Geothermal
Geothermal ksc17Geothermal Energy
In Yellowstone National Park in Wyoming, one of the most popular tourist attractions is a geyser known as Old Faithful." The neat thing about Old Faithful is that it spurts hot steaming water out of the ground at pretty predictable intervals – predictable enough that you can probably time your trip to Yellowstone to see Old Faithful erupt several times a day. If you don't happen to live nearby, you can always use the miracle of technology and check out the Old Faithful webcam.
Video: Old Faithful Geyser Eruption (1:28)
Old Faithful Geyser Eruption
PRESENTER: Old faithful here in Yellowstone National Park in July, getting ready for the eruption here.
[CHEERING]
Old Faithful here.
When you watch Old Faithful erupt, what you are seeing is geothermal energy in action. If we could just place a nice shiny turbine on top of the geyser's cone, whenever Old Faithful erupts (about every hour and a half or so), the force of the steam would spin the turbine, generating a nice flood of low-carbon electricity.
No one seriously talks about generating power from Old Faithful, but the heat beneath the surface of the earth could provide a gigantic store of energy – if only we could get at it at some reasonable cost. There are a few places, like California, Alaska, and Iceland, where geothermal energy is used to generate a lot of electricity (in Iceland's case, basically enough for the whole country). There are a lot more places where engineers are hoping that we could generate even more electricity from geothermal energy, using techniques collectively known as "enhanced geothermal."
In this section, we'll talk about how geothermal energy works and where it is currently used. We'll also talk about the potential, and some possible pitfalls, from enhanced geothermal. One really intriguing idea that we won't talk about in this section is using heat in the very shallow surface (maybe as little as fifteen feet below ground) to heat and cool your home. This idea, called "ground-source heat pumps" or "ground source heat exchange" is growing in popularity for new home construction and has the potential to save a lot of energy in buildings. But we'll wait for that until we talk about energy conservation. Here we'll stick to producing electricity directly from the heat deep within the earth's surface.
Generating Electricity from Geothermal Energy
Generating Electricity from Geothermal Energy azs2Remember how your basic steam turbine works in a power plant that uses fossil fuels: Fuel is burned to heat water in a boiler, to create steam. The steam is used to drive a turbine, which generates electricity. What if you could get all that steam without burning a single ounce of coal, oil or natural gas? That is the appeal of geothermal electricity production. In certain locations (primarily near active or recently active volcanoes) there are very hot rocks deep under the earth’s surface. In these "geothermal" regions, the temperature may rise by 40-50°C every kilometer of depth, so just 3 km, the temperature could be 120 to 150°C, well above the boiling point for water. The rocks in these regions will typically have pore spaces filled with water, and the water may still be in the form of liquid water since the pressure is so high down there (in some very hot areas, the water is actually in the form of steam trapped in the rocks). If you drill a deep well into one of these "geothermal reservoirs", the water will rise up and as it approaches the surface, the pressure decreases and it turns to steam. This steam can then be used to drive a turbine that is attached to a generator to make electricity. In some regards, this is very much like a coal or natural gas electrical plant, except that with geothermal, no fossil fuels are burned, which means no carbon emissions.
There are three basic types of geothermal power plants, depending on the type of hydrothermal reservoir:
- Dry steam plants, which draw steam directly from deep underground (a la Old Faithful);
- Flash steam plants, which draw hot water under high pressure up towards the surface. As the pressure decreases, the water boils, which generates steam to power the turbine;
- Binary steam plants, which utilize hot water (perhaps around 150 degrees Celsius) to vaporize another fluid (one with a lower boiling point). This hot vapor then drives the turbine, generating electricity.
The oldest geothermal plant (1904) in the world is Lardarello, in Italy, which is a dry steam plant. The Geysers, in California, is the largest geothermal installation in the world and the only accessible dry-steam area in the United States (other than Old Faithful and the rest of Yellowstone, which is off-limits). Most modern geothermal plants are “closed-loop” systems, which means that the water (or steam) brought up from the surface is re-injected back into the earth, as shown in the figure below. If the water is not replaced, then eventually, the geothermal reservoir will dry up and cease function.

