Households can hold grid together when big coal units fail

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Last week, Australia’s largest generation unit tripped, sending frequency out of its normal band. What happened next explains why the smart grid has arrived.

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At 8:28pm on Wednesday last week the Kogan Creek coal fired generator in Queensland tripped.

This is Australia’s largest generator and the event instantly withdrew 750MW from the grid causing the frequency to drop below the minimum operating threshold of 49.85Hz.

This frequency disturbance was felt all across the mainland National Electricity Market in an instant, from large generating units to individual houses.

Because frequency changes are felt instantaneously across the NEM, generators and demand response – regardless of location – can be used to help rebalance the system following a disturbance.

By not having to be positioned in key locations on the grid, support can come in the form of smaller, distributed systems acting together.

Such distributed resources offer to add increased stability for lower costs – no single utility or government has to pay for the generator and individuals can lower their power bills by providing grid support.

It is not usually easy to visualise just how “in-sync” frequency is across the grid and therefore why location is (mostly) not important.

Reposit Power provides consumer technology and services for joining, building and operating Virtual Power Plants. As such, Reposit has devices across the NEM at customers’ homes that are constantly monitoring the grid.

The furthest distance between Reposit systems is nearly 2000 kms – from Townsville to Adelaide.

By looking at just the South Australian and Queensland systems over a one minute interval surrounding the trip you can easily identify that the frequencies measured are almost identical for all 1-second samples regardless of location.

The following graphs shows the average frequency at each interval per state – this is second-by-second data across hundreds of systems spanning thousands of kilometres giving near perfect frequencies.

When a trip like Kogan Creek occurs other generators and enabled demand response resources on the grid providing frequency control ancillary services (FCAS) start responding to recover the frequency back to the normal operating range.

Allan O’Neil has compiled a graph of the responses of the various FCAS generators that responded to the Kogan Creek disturbance. The locations of which can be seen below.

Despite the trip happening in Queensland ,it’s clear that the responses came from across the country. A generator in South Australia has the potential to detect and respond just as fast as one in Queensland.

If you’ve read the news lately you will have seen that the South Australia “Tesla big battery” (officially known as the Hornsdale Power Reserve) is doing just that.

Because location is not the most important factor, distributed systems are starting to play a key role in frequency response.

Distributed recovery mostly comes in two forms – Demand Response (DR) from companies such as EnerNOC which was enabled to provide 13MW of demand response during the Kogan Creek trip; and Distributed Energy Resources (DER) which are usually smaller, at-home systems grouped together to form a virtual power plant (VPP) such as Reposit Power’s.

Whilst Reposit didn’t respond to this event, changes in regulation and an ever-expanding fleet will allow them to participate in the future passing on the financial reward to their customers.

Individual systems can monitor the frequency and respond independently – the aggregated response appears as if it were a single generator with significant capacity. This is the premise on which VPPs are built and proven to work.

With DR and DER participation across the NEM rising, FCAS responses from smaller distributed systems can be just as powerful as using large generators but with added benefits.

Home-owners and small businesses get to earn money off their power bills for providing such services and selling their power back to the grid or reducing load in times of need; and the quality of FCAS response from these system is better – being able to respond in milliseconds rather than the several seconds required for a coal unit to spin up and respond.

This also lessens the impact of a single-point-of-failure as we are seeing with the Kogan Creek trip – each of the grid-connected devices is able to operate on their own and hundreds of thousands of these devices would have to simultaneously fail in order to see the type of sudden energy withdrawal that we have seen with the Kogan Creek trip.

The grid of the past – made of just a few large centralised generators – is already beginning its transition out as “big batteries”, DR and DER comes online and are already well established.

We were promised a smart grid. It has arrived.

Mike Leonard is Lead Developer at Reposit Power

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19 Comments
  1. Jon 7 months ago

    Interesting reading thanks.
    Hopefully the market tools for this sort of thing comes together quickly.
    Over time the supply demand of a lot of these network services will push down the price to the benigit if all connected to the grid.

    Long live the grid, it will be around for a long time, just a refreshed smarter version of it.

  2. George Darroch 7 months ago

    Thank you for shining light on this disturbance in the force.

  3. AllanO 7 months ago

    Great article Mike, clearly shows the potential for these distributed resources + smart technology to play an important role in grid management.

  4. Ian 7 months ago

    Presumably someone or something controls the grid frequency like a conductor of an orchestra , how do all these DER and DRs get their signal to react to frequency changes?

    • Mike Leonard 7 months ago

      In the kind of frequency response I’m talking about here – FCAS – the frequency itself is the signal. Each generator (or DR system) registered to participate monitors the frequency – if it goes out of the normal operating range the system decides to respond immediately. As the frequency changes everywhere all at once this is really the best possible signal you could have.

      This is why Reposit was able to monitor but not respond to the frequency, we are very much ready to enable FCAS but are awaiting regulatory changes or an increased number of customers to make this happen.

      Additionally, there is “regulated FCAS” in which the market operator, AEMO, send continuous signal that generators should follow. Due to the nature of how this works I would imagine that this remains only for the larger generators for the foreseeable future.

      • Chris Fraser 7 months ago

        Would you consider then that a new Regulated FCAS signal provided after System Black should be provided by a large generator ? Perhaps because of its rated capacity to be felt from one end of the NEM to the other ?

