New solutions are emerging in the sector capable of using geothermal energy from hot rocks, expanding the exploitable areas: These are the new systems for exploiting geothermal energy: the “closed loop cycles”.
The efficient production and distribution of renewable energy is a challenge for our society. Geothermal energy has the potential to reduce global CO2 emissions and thus allow the transition to a system in which sustainable energy generation is prevalent. Geothermal energy defined as “traditional” uses hydrothermal resources enclosed in porous reservoirs and contained in impermeable rocks which prevent their diffusion. This type of resource, however, is limited to some specific geographical areas such as the areas of Larderello or Amiata in Tuscany. To deal with the problem of having to find thermal reservoirs that have hydrothermal characteristics suitable for energy production, different solutions are emerging that allow the exploitation of geothermal energy from hot rocks. This would therefore allow the widening of the areas in which it is possible to extract geothermal heat.
Figure 1, on the left, shows a schematic of a traditional open system, consisting of two or more wells connected hydrologically – either through natural aquifers or through hydraulic rock fracturing. Figure 1, on the right side, however, shows the representation of the new innovative solutions for the exploitation of geothermal energy in a closed cycle. The solution is based on the installation of a “heat exchanger” for the extraction of geothermal heat directly from the hot rock. The working fluid does not come into contact with the external environment, but follows a closed path inside the pipe.
The solution therefore has the following advantages:
- Increased access to geothermal energy: No need for reservoir permeability or hydraulic fracturing;
- Production of electricity from geothermal energy without emissions into the atmosphere;
- Make it possible to apply it in many contexts: It can deal with various geological and geothermal contexts at different depths.
The solution allows the exploitation of geothermal energy in new areas avoiding the need for a geothermal reservoir, which has so far limited the use of geothermal resources to limited areas of the earth. The solution is adaptable to local geothermal conditions, for new types of community energy models to address the energy transition and promote sustainability. Furthermore, it allows the use of alternative fluids to water to further improve the efficiency of electricity production compared to conventional solutions. Table 1 summarizes the strengths of “closed loop” systems compared to “traditional” geothermal energy.
There are two solutions for this technology, with slightly different technical aspects:
It is a closed system within which a working fluid is contained and circulated. The working fluid is not the fluid of the natural reservoir and enters and leaves the circuit from two different wells (one for the cold fluid inlet and the other for the hot fluid outlet).
It is a similar system, but uses a single well to circulate the fluid in the geothermal rocks from which it extracts the heat, thanks to the DualPipe technology.
Research is very active in this sector, so we expect a new push for geothermal energy in contexts where it has not been possible to apply it until now.