Hoover Dam

According to the U.S. Bureau of Reclamation, Hoover Dam generates around 4 billion kWh of hydroelectric power annually for Nevada, Arizona and California. 

Hydroelectricity sourced from across the West played a large supporting role during the weekend of Aug. 15 and 16 after the California Independent System Operator on Aug. 14 declared a Stage 3 Electrical Emergency, initiating rolling blackouts throughout the state. But chronic drought and water shortages make the future of hydroelectric generation uncertain, even as power providers rely on it to supplement intermittent renewable resources during emergencies.

The Western Area Power Administration, which markets power from 57 hydroelectric dams to wholesale power users in 15 Western states, in an Aug. 15 news release said it provided 760 MWh of reserve hydropower from the Glen Canyon and Hoover dams to meet California's energy demand.

Generation at Hoover Dam ramped up at around 5:30 p.m. Aug. 14, pumping 260 MWh through 9 p.m.; Glen Canyon Dam provided an additional 500 MWh between 7 p.m. Aug. 14 and 1 a.m. Aug. 15, according to a U.S. Bureau of Reclamation news release. The BOR also increased hydropower generation at Davis Dam in Clark County, Nevada, in response to grid destabilization.

Of the remaining dams in the Colorado River Basin, bureau spokesman Marlon Duke told California Energy Markets in a text message that the agency is "maintaining a ready posture and will respond if need be."

The dams are "crucial sources of reserve energy in case of system emergencies," the WAPA news release says. It likened large reservoirs like Lake Mead to batteries, which can quickly dispatch electricity to the grid in a short time.

But water levels at Lake Mead have been in steady decline since 2000. BOR on Aug. 14 released projections estimating that Lake Mead will be low enough in 2021 to trigger drought contingency plans in Arizona and Nevada. These plans, formalized in May 2019 between seven Basin states, the U.S. government and Mexico, trigger water cutbacks when levels drop below 1,090 feet.

Energy agencies are hearing more requests to determine what will and will not count as a "zero-carbon energy resource" under SB 100, California's ambitious clean-energy bill that sets a target of 100-percent carbon-free electricity by 2045. California Energy Commission spokeswoman Lindsay Buckley told CEM in an email that analysis of the role of large hydro will be included in a report on SB 100 due to the Legislature in January.

Buckley said that historically natural gas generation has supplemented lost hydro resources during droughts, but since 2016, renewable generation "began to serve that purpose"—nearly the opposite of what happened over the last weekend, when state agencies called on large hydro to support a grid made unstable due in part to a heat wave and a simultaneous unexpected drop in wind generation.

Hydropower makes up around 15 percent of Pacific Gas & Electric's generation mix, PG&E spokesman Paul Moreno told CEM in an email. He said the utility increased its usage of renewable power to offset dependence on natural gas plants.

"In dry years, PG&E strategically generates less hydropower in the spring so we can save water in our reservoirs for generating power during the summer peak periods, when demand for power is higher," Moreno said. PG&E's water comes from the Pit River in Shasta County and the North Fork Feather River in Plumas and Butte counties. The utility also has a pumped-storage project east of Fresno.

Hydropower makes up 11 percent of San Diego Gas & Electric's generation mix, SDG&E spokeswoman Sara Prince said in an email to CEM, but "since SDG&E purchases power on the open market just like other utilities, any drought conditions that reduce hydro power could place upward pressure on electricity prices systemwide."

SDG&E also called on its pumped-hydro facility at Lake Hodges in response to the emergency. "We ran it at its maximum capacity, 40 MW, when it was needed most," from Aug. 14 to Aug. 19, Prince said.

Flexible hydro resources are "an important part of [Southern California Edison]'s and California's clean energy future," SCE said. "This is true despite decreased renewable energy credit pricing and its impact on the revenue stream of small (renewable portfolio standard-eligible) hydro resources and increasingly costly relicensing requirements that put additional financial pressures on hydro resources."

SCE said it is drawing on its hydro resources more than normal to increase output, but for the hydro plants that don't have reservoir storage and rely instead on river runs, in some cases "there isn't much [water running] given the time of year and low precipitation year to date." 

The loss of hydropower generation during the 2012-2016 drought cost California's three investor-owned utilities around $1.9 billion due to increased natural gas prices and more than $3.8 billion due to increased electricity demand in the same period, according to a study published in June that analyzed the effects of the drought.

The study found that in 2015—the worst year of the drought—in-state hydro generation shrank to 41 percent of average, supplying only 6 percent of California's overall electricity. Electricity prices increased sharply during the same period, due to increased demand for natural gas.

Although in-state wind and solar capacity more than doubled from 2012 to 2016, carbon emissions during the period only modestly declined, also due to drought and declining availability of hydropower, the paper found.

"Drought typically, especially in California, causes a big increase in carbon emissions because you lose hydropower and you have to replace it with natural gas," Jordan Kern, the paper's lead author, said in a phone interview with CEM.

"When hydropower goes away during the droughts of the future, it will have to be replaced by something. Right now, there's really no way to replace that without generation from natural gas plants," he said. 

In addition, increased average temperatures across the West have shifted the availability of hydropower toward earlier parts of the year, as snow melts earlier and more precipitation falls as rain rather than snow. That means that in the temperature spikes of the future, which occur in California mainly in August and September, hydropower might not be available when it is needed most.

"What really breaks the system is heat," Kern said.

Aria covers California and the Southwest from Albuquerque. Her work has appeared in a variety of popular and academic publications.