DESIGN AND OPTIMIZATION OF A GEOTHERMAL ENERGY STORAGE FEEDING A FULLY RENEWABLE DISTRICT HEATING NETWORK

The decarbonization of the building sector is of paramount importance to meet EU objectives in terms of greenhouse gas emissions. Many solutions have been documented in the literature ranging from fuel switching towards biomass or electrification using heat pumps. From the point of view of sustainability and air quality, the electrification of building heating is very promising but requires that electricity is generated from renewable resources like solar and/or wind energy. However, the intermittency and
seasonality of renewable energy production make it difficult to match the heat demand (i.e., photovoltaic panels produce more during summertime when the heat demand is low, and inversely). The contribution presents the design procedure used to find the best energy generation, storage, and transport of a district heating network supplied by photovoltaic panels and using seasonal geothermal energy storage coupled
with short-term battery storage. The optimization problem is solved using a linear programming approach with Gurobi which allows for quick and easy implementation. The rated power and storage capacities are determined together with the optimal operation schedule to target minimum cost and minimum dependency on the electrical grid. The problem of heat losses in geothermal storage receives particular attention as estimated losses are taken into account in the design procedure. Several scenarios considering
different ground thermal conductivities and electricity market prices allow for more secure and reliable decision-making at an early stage of the construction process. A fully renewable system without electrical grid connection is not achievable for the considered scenarios due to economic impracticality. The applied test case is also a good example that could be replicated when similar configurations are encountered.