By reaching 77,2% renewable energy, the district heating network of Chevilly-Larue, L'Haÿ-les-Roses and Villejuif reduces its dependence on gas and controls its costs

In line with the report published by RTE at the end of 2025, geopolitical tensions have reignited debates surrounding the electrification of energy uses. To address these issues, Prime Minister Sébastien Lecornu made initial announcements on April 10th, focusing on housing, transportation, industry, and small businesses. Simultaneously, a mission was entrusted to the Minister Delegate for Energy, Maud Bregeon, to support the contribution of Energy Savings Certificates (CEE) to encourage the shift of the country's energy consumption towards electricity.

It is in such a context that the inter-municipal union for a single purpose (SIVU) for geothermal energy in Chevilly-Larue, L'Haÿ-les-Roses and Villejuif, SEMHACH, the Carrier company and the Hellio group, organized on April 13, 2026 a visit to the geothermal power plant in L'Haÿ-les-Roses, revisiting an electrification operation of the heat network serving 42.000 equivalent homes in the three municipalities of Val-de-Marne.

Within this framework, eight high-temperature heat pumps were installed between the Chevilly-Larue and L'Haÿ-les-Roses sites, supplied by the Carrier group and financed with €1,4 million in Energy Savings Certificates (CEE) secured by the Hellio group. This installation increases the renewable energy mix of the Chevilly-Larue, L'Haÿ-les-Roses, and Villejuif network to 77,2%.

A massively decarbonized heating network, serving the equivalent of 42.000 homes in the heart of Val-de-Marne

The Intermunicipal Syndicate for a Single Purpose (SIVU) for geothermal energy in Chevilly-Larue, L'Haÿ-les-Roses, and Villejuif was created to build and manage a heating network supplying a wide variety of buildings in the area: municipal facilities, apartment buildings, sports facilities, industrial sites, and healthcare facilities, including the Gustave Roussy Institute. To ensure the operation, management, maintenance, and renewal of the installations, the SIVU created the local public company SEMHACH.

The district heating network currently provides heating and hot water to the equivalent of 42.000 homes. It relies primarily on three geothermal power plants with a unit capacity of 12 MW thermal, supplemented by two gas turbine cogeneration units of 8 MW thermal and 5,5 MW electrical each.

Geothermal energy provides nearly 80% of the annual heat production, while the remainder is supplied by centralized and decentralized gas-fired boiler plants, as well as cogeneration units, which are activated according to heating needs and economic conditions. These installations represent a total thermal capacity of approximately 100 MW, ensuring a reliable supply for all subscribers, even during periods of extreme cold, down to -7°C, the reference negative temperature in the Île-de-France region.

According to Mélanie Nowak, President of the SIVU for geothermal energy in Chevilly-Larue, L'Haÿ-les-Roses and Villejuif: “During a now bygone era of stable natural gas prices and low costs, a massive investment in electric heat pump units was made for the district heating network of Chevilly-Larue, L'Haÿ-les-Roses, and Villejuif, in order to decarbonize its production. While this choice seems obvious today, in the midst of a new energy crisis, this project appeared in 2019 to be very significant in terms of investment compared to conventional solutions. The monetization of Energy Savings Certificates by Hellio allowed us to self-finance a large part of these investments, leading to the achievement of one of its main objectives: to produce local energy with a high proportion of renewable energy at a price lower than other energy sources.”

An electrification project for the district heating network in Chevilly-Larue, L'Haÿ-les-Roses and Villejuif, involving the installation of 8 heat pumps

Committed to a decarbonization approach since 2019, SEMHACH has installed eight heat pumps between the Chevilly-Larue and L'Haÿ-les-Roses sites, adding to all the heat production equipment.

Supplied by the Carrier group, these water-to-water heat pumps heat the primary heating circuit by cooling the reinjection water, without impacting the temperature of the deep aquifer, either in the short or long term. They thus generate an additional 14 MW of power while maintaining limited electricity consumption: for 1 MWh of heat produced, less than 0,25 MWh of electricity is required.

This system significantly reduces reliance on fossil fuels. Gas boilers and cogeneration plants are now relegated to a supplementary role, activated only when needed or to ensure grid security. Thanks to this development, the energy mix now comprises 77,2% renewable energy.

Beyond its environmental benefit, this transformation also helps to limit the network's exposure to gas price fluctuations, thus ensuring better cost control for subscribers.

According to Geoffrey Evesque, Director of SEMHACH: “Investing in water-to-water heat pumps represents a major turning point in accelerating geothermal production for our heating network. The end of regulated electricity sales contracts with EDF forced our organizations to rethink part of their energy production. Heat pumps represent a low-carbon and controllable energy solution. They effectively increase our renewable energy production rate while having a significant coefficient of performance.”

To deploy this solution, SEMHACH relied on the technologies of the Carrier group, whose equipment allows for the production of decarbonized heat up to 85°C, while offering operational flexibility.

According to Maxime Gobin, Sales Director for France at Carrier: “Decarbonizing district heating networks requires integrating high-performance, flexible solutions adapted to local constraints. With the installation of a QUATTRO high-temperature solution composed of four 61 XW heat pumps, Carrier provides a technological answer that fully utilizes geothermal resources while significantly reducing reliance on fossil fuels. This project concretely illustrates our ability to support local stakeholders in their energy transition by combining thermodynamic performance, service continuity, and intelligent system management.”

An operation financed to the tune of €1,4 million in CEE premiums, to accelerate the decarbonization of the heating network

To finance this operation, SEMHACH called upon the expertise of Hellio, a specialist in energy management solutions and a delegated authority for the Energy Savings Certificates (CEE) scheme. To address the specific needs of the heat production facilities at the Chevilly-Larue and L'Haÿ-les-Roses sites, the group developed two specific initiatives that secured €1,4 million in subsidies, significantly reducing the remaining costs of this energy-saving project.

Indeed, in order to encourage the most innovative projects, energy saving operations which do not fall within the framework of standardized operation sheets can be awarded CEEs within the framework of so-called “specific” operations which meet a “tailor-made” need.

According to Augustin Bouet-Mouttet, Vice-President of the Hellio group: “Through these specific operations, the Energy Savings Certificates scheme demonstrates its ability to finance tailor-made projects, adapted to complex technical configurations. The completion of this project reflects the recognition of real energy savings and testifies to the Hellio Group's commitment to supporting the decarbonization of local energy infrastructure and accelerating the energy transition of territories, through the mobilization of its financial engineering.”