Most solar panels collect sunlight from the front side that faces the sun.
The bi-facial solar panel has 2 faces, the front face collects the direct sunlight and, the back face captures the reflected sunlight from the ground.
In this way, the bi-facial solar panels generate up to 30% more power than a comparable mono-facial solar panel.
The bi-facial solar panel technology is in existence for decades but was not available commercially due to its expensive production cost.
The drop in the manufacturing cost with time has made this technology available for people.
A few top Bi-facial module manufacturers
There are many manufactures who make bi-facial solar panels.
I am listing a few:
1) Canadian Solar: BiKu (Bifacial Dual cell PERC Module)
Some of its features:
2) LG: NeON 2 Bifacial
3) Waaree: AHNAY Series (Mono PERC)
The Technology of Bi-facial Solar Panels
The bifacial solar modules can be manufactured using monocrystalline silicon cells and polycrystalline silicon cells.
We know that monocrystalline solar cells are made from silicon wafers that have less resistance than the polycrystalline solar cells and we get more current.
Another hand, the polycrystalline silicon cells are manufactured using the fragments of the silicon cell. They are less efficient but they are cheaper too.
Manufacturers are combining the latest technologies to improve the efficiency of the solar cells like pasting a reflective layer at the back of the monocrystalline cells known as PERC technology.
This layer reflects that part of sunlight that passed undeviated from the solar cell, making it available again for solar photo-voltaic effect.
You get more current.
For constructing the bifacial solar modules, the manufacturers encapsulate both sides of the solar cell in a glass, enabling the front and the back sides to capture the sunlight.
The other way is to use glass in the front and transparent polymer for the backside of the solar module.
Using glass on both sides makes solar panel more durable for rain, wind, and other environmental hazards.
In a way, the dual glass coating makes the bifacial solar cells resistant to Potential Induced Degradation.
The Power Rating of Bifacial Modules
Like all other mono-facial solar panels, the bifacial solar panels have power ratings such as 250 watts, 300 watts, or 400 watts.
This value represents the power of the front side under standard test conditions.
The Standard Test Conditions are:
As the rear side of the bifacial solar panels also conducts, they are assigned second power rating known as bifacial gain.
It is the ratio that compares the power produced by the rear side to the front side, measured under standard test conditions.
This is a part datasheet of the BiHiKu model by one of the reputed Solar manufacturers Canadian solar.
Factors affecting the Bifacial Gain
Please check in the above datasheet that the Bifacial gain can be between 5% to 30%.
This gain depends on various factors like:
a) Mounting Structure:
The traditional fixed racking structures are designed to support mono-facial solar panels.
These mounting structures usually cover the back of the solar panels.
For bi-facial solar panels, specially designed mounting structures are made that eliminate or minimize the elements used that can shade the rear of the bi-facial solar panels.
Also, in bi-facial solar panels, the junction box is fitted at its periphery on the contrary it is fitted at the back of the traditional mono-facial solar panel in
In this way, the shading effect is minimised.
The use Single axis trackers (up and down movement of the panels) and the dual axis trackers (left-right and up-down movement) can increase the power output form the bifacial solar panels but they are costly.
A proper cost-benefit analysis is to be done before deciding the use of trackers.
b) Height of the solar panels from the ground
The closer the bifacial panels are installed to the roof; the less reflective light will strike their rear side.
To get the maximum reflected light on the rear of the module, install them at the optimum height.
This optimum height also depends on the tilt angle of the bifacial solar panels.
c) The Tilt Angle
If the tilt angle is more, the rear of the panels is farther from the
ground and it can easily capture the reflected light even if installed at less height from the ground.
On the contrary, the small tilt angle brings the rear of the panels close to the ground, making difficult for the reflected light to strike the back of the module. Hence less current is produced.
Therefore, to capture the reflected light the panels should be installed a higher point than was case with big tilt angles.
You cannot play with tilt angles, these are calculated based on the location.
Interesting Read: How to determine the tilt of the Solar Panels?
If you are living near equator, install them at a lower tilt angle to capture the maximum sunlight.
Similarly, people living far-off from equator should give their panels more angle with the ground to get the maximum sunlight.
The only option is adjusting the height of the modules to get the benefit of reflection.
This process of adjusting the height is more manual and hit & trial.
Check the output of the bifacial solar panels on a clear day at different heights.
The one which gives the maximum current can be the ideal height to get the maximum bifacial gain.
If you assume that the more you increase the panel height, the better the output you get is wrong.
Beyond a certain height, the Bifacial gain is negligible.
d) The Albedo Effect
We know that light surfaces reflect more heat than dark surfaces.
This is called the Albedo effect.
The light surfaces show more Albedo effect than the darker ones.
The light-coloured roofing will reflect more light to the rear of the panel.
Albedo of some roofing materials:
If you already have light-coloured roofing, the Albedo gain would be more and the rear side of the panel will produce more current.
If it is not, the question is does it financially feasible to spend money on light colored roofing and the increased Albedo effect would payback profitably?
Kindly discuss this with your solar installer.
The System Designing
Due to the bifacial gain, the current produced by the bifacial solar panels is more than their traditional counterparts.
Kindly see that with the increase in the bifacial gain, the Imp (Maximum Operating Current) and Isc (Short Circuit Current) are also increasing.
Kindly do the sizing considering the bi-facial gain.
The sizing without considering the increase in current output due to the bifacial gain may damage the wires and the other components connected to the panel.
In this case, taking Isc = 14.48 A instead of 11.14 Amp is the right way for sizing the wires and other solar components.
Pros of Bifacial panels
Cons of Bifacial Panels
The bi-facial solar panels give you a power boost up to 30% more than their traditional solar panels of comparative power rating.
It comes at a cost
You need to have a specially designed mounting structure if you are going for a fixed one.
The single-axis and the dual-axis tracker installed further helps in capturing power from both sides, installing the solar trackers is costly and their automatic machinery needs care and maintenance often.
The point is simple if the percentage increase in the power from the bifacial solar panels is more than the percentage increase in the cost; go ahead with them, you will get more return than the mono-facial solar panel.
Be satisfied with mono-facial solar panels :)
It is better first to get the system design and know its payback before going for solar power installation.
Have you installed bifacial solar panels?
Do share your experience in the comment section.