Geothermal energy is a clean source of reliable electricity and large scale direct use of the hot water derived from the earth that can help solve some of Canada’s greatest challenges, namely providing energy security, economic growth and reducing our CO2 emission
Geo-Exchange vs. Geothermal Energy
Most people think that geothermal means heat pumps and residential heating and cooling- that’s not what we’re talking about, that’s called geo-exchange. The difference is temperature moderator (geo-exchange) vs. a positive thermal source (geothermal). The illustration on the left is a geothermal power plant, whereas the illustration on the rights is a geo-exchange heat pump.
So what is it?
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 5,000°C at the core, and nearly hot enough to boil water on its surface. Earth contains an incredibly vast amount of thermal energy. This heat is used in a geothermal power plant to drive a steam turbine, which creates electricity. Any leftover heat can also be used in a variety of industrial heating applications.
Where does geothermal energy come from?
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.
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.
What is the direct utilization of geothermal heat?
The direct utilization of geothermal heat consists of various forms of heating and cooling to serve practical production and operation uses on an industrial scale. The advantage to pursuing a direct use project are the lower temperature requirements. Many direct use applications only require low to moderate temperature resources (40-150°C). These resources are more widespread than high temperature resources, making them more accessible throughout Canada. Some examples of direct use applications are listed below: