Theoretical studies on a dual-function system integrating solar heating and radiative cooling for year-round energy saving

• A dual-function system of solar heating and radiative cooling was proposed. • Four operation modes could be realised: solar heat storage , heating air, cold storage and cooling air. • Year-round operation can be achieved through mutual adjustment of four modes. • A huge amount of electrical energy could be saved for space heating and cooling in buildings. The Sun (6000 K) and outer space (3 K) are huge reservoirs of heat and cold sources that are sustainable and clean. How to fully utilise these two types of energy throughout the year to address the energy crisis and climate change remains a challenge. In this study, a dual-function system integrating solar heating (SH) and radiative cooling (RC) technologies is proposed, which has four operating modes: heat storage, heating air supply, cold storage and cooling air supply. In the SH and heat storage modes, Graphene and Ag-based nanofluid is adopted as the medium, its heat is transferred to the air through a heat exchanger. In the cold storage and cooling air supply modes, an optimised multi-layer film structure with high emissivity in the atmospheric window is employed, and water and air are employed as the mediums. Through the mutual adjustment of four modes, the system can achieve year-round operation. The system with a panel area of 100 m 2 has a monthly average equivalent electrical energy of 16,590 kW∙h in SH mode and over 8200 kW∙h in RC mode, demonstrating enormous potential application. The temperature of mediums can be easily adjusted by changing their mass flow rate, and the required temperature of supplying air is convenient to adjust by only changing its mass flow rate. This study is of great significance for deepening the understanding of SH and RC technologies and dealing with energy and environmental issues.