Lack of inertia prevents an Australian mine from expanding renewable energy use at its microgrid. The mine operator lays out a path to solve the problem. Sophie Vorrath of Renew Economy reports.
The global resources company behind a ground-breaking project that shifted a West Australian gold mine to a more than 50% mix of wind, solar and battery storage says it could aim much higher in future projects — and has set its sights on a target of 99% renewables.
South Africa-based miner Gold Fields has gained a name in Australia for making its Agnew mine, in Leinster Western Australia, the first major gold mine globally to combine solar, wind, and battery storage, with back-up from the gas generators.
The ground-breaking project, completed in May of this year in partnership with EDL, and with the backing of the Australian Renewable Energy Agency, installed 18 MW of wind power, 4 MW of solar PV, a 13 MW/4 MWh Saft battery energy storage system and an off-grid 21 MW gas/diesel engine power plant.
In a presentation to the Energy & Mines 2020 virtual summit on Tuesday, Gold Fields Australia’s unit manager of electrical operations, James Koerting, said the hybrid power system had overcome stability risks and was running reliably at an annual average of around 54% renewables, and on occasion as high as 78%.
Lacks synthetic inertia
The main reason that it wasn’t operating at a higher renewable capacity was the inability of its chosen battery to deliver synthetic inertia, a critical grid service that will be the major new component of the expanded Tesla big battery at Hornsdale in South Australia, still the biggest lithium-ion battery in the world.
“To further increase Agnew’s renewable fraction towards 100% we would need to increase the installed base of both renewables and storage,” Koerting told the summit.
“But I think aiming for 100% will come at too high a cost, with diminishing returns, so for future projects we’ll set our sights on a more realistic 99%,” he said.
How would this be achieved? Koerting says the key ingredients for emissions reduction for mining microgrids is renewables, plus inertia, plus storage, plus thermal back-up.
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One of the biggest hurdles, he says, is eliminating the thermal back-up, particularly considering the cost of ownership of this low-use asset is much lower than a day of lost production for most mining operations.
But the learnings from the Agnew project have already revealed plenty of room for improvement. Mostly in the energy storage and smart control department of the microgrid.
“As big as [the Agnew] battery is, it only provides the microgrid with supply security as a buffer for gas generators starts. It does not give us the ability to store renewable energy for arbitrage,” Koerting noted.
This leads to a notable inefficiency for the microgrid, where it regularly curtails zero marginal cost energy and LGCs “in favor of shipping and burning hydrocarbons” by running the thermal plant, he said.
Further to this, Agnew’s battery system wasn’t specified for synthetic inertia capability, which means the thermal power station has to run two engines continuously at half load to meet the systems minimum inertia threshold.
According to Koerting, this 2 MW of thermal power will cause renewables to be further curtailed, leading to a total level of solar and wind curtailment that almost disqualified the project from the ARENA funding — until the team was able to convince ARENA that curtailment was the lowest-cost method of pushing up renewable fraction while energy storage costs remained high.
Path to 99%
“It is here where my lessons learned start to [inform] what I think the future of renewable energy projects will look like,” Koerting told the webinar.
“Agnew has a technical constraint that requires us to run at least two gas generators at all times to ensure the minimum system inertia requirements are met.
“But what if we could lift that constraint with another form of inertia and utilize the curtailed energy to drive up the renewable fraction?
“Examples of how we could do this include utilizing the batteries to produce synthetic inertia or to integrate synchronous condenser or a flywheel,” he said.
“Storage …is the next technology frontier for decarbonisation, and with a project like Agnew we already have a platform with curtailed energy ready and waiting to be stored at no additional cost,” Koerting told the summit.
“We are agnostic as to whether it is a battery or another chemical or thermal process, potential energy system such as pumped hydro or hydrogen, as long as it can match the marginal cost of our thermal generation.”
This article originally appeared in Renew Economy and was reposted with permission. The author, Sophie Vorrath, is the deputy editor of Renew Economy and editor of One Step Off the Grid.