In Gironde, underground thermal storage proves its worth

Storing heat underground during the summer for use in winter: this is the concept developed by the start-up AbSolar which inaugurated its first demonstrator, unique in France, combining solar and geothermal energy on Thursday 25 May in Gironde.

Adjoining a 67-unit eco-district in Cadaujac, near Bordeaux, the installation combines a field of solar panels - made in Finland - with an underground thermal storage system.

"The heat produced by the solar panels is injected into the ground. Thanks to a closed water circuit, it can be stored at shallow depth, between a few tens and a few hundred meters", explains Hervé Lautrette, founder of the company AbSolar.

This geothermal specialist created it three years ago in Bègles, in the Bordeaux area, drawing inspiration from a similar project carried out in 2007 in Canada.

During the strong periods of sunshine in summer, the solar panels make it possible to heat water at high temperature, stored in a volume of several thousand cubic meters. In winter, a heat pump restores this thermal energy to supply the accommodation with heating and domestic hot water.

Put into service since June 2022, this concept of SETIS (for Inter-Seasonal Underground Thermal Energy Storage) has enabled the inhabitants of the Cadaujac eco-district to pay less than 300 euros (per household) for their annual water bill. hot and heating.

The demonstrator represented an investment of two million euros, half of which was subsidized by Ademe. It is unique in France, according to the public agency and the competitiveness cluster for subsoil industries Avenia, based in Pau, which is in the process of labeling the project.

"Heat represents 45% of our energy consumption, of which only 20% comes from renewable sources", recalls David Marchal, Ademe's deputy executive director of expertise and programs.

The inauguration took place in the presence of François Bayrou, mayor of Pau and High Commissioner for Planning - the institution had published a report in October promoting the geothermal sector. "Beneath our feet is an incredible eternal boiler on a human scale and free (...) These are solutions whose development will continue in the future," said Mr. Bayrou.

AbSolar aims to attract other eco-districts in France, as well as industrial customers.