I recently stood next to an electrical generator, big enough to power a city the size of Seattle (about 1,000 megawatts, known as a gigawatt). It was surprisingly small, no larger than a classroom with a tall ceiling.
The generator’s spinning shaft could be seen where it connected to the steam turbine, next in line. And backing it up were three more turbines, helping to keep that long shaft spinning at 1,800 revolutions every minute.
The generator doesn’t spin freely because every electrical light and appliance in that gigawatt-sized city is resisting it. It takes a lot of push from the four steam turbines to keep it up to speed. Some power plants create the steam in a boiler heated by burning coal, others by using nuclear fission of uranium-235 to generate the requisite heat. The cleanest method of all is harvesting steam from water sprayed on hot granite a few miles [5 km] underground.
But standing in the electricity half of the power plant, you cannot tell what the heat source is. All you see are the big steam pipes coming in at the far end of the giant hall from an adjacent building. Looking out the big open doors, however, two giant cooling towers are immediately visible.
Nuclear? Not necessarily, as many coal-fired plants also have them. They are used for any steam power plant that cannot use a big body of water to cool the used steam back to hot water, so that it can be reused, flashing again into steam when re-exposed to the heat source, again spinning the turbine.
That wastes about two-thirds of the heat running the boiler; only one-third goes into electricity. Those hollow cooling towers transfer the waste heat to the air and what escapes from the top of the chimney is the mist formed within. But some nuclear plants-–say, the Browns Ferry plant in Alabama–-lack cooling towers because they are allowed to heat up a river or reservoir instead.
To see where the steam pipes are coming from, you can walk out on the balcony, where it is much cooler. There are no tall smokestacks in sight. And the balcony is relatively clean. So there are no coal- or oil-fired boilers nearby. (Turbines run by natural gas, like the ones in aircraft engines run by jet fuel, don’t need steam as a middleman.
So the heat source nearby must be either nuclear or geothermal. How does Sherlock Holmes decide?
First, sniff the Tennessee air. There is no smell of sulfur or suggestion of hot springs. Most existing geothermal plants are exploiting underground hot water not far from the surface and so most are built near hot springs.
The lack of sulfurous odors doesn’t eliminate the possibility that it’s a geothermal plant—it might be a new deep geothermal plant. The oil industry’s deep drilling techniques allow the earth’s internal heat to produce the steam. Drill two nearby wells a few miles down into hot dry granite, pump water down one and steam comes shooting up the other. Run it through a steam turbine and then recirculate it. It’s clean and simple.
But I can easily eliminate the deep geothermal possibility. That’s because of the guard towers. They stand like giant long-legged insects inside a razor-wire fence. Unlike those at a maximum-security prison, they guard a compound against assault from outside. If this were a geothermal plant, it wouldn’t need a small army of guards carrying automatic weapons, wearing camouflage uniforms with a patch saying "Pinkerton Government Services."
There are two heavily built buildings attached to this electrical hall. The nearest one does indeed contain a nuclear reactor, Watts Bar Number One, that is producing all the heat for the steam that spins that classroom-sized generator. The second building’s reactor won’t come on line until 2012, about thirty years late.
Nuclear power plants generate three-fourths of all carbon-free electricity in the U.S.; the rest is mostly hydropower whose expansion possibilities are very limited. Even with the recent expansions, wind and solar yield less than one percent of the clean energy.
Given our urgent need to avoid catastrophic climate change as the Earth heats up, we are going to have to build many gigawatt-scale power plants that use clean energy. Yet the scale of wind farms and solar plantations is only a fraction of a single power plant like this one. A monster solar trough array, like the one in the Mohave Desert in California, is still only 400 megawatts peak. Averaged around the clock, you are lucky to get one-fourth of that.
It’s the same for wind: most of those modern windmills for electricity produce only 1 megawatt max. To get a thousand times as much, a gigawatt, would require an enormous footprint and, for 24-7, a huge amount of energy storage capacity.
I cannot believe that we are going to get a clean 24-7 gigawatt out of wind or solar anytime soon, nor add a few gigs every week. Even if we stopped expanding our energy use, there are more than a hundred new coal-fired plants on the drawing board in the U.S. And it will take a new gigawatt every week in order to retire our 700 gigawatts of existing fossil fuel plants.
That leaves nuclear and geothermal to fill the gigawatt gaps. Deep geothermal has the smallest footprint (no mining, no storage, few guards) and, being relatively old-tech, it is suitable for developing countries with unstable governments. (Once the wells are drilled, it’s just another steam plant operation.)
People keep talking about the climate crisis as if it were merely a long-term problem to be tackled by gradually reforming commuters, substituting better cars and cleaner fuels, building better houses and power plants. That’s a half-century time scale. Unfortunately, much quicker action is needed—before 2020—and it must also ensure that developing countries do not repeat our mistakes by burning their own coal and oil.
While every clean megawatt counts, what we need are gigawatt-scale projects for all new construction, plus a rapid replacement of coal-burning plants. The only clean-energy prospects in the gigawatt range are nuclear and deep geothermal—and only one of them is suitable for most developing countries.
DRAFT for an Op-Ed.
William H. Calvin is a professor at the University of Washington School of Medicine in Seattle and the author of Global Fever: How to Treat Climate Change (University of Chicago Press, 2008).