Via The Union of Concerned Scientists – a leading science-based nonprofit working for a healthy environment and a safer world – 10 things to know about the impending Energy-Water Collision. As the article notes:
“…Energy and water are woven into our daily lives and strongly linked to one another. Producing energy uses water, and providing freshwater uses energy. Both these processes face growing limits and problems. In most power plants, water cools the steam that spins the electricity-generating turbines. Refining transportation fuels requires water, as does producing fuels—for example, mining coal, extracting petroleum, or growing crops for biofuels. Using water in our homes and businesses requires getting it there, treating it, heating it, and more. Because of these links between energy and water, problems for one can create problems for the other. In places where using energy requires a large share of available water, or where water resources are scarce or stressed by competing pressures (such as the needs of farmers or of local ecosystems or, increasingly in many parts of the United States, by climate change), the energy-water connection can turn into a collision—with dangerous implications for both. The 10 facts below summarize the water impacts of our energy choices—and ways to address them.
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THIRSTY FOR POWER—Keeping U.S. power on each day requires more water than 140 New York Cities. More than half of the country’s 104 nuclear power reactors use once-through cooling (see the text box on p. 4).3 Each of these plants withdraws 25 to 60 gallons of water for each kilowatt-hour of electricity it generates.4 Coal plants with similar cooling systems typically withdraw almost as much—20 to 50 gallons per kilowatt-hour—even without considering the water needed to mine coal or store coal waste from power plants (see the text box on p. 3). Those figures mean that for a nuclear or coal plant to generate the electricity for one load of hot-water laundry (using electric appliances), 3 to 10 times more water must be withdrawn at the plant than is used to wash the clothes.5 The electric sector withdraws 143 billion gallons of freshwater per day.2
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WITHDRAWAL SYMPTOMS—In the southeastern United States, power plants account for two-thirds of all withdrawals of freshwater. Nationally, the amount of freshwater withdrawn to cool power plants is roughly the same as that for crop irrigation.6 In the Southeast, electricity’s water withdrawals easily top agriculture’s: power plants there withdraw an average of 0 billion gallons of freshwater every day, or 65 percent of the region’s total.7 Some plants lose or “consume” large amounts of the withdrawn water to evaporation (see the text box on p. 2): a typical 600-megawatt coal-fired power plant consumes more than 2 billion gallons of water per year from nearby lakes, rivers, aquifers, or oceans.8,9
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In HOT WATER—Water discharged from a coal or nuclear plant is hotter—by an average of 17°F in summer—than when it entered the plant.10 Roughly one-third of all U.S. power plants use once-through cooling11 and so return virtually all the water they withdraw. Still, these plants’ significant water withdrawals can have a large impact on water quality, including temperature. Half of all coal plants report releasing water in the summer at peak temperatures of 100°F or more.12 This thermal pollution can stress or kill fish and other wildlife. On Georgia’s Chattahoochee River, for example, several thousand fish perished each summer until Georgia Power retrofitted its coal-fired plants with cooling towers in 2002.13 Coastal power plants discharging warmed seawater can similarly harm local marine ecosystems.14
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HIGH AND DRY—Water troubles can shut down power plants. Just since 2004, water stress has led at least a dozen power plants to temporarily reduce their power output or shut down entirely, and prompted at least eight states to deny new plant proposals.15 During prolonged heat in the summer of 2010, for example, water temperatures in the Tennessee River hit 90°F, forcing the Browns Ferry nuclear plant to significantly cut the power output of all three of its reactors for nearly five consecutive weeks—all while cities in the region were experiencing high power demands for air conditioning.16
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WHAT DOES CLEAN MEAN? Clean energy can mean low carbon and low-water—or not. Increasing energy efficiency will allow us to meet our energy needs with less electricity—and thus with less water use at power plants. Shifting to certain renewable energy technologies, such as wind turbines and solar photovoltaic modules, means generating electricity with essentially no water at all. But water usage by other renewable energy options varies widely. Technologies that can be particularly water-intensive include concentrating solar power (CSP), bioenergy, geothermal, and hydroelectric. Some CSP plants use far less water per unit of energy than a typical coal or nuclear plant to cool steam; other CSP facilities use more.17
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MPG OR GPM?—Powering your car with ethanol may use dozens of gallons of water per mile. The “water footprint” of conventional biofuels, such as corn ethanol, can be very large. Creating a single gallon of ethanol consumes, on average, about 100 gallons of freshwater. In some regions, however, ethanol production can take three or more times that amount—mostly depending on water needs for irrigation.19 Water requirements for some other forms of biofuel are lower. Estimates indicate that it will require only 2 to 10 gallons of water to produce each gallon of “cellulosic” biofuel from drought-resistant grasses and waste wood.20
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THE FLIP SIDE—California uses 19 percent of its electricity and 32 percent of its natural gas for water.22 Just as energy production requires large amounts of water, the inverse is also true: substantial amounts of energy are used to pump, transport, treat, and heat the water we use every day. Nationwide, the EPA estimates, treating and distributing drinking water and wastewater together account for 3 percent of energy use. In some parts of the country, the energy toll is much higher.
