Taming the “Duck” in California

California has been one of the leading states in innovation regarding both the use of, and policies relating to, renewable energy. This also puts the state at the forefront of dealing with the challenges brought by its renewable energy leadership. This fall, the state passed legislation that aims to better align the mismatch between solar production and electricity demand.

On a typical day, energy demand declines at late morning through midday. Demand then sharply peaks in the late afternoon and early evening hours. On a graph depicting this trend, the shape of the line marking this gradual decline in energy demand, followed by a much more rapid rise in demand, suggests the swayed back and head of a duck, thus giving the problem the name “duck curve”.

The growing adoption of solar energy presents a challenge because solar energy production peaks at midday and then declines as the sun begins to set. This creates a mismatch between when solar is needed and when it’s produced. As a result, California’s utilities are using natural gas to generate sufficient electricity during that time period. As an added complication, utilities typically begin using natural gas in the late-morning-to-mid-afternoon period, in order to “ramp up” to its peak usage in the evenings.

The bill, SB 338, requires the state’s utilities to rethink their integrated resource plans (IRPs) to consider ways in which carbon-free power sources can meet consumer energy demand. The legislature wants utilities to solve the problem of the duck curve with renewable sources. Solar storage (i.e., batteries) and demand response systems are two of the means by which this might happen.

“Supply and demand have to be constantly in balance on the grid,” said Laura Wisland, Senior Energy Advisor at the Union of Concerned Scientists. She pointed out that there are days where, because of active natural gas plants at midday, there is considered to be “too much solar” on the grid during that time period, forcing grid operators to curtail part of it.

“One of the reasons why solar gets crowded out of the grid is because the grid operator is running gas plants in the middle of the day, so that they are ready to ramp up in the evening hours to meet evening electricity demand,” Wisland said. “If we can find other resources to meet that demand, we can reduce the need to run gas in the middle of the day, thereby reducing some solar curtailment.”

“This bill, as written, puts the CPUC (California public utilities commission) and utilities on notice that they must make a plan for addressing the ‘duck curve’ with fair and focused use of clean energy resources, so it’s just a first step – but a good one,” said Rosalind Jackson, Managing Director – External Relations for the nonprofit Vote Solar. “The reality is that solar, particularly widely-deployed solar paired with storage and demand response capacity, is extremely reliable and flexible.”

California’s renewable energy leadership offers a model for other states to follow. The aggressive renewable energy and pollution reduction goals the state has set mean it will have to tackle problems, like the duck curve that come from integrating renewables into the grid. How they will do so can serve as important lessons for states looking to follow a similar path.