The image is a diagram titled "Binary Cycle Power Plant," illustrating the operation of a binary cycle geothermal power plant.
- Production Well: On the left side of the diagram, there is a vertical pipe labeled "Production well" which goes down into the ground through various rock layers. This well extracts hot geothermal fluid from beneath the Earth's surface.
- Heat Exchanger: The hot geothermal fluid from the production well is directed into a heat exchanger, represented by a rectangular component with internal structures suggesting heat transfer. Inside the heat exchanger, the geothermal fluid transfers its heat to a secondary working fluid without mixing with it.
- Turbine: Above the heat exchanger, there is a turbine, depicted with blades inside a cylindrical housing. The secondary working fluid, now heated, expands and turns the turbine, converting thermal energy into mechanical energy.
- Generator: Connected to the turbine is a cylindrical component labeled "Generator." The mechanical energy from the turbine is converted into electrical energy by the generator.
- Injection Well: After passing through the heat exchanger, the cooled geothermal fluid is returned to the Earth through another vertical pipe labeled "Injection well," which also goes down through the rock layers.
- Load: On the right side of the diagram, the electrical energy generated is shown being used to power a light bulb, representing the "Load" or the end use of the generated electricity.
- Flow of Fluids: The flow of the geothermal fluid is indicated by arrows, showing movement from the production well, through the heat exchanger, and back into the injection well. The flow of the secondary working fluid is shown entering the turbine.
The diagram uses simple, clear lines and labels to illustrate the process of converting geothermal heat into electricity using a binary cycle system, where the geothermal fluid and the working fluid do not mix.
Geothermal Potential
Geothermal Potential azs2On a global scale, the potential for geothermal energy is quite large. The IPCC estimates that even though just a fraction of the total heat within the Earth can be used to generate geothermal power, we could nevertheless generate about 90 EJ of energy per year, and this is energy that is constantly renewed from within the Earth. Keep in mind that at present, we generate just over 2 EJ per year, so this energy source can definitely expand, but by itself it cannot meet the total global energy demand of 600 EJ.
To harness geothermal energy to generate electricity using any conventional technology (dry steam, flash steam or binary steam), you’ve got to be in the right place, where there is just the right amount of hot fluid or steam in an accessible reservoir. Unfortunately, those places are few and far between. The figure below shows a map of geothermal resources in the U.S., with identified conventional sites marked with dots on the map. All are located in just a handful of western states, plus Alaska.

This is a geothermal resource map of the United States, showing the locations of identified hydrothermal sites and the favorability of Deep Enhanced Geothermal Systems (EGS). It illustrates where geothermal energy potential is highest in the U.S., particularly in the western states, using color gradients to indicate favorability for Enhanced Geothermal Systems (EGS). It also highlights identified hydrothermal sites where underground reservoirs exceed 90°C.
Map Key & Color Coding:
- Dark Red – Most favorable areas for deep EGS.
- Orange & Yellow Shades – Areas with decreasing geothermal favorability.
- Light Yellow – Least favorable geothermal areas.
- Gray Areas – No data available.
- Black Dots – Identified hydrothermal sites (with temperatures above 90°C).
Geothermal Distribution:
- Western U.S. (California, Nevada, Idaho, Oregon, Utah, and parts of Arizona & New Mexico) has the highest geothermal favorability.
- Eastern U.S. has limited areas with geothermal potential, except for some parts of the Appalachian region.
- Alaska contains numerous identified hydrothermal sites.
Text on the Right Side of the Image:
"Map does not include shallow EGS resources, undiscovered hydrothermal resources, or geopressured resources. EGS resource favorability is based on a combination of depth, temperature, and thermal conductivity. The analysis assumes that permeability enhancement can be achieved anywhere the necessary thermal conditions exist. Identified hydrothermal sites are those with measured or estimated reservoir temperatures greater than 90°C. This map was produced by the National Renewable Energy Laboratory for the U.S. Department of Energy, October 13, 2009. Author: Billy J. Roberts."
