Increased use of solar energy in commercial buildings by integrating energy storage.

From a comparison of available thermal energy storage (TES) technologies it can be concluded that the most mature and suitable storage methods for modern commercial buildings in Sweden are storage tanks, either for heat or cold energy, and underground storage solutions such as borehole thermal energy storage (BTES), aquifer storage and energy piles. In this study an integrated solar energy storage system for heating purpose has been designed with BTES, hot water storage tank(s) and solar thermal collectors. The system has been constructed for three different reference buildings in Stockholm and Malmö using the simulation software Polysun, as to investigate the optimal size of BTES system from an economical and energy perspective. The results showed that the optimal storage dimension for the three reference buildings from an economic perspective for a BTES system was 50 % of a building’s peak power demand for heating and tap warm water. The specific energy demand could be lowered significantly for all three buildings, even if applying a weighting factor on the electricity used for the heat pumps. The investment return in the integrated energy storage system turned out to be positive in most cases; however the net present value (NPV) was negative for some of the storage dimensions in the sensitivity analysis. The conclusion from the study is that BTES systems have potential to increase the use of solar energy in modern commercial buildings in a cost effective way, making it easier to reach the future goals of near zero energy buildings (NZEB)