Thermal Energy Storage Integration with Waste Heat: What are the Challenges?

Over the past decade, there have been numerous attempts to use low-grade waste heat (30 oC and 100 oC) for a variety of different applications, especially district heating systems. However, the initial investment in waste heat recovery systems is usually high and the temperature is too low to meet the needs of the different end users. One possible solution is to integrate seasonal thermal energy storage with data centers or other industries that deals with waste heat. This is especially possible when considering borehole thermal energy storage (BTES), as it is highly adaptable, expandable and economical. However, almost all research and technical applications of BTES systems have focused on solar energy storage, with the exception of the projects in Emmaboda (Sweden) and Chifeng (China), where BTES systems have been used to store waste heat. In this paper, the results of a series of measurements on a BTES in Norway are presented and numerical simulations are performed to evaluate the long-term performance of the BTES once it is connected to a continuous supply of waste heat from a data center. The results obtained show how important a long-term prediction of the system performance is for planning and optimization. It was found that the storage temperature and heat recovery of the BTES are lower than expected when the quantity and quality of waste heat is overestimated. It seems that the borehole has the capacity to store  heat at a temperature of more than 75 C, but it may reduce its functionality over time and shorten its lifespan from 30 to 10 years.