Earth: The Operators' Manual
The state of Alaska is known more for oil and gas than for renewable energy resources, but the remote nature of many Alaskan communities calls for different energy solutions that we might use in a more connected part of the world. This video shows how some remote areas of Alaska are using locally-sourced renewable energy to power their communities, rather than relying so much on crude oil that makes up much of the state's economic bounty.
Video: Alaska: America's Renewable State? (10:53)
NARRATOR: Sometimes when Americans hear energy, the next word that comes to mind is crisis. It really doesn't have to be that way. Shirley Jackson, former head of the Nuclear Regulatory Commission, and now president of one of America's leading technical universities, thinks the United States is actually well-placed.
SHIRLEY JACKSON: Well, the U.S. is lucky because we have such a diversity of climates and diversity of geologies and, in the end, diversity of actual energy sources. And that, in fact, makes us very fortunate compared to other parts of the world. They may have a given source of energy, but they don't have the multiple sources.
NARRATOR: Alaska, like the rest of America, has been addicted to oil. Now, can abundant sustainable options make it America's renewable state? Kodiak Island, Alaska, at 3,600 square miles, is about half the size of New Jersey. Getting around almost always involves a boat, or a plane, or a float-plane that's a bit of both. Kodiak's population is less than 14,000, leaving most of the island undeveloped and natural. That beauty is one of Kodiak's economic assets, bringing tourists to watch bears raising cubs and catching fish. Kodiak's human population also catches salmon, with fish exports providing another key source of jobs and income. The island wants to limit imports of dirty and expensive fossil fuels, and tap natural resources to supply as much clean and locally generated energy as possible.
CLIFF DAVIDSON, CHAIRMAN, KODIAK ELECTRIC ASSOCIATION: Fuel prices, because we live on an island, are very expensive. You know, you learn pretty quickly that you need an alternative.
NARRATOR: Kodiak was the first place in Alaska to make wind power a substantial part of the energy mix, with its three 1.5 megawatt turbines on Pillar Mountain.
DARRON SCOTT, CEO, KODIAK ELECTRIC ASSOCIATION: So getting good quality, low-cost sustainable power is really necessary for the long-term viability of the economy of Alaska.
NARRATOR: Upgrades at the Terror Lake hydroelectric plant, plus plans for three more turbines, leave the KEA co-op confident they can hit 95 percent renewables by 2020. Though Kodiak uses diesel as a backup and during repairs, the wind turbines save the island 800,000 gallons of expensive, imported fuel each year. And this matters to the local business community.
JOHN WHIDDON, GENERAL MANAGER, ISLAND SEAFOODS: This morning, we're offloading pink salmon and red salmon, chum salmon and coho that came from the west side of Kodiak-- it keeps us busy, the plants work 24 hours a day, and it's a very, very big industry for Kodiak.
NARRATOR: This processing plant runs 100 percent on renewable energy, so Kodiak's wind power provides a clean, green marketing hook.
JOHN WHIDDON: The package says sustainable seafood, produced in Kodiak, Alaska, with wind-generated renewable energy.
DARRON SCOTT: You got some folks in the community that are really concerned about price. You know, they just want the lowest cost power at their house or at their business. The wind does that. It's less than 50 percent of the cost of power versus diesel. Then you got folks in the town that are very just, environmentally concerned. And they are incredibly excited because it's a whole lot cleaner than diesel is. And then you've got the majority of folks who want both, which is great as well.
NARRATOR: Kodiak is a genuine island, surrounded by ocean, but vast areas of interior Alaska are also islands of habitation, small communities surrounded by open country and dense forests. Many have no road access, and the only way to transport heavy fuel is via rivers like the Yukon. Bear Ketzler is city manager of Tanana, a remote and mainly native Alaskan village at the confluence of the Yukon and Tanana Rivers.
AL "BEAR" KETZLER, CITY MANAGER, TANANA: 90 percent of our bulk freight that comes in, comes by the barge.
NARRATOR: That includes diesel for the power plant and heating oil for homes. Diesel prices increased 83 percent between 2000 and 2005, and utility costs can sometimes be more than one third of a household's income.
