How do bifacial solar panels work? Why should you buy them?

Why Bifacial Solar Panels?

Many companies are offering bifacial solar panels in their own design and capacity. They were first invented half a century ago[1]. Their high costs and limited research inhibited their presence from the beginning of solar photovoltaic technology. A mono-facial solar panel that uses sunlight striking the front side and has aluminum on the rear is an established technology.

The output efficiency of conventional solar panels has always been a tough attribute revolving “now” around 20% with technological advancements[2]. The bifacial solar panels get an upward boost in efficiency by absorbing light from the rear. Latest in the same development, researchers at Australian National University have devised bifacial solar cells which are 29% efficient[3].

Technologies like bifacial solar panels can make solar a major source of energy on the planet. Let us look at how solar panels work and how bifacial panels work.

Working on a Solar Panel

In a photovoltaic (PV) solar system or solar PV generator, the main component is the solar panel. The main component of the solar panel is the solar cell. The solar panel is a circuit of several solar cells. Crystalline silicon is the most used semiconductor in solar cells. The addition of phosphorous to silicon makes n-type or negative silicon. N-type silicon has extra electrons. P-type or positive silicon is made by adding boron as an impurity. P-type silicon has holes or broken bonds.

The n-type silicon and p-type silicon as explained above are the core of the solar cell. The n-type silicon and p-type silicon have a very thin depletion layer between them causing electrons and holes to stay apart. As photons of light energy fall on solar cells, electrons and holes pair via an external circuit. This pairing of electrons and holes in the external circuit generates a direct current. This happens in mono-crystalline, poly-crystalline, and other types of solar panels. This is the photovoltaic effect on which solar panels work.

Mono-facial solar panels generate electricity by light absorbed by the front of the panel. This is an established technology with set specifications and designs.

The latest in conventional solar panels are :

• PERC[5] (Passive Emitter Rear Contact Cell)
• PERT[6] (Passive Emitter Rear Totally Diffused)
• HJT[7] (Heterojunction)
• Topcon[8] (Tunnel Oxide Passivated Contact).

Bifacial solar panels use all the technologies mentioned above with higher performance. PERC+ is the acronym for bifacial modules with passive emitter rear contact technology.

Mono-crystalline silicon cells are more prominent in bifacial solar. Polycrystalline silicon offers lower costs and low energy output. Very high costs and unavailability of other semiconducting materials like cadmium, gallium indium, etc are making them obsolete.

Bifacial solar panels absorb sunlight from the front and the rear face. The mono-facial solar panel inclined at a specific angle from the ground towards the sun absorbs direct irradiation and diffused radiation of the sun mainly. The front side of the one-sided or mono-facial solar panel gets some Albedo as photons of light.

How do bifacial solar panels work?

FACT: Sunlight on any face of the Earth at any given period is 10 thousand times the entire use of the planet for that period.

New developments are happening in the field of solar energy. Maximum use of the sun as an energy resource is possible with more research and development. Bifacial solar is the latest development to increase the output of energy from the same location.

Light is absorbed in direct, diffused, and albedo forms by both sides of the bifacial panel. Both sides of the solar cell absorb light in this new technology. These solar panels have metal connectors on both sides of the panel. These are usually silver or Aluminum. At the front and the rear of the bifacial module, the photovoltaic effect takes place. The connection of solar cells forms a circuit. Glass at the front and rear encapsulates the solar cells. Some manufacturers use transparent polymer back sheets. Bifacial solar panels use a different support structure. Some manufacturers use side frames in their designs.

As the rear of the bifacial solar gets light in form of albedo, diffused and some direct radiation. The photons of light charge the p-type silicon from the rear of the solar cell and holes jump up to the emitter layer of the solar cell. This extra energy from photons from the rear of the solar panels gives rise to the output of electricity generation.

The already established bifacial solar systems or the ones in research have claimed an efficiency increase by 30-40% with installed trackers. With the major dependence on albedo or the reflected light from the ground, the bifacial modules work really great with trackers[9].

Why should you buy Bifacial Solar Panels?

Note: For better performance bifacial solar panels should be at a good height from the ground. This condition does not apply to mono-facial solar panels as they do not require reflected light from the ground. 

