Everything You Need To Know About The Duck Curve

What is the duck curve?

During the grid's operation, a unique curve often emerges, also known as the "duck curve". This curve primarily describes the unique daily variations in net grid load after a high penetration of renewable energy, particularly solar power, is integrated into the system. Its name derives from the resemblance of the net load curve's shape to the silhouette of a duck, and it exhibits the following notable features.

Cause analysis

The formation of the duck curve is mainly due to the integration of substantial renewable energy sources, especially solar power, whose daytime variability causes the net load to exhibit a duck-like pattern within a day.

• The fluctuating characteristics of solar energy during daylight hours, the output of solar power generation will increase accordingly as solar radiation intensifies. This significantly offsets the demand of electricity and keeps the net load (calculated as total load minus solar generation) at a low level. This segment forms the main body of the Duck Curve.
• Under normal circumstances, electricity consumption typically follows a natural pattern of being higher during the day and lower at night. However, with a high proportion of solar power generation, the diurnal variability of solar power generation amplifies the net load variation considerably.

Key Characteristics

The Duck Curve presents the characteristics of low net load at daytime hours, a sharp surge in the early evening, and a return to conventional levels at night. Those pose challenges to the grid's stability. Key features are:

• Low net load during the daytime hours: During peak solar generation periods, the grid can effectively utilize solar resources, reducing the net load on electricity demand significantly.
• A sharp surge in net load in the early evening: As the sun sets, solar power generation capacity rapidly decreases, while household and commercial electricity demand rises sharply, resulting in a sharp and abrupt increase in net load
• High nighttime load: With less support of solar power generation after sunset, net load returns to conventional patterns, requiring the grid to rely on alternative power sources to meet peak demand during evening and nighttime hours.

How to solve the Duck Curve?

Strategies to address the Duck Curve include enhancing grid flexibility, implementing demand-side management, utilizing grid interconnection and cross-regional regulation, are integrating virtual power plants (VPP) and distributed energy resources, as well as establishing more robust power systems through policy and market mechanisms.

Enhancing grid flexibility

By expanding flexible power resources and promoting energy storage technologies, the peak shaving capabilities of conventional generation units can be improved, thereby strengthening the overall flexibility of the power grid.

• Increasing flexible power resources: Enhance the grid's regulating capacity through boosting the proportion of dispatchable power sources such as gas turbines and biomass energy.
• Promoting the energy storage technologies: Mitigate the fluctuations in renewable energy output by adopting the battery energy storage systems (BESS) compressed air energy storage, and flywheel energy storage.
• Optimizing peak shaving performance of conventional units: Carry out flexibility retrofits for coal-fired power units to shorten their startup and shutdown times and reduce their minimum operating load.

Demand-side management

Time-of-use pricing and demand response programs can be employed to shift electricity usage to off-peak hours, which helps to balance the net load.

• Strategies such as time-of-use pricing and demand response incentivize the consumer to shift high-energy load consumption to nighttime periods, thereby smoothing the net load curve.

Grid interconnection and cross-regional regulation

Leveraging UHV transmission networks for power exchange, utilizing time differences and climatic variations across regions to achieve more effective electricity load balancing.

• UHV Power Transmission: Enable efficient power exchange between different regions through ultra-high voltage transmission networks. By leveraging time differences and diverse climatic conditions, electricity load can be balanced more effectively across interconnected grids.

Virtual Power Plants (VPP) and Distributed Energy Resources (DERs)

Aggregating distributed energy resources such as photovoltaic systems, electric vehicles into a virtual power plant (VPP), which supports grid peak shaving and improves controllability.

• By integrating decentralized resources, including solar power, EVs, and home energy storage systems, a “virtual power plant” can be formed to participate in grid peak shaving as a dispatchable resource.

Policies and market mechanisms

Establish a peak shaving ancillary service market and improve the renewable energy integration guarantee mechanism to promote the coordinated development of generation, grid, load, and storage.

• Peak shaving ancillary service market: Provide incentives for flexible resources to support grid stability.
• Enhance renewable energy integration mechanisms: Facilitate the integrated and efficient development of power supply, grid infrastructure, load management, and energy storage systems.

FAQs

Q1: What is the duck curve?
A: The duck curve describes the net load pattern in grids with high solar power, showing a deep daytime drop and steep evening surge in electricity demand.

Q2: Why is the duck curve a grid stability challenge?
A: It creates rapid net load changes, especially at sunset when solar power declines while electricity demand rises sharply.

Q3: How can energy storage help balance the duck curve?
A: Battery and other storage systems store excess solar energy during the day and discharge it during evening peak hours.

Q4: What role do virtual power plants play?
A: VPPs aggregate distributed resources like solar, EVs, and batteries to provide grid services such as peak shaving and flexibility.