U.S. DEPARTMENT OF Energy Efficiency & ENERGY EDUCATION AND WORKFORCE DEVELOPMENT ENERGY Renewable Energy Geothermal Energy (Five Activities) Grades: 5-8 Topic: Geothermal Authors: Laura J. W. Butterfield, Ph.D., Brandon A. Gillette, and Richard Shin Owner: National Renewable Energy Laboratory This educational material is brought to you by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy. Geothermal Energy Laura J. W. Butterfield, Ph.D. Brandon A. Gillette Richard Shin Middle School For the Teacher many scientists and engineers, we’ve realized that only 1% of the geothermal energy contained in the uppermost ten Deep inside the Earth, at depths kilometers of the Earth’s crust is 500 near 150 kilometers, the temperature times that contained in all the oil and and pressure is sufficient to melt rock gas resources of the world! The next into magma. As it becomes less dense, step is designing technology that can the magma begins to flow toward the harness this immense, renewable, and surface. Once it breaks through the low to no - emission energy reservoir. crust it is referred to as lava. Lava is Geothermal energy can be extremely hot; up to 1,250 °C. Average usefully extracted from four different lava temperatures are about 750°C. A types of geologic formations. These normal household oven only reaches include hydrothermal, geopressurized, temperatures near 260°C (500°F)! hot dry rock, and magma. Hydrothermal reservoirs have been the most common source of geothermal energy production worldwide. They contain hot water and/or steam trapped in fractured or porous rock formations by a layer of impermeable rock on top. Hydrothermal fluids can be used directly to heat buildings, greenhouses, and swimming pools, or they can be used to produce steam for electrical power generation. The rock located just above the These power plants typically operate magma is also very hot but remains with fluid temperatures greater than solid. What if we could harness this 130oC. thermal energy and use it to generate Geopressurized resources are electricity or heat homes and from formations where moderately high businesses? We would have a temperature brines are trapped in a domestic, clean, and nearly permeable layer of rock under high inexhaustible energy supply. pressures. These brines are found Geothermal energy is one of the deeper underground than hydrothermal components of the National Energy fluids and have high concentrations of Policy: “Reliable, Affordable, and salt, minerals, and dissolved methane Environmentally Sound Energy for gas. In addition to producing steam for America’s Future”, (pg. 6-5). electrical power generation, minerals Our ancient ancestors knew can be extracted from brines and used about this free and reliable energy. as supplementary revenue for a power They bathed and prepared food in hot plant. This process is known as co­ springs and many cultures considered production. geysers and other surface geothermal Hot dry rock reservoirs are features as sacred places. Today, due generally hot impermeable rocks at to the explorations and calculations of depths shallow enough to be accessible (<3,000 m). Although hot dry rock resources are virtually unlimited in magnitude around the world, only those at shallow depths are currently economical. To extract heat from such formations, the rock must be fractured and a fluid circulation system developed. This is known as an enhanced geothermal system (EGS). The water is then heated by way of conduction as the it passes through the fractures in the rock, thus becoming a hydrothermal fluid. The final source of geothermal Hydrothermal systems also energy is magma, which is partially provide district heating. District systems molten rock. Molten rock is the largest distribute hydrothermal fluid from one global geothermal resource and is found or more geothermal wells through a at depths below 3-10km. Its great depth series of pipes to several individual and high temperature (between 700°C houses and buildings, or blocks of and 1200°C) make the resource difficult buildings. to access and harness. Thus, technology to use magma resources is not well National Science Education developed. Standards by the National Academy Geothermal power is already an of Sciences important energy resource for our nation and the world. Hydrothermal Science Content Standards: plants in the western states now provide Grades 6-8 about 2,500 megawatts of constant, Science As Inquiry reliable electricity, which meets the ¾ Content Standard A: residential power needs for a city of 6 • Abilities necessary to do million people. Over 8,000 megawatts scientific inquiry are currently being produced worldwide. • Understandings about A variety of industries, including scientific inquiry food processing, aquaculture farming, Physical Science lumber drying, and greenhouse ¾ Content Standard B: operations, now benefit from direct • Properties and changes of geothermal heating. The alligators in properties in matter the following picture are grown in • Motions and Forces geothermally heated water in Idaho. • Transfer