California's catastrophic wildfires in 2020 have sent an unprecedented 4 million acres up in smoke — more than in the previous four years combined — and produced five of the state's six largest blazes on record. Wildfire smoke layered the atmosphere with a haze so thick that it effectively erased more than two years of solar power additions on the California ISO grid, the state's primary transmission system, according to an S&P Global Market Intelligence analysis of grid operator and proprietary data.

As entire regions of the state dimmed under a dense orange fog of sunlight-blocking particulate matter, CAISO-connected solar generation dropped to roughly 2.6 TWh in September, slightly below monthly solar output two years ago, grid operator data shows. The reduction came despite the installation of more than 2,000 MW of new large-scale solar resources in the interim two years — added capacity that was entirely eclipsed by wildfire smoke.

The solar production drop in September followed a similar decline in August, when an intense heatwave contributed to California's first rolling blackouts in two decades and widespread lightning storms fueled wildfires across the state.

In addition to fire-triggered transmission system outages and drought-caused hydropower depletion, reduced solar generation from wildfire smoke is one of the emerging risks associated with the changing climate that utilities, independent energy suppliers and grid operators face across the U.S. West. In August, California energy regulators ordered investor-owned utilities to account for such threats in "vulnerability assessments," the nation's first such requirement related to climate change adaptation.

From excess to deficit

Through July, California's solar power plants had been more productive than ever in 2020, producing more electricity during peak midday solar output than the state could consume, which led to record cutbacks of available solar generation. That trend flipped in mid-August as air conditioning use soared along with temperatures, lightning strikes ignited wildfires and California failed to harness all the power it needed to keep the lights on. That led to a probe into the causes of the Aug. 14-15 rotating outages and a sweeping review of the state's grid reliability strategy.

Solar production in California typically declines with shrinking sunlight hours in the months after the summer solstice, unless offset by large new solar farms. Between July and August 2020, solar generation fell 18%, far exceeding the natural month-to-month falloff of recent years, according to CAISO data. During the prior five years, the July-to-August decline never exceeded 6%, as the most devastating fires of those years occurred in October and November.

This year, large wildfires collided with summer peak demand. Airborne particles, which began increasing in mid-August, reached 659 micrograms per cubic meter by Sept. 15, the highest level California has recorded since tracking began in 2000, the U.S. Energy Information Administration said in a recent analysis.

"Although most solar capacity in California is in the southern half of the state and the largest wildfires are currently concentrated in the northern and central parts, offshore winds push wildfire smoke into Southern California," EIA added.

Solar power plant owners and operators felt the pinch.

"We lost 5% to 20% [year-on-year] in August, depending on the [site]," said Benoit Allehaut, managing director of Capital Dynamics Clean Energy and Infrastructure LP. The Capital Dynamics AG affiliate has 25 operational solar projects across the state, according to S&P Global Market Intelligence data.

The impact of wildfires on solar production reinforces the need to balance out variable renewable energy with battery storage, according to Allehaut. The company has invested in one of the world's largest solar-plus-storage systems, currently under construction in Southern California, and also has a recently announced partnership with developer Tenaska Energy Inc. to build 2 GW of stand-alone battery storage near large cities to support local grids when wildfires damage transmission lines.

The unexpected loss of wholesale solar generation in August and September does not include likely additional reductions at the more than 1 million solar-powered homes and businesses in the state, a large share of which are located in Pacific Gas and Electric Co. Northern and Central California service territory, which was heavily affected by this summer's wildfire smoke.

An imperfect grid

California has more than 20,000 MW of solar generation capacity, including roughly 13,000 MW at large-scale facilities and over 9,300 MW of distributed solar at homes and businesses, according to state data. With retail power suppliers required to meet a target of 60% renewable energy by 2030, developers have lined up an additional 9,858 MW of planned solar capacity at large-scale photovoltaic solar plants, many of which are coupled with battery storage, S&P Global Market Intelligence data shows.

If wildfires continue to disrupt solar generation and long-distance power lines, then additional technologies may be needed to help ensure reliability, including distributed battery storage, microgrids and artificial intelligence.

Such technologies could help avert future events like those of Aug. 14-15, when California came up short on options. Grid officials have attributed the resulting rolling blackouts to climate change, an early-evening capacity shortage and an overall lack of planning, rather than laying the blame squarely on intermittent renewable resources. But the current system of generating and delivering electricity is imperfect for the challenge of eliminating carbon emissions, said Chad Steelberg, CEO and co-founder Veritone Inc., which develops artificial intelligence systems.

"The reality is that the grids we are operating today are not optimally compatible with renewable energy resources," Steelberg said.