you may have relaxed in a natural hot springs pool or seen the old faithful geyser blasting hot water into the air in yellowstone national park but have you ever thought of where all that heat comes from well it comes from deep beneath the surface of the earth and it's called geothermal energy and we can use it to generate clean renewable electricity okay here's how geothermal works heat from the earth's crust warms water that is seeped into underground reservoirs in some places when water becomes hot enough it can break through the earth's surface as steam or hot water this usually happens where the earth's crust or plates meet and shift in the past taking advantage of geothermal energy was limited to areas where hot water flowed near the surface but as geothermal technologies advance we can leverage even more of these natural renewable energy sources engineers have developed a few different ways to produce power from geothermal wells drilled into the ground have a look at this it's a dry steam geothermal power plant and it's the most common type of geothermal technology used today underground steam flows directly to a turbine to drive a generator that produces electricity pretty straightforward another geothermal technology is called a flash steam power plant a pump pushes hot fluid into a tank at the surface where it cools as it cools the fluid flashes or quickly turns into vapor the vapor then drives a turbine and powers a generator a binary cycle plant works differently it uses two types of fluid hot fluid from underground heats a second fluid called a heat transfer fluid in a giant heat exchanger the second fluid has a much lower boiling point than the first fluid and so it flashes into vapor at a lower temperature when the second fluid flashes it spins a turbine that drives a generator the environmental benefits of this clean round-the-clock renewable energy source are substantial low emissions small physical footprint and minimal environmental impact the few byproducts that can come up are often re-injected underground geothermal energy can also help recycle wastewater in california wastewater from the city of santa rosa is injected into the ground to generate more geothermal energy some plants do produce solid waste but that solid waste may contain minerals that we can remove and sell which lowers the cost of this energy source the us geological survey estimates that untapped geothermal resources in the united states if developed could supply the equivalent of 10 percent of today's energy needs and cut our dependence on fossil fuels in fact electricity generated by geothermal energy already provides about 60 percent of the power along the northern california coast from the golden gate bridge to the oregon state line geothermal energy helping to push america toward energy independence and a clean renewable way to meet our growing energy demands you