For many, bifacial solar panels must seem like one of those, buy one, get one free supermarket bargains. A solar panel with double the power generation capacity of a standard example in the same size package surely has to be a huge bargain.
Unfortunately, it’s not quite that simple. Bifacial solar panels are definitely very promising and generate more juice than conventional types of the same size. However, there’s a whole bunch of tech fine print involved, and bifacial panels may not be the bargain of the week for everybody.
What Are Bifacial Solar Panels?
All solar panels are made up of many photovoltaic cells mounted in rows on a flat surface. More commonly known as solar cells, these guys convert the energy in sunlight into an electric current that can be harnessed directly or stored in batteries for later use. The solar panels are then arranged together to form arrays sized to meet output needs.
There are two broad categories of solar panels depending on solar cells used in their construction. These are monofacial and bifacial panels.
Monofacial Solar Panels
Conventional or monofacial solar panels use monofacial solar cells to generate power. These cells have only one active photovoltaic surface and the panels they make up generate power from one side only. Fig. 1 below illustrates this arrangement.
The front surface of the panel is covered by a sheet of clear glass, which protects the cells while allowing light to reach them freely. The panel’s backside is covered by a protective opaque plastic sheet that protects the cells from damage but allows no light to penetrate.
Bifacial Solar Panels
Bifacial solar cells are double-sided, meaning they generate power from both the front and backside surfaces of the cell. The technology is not new by any means. The first bifacial solar cells were introduced in 1966. Since then, that technology has made huge advances, and BSC (bifacial solar cell) products are gaining market share steadily. The structure of a bifacial solar cell is illustrated in Fig. 2 below.
The front surfaces of bifacial solar panels are covered with tempered glass sheets. In contrast, the rear surface is protected by glass or a clear plastic sheet, unlike monofacial units with their opaque backing, free light absorption for the solar cells on the front and backside of the bifacial panels.
Bifacial solar panels are often frameless, requiring specialized mounting equipment to prevent damage to the edges of the panels. They are also typically heavier than their monofacial counterparts.
The internal architecture of bifacial panels delivers better thermal efficiency than monofacials of the same rating. All solar panels work best when they are cold, so lower operating temperatures boost the already enhanced solar power numbers.
With conventional solar panels, all the connections and junction boxes are mounted on the back of the panel. In the case of bifacial panels, junction boxes are mounted around the edge of the panel to avoid unnecessary shading.
Bifacial Solar Cell Specifics
There are currently many bifacial solar cell types on the market, each with specific qualities and characteristics. Here are a couple of solar cell types commonly used in bifacial solar panels.
- PERT (Passive emitter rear totally diffused) – Bifaciality: 80-90%
- PERL (Passive emitter rear locally diffused) – Bifaciality: 80-90%
- PERC (Passive emitter rear contact) -Bifaciality: 70-80%
- IBC (Interdigitated back contact) – Bifaciality: 70-80%
- HIT (Heterojunction with intrinsic thin layer) – Bifaciality: 95-100%
Note: Bifaciality refers to the ratio of output power between the rear and front of the bifacial solar panels.
In addition to the package specs of solar cells in general, it may be interesting to note the differences in overall efficiencies of the different types of solar cells.
- Monofacial Monocrystalline – 18 % +
- Bifacial Monocrystalline – 20% +
- Monofacial Thin-Film – 11 to 15 %
- Monofacial Polycrystalline – 15 to 17%
Interesting to note that bifacial solar cells are top of the charts in overall efficiency.
Are Bifacial Solar Panels More Efficient?
The efficiency of bifacial panels is a grey area subject to a lot of variables. It’s easy to assume that the bifacial panels will be twice as powerful because they have twice the power-generating surface area.
That is not the case, though, and while bifacial panels are certainly more productive, they’re nowhere near that magical 100 percent increase figure. In fact, it isn’t easy to calculate exactly how much more efficient bifacial solar installations will be. There are just too many environmental variables at play.
However, they typically produce between 15 and 30 percent more power than their monofacial peers. And they out-perform their conventional cousins under all possible conditions irrespective of location or orientation specifics.