of energy Earth and Space Science ¾ Content Standard D: • Structure of the Earth System Science and Technology Electrical resistivity surveys can show ¾ Content Standard E: how electricity flows through the rock • Abilities of technological and fluid beneath the surface and can design help determine amount of available • Understandings about hydrothermal fluid. science and technology Once a site is identified as having Science in Personal and Social geothermal potential, more exploratory Perspectives wells are drilled and more data is ¾ Content Standard F: collected and analyzed. Only after • Populations, Resources, and extensive checking and rechecking is a Environments site recommended for development as • Science and technology in one of the following energy conversion society systems. History and Nature of Science ¾ Content Standard G: Energy Conversion • Science as a human endeavor The technology used to convert • Nature of science geothermal energy into forms usable for human consumption can be categorized into four groups. The first three: dry Technology Description steam, flash steam, and binary cycle, typically use the hydrothermal fluid, Exploration and Drilling pressurized brine, or EGS resources to generate electricity. The fourth type, Many scientists, including geologists and direct use, requires only hydrothermal hydrologists, chemical and civil fluid, typically at lower temperatures, for engineers, and expert drilling direct use in heating buildings and other technicians come together to collect and structures. The addition of a small-scale analyze information on the electric heat pump into the system characteristics of a potential geothermal allows the use of low temperature resource site. Sites are evaluated based geothermal energy in residences and on three primary criteria: heat content, commercial buildings. fluid content, and permeability of the rock. Fortunately for geothermal explorers, hundreds of thousands of test holes have already been drilled all over the world by oil and gas companies. Researchers are able to use data from these deep wells to obtain information about the thermal energy in the area. These holes can also provide a way to use structural methods such as seismicity, gravity, and magnetic surveys to help determine the permeability beneath the surface. Dry Steam Power Plants Flash Steam Power Plants These were the first type of geothermal In these power plants, hydrothermal power plants to be built. The fluid at temperatures greater than 360°C technology was first used at Lardarello, is pushed to the surface by the high Italy, in 1904, and is still very effective pressure in the subsurface reservoir. As for generating electricity. The plant this very hot fluid reaches the surface, it uses steam that is accessed by drilling enters the separator where the pressure directly into the underground source. drops instantaneously and most of the The steam is piped through a turbine liquid flashes into steam. The force and generator unit, and then condensed generated by the steam is used to drive back into water and injected back into turbines and produce electricity. The the subsurface reservoir. This helps to fluid not flashed into steam leaves the extend the life of the system. Steam separator and rejoins the water from technology is used today at The Geysers the condenser. The fluid is then in northern California, the world's injected back largest single source of geothermal into the Earth power. The emissions from this group of so that the plants consist process can be of excess renewed over steam and and over very small again. An amounts of example of an area using a flash steam sulfur dioxide, operation is the CalEnergy Navy I flash hydrogen geothermal power plant at the Coso sulfide, and carbon dioxide. Because geothermal field. there is no combustion taking place, the levels of these gasses are much lower than emissions from fossil fuel fired power plants. Binary Power Plants geothermal field. Because warm hydrothermal fluid is a more widespread resource than hot fluid or pressurized brines, binary systems have the potential to make a significant contribution to the overall production of geothermally generated electricity. Direct use of hot water from geothermal resources can be used to provide heat for industrial processes, crop drying, or heating buildings. In These are different from dry steam or this method, the hot fluid is pumped flash steam power plants in that the directly into a hydrothermal fluid from the subsurface building’s hot reservoir never comes into contact with water-based the turbine/generator units. In this two- heating system, step process, hydrothermal fluid that is under sidewalks, or not quite hot enough to be used in a into pools. The city flash steam plant is fed into a heat of Klamath Falls, exchanger. Here, heat is transferred Oregon, is located from the hydrothermal fluid to a in an area of “working liquid” with a lower boiling abundant near-surface hydrothermal point than water (usually isobutane or fluid at the southern part of the Cascade isopentane).