Seasonal frequency in the NEM: is VRE continuing to drive it?


The Australian Energy Market Operator (AEMO) reports that the national electricity market (NEM) frequency has improved significantly since implementing the first tranche of generator PFR settings. Frequency deviation has been much narrower, highlighting the benefit of tighter frequency response under normal conditions.

Having said that, in the face of rapid growth of variable renewable energy (VRE) and distributed rooftop solar, frequency control remains a challenge for AEMO, which is yet to be solved.

In this Chart of the Week, I examine how large-scale wind and solar technologies (excluding distributed rooftop solar – DPV) performed against (and impacted) the time-of-day frequency change during the summer and winter of 2021.

As shown in Figure 1 (Summer 2021), the number of frequency deviations that occurred outside the PFR band was largely concentrated around daytime hours (6am-6pm).

Figure 1 clearly shows that frequency tends to deviate less during the early morning hours and significantly more around 3pm, potentially resulting from higher DPV dispatch.

Figure 1: Count of 1 sigma events in VRE dispatch and frequency change in NSW.

Image: Cornwall

This trend may get more pronounced as more rooftop/grid solar connects, creating a steeper frequency rump in the afternoons. Figure 1 indicates that frequency deviation in summer is more correlated to renewable output. This might suggest that in summer, frequency is more impacted by VRE. In winter, we observe the opposite.

As seen in the Figure 2, the number of VRE dispatch intervals (> 40MW) is very similar to summer 2021, however frequency behaves differently. This may suggest that other generators (i.e., coal and gas) have greater impact on frequency during winter.

We have seen a higher number of frequency deviations in the winter than in summer, which supports our hypothesis that frequency is more impacted by coal and gas generators in winter.

Figure 2: Count of 1 sigma events in VRE dispatch and frequency change in NSW.

Image: Cornwall

Can these trends suggest that frequency tend to deviate more during winter? To confirm this further, analysis of DPV, coal, gas, and generator outages needs to be completed.

It is left to be seen how the existing PFR requirements and their associated benefits will incentivise hybrid projects (with/without storage) to provide voluntary and mandatory provision of PFR to help stabilise frequency across the NEM.

In general, it is good news for battery developers and investors as they can have more flexibility when comparing different revenue streams (including potential PFR services) for battery storage assets.

Cornwall Insight Australia’s in-house battery revenue models and subscription services shed light on how prices are likely to evolve going forward, considering the impacts of new regulations.

Author: Andrey Kotov, energy consultant, Cornwall Insights

The views and opinions expressed in this article are the author’s own, and do not necessarily reflect those held by pv magazine.

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