A researcher from the University of Houston has reported a novel type of solar energy harvesting system that could make way for using solar power 24/7.

According to Bo Zhao, a professor at the university’s Department of Mechanical Engineering, the system uses non-reciprocal thermal photonic components and claims to have broken the efficiency record of all existing technologies.

A thermodynamic limit of the solar cell is the maximum theoretically possible conversion efficiency of sunlight into electricity. Traditional solar thermophotovoltaics (STPV) rely on an intermediate layer to tailor sunlight for better efficiency. The front side or the side facing the sun of the intermediate layer is designed to absorb all photons from the sun, converting solar energy into thermal energy.

The thermodynamic efficiency limit of STPVs (85.4%) is still far lower than the Landsberg limit (93.3%) — the ultimate efficiency limit for solar energy harvesting. Landsberg limit is the exergy of incoming heat flow, the maximum amount of work that can be extracted from an incoming heat flow using an engine at a given temperature.

The study finds that the efficiency deficit in harvesting solar energy is caused by the back emission of the intermediate layer in the solar thermophotovoltaics facing toward the sun, which results from the reciprocity of the system. In a reciprocal solar energy harvesting system, a good solar absorber is also a good thermal emitter. Therefore, it inevitably re-emits some of the absorbed energy to the sun, reducing its efficiency. It is known that breaking this reciprocity can lead to increased efficiency.

“Our work highlights the great potential of nonreciprocal thermal photonic components in energy applications. The proposed system offers a new pathway to improve the performance of STPV systems significantly,” said Zhao. “It may pave the way for nonreciprocal systems to be implemented in practical STPV systems currently used in power plants.”

“We propose nonreciprocal STPV systems that utilize an intermediate layer with nonreciprocal radiative properties…such a nonreciprocal intermediate layer can substantially suppress its back emission to the sun and funnel more photon flux towards the cell,” said Zhao.

In what appears to be the primary application scenarios, STPVs can then be coupled with an economical thermal energy storage unit to generate electricity 24/7. This can result in improved efficiency and promises compactness and the dispatchable nature of STPVs.

Mercom previously reported on a team of scientists from the Agency for Science, Technology, and Research and Nanyang Technological University, Singapore, developing technology to turn old solar panels into energy-harvesting thermoelectric material that harvests heat and converts it into electricity.

A team of scientists from Pennsylvania State University recently claimed that nanoparticles boost the efficiency of solar cells not because of the up-conversion but due to enhanced light scattering.