Using renewable energy in preference of fossil fuels may require miners to reconsider the demand requirements of their on-site fleets to suit the economic parameters offered by new power sources.

Research by an Australian and Canadian working group, including Malcolm Powell of the University of Queensland’s Sustainable Minerals Institute, has offered an alternative to a business model that consists of a continuous, unconstrained supply of power, which may lead to a global transformation in an energy-constrained world.

The research involved a case study carried out at an underground satellite operation of what is now BHP’s Prominent Hill copper-gold project in remote South Australia, where solar generation is used.

By the end of the last decade, mining accounted for approximately 10 per cent of Australia’s energy use, with the main sources being diesel (41 per cent), natural gas (33 per cent) and grid electricity (21 per cent). The remainder was supplied by a mixture of other refined fuels, coal, renewables and biofuels.

The main use of this power was for beneficiation operations, vehicles, and machinery.

Under the new paradigm of renewable energy, the research team said, the main characteristics were variability, intermittency and correlation.

These factors, however, combined to erode the ability of a generation system to balance supply to demand.

Of these three factors, variability was fairly predictable and fairly “easy to handle”, while intermittency meant that miners usually received less than they expected, but just how much was not known.

“The standard response is to overbuild generation and storage capacity,” the researchers said.

“The economic driving force of the three characteristics is correlation (which) means that renewables are either generating or not generating in unison.

“This supercharges intermittency because it means that the supply switches between too much and none on a daily basis.

“For grid supplied mines, correlation leads to ‘price separation’ where the price jumps from a very low daytime price to an exorbitant evening price.”

Contrary to common perception, the researchers said, isolated mines were not power supply-limited.

Moreover, the power limit was economic because, due to correlation, the cost of a reliable and constant renewable energy system rapidly entered diminishing returns.

Therefore, the alternative was to simply use renewables to reduce the cost and emissions of diesel fuel.

“This is tenable at present, but as the worldwide motor vehicle fleet electrifies, the cost of liquid fuel distribution will be increasingly borne by a reducing consumer base,” the research said.

“Banking on uninterrupted supplies of cheap diesel introduces yet another risk to the energy/mine equation.

“The solution to this growing list of energy challenges is to couple the energy system to the mine design at the planning stage, and then to run the energy system and mine as a closely coupled organisation.”

Throughout the mine life, flowsheet and equipment selection needed to hold flexibility as a design objective to be co-optimised with energy and production.

At the design stage, the focus should be on addressing variability through flexibility rather than dealing with intermittency via overbuild.

Focusing on variability rather than intermittency solved both problems as the ‘zero’ points in variability demanded either shut down or minimised operations.

Addressing intermittency then becomes a task of extending the minimum operating period.

The recommended process to embed flexibility at the design stage was to survey energy demand and flexibility at a block level, understand minimum operating and maximum rates for each sub-system, actively search for process storage, prioritise flexibility as well as determine start and settling ramp-up and down.

“If the energy profile is ‘peaky’, look for modularised units to allow for staged stepping-up of utilisation,” the research said.

“Armed with this knowledge, engage energy providers and iterate generation/energy storage sets with operations set to co-optimise the mine design.

“The result will be a flexible, scalable, adaptable design, able to better adjust to uncertainties during energy transition and beyond.

“Flexibility will help deliver energy outcomes that will become increasingly necessary as the energy transition continues.

“However, that same flexibility will also produce a more resilient mine operation, able to respond to a range of challenges such as declining (or improving) market conditions, unexpected ore body variations and even political, social or workplace issues.”

The output from the modelled system was then scaled to give an hourly energy output in kilowatts (kWh) per hour of installed solar panels for a year.

This data set was used in the wider system model and the installed capacity was able to be scaled up and down for multiple modelling runs.

The modular basis for solar energy output was also reflected in the other parts of the overall model, including the battery energy storage system (BESS) and the mining fleet.

The BESS was modelled with one, two and four-hour storage duration options with the energy capacity also scalable for multiple modelling runs.

“The results of the energy supply model showed that short-term flexibility of discontinuous operation was economically preferable as an alternative to increasing the capacity of energy storage,” Powell and the other researchers said.

“In other words, reducing the load at opportune time steps reduced the requirement for a larger battery and made for a higher overall net present value when compared to the scenario with higher throughput, but a more expensive, larger battery system.

“It is clear that flexibility on the demand side of the electrical system delivered value to the system, thus to make the most use of any variable renewable energy resource it is beneficial for the energy consumers to be equally variable in energy demand.

“Advances are being made in mine processing equipment to allow for this greater flexibility of energy demand. In addition, as more mine fleet and equipment are electrified there will be more opportunities to shift load to different parts of the day to ensure the overall system can adapt to the available energy, for example charging electric haulage trucks at peak solar production periods.”