December 8, 2022
  • December 8, 2022

Pushing the boundaries of traditional solar devices

By on October 5, 2022 0

The sun is arguably the most important renewable resource, providing energy in the form of heat and light. As recent trends suggest, with solar panels becoming more of a regular sight on people’s homes, harvesting and converting solar energy is becoming increasingly popular.

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Although solar cells are not new, recent advances in photovoltaic cells are nothing short of remarkable. Yet even with the advancements and potential applications of solar energy, there are still limitations to the technology, namely how time of day and weather conditions can limit its use and effectiveness.

Such limitations have led researchers from the University of Houston to develop an innovative solar harvesting device that could potentially generate 24/7 solar power. Bo Zhao, Kalsi’s assistant professor of mechanical engineering, and his doctoral student Sina Jafari Ghalekohneh broke through the boundaries of traditional solar devices.

With our architecture, solar energy harvesting efficiency can be improved up to the thermodynamic limit.

Bo Zhao, Kalsi Assistant Professor of Mechanical Engineering, University of Houston

Reach the upper thermodynamic limit

Typically, thermophotovoltaic (STPV) solar cells work by absorbing sunlight, activating electrons in a semiconductor wafer, and creating current ready to be converted into electrical power. Therefore, STPVs normally consist of layers, one of which is the side that faces the sun and absorbs light (photons).

In this system, photons are converted into thermal energy, but the thermodynamic efficiency of a solar cell exposed to the full power of solar radiation can only reach about 85% of its capacity. This limit, known as the blackbody limit, is quite far from Landsberg’s proposed limit (93.3%) which is considered the optimum limit for harvesting solar energy.

In this work, we show that the efficiency deficit is caused by the inevitable back-emission from the middle layer towards the sun resulting from the reciprocity of the system. We propose non-reciprocal STPV systems that use an intermediate layer with non-reciprocal radiative properties.

Bo Zhao, Kalsi Assistant Professor of Mechanical Engineering, University of Houston

This means that emissions that are typically rejected and redirected back to the energy source – the sun – are instead returned to the cell, thus generating a greater flux of photons.

We show that with such improvement, the non-reciprocal STPV system can reach the Landsberg limit, and practical STPV systems with single-junction photovoltaic cells can also experience a significant increase in efficiency,” Zhao said.

Develop new solar devices

The importance of developing advanced solar technology is now more important than ever due to the global energy shortage and the need to reach net zero (carbon emissions) by 2050, as highlighted by the policy makers and world leaders. To achieve this goal, emissions must be reduced by at least 45% by 2030 to ensure that global warming does not exceed 1.5°C, as recommended by the Paris Agreement.

Therefore, the new solar device that Zhao and Ghalekohneh detailed and described in their journal article Applied physical examination marks an important step towards improving the efficiency of solar technology.

The pair say this new STPV technology could also be combined with cost-effective thermal energy storage units, which, in theory, would create a system capable of producing electricity 24/7, overcoming the limitations of conventional solar cells that rely solely on daylight. or weather conditions.

Our work highlights the great potential of non-reciprocal thermal photonic components in energy applications. The proposed system offers a new way to significantly improve the performance of STPV systems. This could pave the way for the implementation of non-reciprocal systems in the practical STPV systems currently used in power plants.

Bo Zhao, Kalsi Assistant Professor of Mechanical Engineering, University of Houston

In addition to increased efficiency and breaking the limitations of traditional STPVs, this system promises “compactness and shipping,which, in a nutshell, means generating electricity on demand based on market needs – a timely arrival for a world already facing an energy crisis.

References and further reading

Jafari Ghalekohneh, S. and Zhao, B., (2022) Nonreciprocal Solar Thermophotovoltaics. Applied physical examination, [online] 18(3). Available at:

Fickman, L., (2022) The solar harvesting system has the potential to generate solar power 24/7. [online] Available at:

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