The National Climate Action Plan 2050 was adopted by the German government at the end of 2016. It
includes the aim to achieve greenhouse gas neutrality in Germany by the middle of this century.
Extensive social and economic changes are necessary to reach this goal. They include measures
concerning building and housing, industry and economy, the energy sector, mobility, agriculture and
land use.
One of these activities is the extension of geothermal as a base-loadable and decentralised renewable
energy. Round about two third of the costs of deep geothermal projects are allotted to drilling. The
latter accounts for more than the half of the project’s risks, too. Thus, it is possible to reduce costs and
risks significantly by utilizing existing boreholes or reactivating abandoned boreholes. These kinds of
boreholes can be found in the hydrocarbon exploration, mining or balneology. This doctoral thesis
focuses on the last aspect. Geothermal is ideal for spas and comparable facilities, because in their case
there is a yearlong, relatively high heat consumption compared to the electricity demand. In addition,
inlet temperatures of heating systems are relatively low and therefore favorable. A lot of spas and
public swimming baths were constructed in the 70s and 80s and have to be redeveloped or rebuild in
the near future. Therefore, it is now an advantageous moment to substitute the energy supply with
geothermal sources. The different stages of such an endeavour – pre-survey, exploration, drilling,
construction, start-up and operation – are tested at four exemplary national and international projects.
Investigation and compilation of time series of physicochemical and hydrochemical parameters
reaching back 175 years show temporal and spatial changes on thermal water reservoirs induced by
anthropogenic interventions in the underground. Enhanced versions of Piper, Schoeller and Stiff
diagrams are mainly used to evaluate and present data gained in the field and in the laboratory.
Different cation geothermometers are applied to estimate reservoir temperatures.
A brine compact heat exchanger was designed for geothermal exploitation of hydrothermal reservoirs.
The extracted amount of brine and its temperature can be improved by reactivation and deepening of
existing wells improving the heat exchanger performance in the same process. Further energy demand
can be covered by constructing a borehole heat exchanger field. It becomes evident, that all of these
options are economical and amortise within few years. In addition, significant amounts of carbon
dioxide emissions are avoided.
Possible alterations of groundwater properties during the construction of borehole heat exchanger field
can be assessed by a spring monitoring program. Spring monitoring programs facilitate the approval
procedure of public authorities and raise the public acceptance of geothermal projects.
Based on case studies in Bad Nauheim and Bad Soden-Salmünster, Germany, the hydrothermal
potential of existing wells in 15 Hessian towns with thermal water occurrence is evaluated and
amounts 117 GWh/a. | English |
Drucken
Impressum