Why wildfires pose multiple threats to US power sector

For years, wildfire season was largely viewed as a threat to homes, forests and utility infrastructure in the American West. But as smoke from fires blankets large swaths of the country, it is becoming something else too: a power-sector challenge.

That's because the U.S. grid is changing. Solar generation is now the country's fastest-growing electricity source, transmission networks need to move more power over longer distances, and grid operators need accurate weather forecasts to balance supply and demand.

Wildfire smoke interferes with all three.


While smoke is unlikely to derail America's renewable-energy expansion, it is emerging as a new source of operational uncertainty that can reduce solar output, complicate grid management and add stress to transmission systems at precisely the moments when electricity demand is surging.

Here are five reasons wildfires are increasingly affecting the U.S. power system.

SMOKE BLOCK

For a power system increasingly dependent on solar generation, sunlight is fuel.

Wildfire smoke reduces the amount of ‌solar radiation reaching photovoltaic panels by ⁠scattering and ⁠absorbing sunlight before it reaches the ground.

Researchers from Colorado State University found that during California's intense 2020 wildfire season, daily average solar resources near major fires fell by 11% to 17% for the global horizontal irradiance (GHI) that conventional solar panels rely upon, while direct normal irradiance (DNI) plunged by 32% to 42%.

The impacts can be much larger close to active fires. Monthly average reductions reached as much as 25% for GHI and 61% for DNI in heavily smoke-affected areas.

That matters because utility-scale solar is now a major contributor to electricity supply in states such as California, Texas, Arizona and Nevada, where several wildfires are currently burning, according to the National Interagency Fire Center.

As the grid becomes more dependent on solar output, smoke effectively acts as a new weather variable capable of reducing power production across entire regions.

BAD TIMING

Solar losses are arriving when grids can least afford them.

Large fires typically occur during periods of extreme heat, drought and elevated electricity demand. Those same conditions drive greater air conditioning use, pushing power consumption toward seasonal peaks.

In other words, smoke can suppress solar generation just as heat waves are boosting demand.

That creates a potentially ⁠troublesome double hit ‌for grid operators: less renewable power available during periods when electricity consumption is strongest.

Historically, power planners worried about clouds reducing solar output. Increasingly, they must also account for dense smoke plumes that can persist for days or even weeks across large geographic areas.

FLYING BLIND

Grid operators do not merely need power; they need predictable power.

Wildfire smoke can rapidly alter solar output over hundreds of miles, making ⁠solar forecasting more difficult and forcing system operators to procure additional reserves to maintain reliability.

Research by the National Laboratory of the Rockies (formerly the National Renewable Energy Laboratory) examining wildfire impacts on solar generation found smoke-related losses can influence reserve requirements and electricity market outcomes.

The problem is becoming more pronounced as renewable penetration rises.

A fossil-fuel generator can usually be dispatched regardless of atmospheric conditions. Solar output depends on environmental factors, and smoke introduces another layer of uncertainty into forecasts that previously focused on clouds and temperatures.

As a result, wildfire season increasingly resembles a grid-management challenge rather than simply an environmental one.

TRANSMISSION OVERLOAD

The impacts are not limited to power generation.

Research shows wildfire smoke, heat and airborne combustion particles can reduce the insulating properties of air surrounding high-voltage transmission lines.

In extreme circumstances, those conditions can increase the likelihood of flashovers, faults and automatic line trips.

Wildfires themselves can also force transmission outages, while intense heat can increase conductor sag and reduce operational margins.

This is becoming more significant because the U.S. energy transition relies heavily on expanded transmission systems to move renewable power from remote production regions to urban demand centers.

A smoky atmosphere therefore has the potential to affect both electricity production and the infrastructure needed to deliver it.

NOT JUST THE WILD WEST

Perhaps the most important shift is geographical.

Wildfire smoke has become a continental phenomenon.

Canadian fires have repeatedly spread smoke across the Midwest, Northeast and Mid-Atlantic, while Western U.S. fires routinely affect regions hundreds or even thousands of miles from the flames themselves.

The good news is that long-range smoke appears to have a relatively modest impact on average annual solar resources.

Researchers found that outside areas near active fires, average reductions in photovoltaic-relevant GHI generally ⁠remain below 5%, even during major smoke years.

But the finding contains an important caveat. Smoke does not need to have a large annual effect to create operational problems.

Electricity systems are built around managing peak periods and extreme events. A few days of heavily reduced solar output during a major heat wave can matter far more than a small change in annual generation totals.

The encouraging news for renewable-energy advocates is that wildfire smoke does not appear likely to derail America's long-term solar buildout.

Even during extreme fire seasons, researchers find photovoltaic resources remain relatively stable across most of the country on an annual basis.

The less encouraging news is that smoke is becoming yet another climate-driven complication for grid operators already grappling with rising demand, more frequent heat waves and an increasingly weather-dependent generation fleet.

Just as electricity markets learned to manage the risks posed by clouds, wind speed and temperature, they may soon have to treat smoke as a routine part of summer power planning.

In a grid increasingly powered by sunshine, wildfire season is becoming an energy story as much as an environmental one.

The opinions expressed here are those of the author, a columnist for Reuters.