Man-Made Geothermal Power: Wresting Energy from Hot Rocks--One Kilowatt at a Time [Slide Show]
The enhanced system at Soultz in France is the first such artificial geothermal power plant
![Man-Made Geothermal Power: Wresting Energy from Hot Rocks--One Kilowatt at a Time [Slide Show]](https://www.scientificamerican.com/sciam/cache/file/11D4069C-435A-403E-9A4FCA4F74D7CD6A.jpg?w=590&h=393)
Man-Made Geothermal Power: Wresting Energy from Hot Rocks--One Kilowatt at a Time [Slide Show]
- ROCKY ECONOMICS?: All told, the 1.5 megawatts of electricity cost $64.5 million (50 million euros) for research and construction, but the system could potentially produce as much as three megawatts. Electricity could be delivered to the grid for 31 cents (0.24 euro) per kilowatt-hour, according to Graff, though the project is designed to remain simply an experimental prototype. But the residual heat in the water could also be used to heat greenhouses, such as is being done in Iceland—getting more heat out of every gallon (liter) and making the energy source even more attractive. © EITAN HADDOK
- SUSTAINABLE SOURCE?: Engineer Jean-Jacques Graff, director of the site, and geologist Albert Genter, under the drilling derrick GPK2, discuss how long Soultz-sous-Forêts might produce energy. Eventually, the action of the water will cool the rock to the temperature where there will not be enough heat energy to spin turbines. But as it turns out, they actually drilled too deep; turbines can now produce electricity at temperatures as low as 248 degrees F (120 degrees C), which would have necessitated drilling only 9,840 feet (3,000 meters) down. "Even when the rock at a depth of 5,000 meters [16,400 feet] will lose its thermal capacity," Graff says, "it will still be possible to pierce the pipe higher, at around 3,000 meters, because the truth is that we went too deep in that pilot." © EITAN HADDOK
- HARSH BREW: Because the briny water is three times as concentrated as the ocean—13 ounces of salt per gallon (100 grams per liter)—and carries dissolved metals and minerals, as well, it can quickly plug the piping. So the water is filtered and salt-resistant coatings cover all the pipes and exchange systems. © EITAN HADDOK
- LAYING PIPE: At a depth of 14,763 feet (4,500 meters), the fluid—briny water found at that depth—flows through an eight-inch- (20-centimeter-) wide pipe before being released into the rock and migrating another 1,640 feet (5,000 meters) deeper. The rock there is 392 degrees F (200 degrees C) and the fluid migrates about 2,000 feet (600 meters) through it and then is sucked into the extraction pipe. Back at the top 90 minutes later, the solution is still a liquid, but is now roughly 338 degrees F (170 degrees C)—ready to transfer its heat to spin a turbine to generate electricity. This power source is available at all times, delivering a dependable supply of electricity unlike other renewables such as wind and solar. © EITAN HADDOK
- GRANITE FLOOR: The granite 16,400 feet (5,000 meters) down is roughly 392 degrees Fahrenheit (200 degrees Celsius), and has been transformed by faulting and deep hydrothermal fluids into a softer, crumbly rock susceptible to fracturing. Hydrochloric acid and water are injected to clean and reopen those fractures, says geologist Albert Genter, scientific coordinator of the project. In June 2003, injections of pressurized water produced a magnitude 2.9 earthquake, causing concern among local residents, but today acid injection has proved to avoid such negative effects. © EITAN HADDOK
- TERRA WATTS: Soultz-sous-Forêts's enhanced geothermal power plant involved drilling two pairs of boreholes down to deep, fractured rock—one from each pair in which hot fluid is extracted to deliver its calories and the others into which the cooled fluid is injected after it is used to make electricity. © EITAN HADDOK
