Wherever you happen to be listening to this show, at some level beneath your feet the rocks in the Earth reach a temperature hot enough to boil water and create steam.
With steam, you can turn a turbine and create electricity.
If everywhere on Earth is just a few kilometers away from tapping into this source of energy, why don’t we use this everywhere?
Learn more about geothermal energy, its uses, and its limits, on this episode of Everything Everywhere Daily.
Geothermal energy is pretty simple. Geo means Earth, and thermal means heat. Geothermal is just tapping into the heat deep inside the Earth.
Before I get into the detail of how we can get usable energy from the Earth’s heat, I should explain why the Earth is so hot below the surface.
There are two sources of heat inside the Earth. The first comes from the primordial heat from when the Earth was first formed. When all of the loose rocks collided with each other 4 billion years ago, it created an enormous amount of heat from friction. As more and more rocks amalgamated to form the planet, all of that heat became trapped. As rocks aren’t a very good conductor of heat, much of that original heat is still there.
Primordial heat contributes about half the heat inside the Earth.
The other source of heat comes from radioactive decay. As radioactive elements naturally decay, they release heat, which like the primordial heat, is for the most part trapped. The natural radioactive elements which are responsible for this heat are mostly uranium, thorium, and potassium.
Over time, the interior of the Earth is gradually cooling down, but it is a very slow process. The radioactive isotopes eventually get used up, and heat is lost via volcanoes and other fissures in the Earth’s crust.
That being said, we are a long long way from that happening.
Estimates I have read are that there is enough heat in just the top 10km of the Earth’s crust to provide all the energy humanity for over 200 million years.
The Earth’s interior has three major parts: the core, the mantle, and the crust.
Humans live on the crust and we have never drilled beyond the crust. There is a good chance we never will. If you remember back to my episode on the world’s deepest hole, the Kola Superdeep Borehole, it was drilled by the Soviet Union and it was just an effort to try to see how deep they could drill.
It took them 17 years to reach an ultimate depth of 12,262 meters or 40,230 feet.
The thickness of the Earth’s crust can vary dramatically depending on where on the Earth you are. At its thickest, it can be about 80 kilometers and at its thinnest, it is about 1 kilometer.
Geothermal heat has been used for thousands of years in the form of hot springs. If the crust is thin enough, or if there is a fault somewhere in the crust, hot water can rise to the surface creating a hot spring.
The oldest known hot spring dates back to the third century BC at the Huaqing Chi palace in China. The Romans harnessed geothermal heat at their baths in Bath, England, and again outside the town of Meria, Spain.
The town of Chaudes-Aigues in France has been heating homes in the community since the 1400s.
In the 20th century, geothermal heating began to be used for individual buildings and greenhouses in places like Iceland and Idaho.
As electrification became popular in the early 20th century, some inventive people realized that this heat coming from the ground could be used to spin a turbine to produce electricity.
In 1904, Piero Conti created a geothermal turbine at the Larderello springs in Tuscany, Italy. This first geothermal electricity could power four light bulbs. In 1911, it was the location of the world’s first industrial-scale geothermal electrical plant. Today, Larderello produces 10% of all the geothermal electricity in the world.
The simplest type of geothermal power system is called a dry steam system. In this type of system, steam is heated directly from the ground and sent through a turbine, and then once cooled, the water would be pumped back into the ground. These were the first type of geothermal plants and these are the most popular today where steam is easily accessable.
Another type is a flash steam generator. In this, hot water is pumped out of the ground, but it isn’t steam. It is pumped into a low-pressure container which causes it to boil, and it is then run through a turbine.
A third type is called a binary cycle generator. These can use water temperatures that are much lower. The hot water runs through a heat exchange which heats up another fluid with a boiling point lower than water. This second fluid then turns to vapor and is run through a turbine.
The world’s largest geothermal facility is in The Geysers in California which is located about 72 miles north of San Francisco.
The countries which get the highest percentage of their electricity from geothermal are Iceland, El Salvador, Costa Rica, Kenya, and the Philippines which are all over 15%.
What all the countries I’ve mentioned have in common is that they have geothermal facilities located in places where the Earth’s crust is thin, and the heat is easily accessible.
Most are located on the Ring of Fire around the Pacific, the Great Rift Valley in Africa, or between two tectonic plates such as Iceland.
