Scientific and technological progress and future perspectives of the solar assisted heat pump (SAHP) system

Highlights: • Current development of Solar Assisted Heat Pump was investigated. • A recently developed SAHP technology was introduced. • The new SAHP has 30% higher COP and 8–15% higher solar efficiency. • The new SAHP achieves the fast response to building's heat demand. • The future research directions of the SAHP were identified. Among all available solar technologies, solar-assisted heat pump (SAHP) is the most popular technology for low- and medium-temperature applications, i.e., drying, space heating, and water heating. This paper presents a critical review of the SAHP, leading to identification of the key technological challenges with the current SAHP technology, including (1) poor energy performance at low ambient temperatures; (2) difficulty in coupling solar thermal panels with heat pumps to achieve increased operational time and reduced electrical energy usage; (3) mismatch between heat demand of the building and heat supply of the SAHP system; and (4) lack of multi-functional modelling tool. A recently developed SAHP technology is introduced, which can effectively tackle the challenges with the current SAHPs, thus achieving enhanced solar efficiency, improved heat pump energy efficiency, and fast responsive time to the heat demand of buildings. The future research directions of the SAHP were identified: (1) multi-source heat pump; (2) heat pump defrosting capacity using waste heat and renewable energy; (3) advanced heat storage and exchange unit (HSEU) technology; and (4) advanced machine learning and multi-objective evolutionary optimisation models for performance prediction and optimisation of the SAHP using big datasets.