Solar thermal and geothermal integration with low temperature CO 2 DENs

Taking into account the high efficiency of solar thermal collectors and the fact that heating demands represent around 80% of the total energy needs in residential buildings, it is of interest to integrate solar thermal systems to supply HVAC services. However, both solar energy and HVAC needs have strong daily and seasonal variations, and require an efficient long term storage solution. The underground represents an efficient storage medium, which can compensate the latter mismatch; in winter, surplus heat can be extracted to satisfy the strong demand, while in summer, the rejected heat from cooling systems – in addition to the heat produced from the solar thermal collectors can be reinjected in the ground, therefore achieving long term energy storage. Low temperature district energy networks do not only supply heating and cooling to districts, but they also have the ability to harvest heat from renewable or low temperature waste heat sources and to integrate with long term heat storage systems, such as ground storage. This work looks at the integration of low temperature CO2 networks with solar thermal and geothermal storage to provide energy services. Solar thermal collector areas of 12.5 m2/cap are required for typical urban centers to close yearly energy balance in the ground.