Geothermal Heat Supply in Russia

— Geothermal heat supply occupies the second place among the renewable energy sources around the world in installed capacity (70.3 GW) and in the amount of generated thermal energy (163 (TW h)/year). It is outperformed only by solar heat supply (480 GW and 395 (TW h)/year). The use of geothermal heat involves the need to drill wells and fulfill special requirements for development of geothermal fields and construction of heat-supply systems. There are deep (more than 400-m deep) and shallow geothermal heat-supply systems (GHSSs). More than 66 geothermal fields have been explored in 11 regions of Russia, and the operating reserves total more than 300 000 m 3 /day. The installed capacity of Russian GHSSs totals 310 MW. Differences between open- and closed-loop GHSSs are pointed out. For open-loop GHSSs, their typical process circuit arrangements implemented in Krasnodar krai and in the cities of Kizlyar and Makhachkala are presented. The GHSS process circuits with the use of heat pumps (HPs) for recovering the heat of spent geothermal water and systems operating in combination with solar units are considered. Systems that use highly mineralized geothermal heat carriers from different geological horizons with heating of sweet water, as well as GHSSs with pumpless circulation of heat carrier, are described. The article gives examples of GHSSs equipped with geothermal circulation systems (GCSs) implemented in the Khankala geothermal field in the city of Grozny, including the double GCS with the design capacity equal to 8.7 MW and the GCS in the Medvedevka settlement in the Dzhankoi raion of Crimea, a distinctive feature of which is that it uses wellhead methane for generating electricity and for additionally heating the heat carrier in the peaking modes of operation. In constructing open- and closed-loop surface GHSSs, heat pumps are commonly used. In the first case, the heat of underground or surface water bodies is used, while horizontal or vertical heat exchangers are applied in the second case. Examples of geothermal heat-supply systems are given: the surface GHSS in the city of Makhachkala, in which ground heat exchangers in combination with solar units are used, and the GHSS in the city of Krasnodar, which serves for heating an administrative building and for cooling it in summer. The key scientific–technical problems requiring further investigations and development for constructing efficient and competitive geothermal heat-supply systems in different reg