PHREEQC

GeoSolar project proposes to develop innovative coupled mine water geothermal and solar energy storage systems, utilising post-closure mine systems as gigantic thermal batteries and solar energy as heat source. This coupled system will make full use of former mine land for the installation of solar power infrastructure, and former underground mine workings and goaf as thermal energy storage media. The solar energy system will deploy either solar collectors (direct sunlight absorption) or sorption solar heat storage (solid-vapour reaction), depending on the required temperature and volume of re-injected mine water. The underground mine system will include mine workings and goaf acting as a mine water reservoir, and as a gigantic thermal battery. A well doublet for the system includes a hot well at a deep level and a cold well at a shallow level, both drilled to intersect mine workings. In summer, mine water (initially at the very start of the process 20-30 °C) is extracted from the cold well, heated by the solar energy to high temperatures (70-90 °C), and then injected via the hot well back into the coal mine system for thermal energy storage (“charging”). In winter, mine water (60-80 °C) is extracted from the hot well for district heating, and spent colder water (10-20 °C) is injected via the cold well back into the coal mine system (“discharging”). The temperature of mine water for district heating in winter can be further increased by solar energy.