Geothermal energy facts

With all the talk surrounding dwindling fossil fuel reserves, you've probably heard the term geothermal energy being thrown around as one alternative source of power.

But how exactly does geothermal energy work? Can it be a replacement for fossil fuels, or is it simply wishful thinking? In this article, we're going to take a look at how geothermal energy works, as well as its advantages and disadvantages.

Geothermal energy is a renewable power source, the basis of which lies in using hot water reservoirs found under the Earth’s surface. This allows for a two-fold use: producing steam to spin turbines and generate electricity, or directly heating and cooling buildings.

Electricity generation is achieved through 3 main methods, the use of each depending on the particular nature of underground heat sources in a given area.

Large Scale (Electricity)

Dry Steam Power

The first method makes use of a “dry steam” reservoir, an underground collection of water vapor. This steam is piped up into the power plant and spins turbines which produce electricity.

The largest example of such use is “The Geysers”, a large complex of geothermal power plants located close to San Francisco. Together, these plants produce enough power to supply a large metropolitan city, such as San Francisco itself.

Flash Steam Power

The second method makes use of an underground hot water reservoir. This water, usually ranging from 150 °C to 370 °C, is pumped up to the surface through a production well, where it turns to steam due to being released from deep pressure. The resulting steam then powers turbines much like the first method.

Binary-Cycle Power

The third method of producing electricity with geothermal energy is the use of a much cooler water reservoir (120 °C to 180 °C).

Since this temperature is not enough to produce steam the water is pumped and transferred to a heat exchanger, where it is used to heat up a secondary liquid (therefore the term “binary”) such as isopentane, which boils at a lower temperature. Isopentane's boiling point is 28°C, compared to the 100°C of water. The steam produced from this liquid then turns turbines like in the previous methods.

Small Scale (heating/cooling)

Geothermal energy can also be used on a small scale to cool and heat buildings. This is achieved by sending pipes underground, but to a shallower level than with geothermal power plants.

Instead of pumping up water or steam, these pipes send down their own liquid which is heated and then sent back up into the foundation of the building. This is only possible in the winter, as the ground holds heat much better than air or water, and as such is able to heat the house rather than cool it.

Conversely, in the summer the air is hotter than the ground, and therefore the liquid that is sent underground gets cooled.

Geothermal energy seems like a simple enough transfer of heat from the body of the Earth up to the surface, but can it be used on a global scale as a major power source?

We can now take a look at some of the advantages and disadvantages of geothermal energy, to figure out whether it has the potential to help solve the looming energy crisis.

Geothermal energy has a number of substantial advantages. Most importantly, geothermal energy is one of the safest and cleanest ways of generating power. Unlike other sources - such as coal and natural gas - it does not generate any noteworthy greenhouse gases or pollutants which have a variety of negative impacts on the environment.

While there is a small possibility of releasing harmful gases from underground, this is a minuscule fraction of the damage caused by burning fossil fuels. Even a hydroelectric power plant, which produces seemingly clean energy, has larger impact on the environment by damming a river.

Furthermore, geothermal power plants take up very little space in comparison to other types of power plants, simply because they do not require things such as dams, mine shafts, tunnels or open pits.

Another advantage is the fact that geothermal power plants run 24/7 without any stops, because the fuel source is unaffected by outside factors such as weather, and is both renewable and sustainable.

Meanwhile, the source of energy itself is practically free, does not experience any price fluctuations, and does not need to be imported like oil or gas. Lastly, the cost of producing geothermal power is comparable to that of fossil fuels.

With all of these factors in mind, geothermal energy seems like an ideal choice. However, it also has a number of serious disadvantages.

By far the biggest disadvantage of geothermal energy is the inability to build a plant in most places around the world.

A geothermal power plant has several key requirements: the right type of rock that can be drilled through; a stable foundation; large enough steam or hot water reserves; and the availability of said water and steam at a shallow enough depth.

Due to these restrictions the majority of geothermal power plants currently operating around the world are located in areas of tectonic activity, such as New Zealand.

Smaller disadvantages include the possibility of running out of steam or water and the risk of hazardous gases coming up from underground. Furthermore, geothermal power plants are very cost-heavy during construction and take some time to recover these costs, while fossil fuel power pants recover costs quite fast.

Conclusion

In sum, we can conclude that geothermal energy provides tremendous advantages over fossil fuels, but is too restricted by its locational disadvantage. In fact, much due to these restrictions, geothermal energy accounts for only about 0.3% of total power production in the world today.

Nonetheless, it is still a significant source of energy that we should continue to develop and invest into. When coupled with other sustainable energy sources such as solar and wind power, geothermal energy can provide a realistic way to shift away from using fossil fuels entirely.