Solar energy in its non-fossilized forms – wind, hydro, biofuels, tidal, and direct use of the sun’s rays – are called “renewable,” meaning that it does not require vast geological ages to recreate them.
The term, however, can be misleading. All can only be renewed at a pace that natural cycles allow. The amount of solar energy that shines down upon the earth may seem inexhaustible, but it is extremely dilute. In order to match the highly concentrated power of fossil fuels, it must collected over vast areas and then brought together.
It is the collection process that is not inexhaustible and not always renewable. Hydroelectric dams, the most successful form of non-fossilized solar power, back up reservoirs covering hundreds of square miles in order to generate the same amount of electricity produced by a mile-square coal plant (not counting the area required to mine the coal).
Wind farms have to cover almost a hundred square miles to do the same thing. Fueling only a portion of the nation’s automobiles would require dedicating almost our entire inventory of agricultural land to growing biofuels.
Obviously, being “renewable” is not the only standard by which energy sources can be judged.
Geothermal Energy (The Non-Sun ‘Renewable’)
There is one other form of energy that is often grouped with solar and wind as “renewable,” however, that actually has nothing to do with the sun. This is “geothermal” energy. Geothermal energy is created when groundwater comes in contact with the interior heat of the earth. Sometimes this produces “hot springs,” which were long believed to have medicinal qualities.
Where the heat comes close to the surface, steam may emerge as “fumaroles.” In rare instances, groundwater superheated deep in the earth explodes to the surface periodically as a “geyser.” Long regarded as tourist attractions, fumaroles and geysers are now being tapped as “geothermal” sites.
What is the source of geothermal energy? The earth, it turns out, is a very hot place. At the surface, the “cold, cold ground” has an average temperature of 54o F, even when not being warmed by the sun’s rays. Below the surface, the earth’s temperature increases 16 degrees for every 1000 feet of depth. By the time we reach the world’s deepest mine shaft two miles down – the Robinson gold mine in South Africa – the temperature reaches 150 degrees and the tunnels must be air-conditioned for the miners to survive.
That is only the beginning. At 80 miles down we hit the Mohorovicic Discontinuity, discovered by Yugoslav seismologist Andrija Mohorovicic in 1909. At this point the temperature reaches 900o C and rock turns to liquid “magma.” At 1500 miles deep the temperature rises to 3700o C and another discontinuity – the Gutenberg – marks the place where molten rock becomes pure iron and nickel. Below that tremendous pressures turn the iron core solid once again and temperatures reaching 7,000o C – hotter than the surface of the sun.
Where does all this heat energy come from? Some of it is due to gravitational forces. As the earth is pulled inward, some of this force is translated into heat. Another portion is residual heat from the earth’s formation. According to the commonly accepted theory, originally proposed by Immanuel Kant, the solar system precipitated out of a huge swirling dust cloud, where particles kept colliding with each other until they agglomerated into the sun and the planets.
In the later stages, this involved huge collisions among very large objects. These impacts generate large amounts of heat, some of which still remains in the earth’s core. Together gravitational forces and residual heat probably account for about 40 percent of the earth’s temperature – the exact figure has still not been determined.
The other half of the earth’s heat, however, comes from a remarkable diminutive source – the slow breakdown of two of the 90 elements, uranium and thorium. With 92 protons, uranium is the largest natural atom, while thorium (90) is the third largest. Because of their size, they are unstable, meaning they are “radioactive.”
The internal “binding energy” that overrides the mutual repulsion among positively charged protons is occasionally overcome itself. This releases large quantities of energy, which sets subatomic particles in motion, creating large amounts of heat. Incredibly, the slow breakdown of these two radioactive elements, uranium and thorium, is enough to raise the earth’s internal temperature beyond the level of the surface of the sun.
Most geothermal sites are at natural steam vents that are created along geological fault lines, but there is now talk of drilling further down to tap the earth’s internal heat. Drill down ten miles almost anywhere on earth and you will encounter enough heat to boil water. (The deepest oil wells now only go down about five miles.)
Nuclear ‘Terrestrial’ Energy
But here’s a better idea. Why don’t we just take the source of that heat – the uranium or thorium – bring it to the surface, and reproduce or even accelerate the process that produces this heat in a controlled environment?
This is what we do in a “nuclear reactor.”
The process of tapping terrestrial energy and fossilized solar energy are almost identical. What do we do when we build a coal plant? We find stored solar energy beneath the earth’s surface. We mine it, we bring it to the surface, we concentrate it. We ignite it, starting a chain reaction where the energy released from one molecular breakdown triggers a breakdown of the next. We capture the heat to boil water, to produce steam, to drive a turbine, to generate electricity.
What do we do in a nuclear plant? We discover accumulations of terrestrial energy in the earth. We mine it, we bring it to the surface, we concentrate it. We ignite it, starting a chain reaction in which the energy released from one atomic breakdown triggers a breakdown of the next. We use this heat to boil water, to produce steam, to drive a turbine, to generate electricity.
A nuclear reactor is nothing more than terrestrial energy brought to the surface. There is nothing sinful or diabolical about it. We are not defying the laws of nature. Rather, we are working with a process that already takes place in nature.
Many geothermal plants are now almost indistinguishable from nuclear reactors. They have the same parabolic cooling towers that throw excess heat into the atmosphere. The steam rising from a nuclear reactor is just as harmless and potentially beneficial as the steam rising from a geothermal vent. In fact, they are the same thing. They are both terrestrial energy.
This post is excerpted from William Tucker, Terrestrial Energy, (Bartleby Press: 2008), chapter 3. The website of the same name is here.