10 UNDOING THE ENERGY WATER COLLISION We have many tools at hand. A number of technologies oer 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 electric- ity or transportation fuels in the rst place—through more-ecient ap- pliances, 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-ecient closed- loop cooling technologies would increase water consumption, potentially even doubling it, but would reduce water withdrawals by two orders of magnitude. Dry- and hybrid cooling
Power Plant Water Words
Thermoelectric: The conversion of thermal energy (heat) into electricity. Fos- sil fuel and nuclear power plants, as well as some forms of renewable electricity facilities, boil water to create steam that in turn spins electricity-generating turbines. These plants typically use water to cool the steam. In the United States, 90 percent of our electricity comes from thermoelectric power plants that require cooling.
Cooling technologies: The mechanisms used to cool steam in a power plant:
Once-through systems withdraw water from nearby sources (e.g., rivers, lakes, underground aquifers, the ocean), circulate it through pipes to absorb heat from the steam, and discharge the warmer water back to the local source.40
In the arid Southwest, population and water use have grown rapidly in the past couple of decades. This region may double its 2000 population by 2030, according to the U.S. Census Bureau, with potential accompanying increases in demand for water and electricity—and water for electricity. Complicating matters, changes in the region’s climate are expected to lead to large drops in annual runo and water availability by mid-century.
options help address water consump- tion. Such technologies could be particularly important in water- constrained regions. Such cooling technologies would, however, reduce power plant eciency and increase their costs—and, in the case of fossil- fuel-red plants, do nothing to reduce emissions of heat-trapping gases.39
Recirculating (closed-loop) systems reuse cooling water rather than immediately releasing it back to the water source. Such systems withdraw comparatively small amounts of water but lose or “consume” most of it through evaporation.41
Dry-cooling systems use air instead of water to cool the steam exit- ing a turbine. Dry-cooled systems can decrease total power plant water requirements by as much as 90 percent, though adding cost and decreasing eciency.42
Hybrid cooling systems use air for cooling most of the time, but can draw on water during particularly hot periods.
Several steps can be taken to reduce the water demand of some re- newable 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, minimiz- ing reliance on irrigation and switch- ing to low-water perennial crops—or even to waste from cities, farms, and forests—could make it possible to lower the water requirements of biofuel production and reduce heat- trapping emissions.
Given the many connections be- tween 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 benets.
The Union of Concerned Scientists is the leading science-based nonprot working for a healthy environment and a safer world.
This fact sheet, which draws from a growing body of research, is the rst in our “Energy and Water Collision” series that explores the ways in which energy choices aect water resources in the United States, and how this will change in the face of global warming. To download a fully referenced version, visit the UCS website at www.ucsusa.org/energy-water.
© September 2010 Union of Concerned Scientists
photo: Flickr/David Slauson
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