The homes and businesses of Broken Hill’s 17,000 strong-population are set to be powered by renewables to ensure reliable and back-up supply going forward. Under the proposal coming from transmission company Transgrid, the inland mining city in the far west of New South Wales could become home to one of the world’s largest microgrids as its gas turbines that run on diesel fuel get retired.
To leverage the wind and solar generation at Broken Hill, Trangrid is looking at a number of options in its Project Assessment Draft Report (PADR), including compressed air storage, batteries and demand response. “This is an opportunity to look at the technologies available today and give Broken Hill a state-of-the-art, twenty-first century renewable supply,” said Andrew Kingsmill, TransGrid’s Head of Network Planning.
Presently, the city is supplied by a single 220 kV transmission line, Line X2, that runs over 250 km from the southern NSW town of Buronga. During a planned or unplanned outage of Line X2, like during a major storm, Broken Hill has been supplied by Essential Energy’s two back-up gas turbines that run on diesel fuel. Each have nominal capacity rating of 25 MW, which is reduced to 18 MW under adverse ambient temperature conditions and are black-start capable and equipped for islanded operation.
Now, network distributor Essential Energy, who owns the turbines, is planning to divest them and TransGrid is evaluating options for the back-up supply arrangement going forward. Under the new recommendation, the transmission company is looking at grid-scale storage options to underpin its local semi-scheduled generators that are currently unable to operate when Broken Hill is not connected to the rest of the network – the 53 MW Broken Hill Solar Farm and the 200 MW Silverton Wind Farm.
Specifically, Transgrid’s draft report evaluates four non-network solutions that are excluding the use of the existing gas turbines:
Option 1A – 150-200 MW/1,550 MWh compressed air energy storage (CAES) facility
Option 1B – 62.5 MW/250 MWh battery
Option 1C – 73 MW/292 MWh battery
Option 1D – 50 MW/75 MWh battery, 10 MW of demand response
“Most of the time, when the transmission line is in service, the grid-scale storage will be able to store excess renewable energy from south-western New South Wales that would otherwise be spilt, and provide it back to the market when it’s most needed,” said Kingsmill. “When the line is unavailable, the grid-scale storage will work with the wind and solar generation at Broken Hill to reliably power the town. This is a prime example of the value of grid-scale storage in the future power system.”
Transgrid says in its draft report that the abovementioned four solutions fully provided by third parties and the first three variants of these solutions involving either shared ownership or ownership by Transgrid have been assessed using information (including costs) received through stakeholder consultation. While the cost structures have not been presented in the PADR, it appears that Transgrid already has a clear favorite.
“While Option 1A, a non-network opex solution fully provided by a third party, is the preferred option at this stage of the RIT-T, the corresponding option proposed by the same third party involving TransGrid ownership is one of the lowest-ranked options, due to the different regulatory treatment of costs under the RIT-T assessment,” it says in the report.
This means that the Broken Hill microgrid could eventually feature the world’s largest compressed air storage facility. Thus far, the only other such project being developed in Australia is the 5 MW/10 MWh Angas Project in South Australia, which will store excess solar and wind power at a closed underground mine.
As explained by the project proponent, Canada’s Hydrostor, CAES has similar applications and benefits to pumped hydro energy storage with the added benefits of being flexible with location and topography. The Angas fuel-free battery will use electricity from the grid to run a compressor and produce heated, compressed air that can be stored 240 meters underground in a purpose-built cavern and kept at constant pressure using the hydrostatic head from a water column.
During charging, heat from the compressed air is collected and stored before the cooled air displaces water out of the cavern up to a water reservoir on the surface. To discharge, water flows back into the cavern forcing air to the surface under pressure where it is heated with the stored thermal energy and drives a turbine to generate electricity when demand in the electricity grid is high.
Hydrostor has already identified Broken Hill as a near-to-medium term development opportunity that could now come to fruition. The company’s 200 MW compressed air storage facility near Broken Hill was among the projects receiving grants of up to $500,000 for feasibility studies as part of the $75 million NSW Emerging Energy Program. Last year, the funding program awarded a total of $7.1 million for pre-investment studies for some 2,150 MW of energy storage projects and shortlisted another 21 dispatchable projects for capital funding of up to $10 million per project.
TransGrid is accepting written submissions on the report until September 22. The final report is expected to be published in late 2020.
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