WATER:

Warmer average temperatures may reduce summer output of power plants -- study

Climate change poses a threat to the operation of power plants by reducing their ability to cool down with river water, a new study warns.

Specifically, higher average river temperatures, combined with lower river flows because of climate change, could decrease the average power capacity of nuclear and fossil-fuel fired plants by 4.4 to 16 percent in the United States between 2031 and 2060 in the summer, according to the study, published yesterday in Nature Climate Change. The impact of drought and warm water in rivers will be greatest in the southern part of the Mississippi River Basin and on the East Coast, the scientists said.

European power plants also could take a hit, with a 6.3 to 19 percent reduction in their ability to produce electricity in summer, the study says. In Europe, the greatest challenge arises in the southern part of the continent.

"Based on these results, and based on the expected increase in electricity demand, it would be recommended to reconsider strategies with regard to power plant locations and infrastructure to ensure future energy security," said Michelle van Vliet, a researcher at Wageningen University in the Netherlands and a study co-author.

Additionally, severe power shortages -- when thermoelectric production collapses by more than 90 percent -- could increase by a factor of three because of changing water conditions from climate change, the researchers said.

Thermoelectric power plants are among the largest water users in the United States and Europe, constituting about 40 percent of both regions' total surface water withdrawals in a given year. In the United States, these types of plants, which include coal and nuclear generators, produce 91 percent of electricity.

The water dependency of power plants has come to the forefront in recent years during periods of drought and scorching temperatures.

In 2011, more than one Texas power plant cut output because of water scarcity. In Minnesota in 2006, a nuclear plant reduced its electricity generation by more than half because of a heat wave, according to a 2011 report from the Union of Concerned Scientists.

The relationship between lower river flows and reduced capacity at a power plant largely is a supply-and-demand issue. If there is less water available from natural sources because of drought, there is less to cool the plant. The river temperature aspect is a little more complex.

Fish health vs. power production

States set maximum limits for water temperature standards. However, their varying rules largely are consistent and tend to require intake water from rivers into a power plant to not rise higher than 89 degrees Fahrenheit, explained van Vliet. In Europe, there is a continental maximum limit on river water temperature for cooling. So if average summer water temperatures rise, it forces plants to cut back.

Additionally, there are restrictions on the allowable temperature for discharge water from power plants flowing back into waterways, particularly to protect fish.

"If you are a trout, you are not going to be happy in a hot tub," said Kristen Averyt, deputy director of the Western Water Assessment, who did not participate in the research.

She said the power plant issue is problematic, especially since generators have a long operating life.

More than 60 percent of the power plants considered by the study, for example, will still be operating in 2030. That is one reason it is important for utilities to plan ahead and adjust infrastructure investments in the near future, the authors said.

Van Vliet and the other scientists reached their conclusions by comparing various climate and hydrology scenarios and comparing those results with site-specific data for 96 power plants in the United States and Europe.

The projected numbers for reduced power fell in such a wide range because the scientists considered different types of cooling systems at power plants, as well as different climate models.

Plants utilizing "once through" cooling systems, for example, are more dependent on natural sources like rivers for a constant water supply than plants using other cooling systems. They also happen to be prominent in the part of the country -- the Southeast -- where climate change is projected to hit rivers the hardest.

Some power plants more vulnerable than others

The "once through" systems will be the most "strongly impacted" by changing climate conditions in the future, according to the study. The systems pull water out of a natural waterway, circulate it through a power plant and send it back into the waterway.

They differ from "recirculation" cooling systems, where water is withdrawn and held in reservoirs for multiple reuse in a plant.

Averyt said state public utilities commissions will play a major role in outlining the types of cooling systems that can be allowed in the future. U.S. EPA also is a huge player. The agency recently released a rule that will require at least 650 power plants across the country to make significant modifications to their cooling-water intake structure (Greenwire, June 1).

The study highlights several possible remedies. The problem for policymakers is that each comes with drawbacks.

Gas-fired power plants could reduce water vulnerability in comparison to coal-fired and nuclear stations, the researchers said. They can be 58 percent efficient, compared to efficiency of 46 percent and 34 percent, respectively, for coal and nuclear. However, concerns have been raised about pollutants flowing into waterways during natural gas production.

There are also dry-cooling systems that use air rather than water to cool a plant down. But they are expensive, and do not work efficiently when ambient air temperatures are high. Utilities also could consider moving more facilities to the coast, where ocean water is available for cooling, said van Vliet.

Recirculation systems, meanwhile, have their own issues. They withdraw less water per unit of electricity from rivers, but they also ultimately consume more water overall via evaporation, said Averyt, who said she does not have an official opinion on the issue.

"So you might be better in the short term with recirculation, but in the long term, you could be cooking your own goose," Averyt said. "There is no silver bullet."