What Are Bifacial Solar Panels?

When looking to install solar panels businesses and homeowners are often faced with the dilemma of not having enough space to accommodate the number of panels needed to generate sufficient amounts of electricity.

This forces them to compromise by installing as many panels as they can and relying on back-up power from the grid. Or look at installing ground-mounted panels, which are not only more expensive, they take up valuable space.

There is a third option however, bifacial solar panels.

What is a bifacial solar panel?

A bifacial solar panel is effectively a double-sided solar panel which contains solar cells on both the upper and lower sides. This is different from a standard monofacial panel which only has cells on the upper sun-facing side.

To the uninitiated bifacial panels look the same as standard monofacial panels. But there are some important differences between them which buyers need to understand.

Firstly, both sides of the cell are covered in transparent glass to allow light to pass through. Standard monofacial cells have opaque polymer undersides. This makes bifacial cells more durable.

Secondly, bifacial panels sit on adjustable frames which create a gap between the mounting surface and the cells.

Finally, the junction box which usually sits behind a standard solar panel is smaller and mounted on the edge of the array so that it doesn’t cast a shadow over the cells.

How do bifacial solar panels work?

Bifacial solar panels work in much the same way as conventional monofacial panels. An array of solar cells is mounted to collect photons from the sun. The cells then convert this energy into electricity using the photovoltaic effect.

Read our How do solar PV panels work? article to learn more about the photoelectric effect.

The difference lies in the way the solar cells are arranged. Bifacial panels have cells mounted on both sides of the panel. The cells on the upper side collect incident sunlight in the same way as a conventional panel. But the cells on the underside absorb photons reflected off the surface the panel is mounted on. This type of reflected light is called albedo light.

The amount of albedo light the panel absorbs depends on the size of the gap between the surface and the panel. The colour and texture of the surface also have an impact on bifacial performance. White reflects the most albedo light, around 80%, grass by comparison only reflects 23%.

For this reason, most bifacial solar panels are mounted on adjustable frames which can be angled to create a large gap between the cells and the mounting surface. In some cases, the mounting surface is painted white to reflect more light. A reflective sheet of aluminium can also be placed behind the panel to further improve performance.

Monocrystalline vs Polycrystalline?

Most bifacial panels use monocrystalline cells because they are more efficient than polycrystalline cells and work better in low light conditions. The downside to this is that monocrystalline cells are more expensive. This problem is compounded on bifacial panels because they contain twice the number of cells.

Polycrystalline bifacial panels are available as a budget option, but they are less efficient than monocrystalline panels. In use, this type of panel only produces around 6-9% more energy than a standard polycrystalline panel. Or, to put it another way, they produce the same amount of energy as a standard monocrystalline panel for around the same cost.

The following table highlights the differences between cell technologies.

Solar Panel Type	Solar Cell Efficiency
Solar Panel Type: Monofacial monocrystalline	Cell Efficiency: 15-22%
Solar Panel Type: Monofacial polycrystalline	Cell Efficiency: 14-16%
Solar Panel Type: Monofacial thin-film	Cell Efficiency: 11-15%
Solar Panel Type: Bifacial monocrystalline	Cell Efficiency: 20%+

Bifacial solar panel advantages

Improved efficiency

The biggest advantage is the amount of energy they generate compared to standard panels. A monocrystalline bifacial system can generate up to 30% more energy than a standard monofacial array. The exact amount varies depending on the surface they are mounted on.

A recent study by LONGi shows that on average bifacial systems generate 10-12% more energy than a monofacial system. This rises to 27% if the panel is attached to a tracking system which automatically follows the sun to maximise irradiation during the day.

Fewer panels needed

The knock-on effect of improved efficiency is that fewer panels are needed to generate the same amount of energy. If we take an average 20% efficiency gain, you will only need 10 bifacial panels to generate the same energy as 12 monofacial panels. This makes them a great option for homes with limited roof space.

Longer warranties

Because glass is used to protect both sides of the cells, bifacial panels are more durable than monofacial panels. As a result, most bifacial panels are available with 30+ year warranties compared to standard panels which typically come with 20-25 year warranties.

Bifacial solar panel installation options

Another often overlooked advantage to bifacial panels is that they can be mounted both horizontally and vertically. This increases the range of options available to you when looking for a suitable mounting point. There are pros and cons to each however, so check with your local MCS certified engineer to ensure you choose the most efficient option.

Horizontally mounted

Horizontally mounted panels are usually mounted on the roof. In the horizontal plane, the underside of the panel absorbs light reflected from the mounting surface. This is not the most efficient mounting option however since the underside will always generate less energy than the upper side.

Vertically mounted

Vertically mounted panels are usually mounted on the ground in adjustable frames. This allows the angle of the panel to be adjusted to absorb the most amount of sunlight. Ground-mounted panels are more expensive to install than roof mounts however and the panels will take up valuable space in the garden.

Conclusion

Bifacial panels are one of the most important innovations to come from the solar industry in the past decade. The increased efficiency of bifacial panels makes them suitable for a range of commercial and domestic uses. They are most suited for installations with limited space since fewer panels are needed to generate the same amount of energy.

The only downside is that they cost more to install than conventional panels. Historically, this has restricted their use to large commercial installations. But as the technology becomes more popular, manufacturing costs will come down making them more accessible to domestic users as well.