Researchers at Purdue University have come up with a new thermodynamic formula, which reveals that bifacial cells make the double-sided panels generate 15% to 20% more electricity than the conventional monofacial cells on one-sided solar modules.

An increasing number of companies are now moving towards two-sided solar modules, which can convert sunlight reflected from the ground, and more electricity could be generated. It’s still early days to know exactly how much energy these two-sided solar modules could generate but double-sided solar cells are already allowing solar modules to sit vertically on the ground or rooftops and they can also be placed horizontally.

Two physicists at the university have developed a formula that can be used to calculate the maximum amount of electricity that bifacial solar cells could generate in a variety of environments as defined by a thermodynamic limit.

Commenting on the latest development, Muhammad Ashraf Alam, professor of Electrical and Computer Engineering at Purdue University, said, “The formula involves just a simple triangle, but distilling the extremely complicated physics problem to this elegantly simple formulation required years of modeling and research. This triangle will help companies make better decisions on investments in next-generation solar cells and figure out how to design them to be more efficient.”

In a paper published in the Proceedings of the National Academy of Sciences, Alam and co-author Ryyan Khan, professor at East West University in Bangladesh, elaborate on how the formula can be used to calculate the thermodynamic limits of all solar cells developed in the last 50 years.

The scientists hope that these calculations will help solar projects take the full advantage of bifacial cells.

“It took almost 50 years for monofacial cells to show up in the field in a cost-effective way. The technology has been remarkably successful, but we know now that we can’t significantly increase their efficiency anymore or reduce the cost. Our formula will guide and accelerate the development of bifacial technology on a faster time scale,” Alam added.

Alam’s approach is called the “Shockley-Queisser triangle,” as it is built upon the predictions made by researchers William Shockley and Hans-Joachim Queisser on the maximum theoretical efficiency of a monofacial solar cell.

The formula makes it clear that the efficiency of solar cells increases with the amount of energy reflected from the surface. The researchers are of the view that the formula can be used for better design of modules for use on farmlands and windows of buildings in densely populated cities.

Transparent, double-sided modules allow solar power to be generated on farmland without casting shadows that would block crop production. Meanwhile, creating bifacial windows for buildings would foster wider adoption of renewable energy.

The paper also recommends ways to maximize the potential of bifacial cells by manipulating the number of junctions between the semiconductor materials.

Research teams across the globe are trying their best to increase the efficiency of solar cells and make it economically viable.

In September, a team of research scientists from the Australian National University (ANU) achieved a breakthrough in the efficiency of solar cells. The team at ANU achieved a 21.6% solar cell efficiency. This is the highest value attained for perovskite cells that are above specific dimensions. In the current market scenario, rooftop solar panels being installed have an efficiency of 17% to 18%.

Earlier this year, Global PV company Trina Solar announced that its state key laboratory of PV science and technology in China had set a new world record of achieving a high efficiency of  24.58%  for n-type monocrystalline silicon. The bifacial solar cell reached a total-area front side efficiency of 24.58%, without using any dedicated aperture during the illumination.

Image credit: Lumos Solar