Giles Parkinson is founder and editor
The iconic mining city of Broken Hill in the far west of New South Wales is set to host one of the world’s largest renewable mini-grids, powered almost entirely by solar, wind and grid scale storage.
The proposal comes from the transmission company Transgrid, which says it is seizing on the opportunity to replace the city’s ageing back-up diesel generators with “21st century technology”.
The main thrust of this will be investment in storage facilities to support the existing wind and solar resources in the region – principally the 200MW Silverton wind farm (pictured above) and the 52MW Broken Hill solar farm, both owned by the renewables investment fund PARF, part owned by AGL.
The interesting and possibly surprising part of the Transgrid proposal is its choice of storage options. It considered a range of big battery proposals – ranging from 73MW with four hours of storage to 50MW and 90 minutes storage supported by demand response (including one big battery proposal from AGL).
But Transgrid has chosen as its preferred option a huge 150-200MW compressed-air storage facility with 1,550MWh of storage proposed by Canadian company Hydrostor. It will be the world’s biggest compress air energy storage facility.
Transgrid appears to have done this because it prefers “synchronous generation” rather than grid-forming battery inverters – which are relatively new, although recently proven in several smaller off-grid applications and with the Dalrymple battery in South Australia.
The only other such project of note in Australia is a 5MW installation with two hours of storage proposed by Hydrostor for an old zinc mine in South Australia.
Hydrostor has a big blue blob on the map of Australia near Broken Hill that identifies a “near term” development opportunity that could now come true. Like the AGL battery study, its project was one of 14 storage proposals for NSW that received funding by the NSW government for feasibility studies.
Hydrostor describes Compressed Air Energy Storage (CAES) as similar to pumped hydro, delivering long duration storage by using a proprietary thermal management system and the use of purpose-built hard-rock air-storage caverns. Presumably, the mining town of Broken Hill provides plenty of options for such caverns. The air is then released to spin a turbine.
“This creates a wonderful opportunity to bring Broken Hill back up into the 21st century,” Andrew Kingsmill, the head of Transgrid’s network planning told a webinar on Wednesday.
Broken Hill, a city of 17,000 people built on mining and now also a major tourist destination, current gets its electricity supply from a single transmission line that runs over 250km from the southern New South Wales town of Buronga, on the Murray River.
When that line goes down, or there is a major storm that interrupts supplies, its power comes from two 25MW diesel turbines. Even the local wind farm and solar farm are switched off when the line goes down, just as occurs to households with rooftop solar when the local network goes down.
However, the turbine owner, local state-owned distribution network operator Essential Energy, now plans to sell those turbines. And Kingsmill wants to grab the opportunity to replace it with a renewables micro-grid that can power the town when the line is down – making it one of the largest renewable based mini grids in world.
That essentially means the storage will also be able to store excess power from the wind and solar resources, which in turn could relieve pressures further up the transmission line, where there are concerns that solar farms might have to be curtailed when too much power flows east causing congestion on the local grid.
“This would make Broken Hill one of the largest renewable based mini grids in the world with a connexion to the grid,” Kingsmill told a webinar where Transgrid’s transmission plans were unveiled.
He said the storage would help relieve that congestion in southern New South Wales, referring to the new revelation that the state’s three biggest solar farms could be among a dozen solar plants in the south-west region that could have their output cut to stop excessive amounts of power flowing east in a weak part of the grid.
“When the transmission line is unavailable, whether that’s for maintenance, whether that’s for storm activity and unplanned outages, this means we will be able to power Broken Hill entirely from renewable energy,” Kingsmill says.
“This is a prime example of the value of grid- scale storage in the future power system and a project with which TransGrid is proud.
“We’re embarking on a decade of transformation in which together we must take the power system from a 20th century grid that has served us well to a 21st century green that is fit for our future, from a fixed grid built on fixed technology to a flexible and dynamic grid that hosts diverse and novel technologies.”
Transgrid has filed a Project Assessment Draft Report (PADR), which is the second key stage in the lengthy regulatory process it must go under the regulatory investment test (RIT-T), which then allows it to declare the asset to be a regulated investment, and thereby able to recoup the investment from its regulated spending allowance.
This RiT-T process will likely be completed within 12 months, with another two years before the new storage facility is in place.
Kingsmill says the advantage of compressed air is its scale efficient long duration storage. But he is also confident that grid-forming inverters will play a role in the future.
“Today we are solving system strength issues by putting in rotating machines, because we haven’t proved anything better,” he told RenewEconomy. “Once we proven grid forming inverters” they will be readily deployed. And while Dalrymple shows that the technology is ready, and the hardware ready, the integration has not yet been proven at this scale.
“We will pursue some pilot projects on grid forming inverters,” he adds.
Gas options – including installing new turbines, were considered, as were a new transmission line, but quickly dismissed due to cost and lack of market benefits. The costs of the individual storage proposals were not revealed – commercial in confidence – but Transgrid says the market benefits were far superior, with the compress air proposal leading the way.