I really enjoyed writing about the basics of how wind turbines work in my last post so we’re going to stick with the basics today as well. So far, this blog has focused on wind turbines because they have been in the news and exciting new developments have occurred in the wind energy sector. Today we’re going to pivot and discuss geothermal energy: what it is and how it works.
Let us first define what geothermal energy is. The thing is everyone already knows of examples of geothermal energy, possibly without knowing it. Geothermal energy is simply heated underground water whose energy can be utilized to generate electricity. The common examples that you are likely aware of are hot springs and geysers. Geothermal vents, where hot water moves from underground reservoirs to the surface and are located along the borders of tectonic plates so the areas in which geothermal energy is a viable source of energy are limited. However, this does not mean that they cannot be a powerful component to the energy grid. In 2018 geothermal energy plants produced 13.3 GW of energy worldwide. That is 13.3 BILLION Watts of clean energy that was already being produced.
Now, how is geothermal energy harnessed? Well, a lot of the same technology that is used to generate electricity from coal is also used to generate geothermal energy. In a coal plant, coal is burned to heat water that then turns into steam. As the steam escapes it turns turbines that that then turn a drive shaft which turns gears on a generator. That sounds familiar, doesn’t it? Essentially, coal and geothermal energy operate like large kettles. The only difference is that coal plants require the combustion of coal while geothermal energy gets its energy from the rives of magma that exist deep within the earth and heat underground water reservoirs.
There are three major types of geothermal energy produce plants. The first is a Dry Steam system, that simply uses the steam that is naturally created to spin a turbine. The second type is a Flash Steam which is a little bit more complicated. First, we must acknowledge that heated water underground is under much greater pressure than atmospheric pressure above ground. This means that this water can get much hotter and remain as a liquid. For this method, the water usually exceeds 350 degrees Fahrenheit. When this water enters a tank on the surface it flashes into steam and again, spins a turbine. The steam is then collected, condensed, and finally reinjected into the underground reservoir. The final and most complicated geothermal plant is called a Binary Cycle plant. In this system the heated ground water travels through a metal tube that brings it up to the surface. This tube radiates heat and is adjacent to a second tube with a second liquid in it, called a working fluid which has a lower boiling point. The water continues to travel through tube in a loop shape and is returned underground while the second liquid is heated to its boiling point, turned to steam, and used to spin turbines. This second liquid is condensed and collected and returned to its tube to go through the process again.
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