Energy Explained: Minimum Operational Demand

25/08/2020
4 min

Australia’s energy ecosystem is rapidly transforming towards a decentralised, two-way power system, as increasing numbers of households and businesses invest in solar photovoltaic (PV) generation and energy storage capabilities. Evidence of strong sales and installations in 2019 strengthen the confidence that the trend will continue into the future.

While these resources present fresh opportunities for consumers and energy service providers, such as electricity cost savings and new or enhanced products and services, there are also new challenges emerging, such as rapidly declining ‘minimum operational (grid) demand’. 

To set the scene, today ”distributed” solar PV (installed by homes and businesses) is one of the largest generators in both South Australia and in Western Australia. In South Australia, it can provide close to 1 gigawatt of energy to the grid, and in Western Australia (WA) over 28.8% of WA households have rooftop solar PV installed.

What is minimum operational (grid) demand?

Duck curve graph of operational demand

Operational demand means demand supplied from the national power system (or grid). Minimum operational demand means the lowest level of demand from the grid in any given day, week or year.

Minimum operational demand is extremely sensitive to ongoing uptake of solar PV, weather conditions, and local economic activity.  

When consumers’ energy needs, particularly during daylight hours, are being met by their own distributed energy resources (DER) such as solar PV, that results in low demand for energy from the grid.

What are the challenges caused by minimum demand?

As minimum operational demand keeps getting lower, new standards and system services are required to keep the power system secure and reliable.

The challenges include:

  • Voltage management – as demand levels decrease, it can become increasingly challenging to manage transmission network voltages. De-energisation of major transmission lines may become necessary, reducing the resilience of the network. 
  • Unintended disconnection of distributed solar – distributed solar PV demonstrates unintended disconnection behaviour when exposed to power system disturbances. This affects network limits, frequency control, and other aspects of power system operation.
  • Minimum demand thresholds – on rare occasions, a NEM region such as South Australia or Queensland may separate from the rest of the NEM and need to operate as a secure island. While the island exists, it needs operational demand to be high enough so sufficient generation units stay online to provide security services such as system strength, inertia, and frequency control. There is also a need for sufficient demand to operate the minimum generating units to provide these services under normal conditions.
  • Emergency frequency control schemes – under-frequency load shedding (UFLS) is a type of emergency frequency control scheme designed as a last resort to arrest a severe under-frequency disturbance by automatically disconnecting consumers from the grid. With more consumers using power from their own distributed solar PV instead of the grid, this important ‘last resort’ mechanism is less effective for managing severe disturbances.
  • System restart – a minimum quantity of stable load is required to restart the large synchronous units that provide System Restart Ancillary Services (SRAS) to enable system restoration after a major blackout. With large quantities of distributed solar PV operating, there may not be enough stable load, and DER behaviour may be difficult to manage in a small island during the restart process.

What can be done to mitigate the challenges?

The good news is that with prompt action, it should be possible to continue to maintain power system security and simultaneously support a transition to greater amounts of DER.

There are opportunities for innovative technologies to enter the market and help address these challenges.

As an example, utility-scale energy storage could act as a ‘solar soak’ to use excess distributed PV generation. Opportunities are also arising for providers and other stakeholder groups to help address these risks by introducing new products and services to actively manage distributed solar PV and other DER.

These kinds of flexible options are likely to become increasingly important for daily operation.

AEMO is working with industry, jurisdictions, the Energy Security Board (ESB), and market bodies to develop new standards to support cost-effective regulatory and market reforms that are required to keep the power system secure and reliable. This work is underway in both the NEM and Western Australia’s Wholesale Electricity Market (WEM).

AEMO’s action plan includes introducing:

  • Disturbance ride-through capabilities – to require that all new DER installed can keep operating through disturbances, by improving performance standards and enforcing compliance with those standards.
  • Emergency Solar PV shedding capabilities – to require as a condition of connection that all new distributed solar PV, of any capacity, could be disconnected as a last resort, in rare circumstances if severe abnormal operational conditions arise, to protect the overall power system.

Navigating these challenges of minimum demand is an ongoing process, so watch this space as AEMO and the industry continue to explore more ways to ensure the secure and reliable operation of the nation’s energy grids in the best interest of all consumers.

For more detailed explanations of the technical side of our industry in easy-to-understand language, check out other recent instalments from our ‘Energy Explained’ series: system strength, frequency control, frequency and voltage. You can also learn more about the industry from AEMO’s energy experts by enrolling in one of our Energy Education courses. Click here to view upcoming events in AEMO’s Learning Academy. 

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