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Working Group C5.27, “Short-term flexibility in power systems: drivers and solutions”

Increased solar PV and wind generation is significantly driving the demand for short-term power system flexibility. Australia has see a massive proliferation of residential solar photovoltaic (PV) systems in Australia, from less than 100,000 customers a decade ago to more than 2.2 million in 2020 - with the generation capacity of these systems rated at 9 times that of the country’s largest power station.  This presents a significant challenge for the real time balance between production and demand.  Working Group C5.27 has recently completed its Technical Brochure which should be available on e-cigre within the next few weeks.  This TB examines the requirements for short-term flexibility in markets and the various sources that can be used to satisfy this need and the arrangements needed to enable these sources.  The Australian members on this Working Group were Greg Thorpe and Gregor Verbic.

Flexibility is a characteristic of capacity. The more flexible the capacity (in terms of lack of constraints), the better it will be able to serve the short-term needs of the power market.  The key parameters of flexible plant include:

  • Speed of response
  • Size of response
  • Duration of response
  • Whether the response is up or down
  • Whether the resource can be moved around in time

The brochure examines all sources of flexibility, including:

  • Storage, including pumped storage, Electric Vehicles, Vehicle to Grid and batteries;
  • Cross-border capacity between grids;
  • Intermittent resources;
  • Demand response; and
  • Conventional technologies: Hydro, Open and Combined Cycle GT’s, Thermal, Nuclear and combustion engines.

The working group produced a survey that was answered by 22 respondents from five continents, representing a wide range of power system and market characteristics.   Key findings are briefly summarized below.

Drivers of the need for short-term flexibility

Increased wind and solar power coupled with system level forecasting errors and lack of observability  are the most important drivers for short-term flexibility.  Others are the lower levels of  flexibility of some conventional power plants and increased levels of behind the meter generation.

There are significant regional differences. Wind and solar PV at the TSO level were seen as very important in South America, and slightly less in Europe, but not so important in Asia & Oceania and the US.  DSO level solar PV was considered important in all regions. "Changes in energy market design" and "Changing weather patterns" were both seen as having high importance in South America but less so in other regions.

A general conclusion is that the respondents expect the major needs for more flexibility to occur in the time horizons between 5 minutes and 12 hours, and not in the shortest time horizons. This is probably due to geographical smoothing. In this context it should be noted that virtually all respondents were TSOs, and none were DSOs. Because the latter cover smaller geographical areas, they could be more concerned about shorter time horizons (e.g. solar insolation variations on a particular feeder).

Providers of future short-term flexibility

The highest expectations for future flexibility were from existing and new hydro and batteries, with somewhat less for industrial level demand response.  Batteries stand out as the most important future source for the time horizons below 5 minutes.

There are significant regional differences, notably expectations of conventional fossil generation are lowest in Europe, probably related to the continent's climate policies that imply decommissioning of large shares of such generation. Asia and Australia have high expectations from increased AC interconnection, which in Australia's case means between states.

Arrangements to increase future short-term flexibility

The overall most important measures for all continents are:

  • Improve functioning of intraday markets.
  • Lower barriers for participants in balancing markets, including allowing more aggregation.
  • Establish/enhance cooperation between DSOs and TSOs in order to utilize mutual resources.

The last two of these are particularly important in Australia, where the level of decentralised resources is increasing.

The Technical Brochure will  be available shortly in e-cigre