BEAR KETZLER: The increase of energy costs, it jeopardizes everything. It jeopardizes our school, it really jeopardizes the ability for the city to function effectively.
NARRATOR: Communities like Tanana rely on the river for the fish protein that's a large part of a subsistence diet. And the river also provides a cheap and local source of energy.
BEAR KETZLER: We have abundant resources of wood, biomass. Wood that floats down the river, in the spring and the fall time.
NARRATOR: Timber is increasingly replacing oil and diesel in Tanana's communal buildings, like the washeteria, a combination laundromat, public showers and water treatment plant.
DENNIS CHARLEY, CITY OF TANANA, ALASKA: Right now, we don't even need oil, we're just running the whole place off this one wood boiler, which is just amazing.
NARRATOR: Using biomass and solar, the washeteria now uses only one quarter as much heating oil. Instead, the city pays residents to gather sustainable timber, keeping dollars in the local community. And using biomass at the washeteria has proven so cost-effective that the city is planning to install boilers in other public buildings.
BEAR KETZLER: We're going to be one of the first communities on Yukon River that is installing biomass systems on the school. In October of this year we're hoping to have that wood system online, so instead of burning 15,000 gallons of oil throughout this winter, we're hoping to burn about 60 cords of wood. And keep that money local and create a little bit of an economy here.
NARRATOR: The bottom line for Tanana-- savings for the city. Biomass is cheaper, local, cleaner and more sustainable.
BEAR KETZLER Even though we are a very rich state, very blessed to have the oil development that we do have, those days are diminishing. If we're going to make it in rural Alaska, we have to move towards renewable resources. I think we have, you know, less than 10 years to move in that area.
NARRATOR: Winter in Alaska presents extreme challenges. On this January day, it was close to minus 50. Gwen Holdmann is an engineer with the University of Alaska's Center for Energy and Power. She and her husband also raise sled dogs and both are mushers who have raced in the Iditarod. Today's run takes her past the Alaska pipeline, which has transported more than 16 billion barrels of oil since it opened in 1977. Despite the fact that Alaska is rich in fossil fuels, Gwen knows they're limited and expensive. She wants to take advantage of every opportunity to tap renewable energy.
GWEN HOLDMANN: We are an isolated part of the world, and we are still dependent very much on imports, and so becoming more self-reliant on energy is still a real goal here.
NARRATOR: Gwen was part of the team that built the first geothermal power plant in Alaska at Chena hot springs. Bernie Karl runs the Chena Resort and came up with the idea of creating an ice museum from the heat energy of the springs.
BERNIE: Now, you've heard of the Great Wall of China. This is the Great Wall of Chena. There's 800 tons of ice here.
NARRATOR: Bernie is a real American pioneer-- a showman, an entrepreneur, a tinkerer and enthusiast for recycling old machinery because it's cheaper. He and Gwen successfully transformed the hot springs into a geothermal resource that now generates power from lower temperature water than anywhere else on earth.
BERNIE KARL, OWNER, CHENA HOT SPRINGS RESORT: What you're looking at is something that's impossible. I went to the world's best manufacturer of geothermal equipment, and they said, "can't be done". The word can't is not in my vocabulary.
GWEN HOLDMANN, DIRECTOR, ALASKA CENTER FOR ENERGY AND POWER, UAF: It wasn't obvious at first that it could be done because these are low, really moderate temperatures for geothermal. The water that we're talking about here is about the same as a good hot cup of coffee and generating power from that isn't a trivial thing.
NARRATOR: Normal conditions for mid-winter Chena are 3–4 feet of snow, subzero temperatures, and only a few hours of daylight. Heating and lighting costs were staggeringly high. But now the resort runs year-round, with over 90 percent of its electricity coming from the hot springs. Bernie's latest impossible idea is to use geothermal power to make the resort self-sufficient in food even when it's minus 50 outside.
BERNIE: We have 85 kw of lights in here, high-pressure sodium. We're changing it to 8.5 kw of L.E.D.s. Now, this takes 1one tenth of the electricity.
