Aquif

Surficial aquifer geothermal energy involves the thermal exploitation of aquifers located at depths of up to a hundred meters. At these depths, the average temperature of the water remains around ten degrees Celsius, so the heat extracted needs to be raised in order to be used, hence the use of heat pumps (PAC). The term "surface aquifer geothermal energy" is more commonly used to describe the groundwater heat pump sector. Groundwater heat pumps can be used to cover heating, cooling and/or domestic hot water needs. All sectors of application are concerned, from individual housing to industry. Given the cost of the underground structures to be built and installed (production borehole(s), discharge borehole(s), pumping equipment), this technique is best suited to large buildings (from 5,000 to 25,000 m ² , or even more) requiring both cooling and heating, either alternately (summer – winter) or simultaneously. It is therefore mainly intended for large and medium-sized commercial buildings (office buildings, healthcare facilities, hotels, large retail outlets).

Storing thermal energy underground means taking advantage of the properties of geological formations to store energy that is available and surplus to requirements at a given moment – i.e. without immediate use – and to exploit it at a later date during periods of demand. One example is a household waste incineration plant connected to a heating network serving buildings. In summer, the heat produced is not used because there is no demand for it. Injected and stored underground, this heat can be used later in the year during the heating season, thus limiting the need for fossil fuel-based back-up energy. The most common application for underground thermal storage is for heating buildings, but there are other applications too, such as heating vegetable or horticultural greenhouses. In the 1980s, a number of interesting research projects and experiments were carried out, notably in France. But it is mainly in countries such as Switzerland, the Netherlands, Sweden and Germany that work has continued since then. Today, there is a wealth of promising feedback. The lessons learnt should facilitate wider dissemination of the techniques implemented, which fit in well with a more global approach to reducing energy needs, limiting the use of fossil fuels and making the most of renewable or by-product energies, and thus reducing greenhouse gas emissions.