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Alfortville replaces 40-year-old geothermal plant with new triplet system

Alfortville replaces 40-year-old geothermal plant with new triplet system

Built World

New wells secure 90% renewable heat for about 6,000 homes

3 days ago: New geothermal triplet commissioned

Overview

Updated 1 hour ago

Alfortville has heated about 6,000 homes with geothermal energy since 1986. On October 15, 2026, Groupe Coriance commissioned a new triplet — two production wells and one reinjection well — replacing the original plant and raising the network's renewable share to 90%.

The EUR 22.25 million project draws 73°C water from the Dogger aquifer about 2,000 meters down. Public funds from ADEME's Heat Fund (EUR 7.3 million) and the Ile-de-France region (EUR 2.6 million) covered nearly half the cost, keeping heat prices off global fossil-fuel markets.

Why it matters

The new triplet keeps about 6,000 homes on local renewable heat at prices decoupled from global fossil-fuel markets.

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Key Indicators

90%
Renewable share of heating network
Geothermal now covers 90% of the network's energy mix.
~6,000
Housing equivalents served
Regional filings put the exact figure at 6,011 housing equivalents.
€22.25M
Total investment
ADEME and the Ile-de-France region covered EUR 9.9 million of the cost.
53.7 GWh
Planned annual heat production
Regional project filing projects 53.7 GWh per year at 17 MW capacity.

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People Involved

Organizations Involved

Timeline

October 1986 October 2026

6 events Latest: 3 days ago
Tap a bar to jump to that date
  1. New geothermal triplet commissioned

    Latest Infrastructure

    Two production wells and one reinjection well go live, lifting the network's renewable share to 90%.

  2. Drilling officially starts on two new wells

    Construction

    Three-month drilling campaign begins to reach the Dogger aquifer, where water sits at about 73°C.

  3. 40-meter drilling rig installed on site

    Construction

    The rig arrives at the geothermal site on chemin de Villeneuve Saint-Georges.

  4. Alfortville chooses Coriance for new geothermal plant

    Contract

    Mayor Luc Carvounas and Groupe Coriance sign partnership to replace the aging doublet.

  5. City takes over heating network management

    Governance

    Alfortville creates the Centrale de Géothermie Alfortvillaise (CGA) to run the geothermal network.

  6. Original geothermal doublet commissioned

    Infrastructure

    Alfortville starts its heating network, drawing 73°C water from the Dogger aquifer at 275 m³/h.

Scenarios

1

Alfortville extends geothermal network to new buildings

Likely Resolves by Q2 2028

Discussed by: ADEME case study; the city's connection obligation on new construction

Alfortville already requires new buildings to connect to the geothermal network, and an earlier ADEME-funded extension added 466 homes around ZAC Chantereine. If the new plant's capacity allows, the city can keep adding connections and grow the renewable share of the network further.

2

Triplet model spreads to other aging French geothermal plants

Possible Resolves by End of 2028

Discussed by: ThinkGeoEnergy, Groupe Coriance

France's 1980s geothermal boom left many aging doublets across the Paris region. If Alfortville's triplet retrofit proves reliable, Coriance and other operators may apply the same model — two production wells and one reinjection well — to extend other facilities approaching end of life.

3

Alfortville triplet hits 53.7 GWh annual output target

Likely Resolves by Q1 2028

Discussed by: Ile-de-France region project filing

The regional project filing projected 53.7 GWh of annual heat production at 17 MW. The first full year of operation will show whether the triplet delivers on that figure.

Historical Context

2 moments from history that rhyme with this story — and how they unfolded.

October 1986

Alfortville's first geothermal network (1986)

France developed deep geothermal in response to 1970s oil shocks. Alfortville ran a feasibility study in 1983, drilled its first well in 1986, and started the network on October 1, 1986, pulling 73°C water from the Dogger aquifer at 275 m³/h.

Then

The doublet heated buildings across south Alfortville for 40 years, with spent water reinjected to protect the corrosive aquifer.

Now

The system became a model for renewable district heating in the Paris region, but by the 2020s the wells were at end of life and needed replacement.

Why this matters now

This new triplet replaces that original facility — the renewal of a key piece of France's geothermal infrastructure.

2020s

Géoscan exploration of Ile-de-France geothermal resources (2020s)

BRGM's Géoscan project mapped geothermal potential across the Ile-de-France region. Data from the Alfortville drilling confirmed promising flow rates in a reservoir at 40–65°C, deeper and shallower than the Dogger.

Then

The region now sees geothermal as an expandable resource, potentially combined with heat pumps or linked to existing networks.

Now

Regional geothermal could grow beyond the aging 1980s doublets into a wider source of renewable heat.

Why this matters now

Alfortville's borehole data feeds this regional push, showing renewal and expansion rather than just replacement of old wells.

Sources

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