The duck curve is turning into a canyon
August 16, 2023

Lewis Feldon & James Wilson

Solar PV technology is forecast to surpass coal as the world’s largest source of power with capacity tripling in the next five years, per IEA’s Renewables 2022 report. What was once expensive and provided only small amounts of power, now provides real, cheap energy without the need for fuels or even significant maintenance outside bi-annual panel cleanings. However, apart from the land space required, the major drawback is that it is only available when the sun is shining.

How the duck curve is formed

Most single-axis tracking PV panels form a rounded trapezoidal power production shape, where power production ramps up after sunrise and ramps down towards sunset, with peak energy output occurring in the middle of the day. However, in most regions of the world peak demand occurs just after sunset, as people heat their homes and perform cooking and other activities. Because of this, there is a rapid decrease in available power simultaneously with a sharp rise in electrical demand, resulting in a dispatchable energy supply curve shaped like a duck where the duck neck is the increase in required energy.

The effects of the duck curve

Because of this, energy generators must quickly ramp up dispatchable power technologies, which still need to have a power capacity greater than the Solar PV installed in an area. For example, if 1000 MW of PV can satisfy the daytime needs, it can be assumed that the evening peak will be higher and greater than 1000 MW of dispatchable generation. This means that even with a large penetration of solar farms a huge amount of carbon-based generation is still used (notwithstanding that energy production is still required overnight.) This reliance on carbon-based generation not only leads to higher emissions but also results in higher peak prices, as the quick energy ramp-up commands higher prices.

The ”canyon” curve

As the uptake in renewable generation continues to grow in line with the global push towards carbon neutrality, the inevitable increase in solar PV generation is further worsening the duck curve phenomenon into what now appears to be becoming more of a canyon. As an example, CAISO (California’s Independent System Operator) reveals how their load curve has morphed from resembling a duck in 2015 to a canyon in 2023. (image source: IEA.)

The recent gradual growth in solar PV generation further increases the difference between the demand on the network and the available solar generation throughout the day, thus, making the challenges of meeting the demand requirements in the evening as the solar generation ramps down and the demand ramps up even steeper.

Unfortunately, in an attempt to reduce the strain on the network to overcome the steep climb in demand during the evening, the “free” green energy produced by the increased solar PV generation in some instances needs to be curtailed to prevent such a large dip in the net demand. This waste of renewable energy is inefficient and does not align with the global target of becoming carbon neutral and as such, mitigation strategies must be sought.

Mitigation strategies

Since reliable energy is required, it means that dispatchable generation is needed to combat the duck/canyon curve. The majority of dispatchable generation at present is carbon-based such as open-cycle gas turbines which do not help with climate goals.

However, it is possible to still use solar energy after dark, and this is by using energy storage. The good news is that energy storage is evolving rapidly. Energy storage can mean a variety of things, but the principles are the same. If you build PV bigger than required for daytime demand, the excess can be channeled into a storage technology and used at night. The first large-scale storage technologies were pumped-hydro storage, which is still very efficient and practical but requires very specific topographies. Today, battery technologies such as lithium-ion and even newer types such as vanadium-flow and iron-air are beginning to play a big role in our fight against climate change.

Finally, demand-side response can also help. If non-essential loads can be switched off during the peak of the duck/canyon curve, this will also help to mitigate the effects. This can be done via financial incentives where people can be paid for switching off these loads.

How can PSC help?

As energy transition experts, PSC can help with studies related to dealing with the duck/canyon curve, as well as the integration of renewable energy sources, energy storage technologies, and other solutions such as gas turbines.

PSC has recent experience in analyzing and designing large Battery Energy Storage systems (BESS) up to 1GW in size. It is sites like these that can help tackle the ever-deepening duck/canyon curve.

Contact us for more information.