Cross-Border Electricity Flows: Scheduling and Settlement in GB

1. The European Model: Market Coupling

The fundamental driver of electricity flow between countries is simple economics: power flows from where it is cheap to where it is expensive. This helps to lower overall costs and use generation resources more efficiently across the continent. To facilitate this, European countries have developed a highly integrated system called market coupling.

To understand why this system was created and what it does, let's watch a short video.

As the video explains, market coupling is a system where national electricity markets are joined together into a single pan-European market. Instead of traders having to guess price differences and book capacity separately, market coupling does it all in one go. This is often called an implicit auction, because the price of energy and the allocation of interconnector capacity are determined "implicitly" by a single, complex algorithm.

Let's look at a simple example to see how this works in practice.

The key idea is that by coupling markets, the system automatically finds the most efficient outcome. A central algorithm calculates a single set of prices and interconnector flows that maximises economic welfare across all participating countries. This sophisticated process is managed by designated power exchanges known as Nominated Electricity Market Operators (NEMOs), who work with the Transmission System Operators (TSOs) that provide the data on how much physical capacity is available on the interconnectors.

2. The Great Britain Reality: Post-Brexit Trading

This integrated, implicit model is how trading works across the European Union. However, a crucial point for understanding the UK grid is that Great Britain left the EU's Single Day-Ahead Coupling (SDAC) mechanism as part of Brexit.

So, how does the UK trade power with its neighbours now? We've reverted to a different, less integrated method known as explicit auctions for the main day-ahead market.

As the article explains, the process for day-ahead trading on GB interconnectors is now split into two distinct steps:

1. Capacity Auction: First, the interconnector operators hold an auction for the right to use the cable's transmission capacity for each half-hour of the following day. Traders who believe they can profit from a price difference between GB and a neighbouring country will bid for this capacity.
2. Energy Trading: Once a trader has secured capacity, they must then separately trade the energy itself on the respective power exchanges (e.g., buying on the French market and selling on the GB market) to realize their profit. This is known as arbitrage.

This "explicit" method is generally considered less efficient than the "implicit" market coupling used in the EU, as it requires traders to take on more risk and can sometimes lead to the interconnectors not being used as efficiently as possible.

3. Intraday Markets and Settlement in GB

Trading doesn't stop a day ahead. As forecasts for demand and renewable generation get more accurate closer to real-time, traders need to be able to adjust their positions. This happens in the intraday market.

Fortunately, Great Britain remains connected to the European cross-border intraday market, which is known as XBID.

The XBID platform allows for continuous trading across borders right up until an hour before delivery. This means that even though GB is separate from the EU day-ahead market, it is still integrated in the intraday timeframe, allowing for more efficient use of interconnectors closer to real-time.

Settlement in the GB Market

Once a flow of power has been scheduled via either a day-ahead explicit auction or an intraday XBID trade, it needs to be accounted for within the GB grid.

• From the perspective of National Grid ESO (the System Operator), an import of electricity is treated just like a British power station that is generating power.
• An export of electricity is treated like a large factory or city that is consuming power (a demand).

These scheduled flows are submitted into the GB system. The actual electricity flowing through the cables is metered, and the financial settlement—the process of making sure everyone gets paid correctly—is managed by a central body called Elexon under a complex set of rules called the Balancing and Settlement Code (BSC).

We will dive much deeper into the fascinating world of market settlement in Module 12, but for now, the key thing to understand is that interconnector flows are fully integrated into the GB balancing and settlement process as if they were domestic generation or demand.

Conclusion

Today, we've unpacked the commercial mechanisms that drive electricity flows between Great Britain and its neighbours.

Key Takeaways:

• Cross-border electricity flows are economically driven, moving from lower-priced markets to higher-priced ones.
• The main European mechanism is market coupling, an efficient "implicit" auction that schedules energy and transmission capacity together.
• Due to Brexit, GB's day-ahead market now uses explicit auctions, where capacity is auctioned separately from the energy, creating arbitrage opportunities for traders.
• GB remains part of Europe's cross-border intraday market (XBID), allowing for continuous trading closer to real-time.
• Scheduled interconnector flows are treated as generation (imports) or demand (exports) in the GB system and are financially settled through the Balancing and Settlement Code (BSC).

Preview of the next lesson:
This concludes our module on the regulatory framework. We've looked at high-level support mechanisms like CfDs and the market rules for international trading. Now, we're going to shift our focus from the wholesale grid to the companies you interact with directly. The next module, "Electricity Supplier Operations", will explore the business of selling power to homes and businesses. Our first lesson will examine the customer onboarding process and the role of Customer Relationship Management (CRM) systems in electricity supply.