Should Geothermal Energy Be Preferred in a Desalination Process

 In the Paris Basin, for instance, absorption chillers can be placed in grid substations and the primary hot fluid supplied by the geothermal heat plant. The chilled water can be piped to consumers via the same flow circuit used for heating and the same heaters although, in this respect, alternative devices (fan coils, ceiling coolers) would be preferable. Note that each absorption chiller unit needs to be equipped with a cooling tower.

Geothermal undertakings at large, and GDH in particular, are capital intensive owing to the high infrastructure (mining – geothermal wells - and surface - piping) investments required. Those are, on the other hand, compensated by the low running - operation/maintenance – costs. Depending on local geothermal settings (high/low heat flows, shallow/deep seated sources), socio-economic conditions and pricing policies (kWht or m3 of hot water) the average MWht selling price to GDH subscribers varies between 30 and 60 €/Mwht. Given economic (project life), reservoir longevity (cooling breakthrough time) and well physical lifetimes of say thirty years, the question often arises as whether there is a life after these critical thresholds and, if so, for how long. These issues have been thoroughly investigated, in particular in the Paris Basin, where GDH lives extending over 75 to 100 years, i.e. far beyond project life expectations, could be assessed provided the production/injection wells be periodically (every 25-30 years) (re)completed and drilled at adequate reservoir locations, according to corrosion resistant designs. Hence, the projected scenarios meet sustainability requirements.

Close to zero atmospheric emissions of green house gases. Among the indirect non quantified benefits, known as externalities, of GDH ought to be mentioned the contribution to significant reduction of environmentally provoked diseases (asthma among others).

The World Health Organization (WHO) has estimated that 1000 cubic meters per person per year is the benchmark level below which chronic water scarcity is considered to impede development and harm human health. 97.5% of the total global stock of water is saline and only 2.5% is fresh water. Approximately 70% of this global freshwater stock is locked up in polar icecaps and a major part of the remaining 30% lies in remote underground aquifers. In effect, only a miniscule fraction of freshwater (less than 1% of total freshwater or 0.007% of the total global water stock) that is available in rivers, lakes and reservoirs is readily accessible for direct human use. Geothermal energy is a source of renewable energy and the oceans are a major alternative source of water.

Desalination is very energy-intensive, and sustainable energy systems urgently need to be developed. Desalination technology is providing safe drinking water even to some ‘water-rich’ nations where pollution reduced the quality of natural waters. Thus, as a means of augmenting fresh water supplies, desalination contributes significantly to global sustainability. Desalination techniques such as those driven by geothermal heat have increased the range of water resources available for use by a community. Seawater desalination is one of the most promising fields for the application of geothermal energy due to the coincidence, in many places of the world, of water scarcity, seawater availability and geothermal potential. During the 90s the Kimolos Project was a research project that successfully demonstrated the technical feasibility of geothermal seawater desalination using low enthalpy geothermal energy.