitude of factors that play into the implementation of bifacial modules. On a fundamental level, bifacial modules work just like monofacial modules - incident sunlight is absorbed by the semiconductor layers in the solar panel and generates an electric current. The principle difference is the bifacial module&#;s ability to harness solar energy by both direct and indirect solar rays. This is made possible by the addition of a passivated layer on the rear side of the cell, like the front side, in combination with a transparent backside material that allows light to enter from the rear side. Bifacial modules are designed to let in more light. The extra passivation layer increases the amount of sunlight that can be converted to electricity, increasing the cell&#;s efficiency. The most common type of bifacial module cell design used today is referred to as a PERC cell (Passivated Emitter and Rear Cell); its basic structure is shown in Figure 1.
Figure 1: Structure of a PERC cell (Passivated Emitter and Rear Cell) 2
How Much Additional Energy Do Bifacial Cells Produce?
Now that we have a grasp of how bifacial cells can capture energy from backside irradiation, the question becomes just how much additional energy do these cells produce and how can we optimize energy gains through system design?
To answer this question, we can break it down into several parts:
What additional sources of irradiation are present?
Bifacial modules can absorb sunlight from the following sources which are depicted in Figure 2:
Figure 2: Irradiation sources for a bifacial module1.
What design parameters will be influential in determining how much of the irradiation is available to the solar panel?
Albedo: The albedo of any surface is defined as the ratio of reflected light to incident light. Albedo is perhaps the most influential factor over the increased yield produced by bifacial PV systems. Anyone who has experienced a painful &#;snow burn&#; on their face after a day spent skiing can attest that the amount of sunlight reflected from high-albedo surfaces like snow is not to be taken lightly.
Figure 3 below shows the results of a field study conducted by Jinko Solar 6 comparing various ground types, their respective albedos, and corresponding energy generation gains. White paint with the highest albedo of 80-85% expectedly produced the greatest energy gains at 19%, and grass with an albedo of 10-20% produced 7% energy gain 6. Due to the significant influence of albedo on system production, location and environmental conditions are of even greater consequence for bifacial modules than monofacials.
Figure 3: Relationship between rear side energy gain and albedo based on Jinko&#;s field project (Location: Haining, installation height: 1.2m, angle: 30°) 6.
Mounting Considerations: In addition to environmental factors such as albedo, the type of system mounting also has a great effect on the added gain from bifacial modules. Figure 4 compares the simulated energy gain from various systems, showing that bifacials produce a substantial gain, especially when used in combination with Single Axis Tracker (SAT) systems 6. Regardless of what type of racking is used, shading caused by racking elements should be eliminated wherever possible to maximize rear irradiance.
Figure 4: Simulation result of various system configurations and energy gain (Location: Haining, Albedo = 0.35) 6.
Row-to-row distance (Pitch/GCR): The distance between adjacent rows of trackers is known as the pitch or GCR, Ground Coverage Ratio &#; the ratio of module area to land area. This distance directly corresponds to how much surface area is available for incident sunlight to reflect off of the ground onto the backside of the modules. So, it follows that increasing the pitch increases backside irradiation as shown in Figure 5 7. For both monofacial and bifacial systems, increasing the pitch also reduces shading between rows. The study conducted by Jinko referenced above has found that the bifacial gain increases with decreasing GCR (increasing row-to-row distance) and that gains begin to level out at ~10% additional energy around 30% GCR as per Figure 6 6. In this example, further decreasing the GCR could still marginally increase energy generation, but the added value could be outweighed by the added cost of additional leased land this would require.
Figure 5: Effect of pitch on backside irradiation 7.
Figure 6: Correlation between bifacial energy gain and GCR (Location: Haining, angle: 30°, albedo = 0.3) 6.
Height: Similar to the pitch, increasing the height at which modules are mounted directly increases the amount of incident backside radiation, as it allows reflected light from a larger surface area to reach the module. Research has found that increasing the height between 0.5 and ~1.2 meters greatly increases the energy gain as shown in Figure 7 6. In this example, increasing the height beyond 1.2 meters still increases energy gain but at a much lower rate. At this point, the costs of additional racking material may begin to outweigh the energy benefits. The exact height at which bifacial gains saturate and the quantity of energy at which this occurs depends on system-specific design choices and environmental factors, however, these general relationships will hold.
Figure 7: The effect of module installation height on bifacial energy gain (Location: Haining, angle: 30°, albedo = 0.3) 6.
