The surface of our planet is nice and cool. (A little too cool, this time of year.) But not all that far beneath us, it’s anything but. In fact, says Chris Marone, Penn State professor of geosciences, enough heat emanates from the interior of the planet to make 200 cups of hot coffee per hour for each of Earth’s 6.2 billion inhabitants
The Earth consists of three concentric layers. We’re on the crust, hard and thin (from 10 to 100 kilometres thick). Under that is the mantle, made of molten rock and about 2,900 kilometres thick. At the center of the planet lies the core, consisting of an inner part about the size of the moon that is essentially as dense as steel, and an outer core, 2,300 kilometres thick, made of molten metal.
Most of the heat is in the mantle. Some is heat left over from the planet’s condensation out of a cloud of hot dust and gas more than four billion years ago; some is heat left over by friction between heavier materials falling toward the center of the Earth shortly after it formed and the lighter materials forced up as those heavier materials descended, and some is heat produced by the expansion of the inner core (by about a centimeter every thousand years) as the outer core solidifies.
However, around 90 percent of the heat comes from the decay of radioactive isotopes within the mantle. (These radioactive isotopes exist in all rock. Even an ordinary one-kilogram block of granite on the surface emanates as much heat as a .000000001 watt light bulb through radioactive decay.)
When all the radioactive isotopes stabilize and the other heat dissipates, the Earth will freeze from the inside out, becoming as cold and dead as the Moon. (By that time, though, the Sun will probably have swollen into a red giant star and swallowed the planet completely, so no need to worry about keeping warm.)
Humans have used geothermal heat for centuries. They soak in hot water from deep underground (as at the Temple Gardens Spa in Moose Jaw). They grow vegetables in fields heated by natural steam (as in Tuscany) or in greenhouses heated by geothermal water (as in Hungary). They use geothermal heat to dry fish, pasteurize milk, and keep sidewalks and roads ice free. And they heat buildings: houses near Paris were geothermally heated 600 years ago.
Regina almost had its own geothermally heated building. In December of 1979 and January of 1980, a team headed by Dr. Laurence Vigrass at the University of Regina dug a 2,200-metre-deep well on the south side of the campus and brought up 60-degree salt water. The plan was to use the heat from that water to warm up fresh water, which would then have been piped through a field house or athletic complex. The demonstration facility was never built, but the well is still there.
Geothermal use is expanding at double-digit rates in Canada, and is already estimated to be saving 600 million kilowatt-hours of energy a year, offsetting 200,000 tonnes of greenhouse gas emissions. But using geothermal heat in these kinds of passive run-hot-water-through-some-pipes applications is different from using it to generate electricity, which requires not just hot water, but steam that can spin turbines.
In some places, you can get the steam directly from underground. In other places, where you have hot rocks but no hot water, you can inject water to produce steam. (And recover much of the water and pump it back in again for re-use.) Either way, you need a high-temperature geothermal resource, which you tend to find only where the crust is thin or buckled.
In Canada, that means the Rockies, and it’s there, at Meager Mountain, 170 kilometres from Vancouver, that a company called Western GeoPower Corp. is working toward building the country’s first commercial electrical geothermal plant. They’re currently drilling test wells and beginning the environmental assessment. The company says the plant could produce 200 megawatts of steady electricity for 30 years, more cheaply than wind or wave power.
Geothermal is getting a closer look in the U.S., too, where a new study led by MIT says geothermal energy could generate a substantial portion of the electricity the U.S. will need in the future at competitive prices and with minimal environmental impact.
In other words, one of our best ways to mitigate global warming may be to make better use of our warm globe.