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Within 5 minutes a wave of hot water systems switch on in SA adding 250MW of demand to the grid

We are creatures of habit. Look at the spike caused at 11:32pm as something like 27,000 hot water tanks in South Australia suddenly switch on to use cheaper off-peak electricity. This spike is entirely due to pricing plans. It’s entirely avoidable too, but at least it’s predictable. “Scheduled”.

This peak, allegedly, is only a problem if SA is “islanded” — meaning if it can’t rely on the coal generators in Victoria.

Yesterday people were asking why the South Australian demand was peaking at 1am (and why two hours were strangely missing from that graph). “Hot water” is the answer (at least to the first part).

SA Hot water systems add sudden 250MW of demand at 11:30pm. Graph.

SA Hot water systems add sudden 250MW of demand at 11:30pm. Graph.

This graph comes from the AEMO report in Feb 2016. What follows is their electro-nitty-gritty:

Based on previous experience, and as demonstrated in a separation event on 1 November 2015, maintaining the SA power system in a secure operating state is challenging if there are large changes to the supply-demand balance during a period of islanding.

Hot water demand peak
Currently the most concerning of these challenges is the hot water demand peak that occurs at 11:30 pm daily. This is a step change increase in demand of approximately 250 MW, shown in Figure 3. This demand peak is controlled by fixed timers and requires considerable effort to reduce the peak through the adjustment of the time clocks at individual premises. While all new meters installed in SA will have randomised time clocks, all existing meters are set to switch at 11:30 pm.

In its revenue proposal for 2015–16 to 2019–20, SA Power Networks, which owns the time clocks associated with the hot water demand, identified this issue in the context of demand and power quality management. SA Power Networks included $0.56M in its augmentation CAPEX proposal to reprogram 27,000 meters to address the hot water demand spikes observed in SA.18 The Australian Energy Regulator (AER) has approved the funding proposal. The funding proposal provides no information on when SA Power Networks will undertake this work. Currently, if SA is operating as an island, at 11:30 pm there will be a large impact on frequency, potentially resulting in under frequency load shedding if frequency control measures are not in place. While this increase in demand is accounted for in the dispatch demand forecast process, which will pre-emptively increase generation in response to the demand peak, this might not be sufficient to control frequency to within the FOS, as the change in demand might be faster than generation can respond.

AEMO has identified a number of potential control measures to minimise the impact of hot water switching in the short term, however it is important to note that during periods of islanded operation, any or all of these options, while limiting the impact, might not prevent under frequency load shedding from occurring during the hot water peak.

These control measures include:

  •   Temporary increase of SA automatic generation control (AGC) reference frequency to above
  • 50 Hz before the hot water peak occurs.
  • Use of the Load Restoration Tool19 to artificially increase demand seen by AEMO’s
    dispatch process, and subsequently increase dispatched generation for a period prior to the
    demand peak.
  • Temporary increase in Raise Regulation FCAS enabled, if it is available.
  • Use of AEMO’s power of direction under NER clause 4.8.9 to request offline fast start generation
    to start up and synchronise at minimum output prior to the hot water peak. This will provide extra
    generation capacity, inertia, and governor response.

Pity the poor supply side grid managers, but at least they know this “ramp up” is coming, like clockwork every day.


AEMO: Update to Renewables Energy Intergration in South Australia, Feb 2016.

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