Ancillary Services in Mainland Europe

What Are Ancillary Services?

Ancillary services are essential to keep the grid balanced and efficient, so that it can fulfil its primary role of delivering electricity. In simple terms, ancillary services are part of the mechanism that ensures that supply and demand stay in harmony on the grid. While we typically think about power generation when we discuss decarbonising electricity, keeping the grid resilient while doing so – via services like grid frequency control – is equally crucial.

Why Does Frequency Control Matter?

The grid operates on alternating current (AC), meaning that the current flows in a sinusoidal wave at a standard frequency—typically 50Hz or 60Hz, depending on the region. Controlling frequency is essential; if it fluctuates too much, the stability of the entire grid is compromised, putting infrastructure and safety at risk.

Traditional thermal spinning generators, for all their carbon crimes, are actually very good at maintaining grid frequency. These generators spin in sync with the grid, naturally providing “inertia”—the grid’s built-in resistance to sudden changes. This inertia smooths out abrupt shifts in supply or demand, helping to maintain a steady frequency.

‍Challenges with the Shift to Renewables

As we transition to a decentralised, renewable-heavy grid, fewer traditional thermal generators are available to stabilise frequency. Solar and wind are DC generators that use inverters to transform their DC current to AC current. While these inverters can control the frequency of the generator, they do not contribute to the stability of grid frequency in the same way as thermal generators. This creates challenges in keeping the grid frequency stable amid rapid changes in electricity supply or demand.

Batteries to the Rescue!

Here’s where innovation steps in. Battery Energy Storage Systems (BESS) have emerged as a promising solution for frequency control. These batteries can, with extremely fast response times, inject power into the grid to raise the frequency or absorb it to lower the frequency, offering flexibility and resilience in real-time.

‍The Role of Transmission System Operators (TSOs)

The responsibility of maintaining frequency balance lies with Transmission System Operators (TSOs). TSOs continuously monitor supply and demand, procuring the necessary BESS capacity to adjust frequency levels. While some TSOs use direct contracts to procure ancillary services, many operate open markets where providers compete. Rules vary by region, with different requirements for how long assets need to be available, which services can be stacked, and the procurement order.

For an insightful introduction to how these markets work in Europe, watch Laura’s video.