That said, for reference, here are a couple of the variables that affect the output of bifacial solar panels.
The Albedo Effect and Panel Location
The ideal world location for a bifacial solar panel would be a spot with minimal shading and a vertical position that gets direct morning sun on one side and afternoon sun on the other. Obviously, this will seldom be practical.
One way of getting around is to make sure the bifacial panels get good direct front side lighting and strong reflected or albedo light on the back of the array.
Albedo is a scientific term used to define how much light is reflected from a surface. In solar terms, the albedo effect determines how much solar radiation it reflects from surrounding surfaces such as rooftops, snow, the ground, or nearby walls and structures. If the solar panels are placed on a highly reflective surface and have similar surfaces close by, half the battle is won.
Albedo light is measured on a scale of 0 to 1 with 1 being the maximum reflected light in relation to the direct sunlight source. Here are the albedo ratings for a couple of common surface materials.
- Highly reflective roof – 0.6 to 0.7
- White painted surface – 0.5 to 0.9
- Grass – 0.25 to 0.3
- Brick or stone – 0.2 to 0.4
- Red or brown tiles – 0.1 to 0.13
- Plain concrete – 0.1 to 0.35
- White concrete – 0.4 to 0.6
- Corrugated iron roof – 0.1 to 0.16
- Tar and gravel – 0.08 to 0.2
- Asphalt – 0.05 to 0.2
- Snow – 0.2 to 0.9
- Clean ice – 0.6 to 0.9
When you install a bifacial solar panel, this is something you need to consider. Reflecting as much light as possible towards the back of the bifacial panels, the better. Obviously, this will influence the solar panel output.
Developing a “yearly solar path map” is a great tool when choosing how to position any solar array. This is basically a clear idea of the line the sun follows across your site at different times of the year.
If you have this picture in mind, you can choose an orientation for your bifacial solar panels that will capture the maximum direct and reflected sunlight year-round.
Solar tracking systems can offset orientation woes by automatically turning the array to track the sun’s path. The costs involved are generally too high for most people’s budgets, despite how convenient they are. For larger industrial installations using bifacial panels, solar tracking systems are the way to go.
Panel Height and Tilt Angle
Industry studies have shown that bifacial panels mounted at around one meter or three feet and tilt angles between 20 and 30 degrees give the best results and the highest efficiency boosts. Again, these factors will play an important role in the output you can expect.
It’s hard to say exactly what the gains are going to be from using bifacial solar panels. There are just too many variables to nail exact figures. One thing you can be sure of, though, is that there will be some gain in output.
Having a mounting system for your solar panel array adjustable for height, tilt, and swing is a great feature. You can then adjust the array during its run-in to try and find the sweet spot where you get the best solar energy output. This will also let you adjust the array to compensate for seasonal shifts in the sun’s path.
What Are the Pros and Cons of Using Bifacial Solar Panels?
Outside of the obvious increases in power output, bifacial panels offer several other benefits. However, there are also some downsides to using bifacial arrays.
Bifacial Solar Panel Pros
You can present bifacial solar panels in a frameless configuration. This makes the panels more visually appealing than traditional solar systems and earns major kudos in installations such as gazebos, pergolas, privacy screens, and solar awnings.
Improved PID Ratings
Frameless bifacial solar panel construction also reduces the chance of PID (Potential induced degradation) losses. The aluminum frames of conventional panels are conductive and can cause unwanted ion and electron exchange to rob the array of efficiency.
Because bifacial solar panels have a wider range of efficient tilt angles, they can typically be installed in tighter spaces. This plus can add a lot of possibilities when planning an installation. Obviously, their increased solar energy output also means you can reach your solar energy output target with fewer panels and a smaller array footprint.
Under typical conditions, bifacial solar panels with dual tempered glass covers are more durable than monofacials. Bifacial solar panels also generate less heat. Running cooler not only adds to their already increased output but also increases their lifespan.
Bifacial Solar Panel Cons
For bifacial solar panels to deliver optimal performance, they must have their back surfaces exposed to solar radiation. This limits the number of choices users have when deciding on locations for the arrays.