Globally, the total amount of electricity provided by geothermal is only about 1%.
The real question is if the Earth’s heat is located right beneath all our feet, and if it requires no fuel, and it is clean and available 24/7, why don’t we use geothermal power everywhere?
In theory, and I do mean in theory, we could. However, it would be really expensive.
The current geothermal power plants are located where it is cheap to access the Earth’s heat.
As you get away from these places, getting to that heat requires drilling deeper down. More importantly, it almost always requires drilling through bedrock.
Most oil and gas drilling is done through sedimentary rock which is relatively easy to drill through. Igneous rock like basalt or granite is much harder and much more difficult to drill through.
Moreover, the deeper you drill, regardless of what you drill through, the more expensive it gets. To get to a point where temperatures are enough to boil water, you need to drill to about 4 kilometers or about 2 and a half miles.
Moreover, it isn’t just a matter of getting to the heat, you also need groundwater. There are systems known as enhanced geothermal systems which pump water into fractures within the rock.
This has its own set of risks, including the possibility of earthquakes, if the pressure from the injected water dislodged a preexisting fault.
There is some good news on the horizon in terms of lowering the cost of drilling. There have been developments in using high-powered microwaves to blast through bedrock. The system in theory could drill down to 12 miles or 19 kilometers where you could have supercritical heated steam.
Tests are still being run, but if it turns out to be feasible, it could dramatically reduce the costs of drilling geothermal boreholes by 10-fold.
While geothermal electrical generation might get most of the attention, it is not the only, or even necessarily the best method of harnessing the heat of the Earth. Another much simpler use is for heating and cooling.
Geothermal heating and cooling is something that can be set up for almost any building, anywhere in the world. It doesn’t require drilling deep holes.
There are several different methods that can be used, but they all involve digging a hole or a ditch near the building, then running a pipe in the hole, usually in a looping pattern to increase distance, and then burying the pipe.
Depending on the depth of the pipe, and the location of the installation, the temperature below ground will be cooler than the outside air in the summer, and warmer in the winter. At a minimum, you could just pump water through it to exchange heat.
However, there is a much more efficient system known as a ground source heat pump.
A heat pump works on the same principle as a refrigerator, and instead of a single heat exchanger, you have two of them which can be reversed depending of if you want to heat or cool your house.
Heat pumps are much more efficient than alternative heating and cooling system, and they are made more efficient by having a higher heat difference, which is possible by running it through the ground.
Ground source heat pumps can save 30 to 70 percent in heating bills and 20 to 50 percent in cooling bills.
A ground source heat pump is probably one of the simplest and cheapest ways to harness the Earth’s heat to provide energy.
Geothermal heating and cooling systems have been used in greenhouses, and they work especially well in cold climates. With a geothermal heating system, greenhouses can grow citrus fruit, even when there is snow outside.
Currently, and at least for the foreseeable future, geothermal electrical generation will probably be limited to areas that are close to fault lines or volcanoes. While there are still a lot more places where it could be implemented, it probably isn’t something that will be adopted outside of fault zones until drilling technology dramatically improves.
Ground source heat pumps and geothermal heating are something that can be put into practice almost everywhere, right now. If I was building a new home today, it is definitely something I would install
Everything Everywhere Daily is an Airwave Media Podcast.
The executive producer is Darcy Adams.
The associate producers are Thor Thomsen and Peter Bennett.
Today’s review comes from listener 10secfwd over at Apple Podcasts in the United States. They write,
So good. I love being exposed to things I probably wouldn’t had come across otherwise. Short enough to be an easy listen, long enough to provide good context and details of the topic of the day. It has prompted me to look further into some the issues. I love. I am tickled by how fast the host speaks. He is committed to pack as much info as he can in the allotted amount of time.
Thanks, 10secfwd! Believe it or not, as some listeners to the podcast are very well aware, I used to be a very competitive academic debate in both high school and college. One thing most people don’t know about competitive debate in the United States is that they speak very fast. I was easily speaking well above 300 words per minute when I was in my prime.
When I do the podcast, I don’t perceive myself as actually speaking fast. When I listen to this show, and I do listen to my own show every day, I actually have to listen at double speed or else I feel I’m talking too slowly.
Remember, if you leave a review or send me a boostagram, you too can have it read the show.