Tilt angle: For fixed-tilt systems, increasing the tilt angle leads to greater irradiance on the rear side of the module, and so increases bifacials gains (however at steeper angles this will begin to reduce front side gains). Some systems have taken this effect to the extreme, with modules mounted in a totally vertical fashion, as exemplified by a project in Germany shown in Figure 83. This has the effect of capturing more energy in the early morning and late afternoon and reducing peak production values during midday when the sun is directly overhead 8. This should see reduced clipping losses compared to a typical fixed-tilt or tracker system.
Figure 8: A 1 MWp DC vertically mounted east-west bifacial PV system, located in Germany 3.
DC/AC ratio and inverter considerations: The added energy gains from bifacial modules effectively increases the DC/AC ratio, as more DC power is being produced with each module compared to monofacials with the same nameplate power rating. Incorporating bifacials will thus increase the overall operating efficiency of the inverters, as they will be outputting closer to their maximum AC rating a larger portion of the year. However, the counter effect of this is that clipping losses (wasted energy!) during peak production hours will also increase. Generally, these losses are still less than the added gains from bifacial production, so bifacial is still worth the switch5, 6. A visual representation of the increased yield produced by bifacial modules in contrast to clipping losses is shown in Figure 9 &#; here the total energy produced can be visualized by taking the area under each curve. Simulations can be performed, using PVsyst or other yield prediction software, to determine the DC/AC ratio which will maximize year-round energy production while minimizing clipping losses. Essentially, a bifacial system with a lower DC/AC ratio will perform equivalently to a monofacial system with a higher DC/AC ratio &#; bifacial modules give you more bang for your buck.
Figure 9: Visual representation of Energy production over time for bifacial and monofacial systems, showing clipping loss and bifacial gain 5.
How Much Additional Energy Do Bifacial Cells Produce?
As we have seen, there are many things to consider when contemplating the use of bifacial modules - below is a short list of some of their advantages and disadvantages:
Advantages:
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Disadvantages:
Bifacial
Modules on the Global Scene
Over the past several years the amount of bifacial solar installations has seen rapid growth on a global scale. Installed capacity grew globally from only 97 MW in to over 2,600 MW in , an increase of 2,580 percent in just two years [9]. Continuing this trend, between and the bifacial market is forecasted to increase tenfold 9. While incentives and subsidies can differ regionally, the main drive of the implementation of bifacial modules has been their steadily decreasing cost, ever approaching that of their monofacial counterparts. Additionally, monofacial module manufacturing plants can be easily overhauled for bifacial production, reducing the initial cost of supply buildup which is typically a steep hump for new technologies.
In , the overwhelming majority of installed bifacial systems were located in Asia. China has been the traditional leader of the bifacial market due to its Top Runner program which incentivizes new technologies. Asia&#;s percentage share of total global installed capacity is expected to decrease as the U.S. and other countries ramp up acquisition and use of bifacial modules. In the U.S., the Section 201 tariff exemption on imported bifacial solar modules implemented in has been a critical factor in the growth of the U.S. bifacial market 9. A solar market burdened with high module prices due to import tariffs and small domestic manufacturing scale is now seeing an improved supply chain, with bifacial modules made in Southeast Asia now having a significant price advantage. Over the next 5 years, bifacial installations in the U.S. are expected to increase from approximately 500 MW in to over 7,000 MW in .
Figure 10: Forecast of global annual installed bifacial solar capacity, - (MW dc) 9.
Conclusion
It is clear that bifacial modules have real potential for designing more efficient solar systems, and that there are many factors influencing their performance. While this performance will vary from project to project, the use of bifacial modules without changing any design choices will produce increased yields across the board. However, consideration of environmental and economic factors must be taken for each project to determine if bifacial modules are worth the added cost and to maximize financial profits. Perhaps the greatest challenge remaining is to reinforce the bankability of bifacial systems compared to monofacial systems &#; their history is much shorter and validation of bifacial energy modeling is not as generally accepted in the industry yet. New Energy Equity is excited to be part of this new change in the solar industry and has adopted bifacial modules as a standard design choice across several project portfolios. Overall, bifacial modules are a very promising technology and should be expected to slowly become the norm in the solar industry.
How Can New Energy Equity Help You Reach Your Solar Goals?
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The concept of
bifacial solar panels might seem cutting-edge, but its roots stretch back further than you might imagine. Born from a flash of inspiration in the s, this innovative idea remained largely dormant for decades. It wasn't until the early s that bifacial technology began to emerge from the shadows of solar innovation. Unlike traditional solar panels, these innovative devices capture sunlight from both sides, significantly increasing energy yield. By harnessing reflected light from surrounding surfaces, bifacial panels can boost energy production by up to 30% compared to their monofacial counterparts. As the world seeks sustainable energy solutions, bifacial solar panels emerge as a promising option, combining increased efficiency with reduced installation costs.
