The trouble with energy production—or rather, energy transformation—is that we often use “fossil fuels” (which are finite resources) to do it. Such processes involve nuclear fission (with uranium) or burning combustible materials (e.g. coal or oil). This leads to depleted levels of fossil fuels available, and creating too much pollution. It may be ‘cheaper’ to produce energy with fossil fuels, but it’s unsustainable for our future. What will we do with our nuclear power plants after we’ve exhausted uranium supplies? How can we fuel our future sustainably?
You may think solar panels and wind farms are the way to go, but even these have problems: solar panels absorb less energy on cloudy days, and wind farms cannot generate electricity if there isn’t any wind. Even river turbines are prone to requiring optimal conditions. The future needs an efficient way to harness energy from an unlimited resource . . . Yet it may have been under our noses all along: Geothermal Energy.
The core of the earth is made of solid iron, and exceeds temperatures of 5000℃. The heat from this core is continuously being absorbed by the cooler layers which surround it. In general, for every 100 metres you dig underground, the crust temperature of the crust increases by an average of 3℃. The earth’s surface has an average temperature of 14℃, therefore a linear equation can predict the earth’s temperature at a given depth:
Equation predicting earth’s temperature (𝑦, in ℃) based on the depth of the earth’s crust (𝑥, in kilometres) [Source: Stober I & Bucher K]
Using this equation, a depth of 5.5 kilometres into the earth would have a temperature of approximately 180℃. This temperature exceeds the boiling point of water, which evaporates into steam. Although steam is used in fossil fuel energy production, it’s also the primary technique for generating geothermal energy.
Geothermal power plants use the earth’s natural geothermal energy to create steam, then the steam is used to generate electricity. This simplified diagram shows how this works:
In the above diagram, cold water is pumped down a pipe which extends as far as 5.5 kilometres into the earth. The geothermal temperature at these depths average at 180℃. The cold water absorbs the heat energy and becomes hot steam (albeit in liquid form, due to high pressure underground). This hot steam is pumped above the earth’s surface, and travels faster using Bernoulli’s principle (the piping widens above the surface and has lower pressure). The steam has enough energy to turn the steam turbine, and thus power the electricity generator. Then the steam cools down back into a cool liquid once more, and is pumped back into the earth to repeat the cycle. As the earth has an “unlimited” supply of geothermal energy (in terms of the continuing existence of humanity), this is a source of perpetual energy.
In a future of limited fuel resources for human consumption, the prospect of an eco-friendly perpetual energy source is highly desirable. As geothermal energy is present wherever land exists, its abundance will make electricity freely available for everybody, and is therefore ideal for a currency-less society.
As reader Adam has commented, the “perpetual” nature of geothermal energy should be clarified. One prediction of the earth’s core’s cooling rate is a decrease of 100℃ every billion years. So it will cool to 0℃ in approximately 50 billion years. However, another prediction is in 1.1 billion years, the sun’s expansion will overheat the earth and evaporate our oceans (guaranteeing the extinction of life on earth). So essentially, we have 50 billion years of geothermal energy and less than 1 billion years to harness it (if indeed we can).
So Adam is right, it’s perpetual until the earth dies.
Of course, geothermal sites cool as we absorb the earth’s energy, but this can be overcome by digging deeper piping to be closer to our geothermal core (if our technology permits). I should also mention that (unfortunately), not all areas are good candidates for geothermal energy, as they can influence tectonic activity and cause earthquakes to surrounding areas.
Stober I & Bucher K, “Geothermal energy : from theoretical models to exploration and development”, Heidelberg : Springer, published 2013:
Diagram “Converting geothermal energy into electricity”, created by James Kanjo, based on the following source: