Geothermal potential refers to the match between a geothermal resource and demand for thermal energy on the surface. Comparing resources with needs requires much more than the information on context (from very favourable to very unfavourable) provided by geothermal atlases (see box). BRGM's studies on potential supply quantitative data and indicate potential annual production from an aquifer at a given point in time, according to the pattern of demand on the surface.
More accurate assessments of regional potential
At the regional scale, assessments of potential have already been conducted with the ADEME, DREAL and local authorities, for example in Picardy and the Centre Region. Using the same grid as the atlases, or a finer grid, the approach involves identifying and evaluating the resource and comparing the results with demand in terms of existing infrastructure and buildings, to measure the potential contribution of geothermal energy. To assess regional potential, BRGM investigates potential not only in near surface aquifers, but also deeper in the ground with geothermal probes.
Several sources of data are used. To assess user demand on the surface, we first draw on the IGN's TOPO database, which gives a vectorised 3-D description of soils and land use: vegetation, rivers, road and rail infrastructure, buildings, etc. We then add energy consumption figures, mainly supplied by local authorities and energy companies, to the land use information. After cross-referencing the atlas data on resources with the needs estimated from the land use analysis, and integrating the regulatory and technical factors that could limit geothermal energy, we can produce a fairly accurate definition of geothermal potential at every point of the target area.
Nice Méridia, a 26-hectare eco-neighbourhood
A methodology has also been developed to integrate different scales (département, one or more municipalities, neighbourhood, etc.) through a different and more detailed approach, with additional data input, particularly from the MAJIC cadastral files on built-up and vacant land.
In 2013, in a zone in the lower Var valley indicated as highly favourable by the regional atlas, BRGM launched an assessment with the local public planning agency (EPA) of a project for a Technopole in the "Nice Méridia" eco-neighbourhood. We conducted additional investigations across the 26-ha zone, using both sampling and hydrodynamic modelling, to refine our assessment of its potential, to improve the definition of the system to be implemented according to the types of construction considered and to measure possible impacts on two nearby water abstraction points.
Three scenarios (centralised system, decentralised machinery in each building unit and deployment in several stages up to the project's end date in 2028) were submitted to the project developer, together with a technical and economic analysis that included profitability criteria, returns on investments, comparisons with a gas-fired system and avoided CO2 emissions.
Thanks to this methodological approach, we were able to provide the operators with sound decision-making support prior to calling on engineering consultancies. The approach is now also being applied at the intermediate scale - municipal and intermunicipal - for example in the Puy-de-Dôme, in cooperation with the Clermont intermunicipal authority.