Storing heat underground during the summer for use in winter: this is the concept developed by start-up AbSolar, which inaugurated its first demonstrator, the only one of its kind in France, combining solar and geothermal energy in the Gironde region on Thursday.
Adjacent to a 67-home eco-district in Cadaujac, near Bordeaux, the installation combines a field of Finnish-made solar panels 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 depths of between a few dozen and a few hundred meters,” explains Hervé Lautrette, founder of AbSolar. This geothermal specialist created it three years ago in Bègles, near Bordeaux, inspired by a similar project carried out in Canada in 2007.
During peak periods of sunshine in summer, solar panels heat water to a high temperature, storing it in a volume of several thousand cubic metres. In winter, a heat pump releases this thermal energy to supply homes with heating and domestic hot water. In service since June 2022, this SETIS concept (for Stockage d’Energie Thermique Inter-Saisonnier Souterrain) has enabled residents of the Cadaujac eco-neighborhood to pay less than 300 euros (per household) for their annual hot water and heating bill.
The demonstrator represented an investment of two million euros, half of which was subsidized by Ademe. It’s the only one of its kind in France, according to the public agency and the Pau-based Avenia subsoil industries cluster, which is in the process of certifying the project. “Heat accounts for 45% of our energy consumption, of which only 20% comes from renewable sources,” points out David Marchal, deputy executive director of expertise and programs at Ademe.
The inauguration took place in the presence of François Bayrou, Mayor of Pau and High Commissioner for Planning – the institution had published a report promoting the geothermal sector in October. “Beneath our feet lies an incredible eternal boiler on a human scale and free of charge (…) These are solutions whose development will continue in the future,” said Bayrou. AbSolar’s ambition is to attract other eco-neighborhoods in France, as well as industrial customers.
