Solar harvesting maximisation in spectral-splitting photovoltaic-thermal systems via integrated radiative cooling

The mismatch between the energy distribution of the solar spectrum and the spectral response of photovoltaic (PV) cells, along with the elevated operating temperature of the cells, especially in optically concentrating systems, can result in a significant loss of electrical performance and acceleration of ageing. Reducing PV cell temperature and improving spectrum utilisation are two key approaches to improve PV efficiency. As a zero-emission passive cooling technology, radiative cooling (RC) developed recently has promising potential for solar cells. How to integrate RC to make full use of the solar spectrum under highly concentrated conditions, and the quantitative relationship between concentration area and RC area, are still unclear so far. In this study, a spectral-splitting multi-cell photovoltaic-thermal system is integrated with RC technology to maximise solar spectrum utilisation, specifically exploring the relations between concentration and RC to achieve maximum utilisation efficiency. There exists an optimal concentrating ratio that maximises PV efficiency for a given RC area, and the optimal concentrating ratio increases as the RC area and solar cell's bandgap energy increases. In a multi-cell system, the coordinated distribution of RC area among cells can improve the overall efficiency relative to the uniform distribution of RC area. An increasing number of cells can effectively improve efficiency while reducing the required RC area allocated to each cell, providing a more feasible approach for RC application under highly concentrated conditions. The efficiency of this system with a low concentration ratio can achieve the theoretical maximum efficiency of a conventional PV system with a high concentration ratio. The efficiency limit of the proposed solar system can reach 73%, demonstrating the significant potential of the proposed concept in practical applications.