Comparative investigation of energy-saving potential and technical economy of rooftop radiative cooling and photovoltaic systems

Abstract

Building-integrated radiative cooling (RC) and photovoltaic (PV) systems are promising renewable technologies harvesting energy from outer space and the sun, respectively, and can contribute to carbon neutrality. However, due to the limited building envelope area, it is significant to compare the energy-saving potential and technical economy of these two technologies, which helps to determine the system form under different working conditions. This study establishes the thermal models for rooftop RC and PV systems to simulate their temperature, heat transfer flux, and energy-saving performance. Then the energy-saving and economic indicators for comparative investigation are proposed, in which the cooling load reduction is converted into electricity saving to be compared with PV’s electricity generation. The comparison results show that RC roof has a lower energy-saving potential than PV roof during the cooling season in Beijing, China (the energy saving ratio of RC to PV is 0.536). However, the economic cost of equivalent electricity saving during the life cycle is $0.011 and $0.034 per kilowatt-hour for RC and PV systems, respectively, indicating that RC roof is more economical. In addition, applicability analysis indicates that the total cooling capacity of RC roof throughout the cooling season is larger in western and southern China, while the energy-saving potential of PV roof is higher in western and northern China. Moreover, the effects of meteorological parameters, indoor conditions, building roof characteristics, and surface optical properties on RC and PV roofs’ performance are thoroughly analyzed. The parametric analysis shows that RC roof is suitable for buildings with high heat dissipation demand and lightweight envelope structures. It is calculated that the energy yield of the RC roof is comparable to that of the PV roof in a telecommunication base station. This study will pave the way for maximizing the energy-saving potential of limited building roofs and contribute to the efficient utilization of renewable energy.