    • AllanO 7 months ago

      Ian, system frequency changes in response to imbalances between supply and demand: if supply > demand then frequency increases, if supply gravity then speed increases, if engine power < gravity then speed decreases.

      When there's a sudden large imbalance (a "contingency") and consequent move in frequency, like the Kogan Creek trip, resources enabled to participate (demand side or generation) respond automatically to the frequency change – as Mike says it's the best possible signal because it is felt everywhere on the grid and doesn't need central control, beyond deciding well in advance how much response should be provided for a given change in frequency – which is what the contingency FCAS markets do. AEMO predetermines the amount of response needed for (say) a 0.5 Hz change in frequency and "enables" registered contingency FCAS providers to be ready to respond to frequency excursions outside the normal operating range. The amount of response delivered should be broadly proportional to the change in frequency, and doesn't rely on an instruction from AEMO to act.

      Small, slow deviations in frequency away from 50.00 Hz, but within the normal operating range, are managed through Regulation FCAS & AGC (automatic generation control) which sends signals every few seconds to enabled generators and demand side resources to slightly adjust their output / usage.

  5. John Saint-Smith 7 months ago

    It appears that Energy Minister Frydenberg was too quick to condemn the new renewable generation and storage systems being added ‘incautiously’ to the grid by the likes of South Australia’s former Premier Jay Wetherill.

  6. John Boyd 7 months ago

    Also a good counter argument to the often quoted exhortations from well meaning go-it-alone supporters, to get off the grid.

    • Nick Kemp 7 months ago

      They are probably doing it purely for economic reasons. The charges to have a pole put in in Tasmania can be offset by being off grid so if you don’t need the grid why join it?

  7. daw 7 months ago

    Where was Tesla’s beaut big battery rapid response? Missing in action? or incapable of providing the claimed rapid response?
    I also note a fiddle on the time scale of the graphs.
    ~0.1 sec from the start of the event at ~20:27:40 to bottom of the dip ~20:27:50
    thence ~0.5 sec to 1st rise @ ~20:28:00 thence ~0.1 sec for the next fall et seq for each rise or fall period thereafter.
    It gilds the lily a bit does it not.
    It doesn’t show the ending which from a projection of the cyclic swings would take about 3 secs for a full and stable recovery back to 49.85Hz
    It should also be noted that many units (mostly coal fired) responded to assist with the recovery as would be the case if there were no ‘renewables’.
    Is it really that much of an issue anyway?
    How many loads have a need to be within 0.15 Hz anyway?
    ‘We were promised a smart grid. It has arrived.’
    Really? Maybe it has been smart enough all along Given that ‘the smarts’ added haven’t been very great so far.

    • AllanO 7 months ago

      Look at the graphs more carefully then – scales are in hh:mm:ss, not decimals.

      Battery responded precisely as expected – see http://www.wattclarity.com.au/2018/04/when-the-nems-largest-generating-unit-trips/

      Frequency control is very important to system security. Think about multiple sequential contingencies if you’re unconvinced.

      And perhaps come to future discussions with a more open mind my friend.

    • ilma630 7 months ago

      And just how long does the Tesla battery last? Not very long i imagine, so effectively useless for a sustained outage.

      • Giles 7 months ago

        Doesn’t need to last long. As the market operator says, such batteries will play an important role in preventing any outages. So they able to respond quickly to hold the grid together while other machines fire up.

      • remoteone 7 months ago

        The value of the battery is in its fast response (as I understand it, the battery was never thought of as a grid power supply on its own). It can fill in while conventional generators spin up to provide longer term network stability. A few more 100MW batteries distributed across the network would provide insurance against the temporary failures we would expect from the ageing fleet of mostly coal powered generators.

        • Hanrahan 7 months ago

          “The value of the battery is in its fast response”

          Admittedly, that is true. It is good that SA con contribute positively to the national grid occasionally instead of being a perpetual pest.

          BTW hydro only takes a few seconds to come to full power too.

  8. Hanrahan 7 months ago

    Did anyone lose power????

  9. Rick 7 months ago

    Why bother with all this complexity. The NEM is already uneconomic. The fatal blow was allowing subsidised run-whenever-you-like generation on the grid. Intermittency has infected the grid. It is rapidly killing base load and the matching low cost base load coal generation. AEMO even has a term for it “uneconomic bypass”:

    Spoken at 36:30.

    Uneconomic bypass is already happening. The fundamentals are that solar has no benefit of scale and wind has little benefit of scale. Grid scale run-whenever-you-like generators are severely hobbled by the 110% increase over wholesale cost to transmit, distribute and retail power so will never compete with a correctly installed rooftop or car park system. AEMO have forecast that minimum demand in the South Australian network will be zero by 2024. That means all grid scale run-whenever-you-like will have system constrained capacity factors meaning their output will diminish so reduced opportunity for cost recovery. Investment in them will dry up because they can never compete without a decade or so of guaranteed support through sale of LGCs.

    The NEM is already dead economically.

  10. Chris O'Neill 7 months ago

    “individuals can lower their power bills by providing grid support”

    They can but they can only do this if they have a battery or some other system that can temporarily increase power output to make up for the tripped shortfall. Early days.

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