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WATER UNREST—Water supply conflicts are growing across the United States. Particularly in the West, conflicts between competing water users—e.g., farmers, electric utilities, cities—are building. Such conflicts, many of which have an energy dimension, are expected to intensify, especially during periods of drought or other water stress.26 Even without factoring in the exacerbating role of climate change, water supply conflicts involving several major Southwest cities—including Denver, Albuquerque, Las Vegas, and Salt Lake City—are considered highly likely by 2025.27 Such tensions are not confined to arid regions. In the Southeast, for example, prolonged drought brought simmering disputes between Georgia, Tennessee, and other stakeholders over the rights toTennessee River water to a boiling point in 2008.28 By 2030, electric capacity is predicted to grow nearly 30 percent in the western United States and 10 percent in the Southeast,29 a trend that would force the question: With what water?
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CLIMATE COMPLICATIONS—As the climate changes, so does the water cycle. Increasing climate variability—extreme heat and extended drought, in particular— is already testing the resilience of energy and water systems in the Southwest and other regions. Further climate change will pose far-reaching challenges. The Northeast and Midwest can expect more spring flooding and extended summer drought.30 In the Southeast, where both air and water temperatures are expected to rise,31 instances where water is too warm to be used to cool power plants may become far more frequent. Other regions— notably the Southwest—can expect far less runoff and precipitation, especially in the warm months. Longer, more severe droughts will leave arid areas even drier.32 With declining snowpack, for example, flows in the Colorado River are projected to decrease 20 percent below current averages by 2050.33 The net effect nationally will be a more variable and unreliable water situation.34 California’s single biggest user of electricity is the State Water Project.23 This system, serving 29 local water agencies, consumes enough to power more than 450,000 households24—or a city roughly the size of San Diego. Similarly, the Central Arizona Project, a 336-mile aqueduct delivering water to Phoenix and Tucson, is Arizona’s largest electricity user.25
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UNDOING THE ENERGY-WATER COLLISION—We have many tools at hand. A number of technologies offer strong opportunities to address the energy-water collision:
No-water energy: Using technologies such as wind and photovoltaics means doing away entirely with water use for electricity production.38 Reducing the need for generating the electricity or transportation fuels in the first place—through more-efficient appliances, buildings, and vehicles, for example—not only saves money and reduces heat-trapping gases and other pollutants, but also eliminates the corresponding water use.
Low-water energy: Shifting old coal or nuclear plants using once-through cooling to more-water-efficient closed-loop cooling technologies would increase water consumption, potentially even doubling it, but would reduce water withdrawals to lower the water requirements of biofuel production and reduce heat-trapping emissions. Given the many connections between energy and water, the choices we make in the near future about how we produce and use energy will determine not only the extent to which we mitigate the worst impacts of climate change, but also how resilient our energy system is to the variability of our water resources and the many competing demands for it. Smart choices now will mean lower risks, greater energy security, and strong environmental and economic benefits.” by two orders of magnitude. Dry- and hybrid cooling Several steps can be taken to reduce the water demand of some renewable energy options. CSP plants, for example, which are ideally sited in some of the country’s sunniest—and driest—locations, are increasingly turning to dry cooling, despite the higher costs. For biofuels, minimizing reliance on irrigation and switching to low-water perennial crops—or even to waste from cities, farms, and forests—could make it possible.
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