Geothermal is an adjective that Merriam-Webster on-line
defines as: “of, or relating, to the heat of the earth’s interior”. Because it's an adjective, it can be used to modify, for example, “energy”, “power”, or even “development”, all of which are nouns.
In a recent newspaper article
about Iceland, the writer explained that Iceland is considered one of the “greenest” countries because, for example, oil and coal make up only 30 percent of its energy mix.
A few paragraphs later, the writer went on to say that, “It is fitting, then, that the nation has worked hard to explore clean-energy alternatives. Iceland has long used geothermal steam to heat water and spin turbines for electricity.” Pretty interesting, I thought, so I read on. The very next sentence was this: “The only petroleum Iceland uses is in its cars, and it is exploring ways to replace that vestige of oil with sustainable hydrogen power converted from geothermal”.
No, what you just read isn’t a typo on my part -- the sentence ends with the adjective geothermal, but the noun that it is meant to modify it is, well, not very clear. Thinking that was perhaps a typo or a small slip-up, I read on, only to find this a few paragraphs later: “But though Iceland is hailed as a world leader in geothermal development, it produces less geothermal than many other nations -- including ecological bad boy the US., which pumps out approximately 3,000 megawatts of geothermal, and the Philippines.”
The way geothermal is used in this article, it seems the writer and/or the editor could use a bit of a refresher on adjectives.