California Geothermal Comes Up Dry
One of the more attractive forms of green renewable energy is geothermal—harnessing the natural heat of Earth's interior to provide warmth and electricity. Unfortunately, geothermal is really only viable in limited areas around the globe, due to crust thickness and strata type. One of those fortunate places is the American Southwest, the eastern part of California and the states of Nevada, Arizona, New Mexico and Colorado. The sixteen geothermal plants already present in California's the Imperial Valley are among the first signs of what California hopes will become a renewable-energy boom. But without water these plants cannot generate any power, and their water comes from far away—from the already stressed Colorado river.
As reported in The Energy Gap, geothermal energy supplies more than 10,000 megawatts (MW) to 24 countries worldwide, producing enough reliable electricity to meet the needs of 60 million people. The Republic of the Philippines generates 23% of its electricity from geothermal energy and is the world’s second biggest producer behind the US. Geothermal energy can preserve the environment in developing countries while providing stable power for homes, industry and national energy independence. It has helped developing countries such as Indonesia, Mexico, Guatemala, Costa Rica, and the Philippines.
In other countries, the prospects of geothermal energy exploitation are varied. Australia has discovered that its vast interior overlays a huge hot rock deposit, which could supply green energy in the future. In Africa, some experts think the Rift Valley, which stretches from the northern end of the Red Sea down to Mozambique, is ideal for generating geothermal power. The United Nations Environment Programme, headquartered in the Kenyan capital, Nairobi, thinks the geothermal potential of the Rift Valley is 14,000 MW, yet to date only 200 MW actually is captured. Geothermal power enthusiasts say it could provide 10-25% of the region’s energy by 2030.
The US continues to produce more geothermal electricity than any other country, comprising approximately 30% of the world total. Availability of geothermal energy in the US is largely confined to the southwestern and Rocky Mountain parts of the country, as can be seen from the map below.
Rock temperatures at a depth of 6 kilometers (3.7 miles). Source GIA.
In 2007, geothermal was the fourth largest source of renewable energy in the United States. Today the US has about 3,000 MW of geothermal electricity connected to the grid. Geothermal energy generated 14,885 gigawatt-hours of electricity in 2007, which accounted for 4% of renewable energy-based electricity consumption in the US. What is even better is that geothermal is baseload generation, it puts out steady power 24x7.
In California, the state with the largest amount of geothermal power on-line, electricity from geothermal resources accounted for 5% of the state’s electricity generation in 2003 on a per kilowatt hour basis. Geothermal is the largest non-hydro renewable energy source in the state, significantly exceeding wind and solar power combined.
Researchers from the U.S. Department of Energy’s National Renewable Energy Laboratory estimate that fully exploiting a fault line beneath the Imperial Valley's Salton Sea would supply around 2,300 MW of power, the equivalent of a big nuclear power plant. For a number of reasons, the plants cannot just take water out of the sea, but instead must tap into the same source of water that makes the Imperial Valley one of the most productive agricultural areas in the world.
The Imperial Valley’s geothermal plants use deep wells to tap into superheated rocks thousands of meters below the ground. Some of the plants use a process called flashing, in which the hot, pressurized brine that is already present in the rock is extracted. Once brought to the surface, the pressure change causes some of the hot brine to turn to steam, which then drives turbines to generate electricity.
A geothermal flashing plant.
Flashing plants need relatively little cooling water, but flashing works only if the plant sits directly over the hottest part of the geothermal field, which in this case is right on the shores of the Salton Sea. To fully harness the region’s geothermal potential, a different type of plant, called a binary cycle plant, must be used.
In a binary cycle power plant, the heat from geothermal water is used to vaporize a “working fluid.” The vapor then powers a turbine generator. Because binary cycle plants can produce energy at lower temperatures, they can be built almost anywhere in the valley.
Still, for efficient operation, this requires the circulation of water down an injection well, through deep (2 to 5 km) hot rocks with temperatures typically around 200°C. In order to allow the flow of water, tiny fractures are engineered creating an underground heat exchanger. As the water passes through the heat exchanger, it is rapidly heated to a high temperature by contact with the hot rock. The superheated water is then returned via a production well to surface where the heat energy is converted to electricity.
For more than 100 years, California has depended on water shipped from the other side of the Rocky Mountains. To operate, the new geothermal plants require water from the same source that irrigates crops in the Imperial Valley and eventually provides water to the thirsty residents of Los Angeles: the Colorado river.
The waters of the Colorado are governed by agreements collectively known as the Law of the River, which divides up the rights to the water among seven states. The main provisions, set into law in 1922, have never been updated to reflect the region’s rapid growth. The problem now faced by the residents of the American Southwest is one of simple supply and demand—too little of the former and too much of the latter.
Add to this reports that a number of scientists expect climate change to further reduce the river's flow in the future. As reported by IEEE Spectrum, in an article entitled “In the American Southwest, the Energy Problem Is Water,” Tim Barnett and David Pierce, researchers at Scripps Institution of Oceanography, say that competing demands on the water supply will reach a critical point by 2021. “Water deliveries will have to be cut even beyond the most draconian measures,” says Barnett. It looks like the green energy revolution is going to die from thirst before it even gets started. But the impact doesn't end with geothermal power generation.
