The surface has only just been scratched when it comes to harnessing the full potential of geothermal energy. By tapping into the thermal energy resources that are found stored away in the rock and fluid beneath the earth’s surface, electricity can be generated and ideal building temperatures can be achieved, in an affordable and sustainable manner.
Geothermal energy can be used in a multitude of ways. Found in both residential and commercial applications, geothermal energy can be used for much more than simply heating and cooling. Geothermal energy has a great deal of potential and can provide a sustainable, cost-effective alternative to fossil fuels while meeting the world’s future energy needs.
Geothermal water can be found in reservoirs below the earth’s surface and provides a direct source of geothermal energy as a heat source for homes, buildings, and greenhouses. It can be used for drying crops, de-icing roads, and improving oil recovery processes, as well as serving other agricultural and industrial processes.
Geothermal energy has been utilized for thousands of years for bathing and cooking, but its full potential has not been actualized, though applications have become far more advanced. Existing technology only allows for the recovery of geothermal energy from shallow ground levels, while resources at further depths remain untapped.
Clean, sustainable geothermal energy is found at three levels below the earth’s surface: shallow ground; miles below the surface; and at depths where molten magma can be found. The amount of energy being produced by the magma 33 000 feet below the surface contains 50 000 times more energy than all of the world’s oil and gas reserves combined. The shallow ground, up to ten feet below the surface, is characterized by relatively consistent temperatures that range from 50 to 60 degrees Fahrenheit. In the winter, the ground temperature is warmer than the air above ground and in the summer it is cooler, the very principle upon which the technology associated with geothermal heating and cooling is based.
Geothermal heat pumps harness the geothermal resource to heat and cool buildings, providing a hot water source and a low-cost, sustainable alternative to fossil fuel powered sources. The energy contained in the ground beneath the average building is 300 times greater than that required to heat the average building, saving money and energy while reducing emissions. The U.S. Department of Energy estimates that a typical home can save hundreds of dollars in energy costs each year by taking advantage of geothermal heat pumps; these systems are likely to pay for themselves in eight to twelve years. Paired with available tax credits and incentives, it is increasingly affordable to install new, or retrofit homes with, geothermal units.
According to the U.S. Energy Information Administration’s (EIA) 2014 Annual Energy Outlook, over 600 000 ground-source heat pumps are in use in homes and other buildings in the U.S. New installations are occurring at a rate of 60 000 per year. This represents only a small percentage of the U.S. energy market.
Geothermal or ground-source heat pumps are the most conventional method of utilizing geothermal energy for heating and cooling. Geothermal heat pumps are composed of three main components: the ground heat exchanger which consists of a system of pipes called a loop that is buried in the shallow ground and serves as the heat exchange medium; the heat pump unit; and the air delivery system.
In the winter, the heat pump draws air from the ground which passes through the heat exchanger and circulates through the air delivery system or ductwork to heat a building. In the summer, the process is reversed, with the heat pump taking hot air from inside the building and displacing that heat in the buried loop which acts as a heat sink, where the heat is absorbed in the cooler ground temperatures.
Water, or a mixture of water and antifreeze, circulates through the loop system which can be designed vertically or horizontally, open or closed. If an aquifer is available, engineers can develop an open loop, as opposed to a closed loop system, which circulates underground water through the unit, past the heat exchanger to heat or cool, then reinjects the water back into the aquifer, resulting in no emissions.
As a cost-effective and sustainable heating and cooling option, geothermal systems operate quietly and efficiently and require minimal maintenance. As the system operates indoors and underground, it is not subject to inclement weather and will enjoy a longer lifespan as a result. As geothermal systems have advanced, they require less space and can be incorporated into both rural and urban applications.
Geothermal springs, naturally occurring hydrothermal connection systems, are another common method of geothermal energy capture. This occurs when water of a cooler temperature penetrates the earth’s crust, becomes heated and rises to the earth’s surface, creating steam. Once captured, the steam can be used to generate electricity.
Geothermal power plants take advantage of hot water and steam resources in the ground to generate the electricity required for power generation. Natural ground sources of water and steam serve as an alternative to fossil fuels which would be used otherwise to boil water to create the steam necessary to power operations.
Geothermal power plants come in three basic designs: dry steam; flash steam; and binary cycle. Dry steam power plants utilize steam, piping that resource from underground wells to the power plant where it powers a turbine. Steam powered plants can be found in northern California where they are taking advantage of the area’s naturally occurring geysers.
