A crystal ball is not needed but solid, electrical engineering is.
By Phil Kreveld, CT Lab
The Future NEM forum of November 5 attended by representatives of AEMO, major transmission and distribution networks and various associations provided one clear take-out—that there is no detailed plan for a stable and resilient NEM as renewables continue to grow. Similar observation can be made of the Energy Security Board because of its inaction to deal with the single most important facet of the evolving NEM: system strength.
In the plethora of commentary on Australia’s electricity future, system strength (a very meaningful term in electrical engineering) doesn’t get a mention—it’s as if it is seen as a reactionary impulse against wind and solar generation. In fact, system strength maintenance in the NEM will facilitate the continued growth of wind and solar, including ‘behind the meter’ distributed generation.
System strength requires that we not diminish further the current NEM stock of synchronous inertia and spinning reserve, and this has serious financial implications. In short, a new market for capacity—megawatts instead of megawatt-hours is urgently needed—but there’s more.
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As an alternating current network, NEM stability and resilience require two things; a narrowly controlled rate of change of frequency (RoCoF) and voltage stability. Both wind and solar connect to the NEM via power-electronics inverters and neither possesses native features of voltage and frequency stability because they do not have inertia. Proponents of green power talk around this by pointing to small electricity systems like King Island, the Canaries, Hawaii islands etc. conveniently forgetting that many homes in these places have their own backup generators, and that no network operator runs the island grids without a level of synchronous inertia, e.g.: diesel or gas turbines.
System strength not only requires the maintenance of spinning reserve but also control. AEMO does have a measure of control of the NEM, for example in the case of South Australia, islanding the State on some occasions when instability threatens the security of the rest of the NEM. However, AEMO is hampered in its task through the lack of a NEM-wide comprehensive, real-time information and control system. The task, increasingly pressing, is to marshal the appropriate resources in real time, be they batteries, synchronous condensers, and spinning reserve. As to batteries, in as much as they also connect via inverters, they can only work effectively in the presence of rotating inertia as provided by synchronous generators.
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The integrated systems plan of AEMO, which also was a subject at the forum, did not attract meaningful discussion. AEMO’s powerlessness in its ability to force distribution networks to maintain a minimum level of power demand stability is the main reason why the growing penetration of distributed resources in distribution grids will be the cause of more islanding incidents of large portions of the NEM grid. The control of ‘behind the meter’ solar in order to provide zone substation stability is unavoidable and can be made politically acceptable through the use of AI to limit the impact on individual prosumers. The refusal so far to engage with the need for limiting power fluctuation at zone substations is setting the NEM up for an unstable future.
Forums providing opportunities for discussion and the interaction of ideas notwithstanding, it is now high time to come to engineering grips for the NEM, requiring not only new markets for system strength so as to limit the planned retirements of synchronous generators, but to also draft new grid codes for substation stability and to provide engineering oversight as well as new connection codes for household, commercial and industrial solar generation.