What Is a Bifacial Solar Panel
As the name implies, a
bifacial solar panel is a module that has photovoltaic cells on both the front and back sides, designed to capture sunlight from both sides of the panel. Unlike traditional solar panels that only collect light from the front, bifacial panels harness energy from both their front and back surfaces.
These innovative panels typically feature a transparent backing, allowing them to absorb direct sunlight from the front and reflected light from the ground or nearby surfaces on the rear. This dual-sided approach significantly boosts their energy-generating potential.
Key features of bifacial solar panels include:
- Double-sided light absorption
- Increased energy yield (up to 30% more than traditional panels)
- Improved performance in low-light conditions
- Versatility in various installation settings
Bifacial panels are particularly effective in environments with highly reflective surfaces, such as snow, sand, or light-colored roofs. They can be installed vertically, horizontally, or at an angle, making them adaptable to diverse architectural designs and geographical locations.
As the solar industry continues to advance, bifacial panels represent a promising solution for maximizing energy production in both residential and commercial applications. Their ability to generate more power in the same footprint as traditional panels makes them an attractive option for those looking to optimize their solar energy systems.
How Do Bifacial Solar Panels Work
Bifacial
solar panels work by harnessing sunlight from both their front and rear surfaces, maximizing energy capture. The front side operates like a traditional solar panel, converting direct sunlight into electricity. The innovation lies in the panel's rear side, which is designed to absorb reflected and diffused light from the surrounding environment. This is made possible by a transparent or translucent back sheet, allowing light to penetrate both sides of the panel. The specialized photovoltaic cells within are optimized to convert light from any direction into usable energy. The effectiveness of the rear side, known as the bifaciality factor, typically ranges from 65% to 90% of the front side's capacity. Mounting considerations play a crucial role, with elevated installations or reflective surfaces underneath enhancing rear-side production. This dual-sided approach allows bifacial panels to generate more electricity in various lighting conditions, making them particularly effective in environments with high albedo or diffused light.
Bifacial Solar Panels Advantages and Disadvantages
Due to their price and efficiency, bicluster solar panels are growing in popularity. Bifacial panels are becoming more popular than monofacial panels, therefore more residences and businesses are installing them to take advantage of the benefits. But do the benefits really exceed the drawbacks?
Pros of Bifacial Solar Panels
- Increased Energy Production: Bifacial panels yield 5-30% more power than traditional panels. This boost comes from their ability to capture light from both sides, significantly increasing energy output.
- Better Low-Light Performance: These panels excel in capturing diffused and reflected light. This feature extends their daily operational hours and improves performance in less sunny conditions.
- Durability: Most bifacial panels feature a double-glass construction, enhancing their resilience. This robust design typically results in longer warranties and an extended operational lifespan.
- Versatility: Bifacial panels are suitable for various installation types, including ground, rooftop, and carports. Their flexibility allows for creative deployment in diverse settings.
- Potential for Lower LCOE: Higher energy yield can lead to better long-term economics. Over time, the increased production often offsets the higher initial investment.
- Reduced PID: The glass-on-glass design of bifacial panels helps minimize potential induced degradation. This results in more stable performance over the panel's lifetime.
Cons of Bifacial Solar Panels
- Higher Initial Cost: Bifacial solar panels generally come with a higher price tag than conventional models. This increased upfront investment can be a deterrent for some buyers, particularly in residential applications.
- Complex Installation Requirements: Maximizing benefits requires careful planning and potentially more sophisticated mounting systems. Installers need to consider factors like optimal tilt angle, elevation, and surrounding reflective surfaces.
Bifacial Vs. Monofacial Solar Panels
Monofacial solar panels, the traditional choice, feature photovoltaic cells on one side only. They capture direct sunlight from the front surface, with an opaque backing. These panels are less expensive and simpler to install, making them popular for residential rooftop applications.
Bifacial solar panels, in contrast, absorb light from both sides. This dual-sided design captures direct sunlight from the front and reflected or diffused light from the rear. While more expensive, bifacial panels can produce up to 30% more energy under optimal conditions.
The choice between the two depends on the installation environment. Bifacial panels excel in areas with reflective surfaces or elevated installations, while monofacial panels suit standard rooftop setups. Bifacial panels offer higher energy yields per square foot, ideal for maximizing output in limited spaces, but at a higher initial cost.
Are Bifacial Solar Panels Worth It
Determining whether bifacial solar panels are worth the investment depends on several factors. These innovative panels offer the potential for increased energy production, but their value proposition varies based on specific installation conditions and project goals.
For large-scale solar farms or commercial installations with ample space and reflective surfaces, bifacial panels often prove their worth. The additional energy yield, which can range
from 5% to 30% more than traditional panels, can significantly offset the higher initial costs over time. This increased efficiency is particularly valuable in areas with high electricity rates or limited installation space.
