Improving Efficiency of Underground Heat Storage Systems

Abstract

Underground thermal energy storage (UTES) systems are very popular in Europe and are gaining popularity in North America. The first large-scale solar borehole thermal energy storage (UTES) system in Canada has been implemented in the town of Okotoks (McClenahan D, 2006). The second UTES project in Alberta is located in the community of Southwoods in Edmonton (Kantrowitz T. et al., 2013), which proposes to use natural gas cogenerators to generate electricity and heat during the winter to improve electricity generation efficiency and hence reduce overall energy costs. During the generation of electricity, unused heat can be collected and used to heat space and water for domestic use. During the summer, the electrical output from cogeneration exceeds demand, resulting in a seasonal and annual thermal imbalance which UTES can control through the transfer and storage of the excess heat to a UTES system. Most soils in the Edmonton region consist of sandy clays with high moisture content and high thermo-conductivity. Thus, storing heat in such soils would be inefficient since most of the heat would escape before it could be used for heating purposes. However, if such soils could be modified to become good insulators via innovations in jet grouting and soilcrete technologies, UTES systems could become more prevalent as a renewable energy source in areas with highly thermo-conductive soils. This paper proposes to develop the jet grouting and soilcrete theory and conceptual models required to create an insulated enclosure around UTES systems in highly thermo-conductive soils.