West’s Heat Wave Spotlights Solar-Fueled Shift in Electricity Use

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By Bobby Magill

Record July heat in California and Arizona strained the electric power grid in those states, testing its ability to handle extreme temperatures and the rising use of solar power across the Southwest.

More rooftop solar use in extreme heat waves is forcing electric utilities to ask residents to conserve energy later into the evening to prevent blackouts as the highest electricity use from the power grid shifts to later in the evening when the sun’s energy wanes.

The shift in peak electricity demand is emblematic of the conditions to which the West’s electric grid will have to adapt in the coming years as electric utilities build new wind and solar power plants, California mandates new homes to be built with rooftop solar panels, and climate change, scientists expect, leads to more frequent and extreme heat waves.

Peak power usage used to come during the brightest and hottest times of day when rooftop solar panels generate the most power. But residents are now using more power from the grid when the panels generate less power as the sun dips lower on the horizon.

The shift means power companies sometimes use less renewable energy and more fossil fuels to keep the lights on when electricity demand is highest, Brad Albert, vice president of resource management for Arizona Public Service Co., told Bloomberg Environment.

Accommodating that shift during severe heat waves is important to preventing blackouts and equipment failures.

“Energy conservation helps relieve stress on the electric system serving homes and businesses,” Julia Roether, spokeswoman for Southern California Edison, the region’s largest electric utility, told Bloomberg Environment. “Like how a car running at full speed for several days can overheat, electric equipment can experience issues after multiple days of intense heat with high overnight temperatures.”

Extreme Heat

The shift to later peak energy demand was apparent in July when a searing heat wave toppled temperature records throughout Arizona and California, including a new all-time record high for Los Angeles—111 degrees at the University of California-Los Angeles on July 6.

San Diego, which usually sees highs in the mid-70s in July, hit a record 96 degrees the same day. Riverside, Calif., hit 118 degrees on July 17, tying a record. Phoenix hit a record 116 degrees on July 25.

Expecting residents to turn on their coolers en masse, California’s power grid operator, California ISO, issued alerts July 24 and 25 urging residents to cut their electricity use between 5 p.m. and 9 p.m. by setting their air conditioners to 78 degrees and taking other conservation measures.

In previous years, California ISO would ask residents to cut their power use between 4 p.m. and 7 p.m., California ISO spokeswoman Anne Gonzales told Bloomberg Environment.

“That’s because we are seeing more renewables on the system,” Gonzales said.

Strain Shift

Usually, people use the most electricity during the hottest, brightest times of day, when solar power can help power companies rely less on natural gas “peaker” power plants, which are used only during times high demand.

The shift forces companies to use the peaker plants at a time of day when they can’t use as much solar power to supplement the plants that run on fossil fuels, which means they rely more on natural gas and other traditional power sources to keep the lights on when electricity demand is highest.

“We have abundant [solar] resources when the sun is shining, and as the day progresses, that production fades,” Gonzales said.

On hot days, workers return home and crank up their air conditioners just as solar panels begin to produce less power as the sun dips lower in the sky, particularly in Arizona, which does not observe Daylight Saving Time.

“Renewable energy provides an emissions-free source of energy to the grid that reduces the need to generate electricity from fossil fuel-sourced electric generators,” Roether said. “During periods of high electric demand, like the successive days of very high temperatures experienced last week, natural gas-fired electric generation is still a large contributor of energy to the electric grid.”

Adapting to Extremes

Severe heat waves affect the electric power grid in many ways.

“Extreme heat leads to electricity being lost on transmission lines, higher power demand as residents turn up the air conditioning, wildfires that that destroy power lines and solar panels increasingly sensitive to even minor disruptions,” Carlos Coimbra, a mechanical engineering professor on the faculty of the Center for Energy Research at the University of California-San Diego, told Bloomberg Environment.

“A rogue cloud on a very hot day can seriously disrupt local generation, especially when the penetration of solar is very high,” he said.

All of those factors are expected to add strain to the power grid and force electric utilities to build energy storage systems and smarter power grids that are more able to adapt in real time to changes in electricity use and wind and solar power generation that varies with the weather, he said.

“The whole grid needs to operate much more dynamically and smartly than before,” Coimbra said.

Storing the Sun

States and utilities are looking to large batteries to help the electric power grid more effectively handle the variability of solar and wind power.

Storage allows electricity generated using solar and wind to flow onto the power grid when it’s needed the most, even after the sun goes down.

“Energy storage can be used to help meet electric demand during the highest usage hours, which in California is generally between 4 p.m. and 9 p.m. when solar generation resources produce less electricity as the solar intensity diminishes, by charging the battery systems during lower demand hours and discharging during high demand hours,” Roether said.

The California Public Utilities Commission in February set a target for the state’s power sector to cut its greenhouse gas emissions by 61 percent under 1990 levels by 2030, calling for 2 gigawatts of additional energy storage on the grid. The state already has exceeded its mandate to install 1.3 gigawatts of storage by 2024, with more than 1.4 gigawatts of storage installed or under construction, according to Bloomberg data.

Arizona Public Service has plans to install 150 megawatts of large batteries at utility-scale solar power plants across the state over the next several years, Albert said.

Some large solar plants, such as the 250 megawatt Solana solar-thermal power plant in Arizona, can provide electricity for hours after the sun goes down because solar energy storage is integrated into the plant’s design, he said.

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