What is geothermal energy?
It is energy recovered from heat in layers deep beneath the earth’s surface, used to generate electricity.
Geothermal systems harness the heat energy of rock formations like wind turbines harness wind energy—and convert it into mechanical energy, which in turn is converted into electrical energy.
Four main types of geothermal power plants exist:
- Dry steam power plants
- Flash steam power plants
- Hydrothermal power plants
- Enhanced geothermal system (EGS) power plants
Current state of knowledge
Deep geothermal energy in the form of steam is currently used to produce electricity in more than 50 countries (United States, Iceland, Mexico, etc.). In 2015, installed capacity totaled 12.6 GW worldwide, producing 73.5 TWh of energy.
The deep geothermal option is being developed in every corner of the planet. Worldwide installed capacity should reach 21.4 GW in 2020 through public and private investment. Various types of technology exist but a number of technical challenges remain.
In Canada, the Western Canada Sedimentary Basin is of particular interest for its geothermal energy potential. In British Columbia (Meager Creek), the Northwest Territories (Fort Liard) and Saskatchewan (DEEP project near Estevan), hydrothermal geothermal projects (using heat from naturally present hot subsurface water) are at the technical economic study stage. A study has been conducted in Alberta on the potential of deep geothermal energy. In 2016, not a single geothermal power plant had yet been built in Canada.
In Eastern Canada, recent technological progress in drilling to reach geothermal fluids, and in creating and managing geothermal reservoirs kilometres beneath the earth’s surface presage the harnessing of thermal energy at very great depths over the medium to long term.
In Québec, the potential of deep hot rock geothermal energy has been assessed. However, no exploration, demonstration or industrial operation projects have been planned for the medium or long term.
Potential of deep geothermal energy
The U.S. ranks first for electricity generation from geothermal steam. In 2015, U.S. installed capacity totaled 3.45 GW and energy production, 16.6 TWh. Installed capacity there could rise to 5.6 GW in 2020. In the Eastern U.S., deep hot rock electricity generation has an estimated potential of 500 GW, equal to the country’s total installed capacity today.
Québec’s geological environment consists of rock formations potentially thousands of metres deep. In southeastern Québec, geothermal power plants could be powered by reservoirs more than 6 or 7 km beneath the earth’s surface and covering 10% to 15% of the region’s area. The fluid at about 150°C from such reservoirs could power plants with installed capacities of 2 to 5 MW per production site.
Output and costs
Capital costs for an enhanced geothermal system (EGS), including the power plant, drilling and hydraulic stimulation, amount to at least $10,000/kW. The electricity generated would cost between 22¢ and 32¢/kWh, or even more.
Capital costs would drop to at least $6,000/kW once the technology matures. The cost of the electricity generated would then range from 10¢ to 15¢/kWh, or even more.
The efficiency of heat-to-electricity conversion is roughly 10% to 15%, depending on the temperature of the geothermal fluid and the thermodynamic cycle (power cycle) used. Over the medium to long term, however, efficiency could reach or even exceed 25% by using new geothermal fluids and higher-performance power cycles.
Advantages et disadvantages
- EGS geothermal power plants can be installed anywhere, provided drilling is deep enough to reach the desired temperature.
- Generation is predictable and continuous with a load factor exceeding 95%, better than with photovoltaic solar and wind generation, for example, and comparable to some nuclear power plants. An energy storage system is not needed.
- The energy source requires no particular treatment analogous to oil refining or uranium enrichment.
- Power plants being sited directly above the heat source, there is no need to convert and transport fuel, avoiding such hazards as oil spills.
- EGS power plants will not be cost-effective in many regions over the medium term.
- Geothermal energy is a renewable resource, the heat removed from a geothermal reservoir being naturally replenished.
- Systems have a small footprint.
- The vast majority of geothermal power plants emit few greenhouse gases and air pollutants.
- Geothermal systems, and particularly EGSs, have a small environmental footprint throughout their lifecycles.
- Groundwater and surface water contamination can be avoided by proper wastewater management during drilling and hydraulic stimulation operations.
- Water use issues arise in regions with scant water resources.
- Microseismic activity raises concerns.