According to the U.S. Department of Energy (DOE), “Water is used in all phases of energy production and electricity generation. Energy is required to extract, convey, and deliver water of appropriate quality for diverse human uses, and then again to treat wastewaters prior to their return to the environment.” This complex interplay between water and energy, which can go unnoticed by the vast majority of people, but that touches virtually every aspect of our lives, is known as the water-energy nexus.
In a fascinating book titled Thirst for Power: Energy, Water, and Human Survival, author and University of Texas professor Michael E. Webber explains that “[o]verall, about 15 percent of the water the world currently uses goes to making energy in one form or another” including its direct use “for generating power in hydroelectric turbines at dams.” Also known as hydropower, hydroelectricity is “one of the oldest and largest sources of renewable energy,” according to DOE. States like Idaho, Washington and Oregon generate the majority of their electricity with water, and hydroelectricity accounts for over 16% of electricity generation worldwide.
Hydropower harnesses the force of falling water to turn turbines and generate electricity. “The typical design is pretty straightforward,” writes Webber. “[A] dam is built to create a large reservoir of water with a significant elevation differential. The elevation difference between the water behind the dam and the river downstream of the dam creates potential energy that can be converted to mechanical energy (m) from rotating turbines that can be converted to electrical energy (e) from the spinning magnets within a generator.” As water plunges down onto the curved blades of these turbines, it causes them to “rotate on a vertical axis, like a merry-go-round,” according to Webber, thus turning “a shaft that is attached to a generator” and producing electricity to drive our machines and power our homes.
The history of using water to perform work goes back millennia. The ancient Greeks employed water wheels to grind wheat into flour more than 2,000 years ago. But, according to DOE, the “birth of the modern hydropower turbine began in the mid-1700s” with the publication of “Architecture Hydraulique” by a French engineer named Bernard Forest de Bélidor. Other milestones on the path toward modern hydroelectricity generation include the dynamo, which DOE describes as “a device that converts mechanical energy into electric energy.” Dynamos were successfully employed to generate electricity from water turbines in Grand Rapids, Michigan, and Niagara Falls, New York, in the early 1800s. Both of these applications employed direct current, a technology ill suited for carrying large volumes of power over long distances. But Nikola Tesla solved this problem by inventing polyphase alternating current systems capable of minimizing “resistive heating losses in the transmission lines over long distances,” according to the American Physical Society. The advent of alternating current as the primary method of electricity transmission, coupled with improvements in turbine technology and dam design, ushered in the modern era of hydroelectricity generation systems in use to this day.
The process of generating electricity using dams is “highly efficient,” according to Webber, because dams “can usually achieve nearly 90 percent or higher conversion efficiency from the potential energy of the elevated water to electrical energy at the power house.” In addition, hydroelectric power plants can be turned on and off relatively quickly compared to other types of power plants, giving them superior operational flexibility “to meet peak load or to firm up the power grid,” states Webber.
“Hydropower is a site-specific technology,” according to the DOE. Consequently, hydroelectric power plants come in all shapes and sizes. The largest hydroelectricity facility in the U.S., the Grand Coulee Dam on the Columbia River in Washington State, generates just over 7 gigawatts, enough energy to power up to 7 million homes for one year. Meanwhile, the Three Gorges Dam on the Yangtze River in China is the largest such facility in the world. It “has a capacity of 22 gigawatts, about the size of twenty or more nuclear power plants,” explains Webber. “It is so large, the mass of the water in the reservoir slowed the earth’s rotation. By putting nearly 40 billion tons of water elevated to hundreds of meters above sea level, the dam has essentially made the earth a little fatter in the middle and flatter at the top, extending the day by six-hundredths of a microsecond.”
Although hydroelectricity has long been a potent, efficient and reliable source of energy, it is increasingly vulnerable to our shifting climate reality. As extreme drought intensifies across the desert Southwest, for example, even the mightiest dams could be rendered literally powerless. The next issue of Our Water Matters will explore the efforts underway to understand and address these mounting challenges.
Visit energy.gov/energysaver/articles/energy-101-video-hydroelectric-power for a video explaining how hydropower works.
Trey Gerfers serves as general manager of the Presidio County Underground Water Conservation District. A San Antonio native, he has lived in Marfa since 2013 and can be reached at tgerfers@pcuwcd.org.