Germany's duck curve – Integrating renewables into smart grids

About a decade ago, the California ISO came out with its ‘duck curve’ analogy, which shows minimum net load dipping ever lower as greater demand is met by solar during the daytime. Net load is the total electricity demand in the system minus non-dispatchable energy generation sources, aka. wind and solar generation. As higher shares of renewable energy generation drop at night as demand simultaneously ramps up, the neck of the duck is getting steeper and longer, now turning into the infamously dubbed ‘canyon curve’. As such, balancing the seamless integration of renewables and guaranteeing stable electricity supply is becoming increasingly challenging.

Let’s take a step back and look at California’s duck curve, which has been making waves on social media around the globe. 

California's duck curve

Although solar energy provides a fairly predictable reduction in net load, it is not exactly controllable. As more and more solar power is generated, the belly of the duck, aka. minimum net load in the middle of the day, even dropped below zero in 2023. This happens when supply outstrips demand and the remaining power produced can either be curtailed, stored or converted for later use.

This following image shows the transformation of the duck curve into a canyon curve, also in Germany. Simply put, dispatchable resources are reduced during the day but the need for flexibility drastically increases as the sun sets. 

Germany’s changing load profile

This steady increase in solar is also changing Europe’s load profile. If we take a look at Germany’s total load across the entire years of 2015 and 2022, specifically focusing on the renewable share of load and residual load (demand minus variable renewable generation), we notice that more renewable power causes the residual load to drop. At the same time, the spikes become more volatile and extreme as the years pass.

Taking a closer look at total load, renewable energy share of load and residual load from May 2023, we see a clearer picture of how they interact. 

The total load represents overall energy demand in Germany throughout the day aka. higher demand in the morning and early evening, followed by lower demand overnight. Notice that the residual load is a perfect mirror to the renewable share of load. This means when there is a higher share of renewables (usually in the middle of the day), the residual load is lower, and with it reliance on prime movers like coal and gas.

Now let’s compare the lowest residual load in each year from 2015 to 2023 in Germany.

Not quite as clean as its Californian counterpart, but it shows the same general trend of a bigger belly and a duck curve turning into a canyon. As the curves in and out of these dips get steeper, the need for flexibility increases. 

If we isolate 2016 and 2023, this becomes clearer.

Germany’s net-demand in 2023 is forming a significantly lower dip than 2016 with steeper edges on either side. In fact, on 10th April 2023, Germany’s residual load went into negative. While this shows that an increased share of renewables make balancing supply and demand more challenging, these challenges can be overcome with a greater focus on demand-side flexibility (DSF). 

Canyoneering with demand-side flexibility

Here are some possible pathways towards implementing demand-side flexibility in practice:

• Load shifting: Incentivizing consumers to use energy at the right times can go a long way in promoting load shifting; for example – implement time-of-use and dynamic tariffs to even out demand curves.
• Home-storage: better leveraging household batteries allows consumers to turn into prosumers by selling excess electricity back to the grid. Using EVs as additional storage systems with bidirectional charging also turns them into assets that provide flexibility to smart grids. Regulation must catch up with technology and encourage such demand-response programs.
• Utility-storage: large-scale batteries help maintain grid balance with their quick ramp-up times.
• Sector coupling: integrating sectors allows excess clean power to be utilized e.g. using hydrogen to store excess electricity. Similarly, waste heat from industrial processes can be used to generate electricity when demand ramps up and renewable production drops.
• Virtual power plants: aggregating the flexibility of millions of decentralized energy assets allows them to function as a single dispatchable unit. This provides huge potential to provide flexible power that can be used when solar production drops. 

So in summary, we shouldn’t fear the duck, nor the canyon. We simply need to better understand what repercussions clean energy systems have on smart grids and leverage technology to keep our electricity as reliable as possible. The key takeaway is that we have the resources at our disposal, we simply need to make better use of them.