RGreen & Arverne: Investing in Europe’s Geothermal Journey

RGreen Invest is one of the most prominent sustainable investment firms operating in Europe today.

The company manages around US$3.3bn of assets and focuses entirely on investing in sustainable endeavours, including renewable energy infrastructure and climate change mitigation initiatives.

Central to the firm’s philosophy is the notion of energy sovereignty – helping companies and countries establish greater control over the power they use.

One of RGreen’s latest investments is a €52.4m (US$59m) investment in Arverne, France’s leading solutions provider for the geothermal energy sector.

For this investment, RGreen has partnered with Pierre Brossolet, the Founder and CEO of the company, and the money will be channelled through his holding company, GEOGREEN.

The story of Arverne

Arverne was founded in the French town of Pau in 2018, though the company’s roots in geothermal drilling can be traced back much further.

Arverne Drilling Services is the group's boring and well-engineering subsidiary, and it was originally established in 1958. 

It had spent decades working in the oil, gas and mining sectors before Pierre decided to apply this expertise to geothermal energy instead.

Though drilling for an entirely different form of energy, deep geothermal uses many of the same processes, just redirecting them for heat rather than hydrocarbons.

Alongside the drilling business sit 2gré, which sells geothermal heat, and Lithium de France, which is trying to extract lithium from the same hot brine that Arverne pumps to the surface.

From an airport to the Parisian suburbs

Arverne's most remarkable project to date sits beneath one of Europe's busiest airports.

In late 2024 the company drilled two geothermal wells at Paris-Charles de Gaulle airport for the site’s operator, Groupe ADP.

The resulting heat now supplies Terminal 1 with up to 80GWh of energy a year.

Discussing the project at the time, Pierre said: “We firmly believe that underground resources, particularly geothermal energy, are key solutions for the energy transition.”

Arverne has since picked up a 30-year concession, alongside energy group Dalkia, to build and operate a geothermal district heating network for the Paris suburbs of Clichy-sous-Bois and Livry-Gargan, with the scheme worth close to €90m (US$102.6m).

In May this year the company went further still, creating a joint venture called Francilienne de Géothermie with Banque des Territoires, the local investment arm of French state bank Caisse des Dépôts, specifically to develop geothermal projects across the wider Île-de-France region.

That region sits directly above the Dogger aquifer, which is a layer of porous limestone that has made the Paris basin one of the more established geothermal heating markets in Europe for decades.

The company's other major frontier is the Alsace, where Lithium de France began drilling its first geothermal doublet at Schwabwiller in mid-2025 as part of a project designed to produce both heat and lithium from the same wells.

Europe’s geothermal journey

The International Energy Agency’s research suggests that the world’s geothermal resources – at a depth of just 8km – could provide 600TW of power. Currently, global energy demand is just 20TW.

But while its potential is undoubtable, geothermal is just a marginal contributor to Europe's energy mix relative to wind and solar.

That said, the energy source is on the up.

Geothermal district heating output across Europe grew by 4.6% between 2023 and 2024, according to industry body EGEC.

France has particularly high ambitions when it comes to geothermal, with the government hoping to quadruple geothermal production by 2035 to reach 28TWh.

At EU level, member states explicitly endorsed geothermal for the first time in December 2024, and the European Commission is now under pressure from a coalition of nearly 70 businesses and investors to publish a dedicated geothermal strategy.

That coalition, which includes the EGEC and Cleantech for Europe among its signatories, argues the technology could realistically replace up to 42% of Europe's remaining coal and gas generation given enough time and investment.

Why Europe’s geothermal growth has been relatively slow

The barriers holding geothermal back are reasonably well understood, and Arverne's own experience illustrates some of them.

Chief among them is upfront capital risk, since exploration drilling can cost tens of millions of euros before a developer even knows whether a well will actually perform as hoped.

Failure rates for exploratory wells vary massively by geology and country, ranging from under 10% in Hungary and Germany to as much as 30% in the Netherlands according to analysts at Rystad Energy.

As such, geothermal prospecting can be a costly business.

Permitting adds a second layer of friction, with regimes differing so widely between EU member states that developers can feel like they’re starting from scratch every time they cross a border.

Another is public perception, particularly when it comes to the seismic tremors that deep drilling occasionally triggers.

Incidents in Basel, Switzerland and Staufen, Germany, which led to damaged buildings, have shaped public attitudes toward geothermal in some capacity, though it has been noted in reports that seismic risk assessments were inadequate for these projects.

The money behind the ambition

Nicolas Rochon, Founder and CEO of RGreen Invest, has framed the investment in terms of energy security rather than pure financial return.

“We are delighted to partner with Arverne, a national champion that has demonstrated its ability to unlock the exceptional potential of France's geothermal resources to deliver strategic infrastructure that strengthens both French and European energy security,” he says.

Pierre, likewise, is enthusiastic and emphatic about the road ahead, not only for the companies involved but for France as a whole.

“By 2031–2033, Arverne aims to produce around 4TWh of deep geothermal energy annually in France, representing more than half of the targets set out in the national energy roadmap and avoiding close to one million tons of CO₂ compared with natural gas,” he says.

The by-products of these geothermal endeavours will also contribute to Europe’s wider energy transition.

“Annual production of 27,000 tons of lithium carbonate in Alsace will provide enough material to supply batteries for around 800,000 electric vehicles,” Pierre explains.