The Duck Curve and the Example from Spain

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In recent years, due to the boom in the electricity generation from renewable energy sources, the duck curve term has become well known. What is this curve? What are the consequences for electricity systems? What measures can these systems adopt to offset its effects and how can they take advantage of such effects? Below, we will examine all these aspects of the increasingly well-known duck curve.

What is the duck curve?

The duck curve is the name given to the unique shape of the graph showing the difference between the electricity demand of a system with a large share of solar power generation, and the electricity supply from non-renewable sources to that system.

Duck curve California 10/22/2016. Source: CAISO.

This graph shows the gap between demand and non-renewable supply during the hours of the day between sunrise and sunset. It features highly accentuated ramps during these late hours, which typically align with peak demand.

This gives the graph an image resembling the outline of a duck, with “tail” in the early morning hours, “belly” in sunny hours and “neck” and “head” back in the evening hours. Thus, in 2012, CAISO (California ISO) started calling this graph the duck curve and, since then, continues to analyze its evolution.

The gap and the accentuation of the ramps are becoming more evident every year, due to the progressive and incessant incorporation of energy from renewable sources into the energy mix. In 2023, duck curve may be renamed as canyon curve, given the increased depth of that ramp.

Evolution of the duck curve in California. Source: CAISO.

Impact of the duck curve on electrical systems

Broadly speaking, power systems are affected in two main ways: supply security and price disruption.

1. On the one hand, the saturation of renewable generation in the central hours of the day can lead to excessive injection into the grid from PV facilities. This situation also leads to a sharp drop in prices, which may discourage new investments in such utilities.

2. On the other hand, solar PV generation eventually ceases after a rapid drop off during sunset. So, it is necessary to compensate for this lack of generation with large inputs of energy rapidly in order to meet the high demand during those hours without jeopardizing supply security.

In this type of scenario, wholesale market prices experience a significant surge compared to more stable situations. As mentioned, these peaks – both positive and negative – tend to become even more pronounced, due to the [Click on the banner below to read more]

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