How optimised energy management delivers sustainability at the Fekola Gold Mine

By Luke Witmer, General Manager, Data Science, Wärtsilä Energy Storage and Optimization

Since B2Gold first acquired the Fekola gold mine, located in a remote corner of southwest Mali, exploration studies revealed the deposits to be almost double the initial estimates.

A recent site expansion has just been completed, and while the existing power units provide enough power to support the increase in production, the company sought to reduce its energy costs, cut greenhouse gas emissions, and increase power reliability. The addition of a 35MWp solar photovoltaic (PV) plant and 17MW/15MWh of energy storage to the existing 64MW thermal engine plant was decided.

This new energy mix is anticipated to save over 13-million litres of fuel, reduce carbon emissions by thirty-nine thousand tons per year, and generate a payback in just over four years.

Such an elaborate hybrid configuration needs a powerful brain to deliver on all its potential: Wärtsilä’s GEMS, an advanced energy management system, has been set up to control the energy across the fleet of power sources, thermal, renewable, and battery storage. The integration, control, and optimization capabilities provided by GEMS allow the thermal units to be run at the most efficient rate and enable the battery storage to handle the large load step changes and volatility of the solar PV generation assets.

Integrated Hybrid Energy Solution  

In the context of the Fekola mine, which is an off-grid electrical island, the battery is performing a lot of different services simultaneously, including frequency response, voltage support, shifting solar energy, and providing spinning reserves. The energy load is very flat, with a steady consumption rate around 40MW as the mining equipment is operating consistently, 24/7. However, if an engine trips offline and fails, the battery serves as an emergency backstop. The controls reserve enough battery energy capacity to fill the power gap for the time it takes to get another engine started, and the software inside each inverter enables the battery to respond instantaneously to any frequency deviation.

The reciprocating engines operate most efficiently at 85-90 percent of their capacity, this is their “sweet spot”. But if there is a sudden spike in demand, if a little more power is needed, or if mining equipment is coming online, then another engine needs to be run to meet the extra load. With the battery providing spinning reserves, the engines can be kept running at their sweet spot, reducing the overall cost per kilowatt hour. Moreover, with the solar plant providing power during the day, three to four engines can be shut down over this period, providing a quiet time to carry out preventive maintenance. This really helps the maintenance cycle, ensuring that the engines operate in a more efficient manner.

Solar PV volatility can be intense. On a bright day with puffy clouds passing by a solar farm of this size can easily see ramps of 25MW over a couple of minutes. This requires intelligent controls, dynamically checking the amount of solar that can be let into the grid without causing an issue for the engine loadings or without overloading the battery.  

Conducting the Orchestra

The GEMS intelligent software provides the optimization layer that controls all the power sources to ensure that they work together in harmony. The user interface (UI) gives access to all the data and presents it in a user-friendly way. Accessible remotely, all operations are simulated on a digital twin in the cloud to verify the system controls and simulate the most efficient operating scenarios to lower the cost of energy. This is an important software feature, both during and after commissioning as it allows operators to train on the platform ahead of time and familiarise themselves with the automated controls and dynamic curtailment of renewables. The UI provides the forecast for renewables and the battery charge status at any given moment, it can provide push email or phone notifications for alerts; telling operators when to turn off an engine and when to turn it back on.

The software is constantly analysing the data and running the math to solve the economic dispatch requirements and unit commitment constraints to ensure grid reliability and high engine efficiency. Load forecasting integrates the different trends and patterns that are detectable in historic data as well as satellite based solar forecasting to provide a holistic approach to dispatching power. The Fekola site has a sky imager, or cloud tracking camera with a fisheye lens, that provides solar forecasts for the next half hour in high temporal resolution.

To ensure that operators really understand the platform, and have visibility over the advanced controls, the UI provides probability distributions of the solar forecast. Tracking the forecast errors enables operators to see whether the solar is overproducing or underproducing what the forecast was expecting at the time and provides visibility to the operators on the key performance indicators. This feedback is an important part of the machine/human interface and provides operators with insight if an engine is required to be turned on at short notice.

Automated curtailment enables the optimization of the system providing a reactivity that people cannot match. By continually monitoring the engine loadings and battery, the system is ready to clamp down on solar if it gets too volatile or exceeds some spinning reserve requirement. For example, if a large, unexpected cloud arrives, the battery is dispatched to fill the gap while the engines ramp up. Once the cloud disappears, however, the engines remain committed to operating for a few hours, and the solar power is transferred to recharge the battery.

Over time, as load patterns shift, the load forecasting algorithm will also be dynamically updating to match the changing realities of the load. As mining equipment hits layers of harder rock, increasing the power load, the system will adjust and dispatch the engines accordingly.

Hybrid solutions will become the new gold standard for off-grid heavy energy users

The Fekola mine project incorporates the largest off-grid hybrid power solution in the world, demonstrating the growing case for clean energy and its sustainable and economic potential for mines in Africa and beyond.

