The Duck Curve: What is it and what does it mean?

So let’s talk about the duck curve and what it means in the world of renewable energy. But what is the “duck curve?” Does it involve our adorable little animal friends who quack the day away? Well, kinda, but not really.

Put simply, the duck curve is the graphic representation of higher levels of wind and solar on the grid during the day resulting in a high peak load in mid to late evening. The difference in the Duck Curve and a regular load chart is that the duck curve shows two high points of demand and one very low point of demand, with the ramp up in between being extremely sharp. It looks like a duck! Since renewable energy has become more common over the years, the duck curve is appearing more often and is getting worse.

Let’s look at an example of what the duck curve looks like:

 

The duck curve, explained.

As you can see, this chart shows the electric load of the California Independent System Operator (ISO), just think the California grid, on an average spring day. The lines show the net load—the demand for electricity minus the supply of renewable energy—with each line representing a different year, from 2012 to 2020. The chart also shows that energy demand reaches its peak in the morning (between 6 A.M. and 9 A.M.) and afternoon times (between 6 P.M. and 9 P.M). This demand shows that people need more energy as they get prepared for work or school in the morning and when they come home from work or school in the afternoon.

Let’s look at lines 2012 and 2017, for example. Comparatively, the 2012 line is much more smoother than the 2017 line. This is because the feed of a renewable power supply has not yet been introduced. By slowly integrating solar energy, the demand for electricity from the electrical grid becomes smaller and smaller. However, the renewable energy source is not enough to meet the demand in its entirety, especially in those peaks hours that I referenced earlier. So the electric grid is left to pick up the slack, which can sometimes be problematic.

Why is a duck causing problems?

As you can see by the chart, solar energy works best during the bright hours of the day, which makes energy demand lower greatly. We’ll call this the duck’s belly: the lowest point of demand. The demand begins to rise rapidly as the sun sets and people get home at 6 P.M. There’s no sun to power all of the appliances getting turned on by people returning home from work or school, and the grid is left to answer to that high demand. Therefore, the demand rises very rapidly (the duck’s neck) to a peak in the afternoon hours (the duck’s head).

For many decades, energy demand followed a fairly predictable pattern, with very little change in levels of demand. This allowed electrical workers to become experts with sustaining a stable output of energy. Well the duck curve kinda throws a wrench in that. In order to meet the baseline requirement, or “baseload”, utilities run BIG power plants that run on either nuclear or coal, which run around the clock. The problem with coal and nuclear power plants is that they’re expensive to completely startup and shutdown, and are more effective in ramping up or down. Then there’s the “peak load,” which is satisfied by peaker plants that usually run on natural gas, and more frequently renewables.

In order to maintain top efficiency, regulators will often turn peaker power plants off and ramp down the baseline plants during times of very low demand, such as hours of the “duck’s belly.” However, the sudden and rapid increase in demand means that regulators have to quickly turn back on these power plants, which is not only expensive, but could lead to more pollution and high maintenance costs.

Another problem with the duck curve lies in the belly of the duck. In some places, demand becomes so low that grid operators are forced to turn off the peaker power plants and ramp down the baseline power plants. Then, just a few hours later, they all have to get ramped up again with little to no warning, which can cause problems for grid stability.

So problems with the duck curve lie in those sudden and steep changes in demand. Grid operators and regulators struggle to maintain stability and efficiency by turning power plants on and off, causing instability in the power supply, large expense to taxpayers, and pollution to the environment.

So what can we do about the Duck Curve?

One probable solution for the duck curve can be found in a method called interconnection. This strategy involves connecting multiple energy grids together to make a large energy grid. In theory, this would broaden and disperse the load and availability of solar and wind across a larger area, which in turn would flatten the duck curve.

This strategy could provide a long term solution to the problem. However, although the technology already exists, the politics of a large, interconnected grid is unlikely due to “not in my backyard” concerns and securing the rights of way.

The second method of smoothing out the duck curve is committing to the storage of energy generated by solar and wind, instead of immediately sending that energy directly to the grid. The energy can then be “dispatched” when it’s needed, and would almost definitely flatten the curve. This method could prove very expensive to execute in near term however battery storage continues to fall in price and more utilities are actively seeking it as a viable solution.

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