We spent the last few days near Gullfoss and Geysir. We wanted to hike to several waterfalls in the area before venturing again into the Highlands. But it rained hard for the last 24 hours, sometimes heavy enough to make hiking impossible, and fog cut the visibility down. So the hikes were off. Instead we drove about an hour to the Geothermal Exhibition, inside the Hellisheidi power plant near Mount Hengill. We had tried the week before but got there too late, as it was closing. This time we made it.

The plant is about 25 km east of Reykjavik, off Highway 1 toward Hveragerdi. It is a huge building with columns of white steam rising off the hillside.

This is a company museum. The plant is owned and run by ON Power, and the exhibition is theirs, so it tells the company’s story: how good geothermal energy is, how clean the plant is, how well the company runs it. We still found it interesting, and learned things we did not know.

It is a visitor centre built into one side of the working plant, spread over a few floors with displays, screens, and models. The visit is self-guided with an audio guide, in several languages and also in text, and took us a little under an hour.

You cannot go inside the working plant, for safety and security reasons. But you can see into the turbine halls through glass, look over the working area from decks at the back. The exhibition walks through each step, from the heat underground to the electricity and hot water that come out.

Geothermal energy is not a side project in Iceland. It is the base of daily life. About 90% of all homes and buildings in Iceland are heated with geothermal water, piped up from the ground directly into the houses. Almost no one burns oil or gas to stay warm.

It also makes electricity: around a quarter to a third of Iceland’s supply, with most of the rest from hydropower. Together that makes Iceland’s electricity almost entirely renewable. The country’s geothermal plants have a combined capacity of around 785 megawatts across nine main plants, and Hellisheidi, where we were standing, is one of the largest single-site geothermal plants in the world.

This links back to our geology post. Iceland sits on the boundary between two tectonic plates and on top of a hot spot, which is why the island exists and why it has so many volcanoes. The exhibition sits on one of the volcanic belts we described, the one running through the Hengill area, and the plant uses the same heat that drives the volcanoes.

It also shows why the difference between high- and low-temperature geothermal fields matters. High-temperature fields sit near the active volcanic belts, where the rock is hottest. These are used to make electricity, because you need very hot water and steam to spin the turbines, and Hellisheidi is one of them. Low-temperature fields sit away from the belts and give gentler warmth, used mainly for heating water and homes. Both are reached by wells drilled deep into the ground.

The energy touches almost everything in Iceland, often without you noticing. Heating comes first: homes, offices, schools, and the swimming pools and hot pools the country is known for.

Then farming. Iceland grows food in greenhouses heated and lit with geothermal energy, which is how a cold island near the Arctic grows tomatoes, cucumbers, and peppers all year. We saw this at the tomato restaurant we visited earlier, built inside a working greenhouse warmed from below. Industry uses it too, and smaller uses are everywhere, from melting snow off pavements to drying fish.

The part that surprised us most was Carbfix, a carbon capture method the company developed here. A plant like this releases some carbon dioxide with the steam. Carbfix captures it, dissolves it in water, and pumps it deep into the volcanic basalt, where it reacts with the rock and turns to solid calcite stone, locked away for good.

What stood out was the speed. Scientists once thought this would take thousands of years. Carbfix showed that in this basalt, more than 95% of the injected gas turns to stone within about two years. The plant now turns roughly 12,000 tonnes of carbon dioxide into stone every year instead of releasing it, and has done so since 2012. The project is real and the science is sound, and it is exactly what a company likes to put at the front of its exhibition.