Getting Geothermal Energy From Erupting Volcanoes to Produce Electrical Power

One of my fondest memories from elementary school was learning about Pompeii and the eruption of Mount Vesuvius. The pictures forced a purely visceral reaction: charred bodies, blackened, ashen buildings, and paintings of huge plumes of smoke rising into the air. I imagined myself living in the city during the eruption: what would I do? Run inside? Become paralyzed with shock? When I was older and learned about the apocalypse, I thought back to the pictures of Pompeii.

What is less well known is that Vesuvius has erupted three dozen times since the famous explosion in AD 79. That’s thirty-six plumes of ash, blackened landscapes, and apocalyptic scenes. It is still an active volcano, meaning that it could erupt anytime in the near future. But what is truly fascinating about Vesuvius and volcanoes is not the massive amounts of destruction a single eruption can cause. It’s that, for over a hundred years, man has been using the same power that destroyed Pompeii to run toaster ovens in the homes of thousands of families around the world.

Geothermal energy is extracted using two methods: a heat pump system or “hot dry rock” conversion. Heat pumps are large pipes that run from the top of the earth’s crust into a building. In winter, the crust is hot, allowing heat to flow into the building and warm it; in summer, the crust is cold, so warm air flows from the building to the ground. Just picture a giant heat valve and you’ve got the idea.

“Hot dry rock” (or HDR) extraction is slightly more complicated. Deep wells are drilled into hot rock and hot geothermal water is pulled up into tanks. The steam from the water either drives turbines itself, or the water is passed next to a liquid with a low boiling point. The second liquid then vaporizes, which drives turbines.

Geothermal power has been touted recently due to its many benefits. The heat source is almost inexhaustible - imagine a giant sphere of coal the size of the Earth and you’ll understand. Also, geothermal plants are hardy creatures. Wind farms only work if there’s a gust; solar farms only work when the sun is out. Geothermal plants aren’t nearly so finicky - they work day and night, 365 days per year.  They’re the Energizer Bunny of clean energy plants.

So why does the earth’s massive heat reservoir supply less than 1% of the world’s energy? In a few words: hot stuff cools down.  While the earth never cools significantly, the location of a geothermal cools down within a few decades. Thus, a geothermal company would have to construct new plants every time a site gets chilly. In addition, plants tend to deposit the hot geothermal water into rivers. The high levels of mercury and arsenic in the water are dangerous, and excessive amounts in river water will make the water undrinkable.

Vesuvius and other volcanoes make you wonder at the energy packed in our humble planet. Unfortunately, the difficulties and inefficiencies of heat extraction mean that geothermal energy will never be a true powerhouse of renewable energy. But the plants scattered across the world show, once again, that if there’s energy somewhere, we will do our best to harness it.