At the bottom of the lake
The Hoover Dam is one of the most important single structures in the U.S. It provided a symbolic transition out of The Great Depression for most Americans, and employed over 20,000 workers during construction. Today, Lake Mead and the Hoover Dam turbines provide energy and water to 36 million people in the Southwest. This dam has held back a lake for almost 80 years, but it won’t be able to carry our growing thirsty population forever.
As of July 2014:
"Lake Mead, the largest reservoir in the country, has dropped to its lowest level since it was filled in the 1930s, a decline that reflects 14 years of drought and a growing imbalance between the Colorado River's flows and the demands of cities and farms across the Southwest," according to the Desert Sun.
The water level is a full 130 feet down from the highest watermark. In total, the lake was only 39 percent full this summer. All reservoirs will have ups and downs in water levels, but the Hoover Dam is particularly stressed in 2014.
National Geographic reported, "Population growth is one factor affecting the rivers. Over the last century, more people has meant more demand for water. Since first apportioning of river water to seven states through the Colorado River Compact in 1922 and subsequent agreements, the basin states' population has increased nine fold. According to the U.S. Census Bureau, many of the cities dependent on basin water have grown even more: The greater Las Vegas area in 1920 had just over 2,000 people; now it has almost 2 million. In 1900, Phoenix had 5,554 citizens; today it has 1.48 million."
Las Vegas has done a good job of reducing the water it uses in the last decade, for a city that is built in a desert and is famous for its massive outdoor water features. However, no measures will ever make an inefficient idea efficient in using water and electricity. How drastic has the Lake Mead situation become Las Vegas? They are building a new straw.
Popular Science described the new diversion tunnel currently in the works to keep water coming out of Lake Mead:
"Right now, 600 feet beneath the lake’s glassy blue surface, a massive custom-built tunnel-boring machine—almost as long as two football fields and heavier than four 747s—is plowing inch by tedious inch through wet, fractured bedrock. Spanning nearly 24 feet in diameter, its rock-gnawing face is alive with the movement of 44 disc cutters and 23 knives. The Big Gulp–style tunnel it is boring will eventually intersect with a concrete-and-steel riser installed in the bottom of the lake, like a drain. Two intake pipes already carry water from Lake Mead to Las Vegas, about 25 miles to the west. Known as the Third Straw, Intake No. 3 will reach 200 feet deeper into the lake—and keep water flowing for as long as there’s water to pump."
The upper of the two existing straws that take water from Lake Mead was only 50 feet below the surface of the lake this year. If we continue to see drought like this, we will lose the top straw. Beyond the drinking water issues, what does the lower water level mean for the hydroelectricity the dam produces?
With less water in Lake Mead, the turbines in the Hoover Dam don't have as much water pressure as they did when the water level was higher. Less water means less power. The spillway of the dam is 1,221 feet above the lake bottom. The water level projected for May 2016 is 1,064 feet. Before recent turbine upgrades the power plant needed minimum water pressure of 1,050 feet to spin the turbines. With the plant upgrades, they plan to move the minimum pressure down to 950 feet above the turbines. Below 950 feet, major changes would have to be made to harvest a dwindling amount of potential energy, according to EENews.
What would the southwest do if the Hoover Dam continues to produce less electricity and population continues to grow? The Southwest states may call on Utah and Wyoming for help, specifically, wind from Nebraska and salt from Utah. An $8 billion project proposal could help California and other southwest states reduce the electricity load that dams carry. An issue with wind energy is that the windiest places aren’t necessarily close to the largest cities. Additionally, you can’t store wind energy for use when the breeze stops blowing.
Instead of using traditional batteries to store energy, this plan proposes to use compressed air. The electricity from the wind turbines in Nebraska would be used to power compressors that would pump the air into salt caves. In Utah, there are enormous salt deposits that could be hollowed out to serve as tanks. With the electricity from the wind converted to massive air pressure reserves you can precisely control the electric you supply to the grid. A high and low pressure turbine spin when the air is released to generate power to put back into the grid going to California. They could also capture the heat from the turbines to be used locally.
The salt cavern and wind combination are a great marriage of technologies to make wind comparable to fossil fuel power plants. The storage would allow wind energy to provide a smooth supply of energy into the grid, a traditional advantage of fossil fuels. Additionally, only air is being pumped underground, not anything toxic.
Cleantechnica.com reported that the proposed Utah storage facility would have four storage salt tanks. They will be about a ¼ mile tall and 290 feet in diameter. The facility will be able to supply about 60,000 megawatt hours with air pressure up to 1,100 psig. Unlike surface water on a reservoir, air pressure in a tank isn’t lost to evaporation.
One of the most interesting things about this project is the energy company giants that it is attracting. GE, Siemens, Duke Energy, Dresser-Rand, and Magnum Energy are all vying for involvement in air storage systems like this. For renewable energy advocates, it is great to see an idea grab the attention of traditional fossil fuel companies instead of being written off as weak technology. For the next generations of U.S. Citizens, air may replace water as the favorite way to store energy. l
Max Rohr is a graduate of the University of Utah. He is currently an outside salesperson at Shamrock Sales in Denver. He has worked in the hydronics and solar industry for 10 years in the installation, sales and marketing sectors. Rohr is a LEED Green Associate and BPI Building Analyst, and is RPA’s Education Committee Chairman. He can be reached at firstname.lastname@example.org.