Parameters matching of a large-scale solar heating system with pit thermal energy storage and heat pump

Currently, the use of pit thermal energy storage (PTES) for solar energy transfer is becoming increasingly popular. Although the heat pump (HP) can further enhance the thermal storage efficiency of PTES, the parameter matching relationships in the combined system integrated with HP have not been quantified in the literature. For this reason, a large-scale PTES combined heating system incorporating solar collectors and HP is established. A detailed case study confirms the effectiveness of HP integration, demonstrating that the integrated with HP can increase the solar fraction and reduce the levelized cost of heat (LCoH). Subsequently, a comprehensive multi-region analysis across six distinct solar resource and climatic zones through the solar fraction and LCoH as optimization indicators is conducted. The results show that the ratio of solar collector area to the annual heating load should be below 3.5, and below 2 in regions with higher solar radiation. Long-term storage is suitable for most regions, whereas short-term storage fits low-heating-demand areas. Additionally, a smaller collector area requires a larger storage volume. The rated capacity of the HP is generally selected as 50% of the maximum load. The optimal matching relationships increase the net present value by an average of 14.39% and shorten the payback period by an average of 18.92%. In addition, in severe cold and cold zones, the thickness of the XPE insulation on the top and sides is recommended to be 220–240 mm, and 10–20 mm, respectively.