Geothermal Energy (5 Activities)

U.S. DEPARTMENT OFENERGYEnergy Efficiency &Renewable EnergyENERGY EDUCATION AND WORKFORCE DEVELOPMENTGeothermal Energy(Five Activities)Grades: 5-8Topic: GeothermalAuthors: Laura J. W. Butterfield, Ph.D., Brandon A. Gillette,and Richard ShinOwner: National Renewable Energy LaboratoryThis educational material is brought to you by the U.S. Department of Energy’sOffice of Energy Efficiency and Renewable Energy.

Geothermal EnergyLaura J. W. Butterfield, Ph.D.Brandon A. GilletteRichard ShinMiddle School

For the TeacherDeep inside the Earth, at depthsnear 150 kilometers, the temperatureand pressure is sufficient to melt rockinto magma. As it becomes less dense,the magma begins to flow toward thesurface. Once it breaks through thecrust it is referred to as lava. Lava isextremely hot; up to 1,250 C. Averagelava temperatures are about 750 C. Anormal household oven only reachestemperatures near 260 C (500 F)!The rock located just above themagma is also very hot but remainssolid. What if we could harness thisthermal energy and use it to generateelectricity or heat homes andbusinesses? We would have adomestic, clean, and nearlyinexhaustible energy supply.Geothermal energy is one of thecomponents of the National EnergyPolicy: “Reliable, Affordable, andEnvironmentally Sound Energy forAmerica’s Future”, (pg. 6-5).Our ancient ancestors knewabout this free and reliable energy.They bathed and prepared food in hotsprings and many cultures consideredgeysers and other surface geothermalfeatures as sacred places. Today, dueto the explorations and calculations ofmany scientists and engineers, we’verealized that only 1% of the geothermalenergy contained in the uppermost tenkilometers of the Earth’s crust is 500times that contained in all the oil andgas resources of the world! The nextstep is designing technology that canharness this immense, renewable, andlow to no - emission energy reservoir.Geothermal energy can beusefully extracted from four differenttypes of geologic formations. Theseinclude hydrothermal, geopressurized,hot dry rock, and magma.Hydrothermal reservoirs havebeen the most common source ofgeothermal energy productionworldwide. They contain hot waterand/or steam trapped in fractured orporous rock formations by a layer ofimpermeable rock on top. Hydrothermalfluids can be used directly to heatbuildings, greenhouses, and swimmingpools, or they can be used to producesteam for electrical power generation.These power plants typically operatewith fluid temperatures greater than130oC.Geopressurized resources arefrom formations where moderately hightemperature brines are trapped in apermeable layer of rock under highpressures. These brines are founddeeper underground than hydrothermalfluids and have high concentrations ofsalt, minerals, and dissolved methanegas. In addition to producing steam forelectrical power generation, mineralscan be extracted from brines and usedas supplementary revenue for a powerplant. This process is known as co production.Hot dry rock reservoirs aregenerally hot impermeable rocks atdepths shallow enough to be accessible

( 3,000 m). Although hot dry rockresources are virtually unlimited inmagnitude around the world, only thoseat shallow depths are currentlyeconomical. To extract heat from suchformations, the rock must be fracturedand a fluid circulation system developed.This is known as an enhancedgeothermal system (EGS). The water isthen heated by way of conduction asthe it passes through the fractures inthe rock, thus becoming a hydrothermalfluid.The final source of geothermalenergy is magma, which is partiallymolten rock. Molten rock is the largestglobal geothermal resource and is foundat depths below 3-10km. Its great depthand high temperature (between 700 Cand 1200 C) make the resource difficultto access and harness. Thus, technologyto use magma resources is not welldeveloped.Geothermal power is already animportant energy resource for ournation and the world. Hydrothermalplants in the western states now provideabout 2,500 megawatts of constant,reliable electricity, which meets theresidential power needs for a city of 6million people. Over 8,000 megawattsare currently being produced worldwide.A variety of industries, includingfood processing, aquaculture farming,lumber drying, and greenhouseoperations, now benefit from directgeothermal heating. The alligators inthe following picture are grown ingeothermally heated water in Idaho.Hydrothermal systems alsoprovide district heating. District systemsdistribute hydrothermal fluid from oneor more geothermal wells through aseries of pipes to several individualhouses and buildings, or blocks ofbuildings.National Science EducationStandards by the National Academyof SciencesScience Content Standards:Grades 6-8Science As Inquiry¾ Content Standard A: Abilities necessary to doscientific inquiry Understandings aboutscientific inquiryPhysical Science¾ Content Standard B: Properties and changes ofproperties in matter Motions and Forces Transfer of energyEarth and Space Science¾ Content Standard D: Structure of the EarthSystem

