Renewable thermal energy is a highly sought-after resource in many parts of the world, as a measure to reduce our reliance on fossil fuels and electric power as energy sources for space heating of buildings. Shallow geothermal energy is one of the preferred environmentally friendly thermal energy resources in Norway, where heat stored underground is utilized in conventional heat pump systems via 200-300 m deep boreholes. However, the underground space in our urban areas are under continuous development and puts increasing demand on both surface and sub-surface city planning. The public need for infrastructure tunnels, road or railway tunnels, is most often prioritized rather than development of geothermal systems. Tunnels can thus be a hurdle for the planning and further development of geothermal utilization in cities. In many European countries' tunnels are now increasingly considered as a source of thermal energy in their self. Large volumes of rock mass and groundwater are made available in tunnels and the tunnel can be "activated" for harnessing the heat energy within, so called Energy tunnels. The potential for utilizing geothermal energy from Norwegian tunnels via heat pump systems is now being investigated. The tunnels can be activated in several manners, where both passive closed loop systems or active open loop groundwater systems are the two main potential solutions. The applicability of incorporating these systems are here assessed for the Norwegian tunnel design and an initial view on the potential for utilizing our tunnel infrastructure is given. The potential thermal energy available in existing road and railway tunnels alone range in the several TWh scale if all tunnels are activated. The many thousands of kilometers of tunnels in Norway might thus become a future energy resource and a potential pathway to reach our climate goals and to increase the rate of energy transition to renewable energy sources.
KEYWORDS
Geothermal energy; Tunnels; Heating & Cooling Potential; Urban development
