There are two general ways to mine heat—hydrothermal heat mining and Enhanced Geothermal Systems (EGS). For simplicity let’s look at hydrothermal heat mining here and EGS in a separate post.

Hydrothermal heat mining’s modern uses for electricity generation from go back at least 100 years on every continent. Also, people used hot springs before recorded history—the oldest known spa fed by a hot spring goes back to China’s Qin Dynasty (3rd century BCE). In the first century CE, the Romans conquered Britain, and Bath, in what is now Somerset, got its name from the hot springs that the Romans used to feed public baths and for heating. Geothermal’s first use, in addition to baths, was for heating and the oldest geothermal district-heating system has been operating in Chaudes-Aigues (very-hot), France, since the 14^th century.

Most commonly, heat mining involves pumping very hot water out of the Earth and piping it into conventional steam turbines where it turns into high-pressure steam, which, in turn, drives electric dynamos. In some areas, there’s enough water flowing into an underground hot spot to make this work quite well. But water is key and there are many other places that are equally hot, but lack the water.

Think of a geyser like Old Faithful. We’re not advocating piping hot water from that geyser—perish the thought! There are too many other natural sources of very hot water to do the job without ruining a landmark.

For instance, there’s Sonoma Valley in California where Calpine runs its business. Calpine is a publicly traded, electric power–generating company that uses both geothermal and natural gas-fired technologies to generate electricity. Of the 80 power plants in the company’s fleet, 13 are located in Sonoma Valley in an area called The Geysers. The Geysers is the largest producer of hydrothermal energy in North America. Together, the plants have a combined generating capacity of 634 MW of base-load electricity according to the company’s website.¹⁷

Heat in the Earth’s crust is the result of the planet’s molten core—hot, liquid rock kept this way due to radioactivity in the center of the planet. There’s also natural radioactivity in the crust, so there’s a lot of heat down there. Conceptually, heat mining can be compared to using the Earth as a nuclear reactor that heats the water that drives generators. The benefit, in addition to the clean energy it produces, is that there is no nuclear waste to contend with.

Nations on many continents including Europe and Australia are also evaluating heat mining. Alpine nations like Germany, France, Austria, and Italy all have some exposure to hydrothermal power potential. Interestingly, island states and nations sitting atop of fault lines or active volcanoes, such as the Hawaiian Islands and Iceland already generate at least some of their electricity from geothermal wells.

Volcanoes like Mona Loa in Hawaii, the 30 or so volcanoes on Iceland, and even Mt. Vesuvius near Pompeii, Italy, are all potential candidates for geothermal wells and power generation.

But there’s more heat in the Earth’s crust than there are suitable places to extract it. The subsurface rock beds have to be porous enough to allow water to circulate and water needs to be available to conduct the heat to the surface. The point of EGS or Enhanced Geothermal Systems is to supplement the natural rock formations with what’s lacking so that steam extraction can take place. We’ll delve into EGS in the next article.

For now let’s stop for a moment and think about the vast potential of the Earth to produce the clean energy resources we need to power civilization in the 21^st century. It’s really amazing and enormous and it puts fretting over climate change into manageable perspective. We have problems with weather due to climate change but it’s manageable as soon as we give up a few notions about how we live such as total reliance on the current fossil fueled energy paradigm. But if we can internalize the opportunity of alternative power generation we can build a sustainable future that doesn’t ask people to live with less and we can get back to an agenda based on sensible growth.