WA Branch Annual Sir Frank Ledger Breakfast

Source: James Koerting, Energy Manager, Gold Fields Australia

(L to R): Mike Ledger(Sir Frank Ledger’s grandson), Schree Chandran, James Koerting.

James Koerting (Energy Manager, Gold Fields Australia) delivered the keynote address at the 2021 Sir Frank Ledger Breakfast on the topic: The challenges of achieving zero emissions in remote mining operations. Koerting has been one of the leaders in the switch to renewable energy supply for Gold Fields Australia’s local operations. Incidentally, he also revealed that he has a family link to Sir Frank Ledger, whose achievements and founding role in what was to become Materials Australia are honoured each year at this annual breakfast meeting. Gold Fields Australia has been on a strategic journey to convert the primary energy sources for its remote mining operations in Western Australia, establishing renewable energy microgrids at the Agnew, Granny Smith and Gruyere mines. Gold Fields has successively introduced solar, battery, wind and gas hybrid energy systems to augment traditional gas and diesel power units. Its flagship installation at Agnew has led to 54% energy supply from renewable sources and a net 42% reduction in total mine emissions.

Gold Fields is not alone in the move to renewables in mining. Reflecting the international pressure for investment that takes into account Environmental, Social and Governance (ESG) issues, the major mining houses are aiming for a 30% to 40% reduction in greenhouse gas emission by 2030 and net zero, or carbon neutral, operation by 2050. The path to zero emission is based on elimination, and where this is not possible, neutralisation. However, as Koerting noted, if it were easy, it would have been done by now. The factors in the arguments against the change include ‘short mine life’, ‘high risk’, ‘too much capital’, ‘short battery life’, and more. Nevertheless, Gold Fields’ achievements at Agnew show what can be done under the right circumstances. Koerting pointed out that as the mines mature, they become more energy intensive. This is because they become deeper, haul distances increase, and grades usually decline. As such, the longer the mine life, the greater the challenge for net zero operation. However, on the other hand, the greater to opportunity to make longer-term investments to achieve net zero.

The path towards zero emission involves two steps: convert electric energy sources to renewables, and convert diesel fuelled mobile equipment to electric power. The developments at Gold Fields’ operations have been directed at renewable energy but anticipate increased electricity demand as the conversion from diesel proceeds. The renewable component of the Agnew operation has 16 MW of wind power (five turbines) and 4 MW of solar-tracking photovoltaics (PV), supplemented by a 4 MWh lithium-ion battery (which can deliver 13 MW). However, the mine still

requires 18 MW of gas and 3 MW of diesel generation. The total system is operated as a stand-alone micro-grid, with an advanced control system to maintain system security and stability, and to maximise renewable energy use. In the Agnew location, wind speed tends to reduce in the afternoon, while solar power depends not only on time of day, but cloud cover. While the goal is to maximise renewable energy usage, the aim is also to avoid ‘curtailment’, when more energy is produced than can be used. Balancing these two objectives informs the selection and sizing of renewable sources and the battery storage system. The control system has the task of dealing with the variable supply from wind and sun (including cloud cover prediction) and the thermal generation start-up characteristics to maintain overall power supply stability. One of the factors limiting maximum renewable energy usage is the challenge of rapid switching between sources. Koerting explained how inertia support through stored mechanical energy can reduce this limitation. With its capacity to absorb power fluctuations, the old technology of synchronous condensers is making a comeback as a way of maintaining phase and voltage while switching between sources. The field of renewables for remote areas is changing rapidly with solar PV continuing to become cheaper and more efficient. This is partly due to new materials, but also a result of new construction techniques and cheaper sun-tracking. Wind power is relatively mature technology but the challenge for the mining industry is the cost of construction of relatively small installations in remote locations; bringing a 160 tonne crane to Agnew was a significant undertaking. Batteries continue to evolve, with alternatives to lithium-ion now being considered. One of the interesting new proposals for energy storage that Koerting referred to is the gravity-based ‘energy vault’, in which large concrete blocks are raised and lowered, forming a solid equivalent to pumped hydro. Answering questions from the audience, Koerting spoke about some characteristic differences between various parts of the mining industry in relation to net zero carbon operation. Thus, gold mines typically yield a final product – gold bars – and do not have to contend with ‘Scope 3’ emissions produced by their customers; this is very different from iron ore mining. Small short-life gold mines, which are typically built for low capital expenditure, tolerate high operating expenses and so are less likely to be attracted to renewable energy than are long-life mines. The latter can trade higher capital cost against lower operating costs. For mid-tier mines it is a riskbased decision.

All agreed that Koerting provided members and visitors with a very clear and interesting insight into the changes which are rapidly changing the face of the local mining industry.