Review of development from GSHP to UTES in China and other countries

Energy storage technologies (EST) facilitate the efficient utilization of renewable energy sources and energy conservation, and they are expected to be more prevalent in the future. There is a great potential to substitute the use of EST for burning of fossil fuels by using stored heat that would otherwise be wasted and using renewable generation resources. These energy sources can be used more effectively through the addition of short- or long-term energy storage, even to the seasonal thermal energy storage. Underground thermal energy storage (UTES) is one form of EST, and perhaps the most frequently used storage technology in North America and Europe. Gradually it is growing as the application of ground source heat pump (GSHP) with UTES in China. But UTES systems involve complicated unsteady processes that include energy rejection, accumulation, preservation and extraction. This paper reviewed the progress of UTES companioning with GSHP worldwide, and surveyed the development of GSHP and the origination of UTES, especially as to soil/rock UTES. Meanwhile, the basic proposal for development in the future to supply a gap in the field of UTES in China was presented. A coming work should aim to more researching basic problems during the demonstration application, such as investigation of mechanisms, characteristics and performance of the unsteady and transient heat transfer in a complex underground environment, and control strategies of the UTES system. These problems will strengthen theoretical and practical understanding and facilitate more extensive application of UTES in China.