It’s not what you think. Meet the Duck Chart.
In the lively conversation about how to integrate variable renewables such as wind and solar into our electric grid’s generation mix, an unlikely player has entered the fray: a duck. It’s not literally a duck, mind you, but rather a mallard-esque graph—now famously known as the “duck chart”—from the California Independent System Operator (CAISO) in a report released late last year causing quite a stir of late.
Superficially—and with a bit of imagination—its curves look like the profile of a duck, with a tail, fattening belly, steep neck, and head. But it’s what the duck chart actually conveys that’s generating the meat of the conversation.
The duck chart shows the net load CAISO’s central thermal power plants would need to supply when you combine hour-by-hour expected customer electricity demand with the offsetting output from variable renewables (especially solar) over the course of a typical spring day. As the forecast goes to 2015 and beyond, the curve shifts as growing shares of renewable generation are added to the grid, with the belly of the duck sinking deeper and the neck rising more steeply.
That deepening belly and subsequent steep rise to the top of the head is what’s getting so much attention. It makes clear that we will soon face some real challenges in managing the grid if we don’t do something. The good news, though, is that we have plenty of choices about what we can do to ensure continued reliable grid operation of the grid.
Understanding the duck
The belly of the duck sinks deeply during the middle of the day and into early afternoon, when solar output is at its peak, minimizing demand for the grid’s central thermal power plants. That creates a potential over-generation problem. Why? Because our grid is built upon the idea of baseload generation, a baseline level of electricity generation that’s always there, supplied by power plants that are built to more or less run 24/7 at full tilt. Utilities then add other, more flexible generation sources on top of that baseload as demand dictates.
But if solar’s output reduces net utility load too much—as it does in the duck chart’s predictions for years 2015 and beyond—then net load could fall below baseload generation, resulting in a potential excess of electricity production during certain hours that must be addressed.
Meanwhile, solar’s output falls off in mid-afternoon, just as California’s electricity demand peaks, with high demand lasting into evening. It’s a double whammy effect. The result is a rapid spike in utility electricity demand (the steep slope of the duck’s neck). Power plants, especially those fueled by coal and nuclear, weren’t built to ramp up or down that quickly. They’re not the equivalent of an easy-to-operate dimmer switch for the lights in your kitchen. They’re more of an “on or off” type of operation, and it’s difficult, expensive, and time consuming to adjust their level of output. Not exactly compatible with what the duck chart says is coming.
It’s important to note that the duck chart depicts a spring day, when milder temperatures result in relatively modest electricity demand, yet when solar production is relatively strong. By design, therefore, the duck chart illustrates the most extreme circumstances that our electricity grid must be able to accommodate.
Even though the systems weren't optimized for variable renewable resources, the systems have had enough embedded flexibility to ramp up and down to accommodate them. Thankfully, then, we’ve been able to successfully integrate renewables into our existing grid system … until now. The duck chart hints at a time—coming in the near future—when that will be more difficult to do unless we embrace new ways of thinking.
Taming the duck
Thankfully, this is a solvable problem, as others like the Clean Coalition have been pointing out. In fact, this is one of those “good problems to have.” California is among the world leaders in clean energy development, and has the opportunity to consider a host of innovative ways to enhance system flexibility to ensure the electricity needs of consumers can continue to be met in an affordable and reliable manner, even in the face of a growing installed base of solar and wind energy projects.
- Import/Export. Power markets are interconnected, with electricity routinely flowing into or out of a particular region to surrounding regions. The duck chart makes a simplifying assumption, only showing the load and the resources within the CAISO region. In reality, California is connected to other regions that have differing characteristics in terms of electricity usage by customers (by nature of differing climates or time zones) or in terms of the types of generation resources in those regions (such as lower concentrations of solar). This significantly alleviates the concerns of potential over-generation depicted by the belly of the duck, as CAISO would be positioned in those times to export power to surrounding regions.
- Energy efficiency and demand response. California already has a legacy of these demand-side efforts. Still, fully valuing them for resource planning purposes is rarely done. These demand-side resources can change the shape of daily demand, moving power usage into different times of the day. For instance, the mid-day solar power can be used to heat water early or pre-cool homes by starting air conditioners with smart controls well before customers return to their homes after work. New service models, like those of OPower and Nest, have been very promising in changing customers’ usage patterns in ways that can mitigate the challenge depicted by the duck chart.
- Storage. Storage holds a great deal of promise, though the amount that has been installed so far has been small. California, in an effort to create a market for storage, has set a new goal for storage of 1.3 GW. Storage can come in all shapes and sizes. It could be pumped hydro, compressed air, large batteries, or electric vehicles. From a technical perspective, we are able to bring on more storage now. The biggest challenge so far has been cost of these resources, though they're expected to decrease over the next decade.
- Natural gas. This has often been the common answer for integrating renewables. There's a long list of reasons people point to natural gas as the solution. We're familiar with building these types of power plants, the fuel costs have been low for the past few years, and they are also very good at ramping up production quickly and can meet the system needs when the sun starts setting. However, natural gas plants also come with their share of problems. They produce greenhouse gas emissions and there's a long history of price volatility. Additionally, California has an established loading order that gives preference to energy efficiency, demand response, renewables, and distributed generation before turning to other resources to meet the state’s electricity requirements. As such, all of these options should be carefully considered and earnestly pursued before turning to natural gas plants as a solution.
Adding all these up, it’s clear that addressing the duck is not a problem about a lack of options. Instead, the challenge is ensuring that all options are given appropriate consideration in the search for solutions. Appropriately assessing all of these options will require work, including the need to establish appropriate pricing signals to encourage adoption of these resources. Additionally, the utility business model will have to evolve on both sides of the meter.
But this is why leaders choose to lead. In the face of challenge, a leader sets an example for others to follow. While California may be one of the first states to face this duck chart challenge, it won’t be the only one. If it can find the right combination of solutions, it can serve as a national blueprint. So, rather than more conversations about the challenge that the duck chart presents, let's focus on selecting the right combination of solutions among the many in front of us.
Duck image courtesy of shutterstock.com, Duck Chart courtesy of CAISO