A large amount of solar panels, the proliferation of which is great for the environment but exasperates the duck curve.
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The Duck Curve: The Cute-Sounding Problem that’s Getting Worse

Daren Wang
September 21, 2023

As the growing supply of clean energy reshapes the grid, the need for all of us to adapt to a changed energy supply goes up. More homeowners are generating clean power and cutting costs through solar panels, but that’s only the tip of the iceberg. Utility-scale solar, where large fields of solar panels feed energy into the grid, is responsible for a greater percentage of the nation’s electricity supply every day. That’s good news for the climate; however, challenges arise with any significant transition.

One of the biggest issues the energy transition faces is not how much energy we have, but when we have it. The National Renewable Energy Laboratory identified the challenge years ago: the misalignment between solar panel output and peak energy demand. This discrepancy, referred to as the "duck curve," presents complexities for the grid, but solutions are available.

The energy demand curve, when taking into account renewable energy, turns into a duck shape, illustrating why demand and prices spike during dinner time.
The energy demand curve, when taking into account renewable energy, turns into a duck shape, illustrating why demand and prices spike during dinner time. Image Source: CAISO

Why a duck?

When you plot a graph of solar power generation against energy demand, it looks like the profile of a duck’s body. The tail is the minor morning peak corresponding to the wake-up energy needs. Then there’s a midday dip when many are away from home while the sun is generating lots of energy. In the evening, we get a spike in demand as people return home.

The duck curve underscores a critical issue for solar power. Solar panels excel in direct sunlight, peaking during daytime hours when electricity demand is minimal. To make the grid work, we need to synchronize demand and supply.

Rooftop solar panels are popular for their non-intrusive nature and potential to generate surplus energy, which can be sold back to utilities. Yet, their adoption makes the duck curve worse. The more solar panels are deployed, the deeper the curve becomes. Panels over-generate during off-peak hours and struggle to match peak demand, leading to curtailed solar energy during low-demand times.

Adding efficient energy storage solutions is one way to flatten the duck curve. That’s why cheaply storing excess solar energy and releasing it during peak demand periods is so important to the energy transition. Storage technology is advancing, with research and funding directed toward enhancing capacity. Projections suggest a five-fold growth in storage capacity by 2050. This evolution empowers utility companies to harness and deploy solar energy strategically, minimizing low-generation days.

It's about more than just cost

Nowhere is the duck curve more prevalent than in California. And the California duck curve has enormous implications for the climate. When solar or wind isn’t generating energy and stored energy isn’t making up the difference, your local utility needs to get energy from other sources, often from fossil fuels.

Managing the output of various generating plants is a big part of any utility company’s process. There’s baseload energy, which is always running and always available, including overnight. Baseload is the source of energy that keeps your air conditioning on and your car charging while you sleep. These generators tend to be cheaper to run, have newer technology, and run more cleanly and efficiently than older fossil fuel generators. Oftentimes, nuclear power and hydropower make up a chunk of the baseload.

Renewable energy, like solar, contributes during the daytime when the sun is shining. Because it’s only available when conditions are right, sources like solar and wind are considered “intermittent sources.”

But during peak times—the tail and the head on the duck curve--utilities stoke up older, less efficient fossil fuel generators to cover the increased demand. The evening, when people come home from work, turn on the AC and the television, and fire up kitchen appliances to make dinner is the peak of demand, but it happens just as solar generation goes away.

In places like California, where utilities vary their rates based on demand, a program known as “time-of-use” is the most expensive time to use energy. If you’re lucky enough to have a backup battery, this is a good time to use any energy stored in it. This is also the dirtiest time to use energy. When generators have much more capacity than the overall demand, the utilities can operate the generators at their most efficient levels without having to overburden the system. But when the demand is high, they must run the generators at less efficient levels.

Taking it on the road

Think of it like taking your car on a road trip. If you want to get the maximum mileage out of every gallon of gas, you’ll drive at around 55 miles an hour. Most cars are designed to maximize highway mileage around that speed. But if you want to get to your destination quicker, you drive over 70 mph and get fewer miles for each gallon.

When electricity demand is high, utilities can’t drive 55. They have to operate outside their most efficient level. And that means using more fuel and more emissions.

But it’s even worse at really high-demand times. Utilities often bring their “Peaking power plants” or “peaker plants” online to meet the high demand. If running a modern generating plant beyond its maximum efficiency is like driving your car too fast, running a peaker plant is like driving a rusty 1972 Buick with bad spark plugs. It gets terrible mileage, uses much dirtier fuel, and pollutes more. And because it only gets used in emergencies, the owner doesn’t invest much money to maintain it. When you get stuck behind that car, you breathe in the fumes and wonder what it’ll take to get that clunker off the road.

The answer is, “Don’t run your dryer in the evening.”

That’s an oversimplification, but every watt of energy you don’t use during peak times gets us one step closer to permanently retiring those peaker plants from use.

At its heart, this is what OhmConnect is about. By working with consumers to reduce electricity demand during peak times, we help utilities reduce peaker plant usage during the worst parts of the day.

While challenges accompany the expansion of solar power, its positive contribution to reducing fossil fuel dependency is noteworthy. As we find more and cheaper ways to store energy, the impact of the duck curve will diminish, making the grid more dependable and substantially cleaner. Although many are investing in lithium-ion batteries, other technologies, such as pumped hydro, geothermal energy, and even iron batteries offer lower-cost options. The ongoing development of storage solutions underscores the pivotal role solar power plays in enhancing the efficiency and sustainability of our electrical grid.

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