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We will need more fast acting reserve for a successful energy transition

On a sunny Friday afternoon, I found myself pondering fast-acting ancillary services and the barriers they face. Since I’m sure most other normal people also think about such things, I decided to share some of my musings on the topic.

Starting with the ‘basics’ – we know having more renewables on the grid and the phasedown of synchronous thermal generators will result in decreasing system inertia. Lower system inertia will result in grid frequency deviations becoming faster and more common. My assumption here is that the resulting faster change in frequency will require faster-acting ancillary services in order to recover the grid frequency in shorter timescales.

In some counties ‘fast frequency services’, acting on the timescales of a few seconds or less (e.g. as fast as 150ms in Ireland), provide significant value to grid operators and as such we often see them remunerated at higher levels. Furthermore, storage assets and demand side response are often the only asset types that can provide these fast-acting services in the required timeframes.

Energy storage technologies are well suited to providing very fast frequency services. Source: Meng, et al., 2020, with some of my own own observation added in

TechnologyPower rage (MW)Energy rating/storage volume (MWh)Response timeDischarge time
Super capacitors (high voltage)<50<0.2810-20ms1ms to 1 hour
Lithium batteriesUp to 50 or more<50<40msMinutes to hours
Advanced lead acid batteries<40<40<40msSeconds to hours
Flow batteries~3-50<100<40msSeconds to hours
Pumped hydro (for reference)>50MW100 – 10000 GWh20s-10minhours

In terms of the barriers these demand side flexibility technologies face in providing such rapid ancillary services, in my view they can be divided into three categories:

  • Technical barriers
  • Market barriers
  • Regulatory barriers 

From my research, the technical barriers relate primarily to the distributed nature of the demand-side flexibility (DSF) assets providing the ancillary services in the required timeframes. Regarding the distributed nature, things like Low Frequency Demand Disconnection (LFDD) can trip these assets off the grid when they are needed most (see for further discussion on this). Regarding responding fast enough – there are also issues around the required latency of communication meaning that on site frequency metering would be a must. While this would be fine for a larger commercial scale battery, in terms of tapping into smaller loads (read ‘residential’) this would cause some issues.

Market barriers for fast-acting ancillary services provision include the list of barriers that exist for aggregators and storage assets providing any sort of ancillary service / balancing market access. These include prequalification requirements, registration and licensing requirements, minimum bid sizes, lack of DSO/TSO coordination, along with many others. Existing large vertically integrated players within the energy and power markets also present a barrier to competition. These players have been known to abuse their market-dominant positions and are powerful lobbying forces. General market characteristics also come into play – for example, GB and Ireland, as islands, have lower levels of inertia than the highly interconnected mainland European grid, which further drives the need for faster-acting services.

Regulatory barriers can be fairly market-specific (Clean Energy Package should in theory put an end to this in the EU). A further significant regulatory barrier is the specification in legislation of the type of assets that can provide demand side response. For example, in Poland, Romania, Slovakia, Slovenia, and Hungary only generators are allowed to provide primary frequency control services.

Final thoughts on the barriers to remove and challenges to overcome, via fast acting ancillary services:

As European countries adopt the Clean Energy Package, they will be forced to take a more market-based approach – nicely outlined in a report produced as part of the Delta-EE Flexibility Research Service. However, the dominance of vertically integrated players presents a significant challenge to the opening up of these markets. Regulators need to ensure the markets for these ancillary services are neutral and non-discriminatory. Products should be created/defined that link to real-world needs – e.g. based on system inertia. Lastly, the platforms for the procurement of these fast-acting ancillary services need to be conducted in a competitive and transparent manner.


To the diligent reader who has made it thus far – I would be interested to hear your thoughts on the above, especially your own views on the barriers and challenges. There are a few cans of worms I didn’t open – such as the role of grid forming inverters, however my colleague Jon Ferris has that covered (also part of the Delta-EE Flexibility Research Service).

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