Benefits of High-Temperature Storage for Base Load Geothermal Energy

Currently, a large part of the energy used to provide heat to heating network comes from gas boilers, a combustion process where 2.2kg of CO2 is emitted for every m^3 of gas. Deep geothermal energy is implemented more in The Netherlands over the last couple of years as a substitute to the conventional boilers and this is a technique that is proven to be working. However, one problem with geothermal energy is the fact that only base load extraction is possible, whereas the heating demand varies throughout the year. During winter there is an energy shortage while during summer there is a surplus. Hence, seasonal heat storage is seen as a promising technique to increase the portion of green energy in heating networks.High-Temperature Aquifer Thermal Energy Storage (HT-ATES) can bridge the gap between the supply and demand, storing excess produced heat during summer and supplying during the winter months. This research focuses on both the technical aspects as well as the business case of the implementation of such a system in a heating network. Technical simulations are performed where the fluid transport and heat loss processes are modelled. The output of these simulations is used to compare the business cases of a heating network with and without HT-ATES implementation, based on the Levelized Cost Of Heat (LCOH) and total annual CO2 emissions in an economics tool developed in Python. All simulations are based on the situation at the TU Delft Campus, where plans are made for a HT-ATES in the Maassluis formation.The base case shows a thermal recovery efficiency of 0.75 in cycle four. The LCOH for a project with a lifetime of 30 years is 52 €/MWh (14 €/GJ) when HT-ATES is implemented, compared to 61 €/MWh (17 €/GJ) in the case where only geothermal energy and gas boilers are used to supply the heat. Total CO2 emission reductions are 31%. Based on these values, one can conclude that the situation where HT-ATES is included is the economic scenario.On top of the case study, a parameter sensitivity study is performed. The results show that storage volume, storage reservoir permeability and temperature differences between the wells are the key geological and operational parameters when assessing the project feasibility. Economic parameters such as the discount rate and gas prices also have a considerable impact on the economic results. The results of the sensitivity analysis shows that the project in Delft is feasible as long as the future average gas price remains above 21 €/MWh and the discount rate does not exceed 18.3%, while keeping the other variables constant