[1] When we think of heat on planet Earth, we typically think of that generated by the sun and trapped by our atmosphere. However, the earth itself is constantly generating heat from within, through radioactive decay. At its core, temperatures reach 7,200 degrees Fahrenheit, which convects upward through the mantle and into the crust, where rock and water may reach 700 degrees. In some places, this heat emerges to the surface, through geysers, hot springs, and – of course – volcanoes. And while the violent heat of volcanoes is something to fear, much of the heat within the earth’s crust can be useful. Since Paleolithic times, humans have used hot springs for bathing and restoration. More recently, people have recognized that geothermal energy has the potential to generate electricity.
[2] In 1892, Boise, Idaho used geothermal energy to provide direct power to their district heating system. Since then, our technology has improved and the industry has only grown. Geothermal power plants now capture steam and hot water to generate electricity, and today over 12,000 megawatts of geothermal power are produced worldwide, with an additional 30 gigawatts used for direct heating purposes.
[3] There are significant upsides to geothermal power, particularly when compared to more conventional methods of power generation using fossil fuels. Unlike fossil fuels, geothermal energy is renewable. Not only is geothermal energy renewable, but it can be harnessed in relatively environmentally friendly ways. A typical geothermal plant produces approximately 122 kilograms of CO2 per megawatt-hour of electricity. Compare this with the 1,000 kg per MWh of CO2 produced by the average coal power plant, and you can see why geothermal is supported by many environmentalists.
[4] In fact, on an environmental level it is not just the emissions generated by the plant itself, but those generated by all the associated activities. Fossil fuels – including coal and oil – not only require more damaging extraction processes, they also need transporting. This enlarges their carbon footprint significantly. Geothermal energy, on the other hand, is captured where it exists, much like wind and solar energy, two other promising renewable energy sources. However, unlike wind and solar energy, geothermal is a stable resource. Wind and solar power are susceptible to changing conditions; geothermal energy does not fluctuate (although it may change slowly over time) on a daily or hourly basis. Thus the output of a geothermal plant can be predicted with accuracy.
[5] So, if geothermal energy is so wonderful, why does it currently provide only a small percentage of the world’s power? The truth is, there are some downsides to geothermal energy. Firstly, it is not freely available in useful amounts everywhere on earth. Good geothermal reservoirs are not evenly distributed around the planet. And while countries such as Iceland and the Philippines can, by virtue of their location near reservoirs, generate a third of their electricity in this manner, other countries aren’t so lucky. This means that if geothermal power is to be used more widely, it will have to be distributed long-distance, which is costly.
[6] The cost of geothermal is not only associated with distribution. The plant itself may be prohibitively expensive, ranging from two to seven million dollars for a plant capable of generating 1 MW of geothermal power. These high upfront costs apply on a smaller scale as well: installing a geothermal heat pump for your home may cost upward of $20,000. Of course, the return on investment is significant, but such upfront costs tend to deflate potential.
[7] There is one more disadvantage that may come as a surprise. Constructing a geothermal power plant can actually have a negative impact on the stability of the land around and below it. How great of an impact can humans have by tapping into the crust of such a massive piece of rock such as the earth? Well, consider that the construction of a geothermal plant in Switzerland in 1997 triggered an earthquake with a magnitude of 3.4. This may seem less damaging than, say, a meltdown at a nuclear power plant, but as our reach within the earth increases, so may the size of the disasters we create.
