It takes guts to make an investment decision when your primary revenue source is a volatile commodity mostly used to make jewellery. But gold mines often operate very far from convenient and cheap sources of electricity, so locking in your energy costs is a nice way to buy some certainty.

The best sources of energy are clean ones, of course, which is why global miner Gold Fields set sustainable energy company EDL the task of designing and building a power plant to enable its Agnew Gold Mine in Western Australia to become totally self-sufficient.

A primary requirement in the brief was for “reliable” energy, says EDL chief executive James Harman, which is something of a luxury when you’re about 600km northeast of Perth and paying for a connection to mega-miner BHP’s electricity generation capacity. “They were being shut off at times that weren’t convenient,” Harman tells EcoGeneration. “They wanted a reliable power supply.”

The 12MW provided by the BHP transmission line was also not enough to cope with the Agnew mine’s growing energy needs, which had resulted in 6MW of onsite diesel generators being installed. 

A microgrid that prioritized clean energy would also take Gold Fields one step closer to its target of becoming a sustainable mining company.

Wind was the key

The EDL plant is the first hybrid project to power a mine site anywhere in the world, Harman says, but mines aren’t always placed optimally for clean energy resources and so a lot depended on the data collection. “We had a view it was a particularly windy area but we wanted the data to support that,” he says.

“Wind was the key. We knew solar intensity in that area would be good but we had to be satisfied the wind would be reliable, and it has been – it’s been operating at about a 70% renewable penetration. That’s well above what Gold Fields expected.”

The plant includes five Goldwind turbines – that’s 18MW of wind – which were trucked 600km from Geraldton, an eight-day trip for 15 trucks carrying the 70m blades, sections of the 110m towers and all other componentry. The 4MW, 10,700-panel solar system includes some bifacial modules and a 13MW/4MWh Saft battery smooths generation and provides reserve. The battery has already been called upon during unplanned system events.

The configuration of generation assets was determined by successive rounds of technical modelling in conjunction with competitive tendering to deliver the lowest levelised cost of electricity.

The Agnew microgrid is run by an onsite EDL team and remotely from its Perth or Brisbane offices.

The remaining energy needs are met with an 18MW gas plant – enough to supply the mine if wind and solar are not generating – and 3MW of backup diesel.

EDL had form in remote locations, having delivered the Coober Pedy 9.3MW wind-solar-battery-diesel hybrid system in 2017, which sees the local grid run about 70% renewables with a record 94 hours uninterrupted of 100% renewables.

Central control

The data collected at the Agnew site showed the wind generally blew at night, making a wind farm an ideal complement for solar. “That’s the combination you need to get these high penetrations of renewables,” Harman says. “But you’ve got to have the smarts to combine them in a way that doesn’t disrupt the load.”

Demand at the site varies between 8MW and 17MW and is dominated by a process plant, including mills and a crusher, and underground ventilation. “They can turn a piece of kit on and the load can double in a matter of seconds,” Harman says. “The way the battery and integrated technology works keeps the reliable power generating instantaneously – you can’t have the power cut to the essential mining operations.”

The mine runs its operations how it likes, regardless of the sun or wind, which leaves EDL to control output so that clean energy makes up as much of the load as possible. “We’re following the mine’s demand,” says Harman, before explaining that EDL is interested in working on solutions for mines where output from an energy system can be timed to production. “In mines that might otherwise be uneconomic customers are looking at running large bits of kit at times when renewables are high,” he says. “That sort of thinking is starting to come through in some of the other miners we are talking to.”

Harman won’t comment on payback or Gold Fields’ expected return for the $112 million project – which included the cost of a gas pipeline and is underpinned by a 10-year power purchase agreement – other than to say “it’s utility-type returns.” EDL has a portfolio of 99 energy projects across five countries and “you have to be confident around how the system is going to operate because of the performance guarantees – we’re guaranteeing it’s going to be 99.9% reliable.” The Australian Renewable Energy Agency provided $13.5 million in funding for the project under its Advancing Renewables Program.

Over the long term EDL expects the power station will provide the mine with more than 50% renewable energy.

“It’s the future for energy supply in a place like Australia,” he says.