US company Fervo Energy began selling electricity to the grid from its Cape Station plant on 30 September - a day ahead of schedule. That makes it the first company in so-called enhanced geothermal energy to reach actual commercial sales, rather than just demonstrations and investor presentations.

The start is modest; the ambitions aren't. The plant was synchronised with the grid about a week ago, and for now the first third of the planned 100 megawatts is running. The whole site, according to the company, could produce up to 4 gigawatts. From the first shovel to commercial operation, the first unit took 23 months to build, and Fervo wants to finish the next ones in 18.

"No team has ever built a project like this anywhere in the world, and we did it ahead of schedule," said Tim Latimer, Fervo's co-founder and CEO. Modesty clearly isn't part of the business plan - but in this case there is at least a power plant that actually works.

The difference from conventional geothermal energy is depth. Until now, heat sources close to the surface were used, so geothermal plants could only be built where nature is generous - Iceland, Tuscany, New Zealand. Fervo and a few other companies drill deeper, where the rock is hotter, using techniques and equipment borrowed from the oil and gas industry. The irony is hard to miss: the tools of the fossil era are now digging for energy that involves no burning at all.

The real audience for this plant is data centres. AI companies are looking for power from everywhere, and a geothermal plant can be built in phases - just like data centres themselves, so new servers come online as demand grows. Google, Southern California Edison and others have already committed to buying power from Cape Station.

Fervo was founded in 2017 and as a start-up raised more than 1.3 billion dollars (around 1.1 billion euros) from investors such as Breakthrough Energy Ventures, and in May it went public with an IPO that raised 1.9 billion dollars (around 1.6 billion euros). Macedonia has thermal springs from Katlanovo to Negorci. Will the heat lying much deeper down ever become electricity too?