Residential applications present a more nuanced scenario. While the energy boost is appealing, the higher upfront costs and potential installation complexities may extend the payback period. Homeowners should carefully consider their roof orientation, local climate, and surrounding reflective surfaces to assess the potential benefits.
How to Install Bifacial Solar Panels
Installing bifacial solar panels is a smart way to boost your energy efficiency. Here's a concise five-step guide to help you get started:
1. Site Assessment and Planning
Begin by evaluating your site to identify the optimal location for your bifacial solar panels. Choose areas with high reflectivity, such as snow-covered or sandy regions, to maximize the panels' efficiency. Ensure there are no obstructions like trees or buildings that might cast shadows on the panels. Additionally, check local regulations and obtain any necessary permits to comply with legal requirements.
2. Choose and Prepare the Mounting System
Select a mounting system that supports bifacial panels, such as ground mounts, rooftop mounts, or tracking systems. Prepare your installation site by clearing debris and leveling the ground if you&#;re using a ground mount. For rooftop installations, ensure the roof is structurally sound and can support the panels' weight. Assemble and install the mounting system according to the manufacturer&#;s instructions, ensuring it is securely anchored.
3. Install the Bifacial Solar Panels
Carefully mount the bifacial solar panels onto the prepared system. Secure the panels using the provided clamps or brackets, ensuring there&#;s adequate space between the panels and the surface below to allow reflected light to reach the underside. Proper installation is crucial for both stability and efficiency.
4. Connect Electrical Components
Connect the solar panels to the inverter and integrate them into your home&#;s electrical system. Ensure all electrical connections are properly insulated and waterproofed to prevent any hazards. It&#;s highly recommended to hire a certified electrician for this step to ensure safety and compliance with local electrical codes.
5. Optimize and Monitor
Adjust the angle and orientation of the panels to maximize exposure to both direct and reflected sunlight. Tracking systems can be particularly beneficial for this purpose. After installation, test the system to ensure it&#;s functioning correctly and monitor its performance regularly. Clean the panels periodically to remove any dirt or debris and schedule maintenance checks to ensure long-term efficiency and durability.
Tips for Installing a Bifacial Solar System
- Don't Block the Back Sides of the Panels.
Bifacial solar panels capture sunlight from both sides, boosting energy generation. Ensure that inverters or racking do not block the back of the panels. If racks are necessary, leave space to allow sunlight to reach the cells.
- Allow Space Between Panel Rows.
Leave 3-5 inches between panel rows to let snow fall through in winter, preventing pile-up and aiding in melting, which produces heat for the panels.
- Maintain 42.5 Inches Between the Ground and the Panels.
The IEEE recommends a 42.5-inch height from the ground to allow snow to accumulate without shading the panels and to ensure optimal performance.
- Use Reflective, Light-Colored Materials Under the Panels.
For maximum power output, avoid dark and non-reflective surfaces under the panels. Use reflective, light-colored materials or white EPDM for rooftop installations.
Conclusion
Bifacial solar panels offer significant advantages in energy generation by capturing sunlight from both sides, making them a smart choice for maximizing efficiency. When installing these panels, ensure that the back side remains unobstructed, allow sufficient spacing between panel rows, and maintain an optimal height from the ground. Additionally, use reflective, light-colored materials underneath the panels to further enhance their performance.
For those seeking high-quality bifacial solar panels, the
Renogy Bifacial 220 Watt 12 Volt Monocrystalline Solar Panel is an excellent option. With its advanced bifacial design, this panel can generate up to 285 Watts, significantly outperforming traditional mono-facial panels. Its ten bus bars ensure excellent performance even when partially shaded, and the PERC monocrystalline cells help reduce heat and increase voltage, optimizing overall efficiency.
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Renogy for reliable and high-performance bifacial solar panels that meet your energy needs while maximizing power output and efficiency.
Frequently Asked Questions about Bifacial Solar Panels
1. How efficient are bifacial solar panels?
Bifacial solar panels can be
up to 30% more efficient than traditional monofacial panels due to their ability to capture sunlight from both the front and back surfaces. This dual-sided light absorption significantly boosts their overall energy output.
2. Can you use bifacial solar panels on a roof?
Yes, bifacial solar panels can be installed on a roof. For optimal performance, use reflective, light-colored roofing materials to enhance the sunlight reaching the back side of the panels, maximizing their efficiency.
3. What is the average cost of bifacial solar panels?
The average cost of bifacial solar panels ranges
from $0.50 to $0.70 per watt, translating to approximately $500 to $700 for a 1-kilowatt system. Prices vary based on brand, quality, and installation factors.
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