The Hornsdale Power Reserve Battery Energy Storage System (HPR) – the world’s largest lithium-ion battery – underwent its first charges and discharges into the grid at the end of November 2017. The Australian Energy Market Operator’s (AEMO) recent paper, Initial Operation of the Hornsdale Power Reserve Battery Energy Storage System, highlights the results from this initial period of operation and outlines what future large-scale batteries can learn from this system.

The battery covers approximately one hectare of land, located at the Hornsdale Wind Farm 15km north of Jamestown, near Adelaide in South Australia. The HPR is connected adjacent to the 300MW Hornsdale Wind Farm.

The HPR provides a range of services under commercial agreements between the South Australian Government, Tesla (the battery technology provider), and NEOEN (the operator of the Hornsdale Wind Farm and the battery system).

Operation of the HPR to date suggests that it can provide a range of valuable power system services, including rapid, accurate frequency response and control.

Rated at 100MW discharge and 80MW charge, the HPR battery has an energy storage capacity of 129MWh. This means the HPR battery is able to provide 100MW of services into the National Electricity Market (NEM), for a duration of 1.29 hours.

Under normal conditions, 30MW of the battery’s discharge capacity is made available to NEOEN for commercial operation in the NEM. Of the battery’s total 129MWh energy storage capacity, 119MWh may be used for this mode of operation.

The remaining 70MW of battery discharge capacity is reserved for power system reliability purposes. This 70MW reserve capacity has not been dispatched to date.

Under arrangements with the South Australian Government, this capacity is offered into the NEM at the Market Price Cap, ensuring this component of the HPR will not be dispatched ahead of other generation in South Australia.

Providing high-quality frequency control

The HPR is registered to provide all eight Frequency Control Ancillary Services (FCAS) markets, and this is the first time regulation FCAS has been provided in the NEM by any technology other than conventional synchronous generation.

AEMO’s central Automatic Generation Control (AGC) system can be used to control the HPR, and this is the normal control arrangement most of the time. AGC control allows AEMO to send a new MW setpoint to the battery at a rate of up to once every four seconds.

This enables the HPR to provide regulation FCAS in South Australia. This market has seen high prices for this service for the two years prior to the battery becoming operational.

Regulation FCAS incrementally adjusts the output of the battery up or down, away from an underlying energy dispatch target, to correct slow moving frequency changes across the NEM. Up to 30MW of the battery’s output capacity is available for provision of regulation FCAS.

Data available to AEMO demonstrates that the regulation FCAS provided by the HPR is both rapid and precise, compared to the service typically provided by a conventional synchronous generation unit.

While experience shows that the HPR is capable of providing very high quality regulation FCAS, regulation FCAS arrangements in the NEM do not currently recognise differences in the “quality” of service delivery.

The Market Ancillary Services Specification (MASS), which specifies each market ancillary service and how it is to be quantified, does not address performance requirements for regulation FCAS. All regulation FCAS is essentially considered to be equal and interchangeable, and providers are paid the same price per MW of enabled service, regardless of performance.

This method of assessing and commodifying frequency response involves performance assessment against a slow moving change in frequency, and therefore does not recognise, or reward, the more rapid response capabilities of batteries, and some other inverter-based technologies.

Changes in how frequency response is assessed and paid for may be required in order to acknowledge the high performance and quality of regulation response available from batteries.

In some overseas markets, new frequency control services with very short delivery time requirements have been established, which are typically only fulfilled by batteries.

Care would be required in establishing new markets, or modifying the assessment of frequency response capabilities in the NEM, to consider the current complex interactions between the dispatch of FCAS and energy in the NEM, the potential need to maintain technology neutrality, and the potential for limited competition in the delivery of any newly defined services.

AEMO will work with industry to undertake formal consultation on the necessary modifications to the MASS.

Further opportunities for future large batteries

The funding arrangements for the HPR meant there was a focus on ensuring all its capabilities were fully utilised to maximise power system security for South Australia.

This included engagement with AEMO when control settings and operating arrangements were determined, in a way that would not typically occur for other generation development (where the project developer is responding to existing market signals and arrangements).

Future development of batteries outside of South Australia might not result in the provision of similar services, due to the way FCAS are currently quantified and rewarded, as well as the voluntary nature of participation in the FCAS market, and in frequency control arrangements more broadly.

Where other large batteries are established under government incentive schemes, there could be a role for a more prescriptive provision of system security services, to maximise the benefits to the power system that such devices can provide.

Current FCAS market arrangements could also be modified to specifically recognise the rapid and accurate response capabilities of batteries, and therefore enhance their ability to earn income from providing them.

Additional control schemes

The HPR has been configured to provide a contingency FCAS response at all times, irrespective of FCAS market outcomes, using the full technical operating range of the battery.

Because major frequency deviations in the NEM are (fortunately) rare, actual full delivery of this service has not yet been demonstrated.

The HPR is also included in a new control scheme intended to prevent the likelihood of the South Australian power system separating from the rest of the NEM as a result of a sudden increase in flow on the Heywood Interconnector.

The System Integrity Protection Scheme (SIPS) was developed by ElectraNet and reviewed by AEMO, and it is being implemented by ElectraNet under the Network Loading Control Ancillary Services (NLCAS) framework.

The SIPS control scheme is intended to detect high flows on the Heywood Interconnector and trigger the HPR to start discharging at 100MW as quickly as possible.

Future batteries installed in South Australia may also be included in this control scheme. A key feature of this control scheme is the very rapid response that can be achieved using battery systems.

The South Australian NLCAS requires 10MWh of the HPR’s total energy storage capacity to be reserved for the control scheme. It is expected to be fully commissioned in the second quarter of 2018.

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