Science and Technology¾ Content Standard E: Abilities of technologicaldesign Understandings aboutscience and technologyScience in Personal and SocialPerspectives¾ Content Standard F: Populations, Resources, andEnvironments Science and technology insocietyHistory and Nature of Science¾ Content Standard G: Science as a humanendeavor Nature of scienceTechnology DescriptionExploration and DrillingMany scientists, including geologists andhydrologists, chemical and civilengineers, and expert drillingtechnicians come together to collect andanalyze information on thecharacteristics of a potential geothermalresource site. Sites are evaluated basedon three primary criteria: heat content,fluid content, and permeability of therock.Fortunately for geothermalexplorers, hundreds of thousands of testholes have already been drilled all overthe world by oil and gas companies.Researchers are able to use data fromthese deep wells to obtain informationabout the thermal energy in the area.These holes can also provide a way touse structural methods such asseismicity, gravity, and magneticsurveys to help determine thepermeability beneath the surface.Electrical resistivity surveys can showhow electricity flows through the rockand fluid beneath the surface and canhelp determine amount of availablehydrothermal fluid.Once a site is identified as havinggeothermal potential, more exploratorywells are drilled and more data iscollected and analyzed. Only afterextensive checking and rechecking is asite recommended for development asone of the following energy conversionsystems.Energy ConversionThe technology used to convertgeothermal energy into forms usable forhuman consumption can be categorizedinto four groups. The first three: drysteam, flash steam, and binary cycle,typically use the hydrothermal fluid,pressurized brine, or EGS resources togenerate electricity. The fourth type,direct use, requires only hydrothermalfluid, typically at lower temperatures, fordirect use in heating buildings and otherstructures. The addition of a small-scaleelectric heat pump into the systemallows the use of low temperaturegeothermal energy in residences andcommercial buildings.

Dry Steam Power PlantsFlash Steam Power PlantsThese were the first type of geothermalpower plants to be built. Thetechnology was first used at Lardarello,Italy, in 1904, and is still very effectivefor generating electricity. The plantuses steam that is accessed by drillingdirectly into the underground source.The steam is piped through a turbineand generator unit, and then condensedback into water and injected back intothe subsurface reservoir. This helps toextend the life of the system. Steamtechnology is used today at The Geysersin northern California, the world'slargest single source of geothermalpower. The emissions from this group ofplants consistof excesssteam andvery smallamounts ofsulfur dioxide,hydrogensulfide, and carbon dioxide. Becausethere is no combustion taking place, thelevels of these gasses are much lowerthan emissions from fossil fuel firedpower plants.In these power plants, hydrothermalfluid at temperatures greater than 360 Cis pushed to the surface by the highpressure in the subsurface reservoir. Asthis very hot fluid reaches the surface, itenters the separator where the pressuredrops instantaneously and most of theliquid flashes into steam. The forcegenerated by the steam is used to driveturbines and produce electricity. Thefluid not flashed into steam leaves theseparator and rejoins the water fromthe condenser. The fluid is theninjected backinto the Earthso that theprocess can berenewed overand overagain. Anexample of an area using a flash steamoperation is the CalEnergy Navy I flashgeothermal power plant at the Cosogeothermal field.

Binary Power PlantsThese are different from dry steam orflash steam power plants in that thehydrothermal fluid from the subsurfacereservoir never comes into contact withthe turbine/generator units. In this twostep process, hydrothermal fluid that isnot quite hot enough to be used in aflash steam plant is fed into a heatexchanger. Here, heat is transferredfrom the hydrothermal fluid to a“working liquid” with a lower boilingpoint than water (usually isobutane orisopentane). The working liquid turnsinto an energized vapor much like thesteam in the flash power plant and turnsthe turbine/generator unit, producingelectricity. The hydrothermal fluid andthe working liquid are both contained in“closed loops” and never come incontact with each another. The vaporfrom the working liquid is condensedand the hydrothermal fluid is returnedto the earth. This cycle can be repeatedas quickly as the Earth can reheat thefluid. An example of an area using aBinary Cycle power generation system isthe Mammoth Pacific binary geothermalpower plants at the Casa Diablogeothermalfield. Becausewarmhydrothermalfluid is a morewidespreadresource thanhot fluid or pressurized brines, binarysystems have the potential to make asignificant contribution to the overallproduction of geothermally generatedelectricity.Direct use of hot water fromgeothermal resources can be used toprovide heat for industrial processes,crop drying, or heating buildings. Inthis method, the hot fluid is pumpeddirectly into abuilding’s hotwater-basedheating system,under sidewalks, orinto pools. The cityof Klamath Falls,Oregon, is locatedin an area ofabundant near-surface hydrothermalfluid at the southern part of the CascadeRange. The Oregon Institute ofTechnology is actually heated by thisdirect-use system. Sidewalks in thearea have tubes buried beneath them soas to prevent the buildup of snow andice in the winter. Other examples ofdirect use geothermal resources existacross the entire western United Statesincluding the Capitol Mall in Boise,Idaho. Here, the city’s geothermaldistrict heating system heats even theIdaho State Capitol Building.Geothermal water is also used by localindustries in greenhouses, at fish farms,and by dairies.