That’s according to a paper published last month by Arizona State University researchers, who found 46 percent of existing power capacity in the West is vulnerable to the impacts of climate change.

Power companies are likely overestimating their ability to meet future electricity needs and are not taking into account how more heat and drought events will diminish power generation capacity in different ways,  the authors of the paper wrote.

But for their part, Arizona’s largest power providers say that climate change projections have influenced their future development plans, including goals for renewable energy generation, power supply forecasts and future power plant construction plans.

“A lot of these concerns brought up in the study — water availability, grid reliability and demand risk -- have been a standard part of our planning process for many years,” said Tom Cooper, director of resource planning and development at Salt River Project. “The concepts aren’t new, we just have to continue to think about how do the interrelated effects of climate change continue to influence those pieces.”

A blow to power

The ASU researchers predicted that climate change will reduce average summertime generating capacity by 1 percent to 3 percent, with reductions of up to 8.8 percent under a 10-year drought.

Increasing air temperatures, for example, pose a problem for power plants with combustion and combined cycle turbines because as the air gets hotter it becomes less dense. As it flows through turbines, the machines aren’t able to extract as much energy from that air, reducing their effectiveness, said Matthew Bartos, a research scientist in ASU’s School of Sustainable Engineering and the Built Environment.

Warmer water in the reservoirs and streams used by power plants can also affect their generating capacity. Water is used for cooling, but if incoming liquid is warmer, power plants will require more of it to absorb the same amount of heat, potentially putting more stress on water supplies, Bartos said.

At the same time, dwindling streamflow due to drought and declining snowpack means less water will be available for power plants to use for those cooling purposes. Power plants already use 40 percent of the surface water withdrawn in the United States, according to the National Climate Assessment, produced by the U.S. Global Change Research Program.

Declines in available surface water will affect hydroelectricity as well, because there will be less water available to push through turbines in dams across the West, the paper said.

Compounding the problem is that drought and heat-related effects on power generation tend to come at times when demand is highest, the paper said.

Power resiliency

But not all power sources will be equally affected by climate change. Renewables are generally less susceptible to the effects of climate change and can be expected to create a more resilient power grid, the paper said. The authors' recommendations also included strengthening transmission capacity, encouraging conservation strategies and putting more weight on local climate constraints when building new power plants.

In response to the paper, both Salt River Project and Arizona Public Service Company said they are implementing at least some of those recommendations already.

Renewables and energy efficiency are two of the fastest growing segments in APS’s long-term plan. Solar photovoltaic and wind power resources are expected to double by 2029, while coal generation will not grow at all, according to the plan.

The company also recently completed a 500-kilovolt power line from Phoenix to Yuma to not only increase energy reliability in the area but also expand capacity to bring in electricity from solar projects in the southwest part of the state, said Jim Wilde, director of resource planning at APS.

The utility has a goal of implementing energy conservation practices that reduce energy consumption by 22 percent over projected standard retail sales by 2020 as well.

SRP has its own goal of making sustainable energy 20 percent of its portfolio by 2020, up from 14 percent now, Cooper said.

Both companies, however, have taken criticism for raising or proposing to raise monthly fees on new residential solar customers, with APS recently proposing a $21 fee that’s more than four times higher than what solar users are paying now. SRP imposed a $50 fee on new solar customers in February.

Both APS and SRP are also considering the intensity of water usage in new power plant design. APS is assuming that all newly constructed power plants will have cooling technologies that use only air or a combination of air and water, Wilde said. The hybrid technology is already being installed in a renovated APS power station in Tempe and will use about 150 gallons of water per megawatt hour versus the 1,000 gallons per megawatt hour old steam units use, Wilde said. Cooper said SRP “recognizes air cooling as an option.”

Cooper also said falling surface water levels might force SRP to change when and how much it relies on its hydroelectric operations. In the future, the utility might reserve water resources to be used only during peak energy demand hours, he said.

In terms of how generation capacity will be affected by climate change, the two companies said their planning reserve margins — 15 percent in APS’s case — are large enough to accommodate what’s projected by the ASU paper. The companies already deal with a 5 percent to 10 percent reduction in capacity during the summer, Wilde and Cooper said. They also said that the companies have the ability to adapt relatively quickly as climate conditions continue to shift.

“Climate change is expected to happen slowly over time. We can construct a new solar plant in as little as two years,” Wilde said. “The way we look at it is utilities in general can respond to climate change very quickly.”