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Geothermal energy: sustainable and inexpensive

Geothermal energy involves almost no CO2 emission, and benefits users financially. The initial investment is balanced by a short return time and fossil fuel independence. TNO assesses permit applications for exploration and exploitation on behalf of the economic affairs ministry. We also produce geothermal maps and are developing a thermoGIS for rapid location-specific geothermal feasibility analyses.

Instead of heating a greenhouse by gas, horticulture greenhouse farmers have the option of geothermal energy by pumping up hot water through a production well from an aquifer – an underground water-bearing layer. The water is pumped back through an injection well after releasing its heat in a heat exchanger. A production and an injection well form what is known as a doublet, which, being a closed system, does not require users to discharge any surplus, possibly saline, groundwater. Other benefits are an above-ground space requirement of only a few square metres, no CO2 emission, and no noise. The security of supply is excellent. System life is some thirty or forty years, and enough heat can be supplied for multiple simultaneous users, such as horticulture greenhouse farms and residential areas. Deep geothermal energy can also be used for generating electricity. This is why geothermal energy is set to play an important spatial planning role for local authorities, housing corporations, horticulture greenhouse farms and electricity generators.

TNO is investigating new application areas for geothermal energy, such as enhanced geothermal systems (EGS), which use geothermal energy to generate electricity. Despite the substantial initial investment, geothermal systems pay for themselves within just a few years. What does obtaining a permit involve? A single applicant or consortium requests a firm of consultants to carry out a location survey: is the local subsurface potentially suitable? If so, the consultancy will assist the users in drafting an application for an exploration permit. The application must identify the ground layer to be targeted, its geological structure, capital expenditure estimates, and the expected return period. The application must be submitted to the Ministry of Economic Affairs and assessed independently by TNO. Work on drilling of an exploration well may begin once an application is approved. The results are included in an extraction permit application, which proceeds along the same lines as the exploration permit. Once approved, underground water may be extracted.

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