We date the use of geothermal energy to the period of 10,000 years ago when people used thermal springs for cooking and for hot baths. In the 14th century AD in Chaudes-Aigues, France, they used geothermal energy as a local heating system. However, the economic and energy potential of geothermal energy began to develop only in the 19th century. The first geothermal power plant was built in Italy in the early 20th century in 1904.

Geothermal energy accumulates inside the earth. By slowly penetrating the surface, thermal fluxes are formed, which have an average of 0.063 W / m2. The thermal gradient measures the increase in temperature per unit length: near the earth's surface, the thermal gradient that drives the geothermal heat flux is approximately equal to 30 ° C / km. This means it reaches an average of 100 ° C per approximately 3 km in length. These data lead to the conclusion that the resulting power is very high, but it is spread over such a large area that its density is very low. It is much lower than the heat flux density coming from the sun in clear weather. This makes the use of this energy more complex, but in regions with unusually large geothermal springs, the geothermal gradient is larger than average. In such places, it is possible to find temperatures of up to 200 ° C at depths of 1500 and 2500 m.

Geothermal energy accumulates inside the earth. By slowly penetrating the surface, thermal fluxes are formed, which have an average of 0.063 W / m2. The thermal gradient measures the increase in temperature per unit length: near the earth's surface, the thermal gradient that drives the geothermal heat flux is approximately equal to 30 ° C / km. This means it reaches an average of 100 ° C per approximately 3 km in length. These data lead to the conclusion that the resulting power is very high, but it is spread over such a large area that its density is very low. It is much lower than the heat flux density coming from the sun in clear weather. This makes the use of this energy more complex, but in regions with unusually large geothermal springs, the geothermal gradient is larger than average. In such places, it is possible to find temperatures of up to 200 ° C at depths of 1500 and 2500 m.

Experience in Slovakia

In the first phases of geothermal well drilling, similar procedures and obstacles are envisaged as in the case of oil wells. Absolute confirmation of the existence of the geothermal source, its capacity and yield is realized through an exploratory well and subsequent hydrodynamic test. The implementation of geothermal projects is investment-intensive, the amount of investment and economic profitability is directly related to the parameters of the source as well as the size of the installation. In the case of geothermal projects, it is always necessary to consider a certain degree of geological risk, which can be reduced or eliminated with the right approach within the quality of pre-project preparation. The development of geothermal projects takes about 7 years from their initial phase. It is already clear from the length of the initial phase of the project that this is a very financially demanding project, which is also one of the reasons why this energy sector is not widespread. However, this time horizon may vary depending on the legislative environment (permitting processes and support system), geological conditions and the availability of information on geological conditions, the country's economic level and access to finance. The common practice of supporting geothermal energy abroad is either the direct participation of the state in the project, thus partly assuming the financial burden, or support by additional payments. Other support options include interest-free loans, tax breaks and free land rentals.

For the implementation and execution of work in the field of geothermal project development, it is necessary to follow the legislative framework in the field of geology, water resources, construction, energy, and environmental protection. It is always necessary to follow the law and therefore it is crucial to know the current wording of laws and procedures that directly affect all aspects of the future project. We can provide consultation to SAPI members who are interested in learning more about Slovak legislation interfering with geothermal resources.

An important factor for choosing the right location is also the evaluation of the socio-economic characteristics of the area of ​​interest. In order to make the best use of heat or residual heat from geothermal sources, it is necessary that there is a DH system in the area to which the source could be connected, or industry and economic enterprises using heat in the values ​​expected in the area. It is also important to map the area in terms of supply and demand for energy resources. The production of electricity itself is not so dependent on the above factors, but for the efficient use of residual heat, it is appropriate to take into account the above factors.

Various methods are used to carry out the surveys, which must be identified by an appropriate team of experts. Most of the survey methods used today have no negative impact on the environment.

After the completion of surveys, their evaluation and reassessment of the geothermal potential of the site based on new and old data, and in case of positive output, it is necessary to identify specific sites/land where the best precondition for geothermal energy exploitation and where a test well will be drilled. It is also necessary to supplement the preliminary use study started in the first phase of development with new knowledge and to make possible adjustments within the project planning.

Each drilling depth deeper than 500 m must undergo a mandatory assessment under the EIA Act, as well as obtain the necessary permits related to the use of geothermal water.

The implementation of the well and the technology used is directly dependent on the geothermal and geological conditions, the planned method of use and thus the planned depth of the well. As part of long-term resource retention and complete reduction of the impact of geothermal projects on the environment, the implementation of a second exploratory well, the so-called re-injection well, which serves to push used geothermal water back into the geothermal collector, is recommended. All this in a closed cycle with the production well, which has the effect of preventing any contact of geothermal water with the earth's surface, as well as adding water to the underground collector for its reheating and use. This process will ensure zero emissions, carbon neutrality and long-term sustainability of the project.

The National Energy and Climate Plan of the Slovak Republic does not envisage a significant development of geothermal energy in Slovakia in the period 2020-2022 due to the high costs currently associated with geothermal energy. According to the Plan, production from geothermal could start from 2024 with an installed capacity of 4 MW for each year until 2030, when, according to the Plan, we could have 28 MW of installed electricity from geothermal sources in Slovakia. The NECP points out that so far the production of energy from RES has been focused on the production of electricity, at most on cogeneration. In the future, financial support should also be focused on heat production, where geothermal has great potential. Support can be provided in the form of a green bonus or a surcharge. [1] Support for the use of geothermal energy in the electricity and heating sectors is also foreseen in the Recovery Plan.

[1] Source: NECP SR