As the cost of batteries and solar panels continues to become more competitive, hybrid solutions are proving to be a realistic and effective means for increasing energy reliability and lowering operating costs in any context, thus freeing up resources to improve the human condition; whether through cheaper materials and gainful employment, or by providing broader access to reliable electricity for healthcare, education, and improved quality of life. 

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MINING|The science of addressing climate change

Climate change is exacerbating many of the risks that mines already face in their daily operations and needs to be factored into planning decisions right from the pre-feasibility stage of projects.

Water management, for example, is becoming more complex as rainfall patterns in many areas start to change in frequency and intensity, according to Philippa Burmeister, principal scientist at SRK Consulting. “This affects mines’ management of their surface water and groundwater resources, as well as biodiversity and wetland management,” she explains.

“Climate change has implications for infrastructure design, as it raises the risk of flooding, water insecurity, and environmental damage.”

PHILIPPA BURMEISTER, PRINCIPAL SCIENTIST, SRK CONSULTING

Water balance

As an example, she highlighted the importance of water balance as a key aspect of tailings dam design. Here, historical rainfall data is a crucial part of the information necessary to ensure dams’ safe operation in the long term. “As rainfall variability and intensity change, the historical data becomes less reliable in guiding design parameters,” she says. “Operations generally are more likely to be disrupted due to severe weather events like floods or droughts. For instance, heavier storm events may increase water volumes seeping into mine workings, requiring more pumping capacity.”

Ashleigh Maritz, senior environmental scientist at SRK Consulting, notes that climate change is also likely to affect the livelihood resilience of mining communities. “As temperatures and rainfall patterns change, traditional forms of livelihood could be threatened, making communities more reliant on the mines for income and corporate social investment.”

Social licence

“The way that a mine engages with their stakeholders and supports communities is therefore critical, as it is vital to maintaining its social licence to operate,” adds Maritz.

She pointed out that an important outcome of climate change is likely to be a scarcity of precious resources like water – which could set mines in direct competition with local communities. Rising average temperatures in some regions may also lead to the geographic spread of communicable diseases like malaria – which may affect employees and surrounding communities.

Impacts on public infrastructure will also have a knock-on effect on mines. More frequent flooding or drought will change municipalities’ planning and investment in water supply or stormwater facilities. This may disadvantage the mines or affect mines’ social license to operate.

 “This will demand not just a technical solution but careful relationship building so that platforms are created for collaborative and long-term answers with buy-in from all stakeholders,” Maritz attests.

Risk and compliance

Burmeister adds that mining clients are increasingly cognisant of climate change risk. Industry standards are evolving – even in advance of national standards or requirements.

“With financial institutions also seeing the potential risks to their investments posed by climate change, they are increasingly stipulating that climate change issues are addressed in planning studies for mining projects.”

Philippa Burmeister, principal scientist at SRK Consulting

To effectively address the varied risks that accompany climate change, she emphasised that solutions need to be integrated. In other words, technical input must be coordinated across a range of professional disciplines. It is crucial that climate change impacts be ‘mainstreamed’ into various technical disciplines if it is to be effectively addressed.

“Our philosophy at SRK is that climate change must be considered by all disciplines in the project team,” she said. “This includes expertise in various facets of engineering, as well as in the natural and social sciences.”

SRK uses a range of quantitative and qualitative methods to investigate clients’ exposure to climate change risk. These include measuring the project’s greenhouse gas emissions as part of its environmental impact assessment and applying climate change models to identify specific project risks posed by predicted changes in climatic conditions.

Innovating for sustainability

SRK is looking at developing site-specific climate change-related rainfall models for its mining clients, to better inform their project and operational planning.

“By integrating SRK’s professional input, we ensure not only that clients are compliant with regulations, but that the many and varied risks of climate change are addressed in their projects,” she says. “This makes them more sustainable and robust in the longer term.”

Maritz noted that the science of climate change modelling is relatively young, leading the company to take an adaptive and dynamic approach – while leveraging off partnerships to develop and apply the power of predictive modelling.

“This assists us in pioneering strategies and tools to manage climate change risks, from initial mine design and operational technical inputs through to social transitioning and mine closure,” she shares.  “While monitoring is being undertaken extensively at most mine sites, the interpretation of the data is critical to identifying trends that could prevent undesirable events.”

Digital and data

A key concern for SRK has been the development of better data processing and analysis capacity for the considerable mine data that is already available. This helps guide decision-making around climate change and the risks it poses.

“SRK recently established a dedicated data services unit that works closely with the climate change team to leverage and evolve the latest digital technologies,” she says. “For instance, as part of an innovation project, the team is developing an interactive mining map of South Africa; this provides a coordinated source of geo-located data on various aspects and stages of mining.”

SRK is also looking at developing site-specific climate change-related rainfall models for its mining clients, to better inform their project and operational planning. To support its ongoing innovation efforts, the company holds an annual innovation conference that fosters collaboration between specialists and opens doors to valuable applications.

www.srk.co.za

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