Science:

Our Energy Vocabulary: The Words We Use for the Stuff We Can't See (Energy Collective)

Is geothermal energy renewable or sustainable?

It’s hard to talk about energy. Just ask any science teacher who has tried to define energy in a classroom. People stare blankly when you say, “It’s the ability to do work.” They furrow their brow when you tell them it’s not the same thing as “power.” You lose them completely if you bring up the laws of thermodynamics.

And yet, this thing that defies simple definition is critical to everything we do. Energy is fundamental to all facets of life on Earth. So it’s no surprise that folks who spend their days talking about energy have had to develop a special vocabulary, in order to have concrete discussions about an enigmatic concept.

Consider geothermal energy, which is commonly referred to as a renewable energy source. When underground hot water is tapped to generate electricity, the lost heat is then replenished over time from the large reserves of heat inside the planet. (See Chapter 4 of this IPCC special report for some helpful information on geothermal energy.) While the amount of heat stored in Earth’s core is massive (~1031J), it is also finite. We can’t get more after it’s gone. So is geothermal energy actually renewable?

To avoid this kind of semantic quibbling, many people (especially fans of nuclear energy) prefer the word “sustainable” to describe energy sources which humans could continue to exploit for many, many years.

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