It is easy to think of renewable energy sources being the ones that come from above. Wind and solar, after all, are both up in the air. Underground energy tends to be associated with fossil fuels.
Well, there is one underground renewable energy: geothermal. This trusty energy source has been growing at about 300 MW a year. While this still only accounts for 1% of world output, it’s clean and it’s going places.
You might find yourself wondering, “How does geothermal energy work?” That is a solid question that we aim to explain here.
This guide will walk you through energy production, what facilities harness it, and even how to apply it to a home.
How Does Geothermal Energy Work?
Nearly all power generation works in the same fashion: ie a turbine pushes a generator which creates a current.
Wind power does this directly. Nuclear and fossil fuel plants do it by producing steam by a heating method.
Like wind power, geothermal cuts out the fuel source by harnessing steam that already exists.
The following will explain where geothermal energy comes from and various methods to harness it.
Vents, Geysers, and Magma
The internal heat of the earth does the work to create the steam we harness. The planet gets its heat internally from its pressure and density and externally from the sun.
The internal heat constantly melts and resolidifies dense metals such as iron and nickel. Magma is a collection of fluid silicon, basalt, and peridotite materials.
This flowing liquid furnace sometimes comes to the surface in the form of volcanoes. At other times, it brushes up against underground reservoirs of water.
These reservoirs superheat and create pressure. Eventually, this pressure escapes in the form of a vent, when it trickles, or a geyser when it periodically erupts.
How geothermal energy works is we capture this steam and produce power in one of the following five ways.
Once the power is generated, pumps return the water to the earth via a process of injection wells. This return of materials is safe and completes the loop making geothermal energy a renewable energy source.
Binary Cycle Plants
An advanced plant concept, binary cycle plants use steam to heat and power a secondary liquid (usually isobutene).
This secondary liquid boils and the steam from that pushes a turbine which creates a charge through a generator.
This liquid then cools and is recollected to be used again.
The heat from the geothermal steam is lost but the water returns into the ground where it can be heated again. This makes a safe and eco-friendly loop with no contamination of the water being cycled in the process.
Flash Steam Plants
These plants also indirectly use the heated water.
Geothermally heated water is pumped at pressure into a tank. This tank is known as a ‘flash tank’. Since the tank is cooler than the outside temperature, the water inside flashes into steam.
This steam then powers a turbine. The water vapor is condensed back into fluid water and injected back into the ground.
The purpose of this system is to maximize the power output by generating sudden stream pressure. This also allows the plant to regulate generation which gives the machinery longevity.
Dry Steam Plants
The first, and most common of geothermal energy plants, is the dry steam model.
These plants directly pipe steam from a reservoir into a turbine. The turbine spins and the steam condenses as it cools. The resulting water is then recaptured and injected back into the ground.
This model is cheap to make and straightforward in its engineering. The downside, of course, is that they are less efficient than others mentioned here.
Small Scale
Now that we’ve gone over the large-scale power plants, we’ll also talk about direct geothermal energy heating. These systems exist to create heat for homes and businesses through direct interchanges.
These systems don’t only heat but can also cool a structure.
Closed Loop Systems
The principle behind geothermal heating and cooling is a reliance on the temperature of the ground. The temperature fluctuates close to the surface throughout the year. However, between 200 and 400 feet down the temperature remains between 50 – 60 Fahrenheit all the time.
There are three variations on the closed-loop system. These variations account for factors such as soil type, size of structure, and proximity to water.
They all work the same way, however. A mixture of water/antifreeze flows through a loop of pipes through the ground and into the home. From there compressors push the air through the ducts the same as any HVAC system.
Because the temperature is constant where the pipes flow, different effects are achieved across the year. In the summer, when the outside temp is high the pipe system is cooler than external air. In winter, the pipes will be warmer than outside temps.
Proposals have popped up in some areas demanding that these systems be part of any new housing project. There is simply no beating the efficiency and savings of these systems.
Open Loop Systems
Open loop systems only work near bodies of water (though underground aquifers count without needing a lake). Water is pumped from the source and into the same type of heat pump and duct compressor as a closed loop. Then the water is pumped back out to the same water source, or another one, depending. Since only water is flowing through the system, there is no pollution or additive issue to worry about.
The temp of the water remains constant at depth just like the closed loop systems. The result is much the same with one difference: fluid mixture.
The closed-loop system, though safe, does have a mixture that needs to be flushed occasionally. That mixture shouldn’t go back into the ground.
Find Your Energy
Armed with this knowledge, you can explain to friends and family who want to know how geothermal energy works. If you already know a lot about renewable energies and want to learn more, check out our articles on the topic here.
