High temperature borehole thermal energy storage - A case study

Abstract

Combining High-Temperature Borehole Thermal Energy Storages (HT-BTES) with existing Combined Heat and Power (CHP) systems running on waste fuels seems to be a promising approach to increase the energy efficiency of district heating systems through recovery of excess heat summertime from the waste-to-energy operation. This paper presents a case study from Sweden where the potential for charging and discharging waste heat at 95°C from a CHP-plant in summer into and from a HT-BTES is investigated. The interaction between the HT-BTES and the CHP-plant has been simulated with the software tool TRNSYS using the DST (Duct Ground Heat Storage Model) and a number of other TRNSYS tools. The aim of the study has been to design the size and operation of the HT-BTES with regard to energy and power coverage. Several different potential system configurations are presented in this paper, with 1 300 to 1 500 boreholes of 300 m depth. The result shows that it is possible to retrieve around 93 GWh/year of stored heat winter time, with the use of heat pumps using ammoniac as refrigerant. The discharge temperatures from the BTES range between 40-60°C, and up to 70°C in the initial discharge period.