Finally, why should you buy bifacial modules as compared to mono-facial modules? As noted, the bifacial solar modules need to be at a certain height from the ground to get the best results. In short, the lower the height of the solar panel from the ground, the less the reflection and so less the energy output[10].

Let us look at the reasons why to buy bifacial solar panels:

• Increase in Efficiency:

The bifacial module increases the efficiency of a similar mono-facial module by 5-30%. However, with the right ground type like white concrete and a tracking system, the efficiency of bifacial solar panels can be more than 27%. Where mono-facial have an average efficiency of 18%, bifacial solar panels have 20% efficiency[12]. High-efficiency panels are needed of the hour and if you have enough height (at least 18 inches or more) with a good reflective surface then they are profitable.

• Lower BOS costs

BOS costs are the Balance of System costs which is the sum of all the costs related to designing, labour, installation, wiring, inverter, etc, except solar panel costs. With Bifacial solar panels generating more electricity from the same place, it reduces the BOS costs. By using less number of modules as compared to conventional panels, the bifacial panels lower the BOS costs.

• Less space required

Few bifacial solar panels generate the same amount of electricity compared to conventional ones. Thus, fewer panels require less space. Like assuming for any location 1kW of mono-facial/conventional solar installation requires 10m2 of space, bifacial might give 1kW from 7m2. If space is an issue or if you want to get more energy out from the same space, bifacial is good.

• Lower LCOE

Levelized cost of energy or LCOE is the cost of energy production for the lifetime of a solar project divided by the total energy generated. With high energy generation with reduced BOS costs etc, lower LCOE is expected by researchers. Theoretically and from initial research on the LCOE of bifacial solar modules, it seems to be lower than conventional panels. With time more data will reveal the LCOE of bifacial solar panels[13].

• Panel angle manoeuvring

Easy maneuverability is possible with bifacial solar panels. Because both sides absorb light there is less shading loss with these panels. Panels can tilt and track to get maximum sunlight from both sides. Or the panels can track the sun as per the maximum generation available. Compared to mono-facial solar panels, bifacial can give additional generation with easy maneuverability. At different tilt angles, bifacial panels capture maximum albedo. Also tracking to the position of the sun, the shading effect reduces.

• Better in bad weather

During overcast, cloudy, rainy weather conditions of the day, the power production from solar panels is significantly reduced. In the case of bifacial solar panels, with both sides absorbing light, better energy generation happens. It does not mean, bifacial solar panels will generate a lot more energy than mono-facial panels but a little more for sure.

Bifacial solar modules are here to stay because of their added advantages as compared to mono-facial ones. As more installations of bifacial solar panels happen, more data will confirm its benefits.

Did you know?

Solar Edition publishes this trending article with new top 10 PV solar panels monthly since 2019. We publish two Top 10 Solar Panels lists, 

• Monthly, the best solar panels list.
• Quarterly, Top 10 solar panels for industrial-scale, 72 cells (Q1,2,3,4)

[1] https://www.researchgate.net/publication/251333222_The_early_history_of_bifacial_solar_cells

[2] https://www.forbes.com/advisor/home-improvement/most-efficient-solar-panels/

[3] https://www.forbes.com/sites/arielcohen/2021/08/30/dual-sided-solar-panel-breakthrough-means-massive-efficiency-gains/?sh=27ff2da85b24

[4] https://www.piqsels.com/en/public-domain-photo-smkkx

[5] https://medium.com/@kengsiewchan/perc-solar-cells-3eb275804ded

[6] https://www.kschan.com/what-is-a-pert-solar-cell/

[7] https://huasun.net/product/hjt-solar-cell/

[8] https://www.kschan.com/what-is-a-topcon-solar-cell/

[9] https://mercomindia.com/tracking-bifacial-solar-modules/

[10] https://www.firstsolar.com/en-IN/-/media/First-Solar/Technical-Documents/Bifacial-Documents/Bifacial-Modules-2-Sides-To-Every-Solar-Panel-white-paper-burns-mcdonnell-09120.ashx

[11] https://www.flickr.com/photos/solar_decathlon/6193582342/in/photostream/

[12] https://goenergylink.com/blog/bifacial-solar-increases-energy-efficiency/

[13] https://www.nrel.gov/docs/fy19osti/74090.pdf