Study on Auxiliary Heat Sources in Solar Hot Water System in China

The solar hot water system (SHW) has the potential to reduce household energy usage substantially and also provide external benefits of reducing emissions of CO2 and other pollutants. But SHW is unstable due to changing outdoor climate, which needs auxiliary heat source to meet continuous hot water demand. Despite previous studies have proposed the suitable solar fraction in different regions of China, the reasonable auxiliary heat source form in different regions should be somewhat different due to geographic variations and local conditions, and needs further study. This paper analyzes the adaptability of the auxiliary heat source s in different regions, which helps to guide the applications of SHW in China. The optimal solar fraction and regional adaptability of auxiliary heat source from aspects of energy efficiency, economic performance and carbon emission reduction during the life cycle in 31 capital cities in China are discussed by using Geographical Information System (GIS) mapping techniques and RETScreen tool. The residential solar hot water system based model is developed, and the geographic variations in the solar resource, supply water temperature, local energy price, hot water usage, and available incentives are selected for analysis. The results show that the suitable auxiliary heat source form and optimized solar fraction vary in different regions. For example, towngas boosted SHW is appropriate for most regions especially in the west region of China. The heat pump boosted SHW is a good choice in the southern coast region. This study helps to guide policy making and design for the solar hot water system.