The Colorado is also a huge source of hydroelectric power that supplies the Southwest with much of its energy. Beyond the energy that comes directly in the form of hydropower, the river's waters are also essential for the operation of thermoelectric power plants, which rely on it for cooling. “The more energy people need, the more water you need for power plants,” says Mike Hightower, an engineer at Sandia National Laboratories.
A Dam Mess
When Hoover Dam was finished in 1936, it was the largest dam in the world and a modern marvel. Still an impressive structure, the Dam is a National Historic Landmark and has been rated as one of America's Seven Modern Civil Engineering Wonders by the American Society of Civil Engineers. It tamed the wild river and created a tranquil reservoir—Lake Mead. Lake Mead doesn't just provide water for Hoover Dam's generators, its reservoir supplies 90% of Las Vegas’s water.
The lake is 1200 feet (372 meters) deep when full, but that level hasn’t been seen in 10 years. Since 1999, Lake Mead has dropped about 1% a year. Today Lake Mead's retreating water line has exposed a broad white stripe of calcite that has been dubbed the “bathtub ring” by locals. It serves to highlight the plight of the shrinking lake. By 2012, the lake’s surface could fall below the existing pipe that delivers water to Las Vegas.
Shrinking Lake Mead now sports a “bathtub ring”
Hoover Dam’s 17 turbines have a combined generating capacity of 2080 MW, when the reservoir is filled to its normal levels. As the water levels drop over the course of a year, that capacity diminishes. By February, the lake’s decline cuts the dam’s capacity by a fifth. But lower output is only the first sign of trouble.
When the lake level sinks the water pressure driving the generator turbines also drops. If the pressure gets too low the turbine blades begin to cavitate—vapor bubbles form on the turbine blades—causing the generators to shudder violently. “The magic number is 320 meters,” says Hoover facilities manager Peter DiDonato. “That’s when the turbines start to shake. You can feel it. The whole building will shake.”
The vibration can damage the turbines to the extent that the engineers may have to stop the generators altogether. Shutting down the generators could be a a major problem for the three states that depend on the dam for electric power. The dam’s stakeholders are now investing millions of dollars in new turbines that reduce the threat of cavitation and can function at lower lake elevations. Engineers plan to begin installing the new turbines in 2010, but new turbines will not put more water into the dwindling lake. Plus, there are more problems farther up river.
Lake Powell, situated on the border of Utah and Arizona, is the Colorado’s other major manmade reservoir. Formed by damming the river at Glen Canyon, the picturesque lake provides a recreation area for people from surrounding states and drinking water for Phoenix and Tucson, two of the fastest-growing cities in the US. It also provides water for the Central Arizona Project (CAP), a sprawling water distribution scheme that uses hundreds of pumps, canals, and dams to transport water from the Colorado to much of Arizona.
On the Arizona side of the lake, a pumping station pulls water from a brand new tunnel below the lake’s surface to cool the Navajo Generating Station, a 2.25-gigawatt coal-fired plant located on the Navajo Nation reservation. It was built to provide electricity for the CAP, but today it powers cities from Tucson to Los Angeles. The Navajo plant depends on Colorado River water to cool the steam from its turbines, condensing the water for reuse in the plant’s boilers. Like the water supply for Las Vegas, water for the plant has been imperiled by low lake levels, leading to the drilling of new, deeper intake pipes.
The Navajo Generating Station.
The American Southwest has experienced decade long droughts in the past—the drought that killed the Anasazi culture and the famous dust bowl of the 1930s are but two examples. The onset of such droughts has nothing to do with global warming, but a new prolonged drought could definitely cause major disruption of renewable energy development. Hydroelectric output would obviously be affected, but so would output from new green geothermal and concentrating solar plants as well. Toss in the dirty old coal fired plants and most every power source in the Southwest is in peril.
There is an interesting aside involving the Navajo power plant, which highlights the strange alliances that arise when eco-activism, energy policy, water conservation and the economy collide. The Navajo Nation has joined other Native American leaders in assailing environmentalists who have sought to block or shut down coal-fired power plants that provide vital jobs and revenue to tribes in northern Arizona. The result is a conflict that pits environmentalism against native rights.
According to the Native American Times, Navajo Nation President Joe Shirley, Jr., voiced strong support for a resolution by the Hopi Tribe, declaring environmental groups unwelcome on Hopi land. “I stand with the Hopi Nation,” President Shirley said. “Unlike ever before, environmental activists and organizations are among the greatest threat to tribal sovereignty, tribal self-determination, and our quest for independence.”
There is a timely, home-grown solution to all these problems: a New Mexico-based company named Hyperion Power Generation has developed a self-contained, long lasting, miniature nuclear reactor, capable of powering 25,000 homes. It needs no water, produces no emissions and literally runs itself. Unfortunately, myopic bureaucrats in the US DOE and the Obama Administration would rather concentration on clean coal and biofuels, two technologies that require even more freshwater than the power sources they would replace. Now that is change we don't need.
Be safe, enjoy the interglacial and stay skeptical.
Imperial Valley Crops and geothermal plants compete for water.