Deep Aquifere
Overview

If sufficient groundwater is present in a depth of 1 to 3 km, it can be worthwhile itself to directly use the warmth from it. If the temperature reaches or exceeds 100° C, even the possibility exists of producing electricity!

The opening and use of deep Aquifers to gain warmth for the urban long-distance heating pipeline nets began in Europe in the 70's, whereby in France the strongest development of this usage of geothermal energy was registered. In the other Switzerland-surrounding countries, numerous plants in Germany, as well as in Austria and Italy can be found.

In regions with normal geothermal gradients, about 30 °C/km, which is the case in central Switzerland, the temperature in the deep Aquifer of  1km depth is about 40 °C and approximately 70 °C in 2 km depth.

If the water in this depth is only easily mineralized (less than 2 g/l) and is there the possibility given to derive the water cooled down after the extraction of heat into a waterstream - river or lake - or a pile then only one supply-drilling, a so-called Singlette is sufficient. If the water in this depth should exhibit however a mineral content of over 2 g/l, the cooled-down water must be injected back into the underground with the help of a second drilling (doublet).

Promoted by a drilling risk warranty of the federation, in the years 1987 to 1998 12 geothermal deep-wells in Switzerland were opened. Altogether there were five successes, one partial success and six failures in the sense of the risk warranty - that means “dry” drillings or to small amount of water supply. One drilling of the six failures could nevertheless be supplied to a geothermal usage: the drilling in Weissbad (Canton of Appenzell) was developed as “deep” terrestrial heat probe.

With successfully run of the deep wells the energetically meaningful use is in the main focus. With the Thermalwatersupply for therapeutic baths, should be proceeded for example according to the “cascade principle”. After the use for the actual bath usage (with decreasing temperatures) also the health establishments themselves and the heating of greenhouses  as a last step, can be done e.g. in Schinznach-Bad (Canton of Aargau).

 

 

Prinzipschema einer geothermischen Dubletten-Anlage für die Nutzung eines tiefen Aquifer.
Schematic diagram of a geothermal doublet plant
for the use of a deep Aquifer.

 

 

Function mode of a doublet plant

Over a supply drilling, warm Thermalwater is pumped with the help of a submerged pump to the surface, where a heat exchanger and a downstreamed heat pump are used for the rise to the desired heating temperature. The heating cycle supplies the consumer in form of a long-distance heating pipeline. The cooled down water is led back with a injection-drilling into the Aquifer.