The most common of the three basic designs of geothermal power plants, the flash steam plant uses geothermal water reservoirs and the resulting steam to power turbines or generators. Drawing from the heat of the water which exceeds 360 degrees Fahrenheit, water and steam are separated as they pass through underground wells, while any excess water is reinjected to create a sustainable system.
The third basic design of geothermal power plants, the binary cycle system, utilizes water with lower temperatures, 225 to 360 degrees Fahrenheit, using the water’s heat to boil a working fluid or organic compound with a low boiling point. The working fluid is vaporized in the heat exchanger and used to power a turbine, with any excess water being reinjected into the ground for reheating.
Localities, regions, states, and countries are increasingly recognizing the potential and value of geothermal resources. Many residential and commercial applications are taking advantage of these affordable and sustainable alternatives to reduce reliance on fossil fuels, and to mitigate the associated environmental and social risks. The Geothermal Energy Association (GEA) reported that by 2013 more than 11 700 megawatts of large, utility scale geothermal operations were ongoing globally, a capacity that was expected to double in the coming years. These facilities have the capacity to produce 68 billion kilowatt-hours of electricity, the equivalent required to meet the needs of over 6 million U.S. households.
The U.S. is a leader in geothermal energy capacity, with more than 3 300 megawatts of capacity located in eight states, the majority coming from California. Geothermal energy shows great potential for the U.S. energy market as it provides a cleaner, more sustainable alternative for energy production that addresses changing economic and environmental policies and regulations.
In Canada, geothermal energy could address some of the country’s greatest challenges. Geothermal energy offers great opportunity when considering emissions reduction targets, energy security, economic diversity, job creation, and the development of northern and remote communities by providing localized electricity, heat, and increased food security through agricultural applications.
Geothermal energy could also serve to offset emissions when used in co-production in other industries, most specifically the oil and gas sector. There is an estimated 5 000 megawatts of shallow ground resources available, which has the capacity to displace coal fired power, offsetting 25 megatonnes of CO₂ emission each year as a result.
The development of these resources could effectively create 8 500 operations and maintenance jobs, in addition to 20 000 part time construction jobs. There is also an estimated 10 000 megawatts of energy available in deeper subterranean levels, resources that require further technological advancement to harness their full potential.
Technological developments such as Enhanced Geothermal Systems (EGS) and the co-production of geothermal energy in the oil and gas industry are ways in which the full potential of geothermal resources can be actualized. Though geothermal heat can be found everywhere beneath the earth’s surface, the conditions that circulate water to the surface are not as common. EGS attempts to capture heat from dry areas and hot rock reservoirs that are located at greater depths. High-pressure water is used to break up hot rock reservoirs and as water is pumped through, it naturally rises to the surface, heats up, and becomes steam that is captured to generate power.
Significant investments and research are supporting the development of EGS and co-production activities, with EGS steps away from large-scale commercial application. One risk associated with EGS is seismic activity, similar to the risks associated with hydraulic fracturing. These impacts can be lessened through careful site selection, stringent monitoring and site assessment activities.
Co-production of geothermal energy in oil and gas wells can take advantage of existing reservoirs where high-temperature water and geothermal energy is located. Research conducted by MIT indicates that the U.S. has the potential for 44 000 megawatts of geothermal capacity to be developed by 2050 through the co-production of geothermal energy in oil and gas wells. What has been regarded as an inconvenience by companies who are operating in these oil and gas fields, an average of 25 billion barrels of hot water is produced at these sites each year, and could be utilized to generate upwards of 3 gigawatts of energy. Co-production could improve profitability and environmental performance in the oil and gas industry, at a time when it needs it the most.
Binary cycle systems, when used in conjunction with wind and solar power generation, offer a flexible alternative to coal and nuclear power, serving as a means of balancing production when necessary. Binary cycle systems can ramp production up and down to balance variable supplies from other alternative energy sources, further contributing to energy security and sustainability moving forward.
There is a commitment from homeowners and governments to take advantage of this clean, affordable, and sustainable resource to heat, cool, and power buildings across the world. Geothermal energy has the capacity to power the future and with advances in technology it will be possible to harness geothermal energy’s full potential while maximizing its multiple benefits on a global scale.