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| 03/07/18

Reading the fine print on the world’s biggest battery


Elon Musk’s firm Tesla dazzled journalists with delivery of the world’s biggest battery to South Australia mere days ahead of a December 1 deadline imposed by a bet that the billionaire electric-car-and-rocket impresario had made on Twitter that his workers could build it in 100 days or it would be free.

The media fanfare prompted by this clever exercise in marketing has since died down, but energy experts are now raising eyebrows as the lithium-ion Hornsdale Power Reserve battery charged up by wind turbines responds in record time—mere milliseconds—to power outages.

This success prompted a flurry of declarations that the South Australian example shows how variable wind energy, plus battery storage, makes obsolete conventional dispatchable (available at any time) clean energy sources such as hydro or nuclear.

But a closer inspection of the Honsdale Power Reserve reminds us that utility-scale batteries are intended by electric companies not as storage, but for something just as important that is sometimes overlooked by the public: ancillary services.

Within two weeks of the battery’s installation in the middle of the punishing South Australian summer that regularly produces power outages, a unit at the coal-fired Loy Yang plant, one of the country’s largest power stations, unexpectedly tripped (suddenly went offline) and stopped supplying electricity.

The Hornsdale Power Reserve battery system pumped 7MW into the national electricity grid within a stunning 140 milliseconds. A few weeks later, a different unit at the same plant tripped and this time the Tesla battery delivered a burst of 16MW into the system again in milliseconds, which has been described by the state’s energy minister as a record compared to the typical 10-15 minute response time of conventional backup.

The estimated $50 million, 129MWh battery comprises about 640 Tesla Powerpacks. It is equivalent to the amount of batteries required to run 1,300 Model S Tesla cars. Fully charged, the Hornsdale Power Reserve can provide the electricity needs of roughly 30,000 homes for about an hour.

But that’s not a long time. Its selling point is not the amount of energy it can store— as lithium-ion batteries cannot store energy for much longer than a few weeks—but how fast it can deliver it. Its role is thus not long-term or even medium-term storage, but instead to provide millisecond-fast network ancillary services that, up to now, have taken seconds or minutes to provide. The real value is in contingency services, or responding to unexpected trips and outages, and regulation services, or supporting day-to-day stability, by helping to close gaps between supply and demand.

And indeed, alongside the battery, the other backup for the grid is another, existing coal plant, which took over from the Tesla battery during the recent trips.

The Tesla battery is also just one element of the state government’s $550 million plan that will see the construction of 276MW of gas- and diesel-powered generators to ensure better reliability following a politically contentious series of blackouts.

What Tesla demonstrated was the viability of using a renewables-plus-battery system as a much faster emergency response than has previously existed, providing a much-needed bridge until other slower but less short-lived back-up (in South Australia that still means fossil fuels) can come online.

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