Specialized Mounting Requirements
Because bifacial solar panels generate power from both sides, they cannot shade the rear surface. This means conventional panel mounting methods won’t work.
For example, replacing your traditional solar panels with bifacial will require a completely new set of mounts. In addition, bifacial mounts need to accommodate frameless panels, which are less robust on their edges while being heavier than monofacials.
Aerodynamic Lift Implications
You can generally mount bifacial solar panels higher than conventional arrays. You can also mount a bifacial module at higher tilt angles. This can turn your shiny new bifacial panels into the equivalent of an F15’s wing. The strain placed on the installation due to the increased lift the panels generate will add to the mounting requirements. Unfortunately, this will surely harm your budget.
Speaking of budgets, bifacial solar panels are more expensive to produce, which can hit you hard at the checkout. Overall, the cost of bifacial solar panels is coming down fairly quickly.
On top of that, the increased output savings tends to offset the initial cost quite a bit.
What Installations Are Bifacial Solar Panels Best Suited For?
As attractive as they are as solar power solutions, bifacial panels present some installation challenges for residential users. To work properly they depend on receiving direct sunlight on the front surface of the panels and reflected light at the rear of the panels.
Due to on-site realities, many homeowners choose to install rooftop solar panels. This is a no-go for bifacial solar panels as the array lies flat on the roof, allowing no light to reach the rear of the array.
For most residential installations, this limits the choices to ground mount locations. Only buildings with flat roof areas would be suitable for bifacial module setups. Remember that you should ideally optimize the cladding or paint used on the flat roof to maximize the albedo effect.
If space allows for ground-mount installations, this is not a problem, but many homeowners don’t have the luxury of suitable open ground. Increased installation costs and red tape are also detractors with ground mount systems.
Ground mount installations generally cost more, require specialized mounting hardware, and may need special zoning and electrical coding permits.
On the positive side, ground-mounted arrays are easy to adjust, making maintenance much more accessible.
Residential Installation Checklist
If you are considering installing a bifacial solar panel grid in your home, here is a quick checklist that may help with the decision.
- Is a ground mount installation feasible on your property?
- Would a ground-mounted array of solar panels detract from the aesthetic appeal or value of your property?
- Do you have large sandy areas or concrete slabs used as a reflective base for the solar panels?
- Do you have snow cover on your property for long periods of the year?
- Will you prepare to have solar awnings fitted above your windows?
- Does your house have any flat-roofed areas, and could they be painted in reflective colors?
- Will you prepare to build pergolas on your property?
- Will you prepare to install solar privacy screens on your property?
Essentially, if you can honestly answer yes to only one or a couple of these questions, bifacial panels are definitely a choice worth considering.
Bifacial solar panels really shine in large-scale commercial installations. Larger budgets and fewer space constraints allow commercial installers to tap into the potential of bifacial solar technology fully. Large arrays, solar tracking mounts, and custom design sites, and ground plane surfaces see some of the highest efficiency figures possible from the technology.
The bottom line is this. Domestic solar users can certainly benefit from installing bifacial panels instead of traditional solar panels. Unfortunately, those choosing a rooftop setup will have to settle for monofacial solar panel arrays. Ground mount installations are more expensive, but they have other benefits, and the increased power output would eventually even the score.
On the other hand, commercial operators are the real winners, and it’s these types of installations that will surely drive the development of bifacial panels and ensure their future.
What Is the Future of Bifacial Solar Panels?
Bifacial solar technology is definitely here to stay. Presently bifacial solar panel’s market share is around 20 percent. However, with the cost gap between bifacial and monofacial technologies shrinking yearly, and improvements in bifacial PV tech in general, that gap will explode in the next decade.
The International Technology Roadmap for Photovoltaic’s (ITRPV) 2020 forecast for BSC market share predicts that bifacial panels will own 70 percent of the PV market by 2030. This is an advantage for solar panel manufacturers who are working tirelessly to capitalize on the trend. Without any doubt, bifacial solar panels are a fundamental part of the future of the solar industry.
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