Water Adds New Constraints to Power  

The NYT has an article on how water availability is becoming a constraining factor for the development of new power generation capacity (except for solar PV and wind power, which don't require any) - Water Adds New Constraints to Power.

In the Mojave Desert, solar developers are scrambling to secure permits to build vast expanses of new generating capacity. But they are discovering that cost and carbon emissions are not the only limiting factors in new energy decisions in California. They are bumping up against water scarcity.

In the United States, thermoelectric power generation — mainly coal, nuclear and natural gas — accounted for 41 percent of U.S. freshwater withdrawals in 2005, U.S. Geological Society data show.

“Typically, project developers have wanted to use water for cooling because it’s more efficient and capital costs are less,” said Terry O’Brien, the California Energy Commission’s deputy director for power plant licensing. “That makes the project more economic.”

But there is a growing awareness in California and throughout the United States that the use of water for energy generation may be reaching its limits.

California has extensive experience with water shortages, resulting in its adoption of a policy, included in the energy commission’s 2003 Integrated Energy Policy Report, that discourages freshwater use for power plant cooling. The commission’s regularly updated reports provide current data and set the parameters for state energy and conservation policies.

“It’s just not possible anymore in California, and increasingly anywhere, to find unlimited water for the old water-intensive cooling systems,” said Peter Gleick, president of the Pacific Institute, which researches water issues and advises on policy. “If you want to build a big central power plant, whether it’s oil, gas or nuclear, you can’t take the water for granted.”

In the past decade, water availability has increasingly had an effect on the reliability of power supplies in many countries, with droughts leading to temporary closings of nuclear plants in Australia, France, Germany, Romania and Spain. Similar shutdowns have been threatened in the United States.

For a thermoelectric plant, the cooling technology used is the biggest factor in its water needs.

Once-through cooling, an inexpensive, energy-efficient and therefore widely used process, sucks up huge quantities of river, lake, or sea water. A typical 500-megawatt power plant takes in almost 19 million gallons, or 72 million liters, an hour, according to a 2005 report from the U.S. Department of Energy.

After running through the plant, almost all of this is returned to the river, lake or ocean. The used water, however, may be polluted, and the heat that it has absorbed can be lethal to fish, while the intake can kill wildlife and microorganisms. Research of the environmental consequences has led to tighter regulations in recent years, making it nearly impossible to get permits for new plants using once-through cooling anywhere in the United States.

The California state water board, going further, adopted rules this month tightening environmental protection requirements for existing coastal once-through plants — a step toward phasing out the technology at 19 plants. The U.S. Environmental Protection Agency is evaluating whether to follow California’s lead.

As once-through cooling has fallen out of favor, wet cooling, which exploits the chilling effect of evaporation, has become more common. It uses only about 3 percent of the water needed for once-through cooling — but it loses 90 percent of that to vapor. Wet-cooling systems are more expensive to build than once-through and consume as much as 3 percent of the energy generated by the plant. But a point in their favor is that they can use non-freshwater sources, like wastewater or mine pools.

Recent government data show that 56 percent of U.S. thermoelectric generating capacity is now wet-cooled, against 43 percent using once-through systems.

A newer process, dry cooling, which uses fans to push waste heat into the atmosphere instead of into water, is still more expensive and less efficient. On hot days, as much as 15 percent of the energy generated by a plant may be expended on cooling, according to the Electric Power Research Institute, a research body funded by the energy industry.