- Overview of Capacity Calculation Methodology (CCM) project
- Methodology and processes
- Updates and newsletter
- Upcoming Stakeholder Events
- Day-ahead (DA) and Intraday (ID) (ATCE) Capacity Calculation
- DA/ID (ATCE) CCM EPR
- Post go-live of DA/ID (ATCE)
- Intraday (ID) Flow-based Capacity Calculation
- Long-term (LT) Capacity Calculation
- Balancing timeframe (BT)
Flow based basic information
Flow-based capacity calculation in short is a method used in electricity markets to determine the maximum amount of electricity that can be transferred between different bidding zones while considering the physical constraints of the transmission network.
Flow-based (FB) is closely related to several key regulations and guidelines in the European electricity market, including the Capacity Calculation Methodology (CCM), the System Operation Guideline (SO GL), and the Capacity Allocation and Congestion Management (CACM) regulation.
Capacity calculation is the process of translating the complex physical grid into a simplified form that can be understood and applied by the Nominated Electricity Market Operators (NEMOs). The purpose of capacity calculation is to translate physical transmission limits in the power-grid into limits on commercial trades at par with the market design and operational security.
Capacity calculation is a legal obligation for the TSOs to be carried out in a common coordinated process within each Coordinated Capacity calculation Region (CCR). In the Nordics, the coordinated capacity calculation is done by the Regional Coordination Centre (RCC). Nordic TSOs (Energinet, Svenska Kraftnät, Statnett and Fingrid) are responsible to deliver the local/national input to the coordinated capacity calculation process. The legal background for capacity calculation is provided by both national legislations, and the CACM GL, the FCA GL, SO GL and the Nordic CCM.
Why Flow-based
CACM GL states “There are two permissible approaches when calculating cross-zonal capacity: flow-based or based on coordinated net transmission capacity. The flow-based approach should be used as a primary approach for day-ahead and intraday capacity calculation where cross-zonal capacity between bidding zones is highly interdependent.”
In the electricity markets, the transmission grid constrains how much electricity can be transferred between any two points in the grid. It is unrealistic to do unlimited expansion of the transmission grid, thus there is a need to have a methodology to optimize the utilization of the transmission grid.
In the Flow-based approach, complex and physical limits of the grid are taken into account when determining cross-zonal capacities and expressed in a simplified manner. Algorithms used to calculate the electricity prices and volumes are simplified in order to meet operational requirements.
Renewable energy also creates a need for optimizing the limited transmission capacity. When integrated into an electricity system, renewable energy sources are often concentrated in specific geographical areas due to favorable conditions and weather patterns, such as wind moving across regions, leading to significant variations in production volumes. To manage these differences, it is essential to transport large amounts of electrical power across different areas.
Key elements of Flow-based capacity calculation
The Flow-based approach provides capacities for commercial power exchanges by the introduction of PTDFs and RAMs.
- Power Transfer Distribution Factors (PTDFs): represent how power flows through the network when electricity is exchanged between zones. They help in understanding the impact of transactions on the network's physical limits.
- Remaining Available Margin (RAM): is the available capacity for commercial exchanges after accounting for the physical constraints and already committed transactions. It ensures that the network remains secure and stable.
Other key elements in the Flow-based model are:
- Critical Network Elements and Contingencies (CNECs): network elements and relevant contingencies that impact capacity calculation are identified. This helps in understanding the constraints and ensuring the security of the transmission network.
- Reliability Margin (RM): A methodology is established for determining the reliability margin, which accounts for uncertainties in the capacity calculation process and ensures operational security.
- Generation Shift Keys (GSKs): are used to model changes in generation in response to the net position changes of each bidding zone.
Flow-based capacities are integrated into the market coupling processes, where transmission capacity is allocated simultaneously with energy trading. This helps in optimizing the use of the network and reducing congestion.
By considering the actual physical flows, flow-based capacity calculation aims to improve the operational security and economic efficiency of the electricity market.
Further material
Flow-based for beginners (video): https://youtu.be/TrgaxZuvSjc
Differences between NTC and Flow-based are presented in stakeholder material: CCM project - Stakeholder Forum 12.12.2019
General information on the Nordic RCC website: Nordic RCC/Flow-Based