The World in 2050_ Four Forces Shaping Civilization's Northern Future - Laurence C. Smith [56]
In the first study of its kind, Martin Pasqualetti, a professor in the School of Geographical Sciences and Urban Planning at Arizona State University,239 scrutinized how much water consumption (i.e., evaporation) Arizona’s different energy technologies require in order to produce one megawatt-hour of electricity. What he found may surprise you:
Water Losses Embedded in Arizona Electricity Generation
From Pasqualetti’s data we learn that the water consumption of energy production is not only large, but varies tremendously depending on the type of energy being used. For example, a nuclear power plant evaporates about 785 gallons of water to generate one megawatt-hour of electricity, whereas natural gas power plants evaporate considerably less (especially modern combined-cycle plants, which evaporate about 195 gallons per megawatt-hour). This means that an average house in Phoenix, using twenty megawatt-hours per year, will unknowingly evaporate nearly 16,000 gallons of water if its electricity comes from a nuclear power plant, but only about 3,900 gallons if it comes from a combined-cycle natural gas plant. More virtual water.
To put that number into perspective, 15,000 gallons is roughly what a typical Phoenix household with irrigated landscaping uses in two weeks. So this “embedded” water is not an enormous amount, but still significant in such a dry place. But the big surprise here is that in terms of electricity generation, hydropower, of all things, is the worst water waster,240 followed by concentrated solar thermal (CSP) technology, then nuclear. Arizona does not grow biofuel crops, but other studies show biofuels are even worse than hydro in terms of water consumption.241 Thus biofuels, hydropower, and nuclear energy, while hailed for being carbon-neutral (or nearly so), are worse even than coal when it comes to water consumption. Of the renewables, only wind and solar photovoltaics are truly benign—something, Pasqualetti points out, that would make solar photovoltaics more cost-competitive if the price of the saved water was taken into account.
The water-energy nexus works both ways. Examined in the opposite direction, energy is needed at every step along the way to deliver clean water to a house. Take again, for example, our typical Phoenix home, which consumes about an acre-foot of water per year. It requires two megawatt-hours of electricity—roughly 10% of the home’s total energy use—to pump that acre-foot uphill from the Colorado River some two hundred miles away, purify it, and pressurize it locally. But those megawatt-hours never appear on any electric bill; they are embedded within the water bill itself. Remarkably, almost all the cost of providing drinking water to Phoenix households is for the energy embodied within it, not for the water.
“Indeed,” says Pasqualetti, “water and energy are married to one another. Water is needed in electrical generating stations if they are to run efficiently. Energy, on the other hand, is needed to provide our houses with safe drinking water. How much of each commodity is needed to provide the other is something not well appreciated by the public.”242
It is something not well appreciated by politicians and planners either. Instead of recognizing this marriage between energy and water, their respective planning and regulatory agencies are almost always totally separate entities. “Energy analysts have typically ignored the water requirements of their proposed measures to meet stated energy security goals. Water analysts have typically ignored the energy requirements to meet stated water goals,” concluded a recent Oak Ridge National Laboratory report.243 Historically we have gotten away with this thanks to cheap water, cheap energy, or both. That cushion will continue to narrow as supplies of both tighten out to 2050.
One of the most widely anticipated