EIA: California's Solar-Energy-Based 'Duck Curves' Getting Worse

---

Written by Paul Wiseman for Industrial Info Resources (Sugar Land, Texas)--Solar energy's goal of reducing reliance on fossil fuel power generation is less clear than it might seem, because even when solar is at its peak, in the afternoons, gas-fired plants must stand at the ready, even when the "duck curve" says it's not needed.

What duck? Here's the story. Solar and wind are both intermittent, but solar is at least somewhat predictably so. It's strongest in the middle of the day--when it is less needed than the mornings before or evenings after. In the summer, most people are at work or out somewhere, meaning their thermostats are in "away" mode, so their air conditioners are mostly quiet.

So there's already a drop in demand--and when that diminished demand is covered--or exceeded--by solar power, the graph of power consumption looks like a duck. It rises in the morning when people get ready for work (the tail of the duck), sways down during midday (the back), ramps up around quitting time (the head), then slopes down again at bedtime, heading into its lowest need of the 24-hour period (the head and the bill).

First identified by the National Renewable Energy Laboratory in 2008 and named by the California Independent System Operator (CAISO), which operates the grid, the duck's back curve has gotten worse as solar power--both utility scale and distributed (home and business rooftop collectors)--has multiplied in recent years, says the EIA.

"As solar capacity in California continues to grow, the midday dip in net load is getting lower, presenting challenges for grid operators," says the EIA's report entitled "As solar capacity grows, duck curves are getting deeper in California."

Solar and wind generation can't be adjusted by humans--they're at the whim of Nature. So the adjustment must be made by the traditionals of nuclear, natural gas and coal.

The first issue with this up-and-down swing involves stress on the grid. As the day's highest demand ramps up on late afternoon, solar power quickly drops off--meaning conventional plants must get in gear quickly to make up the difference. Plus, there actually may be too much solar power in the mid-afternoon, meaning even that may need to be curtailed, the report notes.

The second issue is that, while traditional power plants must still have enough capacity to supply all grid needs--a condition known as "base load" power--they are now only utilized at that level for a few hours. That diminished usage may not generate enough income to make them economical to maintain. If they then have to retire unreplaced, the grid strain will only get worse.

And some green power opponents have pointed out that even if they're not running at capacity, the fossil fuel plants must run at a certain level all day--idling, so to speak. So even when solar power is at its peak, this renewable energy is not reducing as much pollution as it claims.

Batteries
Some power industry thinkers have suggested ramping up batter storage capacity to replace some of the baseline power load currently shouldered by conventional power plants. The EIA notes, "Storing some midday solar generation flattens the duck's curve, and dispatching the stored solar generation in the evening shortens the duck's neck. Battery storage is swiftly being constructed in California; it's grown from 0.2 gigawatts (GW) in 2018 to 4.9 GW as of April 2023. Operators plan to build another 4.5 GW of battery storage capacity in the state by the end of the year, according to our Preliminary Monthly Electric Generator Inventory." And some forecasters see utility-scale battery capacity growing five-fold by 2050 in the U.S. as a whole.

But will it be enough? Not likely, says the North American Electric Reliability Corporation (NERC).

In a report from July 2022, the agency's director of reliability assessment and performance analysis, John Moura said, "Batteries aren't going to do it, and we're going to need a backup fuel for wind and solar. So this is important to invest in." Moura also indicated more investment in gas infrastructure is needed as natural gas is a bridge fuel needed to back up wind and solar because of their inherent intermittency.

Others have suggested the solution could lie in a more integrated western grid, which would allow excess afternoon solar power to be exported instead of curtailed. It would also presumably allow base load electricity to be imported from elsewhere to ease the strain on California's conventional plants.

While pioneered in California because of its widespread green policies and abundant yellow rays, the issue is spreading--with different mascots. In Texas, it's an armadillo curve, using the back for the morning, neck for the afternoon and the ear for the evening surge, then the snout for the nighttime drop. Other states have other regionally appropriate symbols.

Industrial Info Resources (IIR) is the leading provider of industrial market intelligence. Since 1983, IIR has provided comprehensive research, news and analysis on the industrial process, manufacturing and energy related industries. IIR's Global Market Intelligence (GMI) helps companies identify and pursue trends across multiple markets with access to real, qualified and validated plant and project opportunities. Across the world, IIR is tracking over 200,000 current and future projects worth $17.8 Trillion (USD).