What Is Geothermal?
You may have asked…
Geothermal Power Plant
What is Geothermal Energy?
In its simplest terms, geothermal means earth-heat. It is related to the thermal energy of Earth’s interior. On a large scale, the intensity of this thermal energy increases with depth, that is, the temperature of the Earth increases as we travel closer to its centre. A global average for Earth’s geothermal gradient (temperature increase with depth) is approximately 30°C/km. For example, if we merely removed the outer 3 km of Earth’s outer surface, it would be a sphere 5000°C at the core, and nearly hot enough to boil water on its surface. Earth contains an incredibly vast amount of thermal energy.
Where Does Geothermal Energy Come From?
Geothermal energy has two primary sources, primordial heat, and radioactive decay. Primordial heat is what resulted from the creation of Earth 4.5 billion years ago, when the energy and mass from colliding cosmic matter made Earth a large, hot piece of space debris. As Earth’s outside cooled, it then acted as an insulator for the heat in the middle, which is why Earth is still cool and hospitable on the outside, and hot-rock and metal at its core.
© 2000 Geothermal Education Office
Some of the elements that were part of Earth’s original composition were radioactive. As those radioactive elements continue to decay below us (very slowly), they generate additional thermal energy and heat the Earth’s interior.
Of course, some of the heat still seeps through the ‘insulation’, the evidence of this is volcanic features like those in Hawaii, New Zealand, Japan and Italy.
How Can We Use Geothermal Energy?
A vast majority of the world’s power production involves the use of hot water. Sources like nuclear, coal and natural gas harness different processes (i.e. radioactive decay, combustion) to heat water into steam, which is run through a turbine to generate electricity. Geothermal energy uses the escaping heat from Earth’s core as a means to heat water and produce electricity. By drilling deep into the Earth’s interior, we find temperatures suitably high to produce electricity.
Sometimes when we drill deep, there is hot water where the rock is porous (has space for fluids). In this case, we can extract the water from depth and through specialized equipment, use it to produce electricity (explained further on). If there is no water, but the rocks are very hot where we drill, it is possible to inject water to create an enhanced geothermal system (EGS) and hot water where it did not exist before. By using Earth’s thermal energy to heat water instead of processes with harmful by-products like coal and nuclear, geothermal energy can produce clean, reliable electricity as long as heat continues to seep from Earth’s interior (as it has for 4.5 billion years). Further, it is sustainable power because once we have extracted the thermal energy from the water or steam, it can be continuously re-injected deep underground to obtain more geothermal heat.
Aside from producing power, we also use hot, geothermal water for heating pools (i.e. hot springs), district heating, agriculture and laundries, to name a few. This is called direct-use geothermal because the heat is used directly from the water to serve a function.
How is Electricity Produced from Geothermal Heat?
There are two commonly used processes when creating electricity from geothermal sources. The first, flash geothermal, is generally associated with higher temperature geothermal sources ( >180°C). Because the pressure of the subsurface environment is much greater than at the Earth’s surface, water can exist as a liquid at very high temperatures. The high temperature, high pressure water is brought to surface, where it is enters a low pressure chamber and ‘flashes’ into steam. The pressure created by this steam is channeled through a turbine, which spins to generate electrical power. Once the steam has exited the turbine, it is either released into the atmosphere as water vapor, or it cools back into liquid water and is injected back underground.
© 2000 Geothermal Education Office
The second common method, binary geothermal, is common with lower temperature geothermal resources. It operates on the same principle that when a liquid is heated into a vapor, the resulting pressure can drive a turbine. However, because the temperatures are often too low to ‘flash’ water in a binary system, we must transfer the heat of water to a separate liquid with a lower boiling temperature. The separate liquid is called a ‘working fluid’. When the hot geothermal water is brought to surface from deep underground, it is run through a ‘heat exchanger’ which transfers the heat from the geothermal water to the liquid working fluid. Because the working fluid boils at a low temperature, it vaporizes readily with less geothermal heat, and this vaporization produces enough pressure to drive a turbine. What makes a binary system unique is that it operates as a 2 closed-loops (hence, binary); neither the geothermal water nor the working fluid are exposed to the surface environment. All the water that is brought to surface is re-injected, and after vaporizing, the working fluid is cooled to its liquid state, so it may repeat the process. There are no-emissions in the binary geothermal cycle.
© 2000 Geothermal Education Office
Why Aren’t We Using Geothermal Power Now?
Many countries including the United States, Mexico, Japan, Iceland and The Philippines are already taking advantage of their geothermal resources for electricity production. It is true that anywhere in world, at some depth below your feet exists enough geothermal heat to use for geothermal power. However, to reach that depth we must drill, and drilling costs increase exponentially with depth. At our present level of drilling technology, we are able to harness the highest quality geothermal resources, which are those located closest to Earth’s surface
Ring of Fire
The distribution of the highest quality geothermal resources is generally limited to locations with a high level of tectonic activity, where the Earth’s tectonic plates are interacting. You may have heard of the ‘Ring of Fire’ which circles the pacific ocean; a lot of tectonic activity occurs along this ring, and the geologic conditions of this activity permit large amounts of heat to rise to Earth’s surface (which occasionally results in volcanism). Therefore, there are a limited amount of countries that can use geothermal power extensively given the current level of technology. However, research continues into how we can reduce the expense of drilling and improve the efficiency of geothermal power plants, both which will allow more areas to take advantage of this outstanding resource.
In spite of their proven geothermal resources, some countries lag behind others in geothermal power production for political reasons. In their infancy, most renewable energy markets require government support, through policy and funding, to reach critical-mass and compete competitively on price. For nearly 25 years, geothermal science has not been funded by the Canadian Federal Government. Our limited data proves that Western Canada has extensive geothermal potential. Technology has improved considerably since the government last looked at geothermal power.
What is missing?
Spread your new awareness with your friends, family and colleagues that care about a sustainable energy future and become a member of CanGEA! Every new member brings us one voice closer to geothermal power in Canada! Please visit our links page for more resources on geothermal energy and thanks for thawing the freeze on geothermal energy!
Low Temperature (Heat Pumps) versus High Temperature Geothermal Resources
Recent public interest in geothermal energy has led to some confusion on the different forms of geothermal energy that are related to different types of geothermal resources.
A complicating factor is that different people use different terms to describe essentially the same thing. Traditionally, geothermal energy was related to high temperature resources that are needed for power generation and direct heating. However, the value of lower temperature resources for recreational use and GeoExchange has broadened the definition of geothermal energy.
GeoExchange is the industry’s term used to describe an alternative to traditional oil- gas- or coal-fired heating, ventilation and air conditioning (HVAC) systems. The idea is to take advantage of the ground’s heating and cooling properties (the same properties that make any basement cooler in the summer and warmer in the winter) to heat or cool entire buildings. This heat ‘exchange’ between the ground and the building is accomplished by using standard pump and compressor technology. Geoexchange systems have also been referred to as earth energy systems, or geothermal heat pump systems.
In recognition that geothermal energy has a spectrum of energy resources, CanGEA has recently signed a Memorandum of Understanding (MOU) with the Canadian GeoExchange Coalition. Our mutual goal is to encourage cooperation programs in the field of geothermal energy and geothermal heat pump technology.
The Natural Resources Canada (NRCan) also has more information about the different types of geothermal energy, visit http://www.canren.gc.ca/tech_appl/index.asp?CaID=3