NARRATOR: For the past 6 years, Chena has hosted a renewable energy fair. One keynote speaker was U.S. Senator Lisa Murkowski.
LISA MURKOWSKI, US SENATOR, ALASKA: I'm a Republican. Republicans by definition are seemingly more conservative. What is more conservative than harnessing what is available and around us in a long-term, sustainable way? We have more renewable opportunities here in Alaska than any other place in the world. We've got incredible river systems. We have 33,000 miles of coastline, the power of the tides, the power of the currents. We have biomass potential. &It is just beyond belief. As diverse and as big and remote and as costly as things are in Alaska, if we can demonstrate that it can be done here, think about the hope that it provides. They'll look at us and say, "Wow, if Alaska can do it, we can do this. We can take control of our energy future."
Enhanced Geothermal
Enhanced Geothermal azs2Most places do not have that right combination of an accessible, large reservoir of underground heat. Instead, reservoirs are more dispersed, in geologic formations with less permeability (this naturally inhibits the flow of hot fluid towards the surface). Engineers have discovered how to alter the subsurface to create man-made reservoirs of hot water that could be tapped to produce electricity, in either a flash steam or (with higher potential) a binary steam technology configuration. The process of engineering a geothermal reservoir underground is known as “enhanced geothermal systems” or EGS. As the resource map in Figure 2 shows, EGS could be done in a lot more places than conventional geothermal. Hundreds of thousands of gigawatts of power, basically enough to run the United States several times over, could potentially be harnessed through EGS.
Required Video/Reading:
The US Department of Energy has a nice animation outlining how EGS works: How an Enhanced Geothermal System Works. Also, check out the interactive image of the EGS on the same page to gain a deeper understanding. Note: This animation requires Flash. If you don't have Flash installed, click the link to the Text Version of the animation.
The basic idea behind EGS is to fracture hot rocks deep within the earth to create channels or networks through which water could flow. When water is injected into these networks, the heat from the rocks boils the water directly, or the now-hot water is transported to the surface where it is used to boil a working fluid, much like a binary steam plant. Fracturing of the rock occurs via “hydraulic fracturing,” under which water is injected into the rock formation at high pressures, causing the rock to fracture. This is actually very similar to the way that natural gas and oil is being extracted from shale. So we can “frack” for geothermal in much the same way that we frack for oil and gas.
Barriers to Adoption of Geothermal Power Generation
Barriers to Adoption of Geothermal Power Generation azs2Only a few countries use geothermal resources as a major source of electricity production –Iceland, El Salvador, and the Philippines all use geothermal for more than 25% of total electricity generation within those countries. New Zealand is the next (but distant) largest at 10%. Where hydrothermal resources are easy to access, they have often been utilized. The trouble is, there just aren’t that many Old Faithfuls in the world.
EGS represents the most significant potential for geothermal electricity production, but other than a few small military or pilot projects, the systems have not really caught on commercially. One of the big reasons is cost – like many low-carbon electricity technologies, EGS is inexpensive to run but very costly to build. Drilling geothermal wells is much more expensive than drilling conventional oil or gas wells, so electricity prices would probably need to increase by 25% or more (relative to current averages) to make EGS a financially viable technology.
Perhaps a more serious challenge for EGS is “induced seismicity,” which is a fancy term for causing earthquakes. EGS wells that were drilled below Basel, Switzerland caused over 10,000 small tremors (less than 3.5 on the Richter scale) within just a few days following the start of the hydraulic fracturing process. In Oregon, a test EGS well is being monitored for induced seismic activity – you can see some neat real-time earthquake data at Induced Seismicity (U.S. Department of Energy: Energy Efficiency and Renewable Energy.
Induced seismicity occurs whenever hydraulic fracturing (related to EGS or developing a natural gas well) takes place, but in most cases, the earthquakes are so small they are not felt. However, if the hydraulic fracturing occurs near pre-existing faults (which are often not visible at the surface), then larger earthquakes can and do occur, and some of these are strong enough to cause minor damage to buildings nearby.