Solar and wind energy generation are increasingly prevalent in California’s CAISO electricity market, but renewables’ intermittent generation is limiting their market share. The sun doesn’t shine continuously and the wind doesn’t always blow, leaving gaps in a generation that can only be filled by nuclear, batteries, natural gas, or other sources. Subtracting out renewable generation from total load yields net load; charting this over a typical day produces something that looks like a duck. This so-called “duck curve” shows typically show net load rising in the early daylight hours, dropping substantially during peak midday solar generation, and rising rapidly as the night comes. Every year the “belly” – or the net load during peak generation hours – has gotten shorter and shorter, limiting solar’s attractiveness. CAISO is not a growing market for natural gas, but the fuel may have a role for years and even decades due to the duck curve. 

CAISO’s electricity demand profile

Electricity demand varies by market, temperature, and season, but it tends to follow a generally predictable pattern. Demand tends to fall from midnight to daylight as consumers sleep; rises as people wake up and enter businesses; increases throughout the day on greater business/residential activity; and peaks around 6 – 8 PM, when consumers arrive at home (and turn on appliances) or head to restaurants and retailers. In the summer this pattern is most pronounced. We’ve selected a typical day in August 2021 to show California’s electricity profile.

As you can see above, we’ve segmented a typical electricity demand profile into two lines: a black “load curve” line, which shows total demand; and a red “net load curve” line, which subtracts renewables generation from the total demand. Solar output begins at daylight, or around 6 AM, causing natural gas and other baseload power sources to “ramp down.” After solar generation peaks at 11 AM – 1 PM, however, natural gas and other baseload sources must “ramp up” generation to provide electricity supply for 6 – 8 PM peak demand. After the sun goes down, CAISO is almost entirely reliant on natural gas, nuclear, and geothermal baseload power sources, plus some wind and coal generation.

Seasonality and the duck curve

August, typically the hottest month of the year, is often the most favorable for solar generation. What about when the weather is more temperate, like in April? We find that net load continues to decrease amid California’s enormous solar expansion, causing significant economic and system curtailment. As electricity from solar generation enters the grid, power prices tend to drop amid increasing supply, rendering additional generation less economic.

Moreover, too much generation can lead to physical curtailment as transmission lines get clogged. These dynamics will pressure the attractiveness of solar generation – but also could give rise to a higher reliance on gas peaking plants and/or longer-duration storage such as utility-scale batteries. For a deeper dive into CAISO’s solar/battery mix, drop us a line: info@enkonenergy.com

A healthier duck curve?

To make California’s duck curve more manageable, the state will require some solution: either more natural gas storage and peaking plants, greater battery storage, or, most likely, all of the above. We think California natural gas could play an important role in making the duck curve more manageable. In a future edition, we’ll discuss the duck curve’s growing impact on California gas storage operations.