Answer:
Explanation: Geothermal energy industry is fond of calling it “the sun beneath our feet.” The heat is continuously replenished by the decay of naturally occurring radioactive elements, at a flow rate of roughly 30 terawatts, almost double all human energy consumption. That process is expected to continue for billions of years.
The ARPA-E project AltaRock Energy estimates that “just 0.1% of the heat content of Earth could supply humanity’s total energy needs for 2 million years.” There’s enough energy in the Earth’s crust, just a few miles down, to power all of human civilization for generations to come. All we have to do is tap into it.
Tapping into it, though, turns out to be pretty tricky.
The easiest way to do so is to make direct use of the heat where it breaks the surface, in hot springs, geysers, and fumaroles (steam vents near volcanic activity). The warm water can be used for bathing or washing, and the heat for cooking. Using geothermal energy this way has been around since the earliest humans, going back at least to the Middle Paleolithic.
Slightly more sophisticated is tapping into naturally occurring reservoirs of geothermal heat close to the surface to heat buildings. In the 1890s, the city of Boise, Idaho, tapped one to create the US’s first district heating system, whereby one central source of heat feeds into multiple commercial and residential buildings. (Boise’s downtown still uses it.)
After that came digging deeper and using the heat to generate electricity. The first commercial geothermal power plant in the US was opened in 1960 in the Geysers, California; there are more than 60 operating in the US today.
The technology for accessing deep geothermal is developing at a dizzying pace these days. Let’s take a look at its basic forms, from established to experimental.