Extreme Heat, Peak Load and Demand Response: Record Summer 2018 Challenges Grid Operators Nationwide

5 min read

Wherever you live, you may have experienced a hot summer. But since many of us live and work in California, let’s talk about what our summer was like. As you know, California sweltered in July—the warmest month ever recorded in the Golden State. On July 6, Los Angeles hit a new all-time record high—111 degrees F. Even coastal San Diego, which normally enjoys mid-70s weather in July, reached 96 degrees that day.

On July 24 and 25, as temperatures soared, wildfires burned, and hydropower and gas supplies tightened, the California Independent System Operator (CAISO) issued calls to consumers statewide to voluntarily ratchet down electricity use. The alerts succeeded in lowering demand by 990 megawatts (MW) over the two days, helping the system get over high forecasted peaks.

Overall, the continental United States sweated out the 11th warmest July on record.
May through July ranked as the warmest three-month period ever, with a national average of 70.9 degrees, 3.4 degrees above average.

mean temperature percentiles

As record heat gripped most of the nation this summer, electric utilities, regional transmission organizations and system operators fought to feed hungry air conditioners and keep the grid balanced.

peak vs average load in new york state

ere are some selected highlights:

July 2—The New York ISO recorded a peak demand of 32,810 MW, its highest level in five years.  Source: NYISO

summer peak demand for PJM RTO

July 3—The PJM Interconnection, which includes 13 mid-Atlantic states, reached 144,557 MW of demand—the highest level since 2016. Source: PJM

peak hourly load for electricity reliability council of Texas

July 19—The Electricity Reliability Council of Texas (ERCOT) reached a new all-time hourly peak load of 72,192 MW, only to be exceeded the next day, with loads reaching 73,259 MW. Source: ERCOT

Grid Managers Deploy DR and Other Tools

Grid managers turn to a number of gadgets in their toolboxes to ensure adequate supplies. In CAISO’s case, for example, in addition to issuing “Flex Alert” calls for voluntary conservation, the ISO has restricted maintenance operations at power plants and transmission facilities in order to keep them running. As of the end of July, CAISO had already issued 18 such calls—the most since 2012, when it recorded 23.

CAISO expects the continued hot weather to result in more Flex Alerts this summer. CAISO can also turn to demand response (DR) by issuing warnings or declaring emergencies. So far this year, the ISO has called two transmission emergencies but no mandatory DR events. Transmission emergencies are declared when there’s a threat to transmission system capability, such as line and transformer overloads.

Reserve Margins Shrink

Energy providers typically design generation capacity to meet peak demand and then add an extra measure of reserve margin of least 15 percent. But even that may not be enough in the face of a changing climate. Heat waves reduce the output capacity and efficiency of gas-fired combustion turbines. Multiple days of intense heat and higher nighttime temperatures can push transmission and distribution equipment to the breaking point.

summer 2017 to summer 2018 anticipated reserve margins year to year change
NERC 2018 Summer Reliability Assessment

In Texas, faced with heat waves, coal power plant retirements, and strong population and economic growth, ERCOT operated this summer on a reserve margin of only 10.9 percent. That’s low!—lower than its planned reserve margin of 13.8 percent and the 15 percent recommended by the North American Electric Reliability Corp. So far, DR programs and high day-ahead wholesale prices, which temper demand, have helped ERCOT meet demand without any widespread loss of load to the system.

During another heat wave in 2011, ERCOT declared several emergencies in an effort to reduce electric demand. It avoided rolling power outages through DR and interruptible load contractual agreements, calls for voluntary conservation and execution of short-term contracts that brought four generators back online.

A 2017 study[1]from the National Academy of Sciences found that the effects of climate change could require an additional $180 million in peak generating capacity by the end of the century. “Climate change is projected to have severe impacts on the frequency and intensity of peak electricity demand across the United States,” the reports authors said.

Solar PV Shifts the Peak

In a new twist, grid and power organizations must adapt to changing patterns of energy supply and demand brought on by increasing use of solar photovoltaic (PV) energy. When the sun dips below the horizon or goes behind a cloud, the sudden loss in energy from solar PV forces grid operators to react quickly. In fact, the peak energy demand window has shifted in California and Arizona as a result of higher levels of solar energy.

In previous years, CAISO would ask consumers to save energy between 4 and 7 p.m. Now, as solar generation fades toward evening, the peak has shifted to between 5 and 9 p.m. That forces energy companies to rely on natural gas peaker plants and other traditional power sources to keep pace.

Energy Storage Adds Flexible Capacity

You can’t store sunlight, but you can store energy in batteries. So it’s no wonder that utilities are investing more in energy storage and smart grid technologies as a way to fold in more renewables. The Los Angeles Department of Water and Power is even floating a $3 billion plan to turn the Hoover Dam into a giant battery through pumped storage.

The California Public Utilities Commission has called 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.

“The whole grid needs to operate much more dynamically and smartly than before,” Carlos Coimbra, a mechanical engineering professor at the Center for Energy Research at the University of California-San Diego, told Bloomberg Environment.

Managing Flexible Capacity at the Grid Edge

The new normal is testing system operators and energy companies alike. Extreme heat forces electricity losses on transmission lines, raises demand as residents turn up air conditioning, and leads to wildfires that fry power lines and reduce inverter-based solar PV output. Meanwhile, grid managers need to incorporate higher levels of intermittent energy from renewables.

“The need to manage flexible capacity at the grid edge has never been greater,” said Dr. Amit Narayan, chief executive officer of AutoGrid. “We’re working with energy companies worldwide to help them control grid assets at scale and in real time so they can bring costs down, add to system reliability and decarbonize the grid.”

[1]Proceedings of the National Academy of Sciences of the United States, 2/21/2017, Vol. 114, Issue 8

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