Tuesday,January 19, 2021 / 09:00AM / By Luke Witmer, GM,Data Science, Wartsila Energy Storage and Optimization / Header Image Credit: Wartsila

SinceB2Gold first acquired the Fekola gold mine, located in a remote corner ofsouthwest Mali, exploration studies revealed the deposits to be almost doublethe initial estimates. A recent site expansion has just been completed, andwhile 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 storageto the existing 64MW thermal engine plant was decided. This new energy mix isanticipated to save over 13 million litres of fuel, reduce carbon emissions bythirty-nine thousand tons per year, and generate a payback in just over fouryears.

Such anelaborate hybrid configuration needs a powerful brain to deliver on all itspotential: Wartsila's GEMS, an advanced energy management system, has been setup to control the energy across the fleet of power sources, thermal, renewable,and battery storage. The integration, control, and optimization capabilitiesprovided by GEMS allow the thermal units to be run at the most efficient rateand enable the battery storage to handle the large load step changes andvolatility of the solar PV generation assets. 

IntegratedHybrid Energy Solution  

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

The reciprocatingengines operate most efficiently at 85-90 percent of their capacity, this istheir "sweet spot". But if there is a sudden spike in demand, if a little morepower is needed, or if mining equipment is coming online, then another engineneeds to be run to meet the extra load. With the battery providing spinningreserves, the engines can be kept running at their sweet spot, reducing theoverall cost per kilowatt hour. Moreover, with the solar plant providing powerduring the day, three to four engines can be shut down over this period,providing a quiet time to carry out preventive maintenance. This really helpsthe maintenance cycle, ensuring that the engines operate in a more efficientmanner.

Solar PVvolatility can be intense. On a bright day with puffy clouds passing by a solarfarm of this size can easily see ramps of 25MW over a couple of minutes. Thisrequires intelligent controls, dynamically checking the amount of solar thatcan be let into the grid without causing an issue for the engine loadings orwithout overloading the battery.  

Conductingthe Orchestra

The GEMSintelligent software provides the optimization layer that controls all the powersources to ensure that they work together in harmony. The user interface (UI) givesaccess to all the data and presents it in a user-friendly way. Accessibleremotely, all operations are simulated on a digital twin in the cloud to verifythe system controls and simulate the most efficient operating scenarios tolower the cost of energy. This is an important software feature, both duringand after commissioning as it allows operators to train on the platform aheadof time and familiarise themselves with the automated controls and dynamiccurtailment of renewables. The UI provides the forecast for renewables and thebattery charge status at any given moment, it can provide push email or phonenotifications for alerts; telling operators when to turn off an engine and whento turn it back on.

Thesoftware is constantly analysing the data and running the math to solve theeconomic dispatch requirements and unit commitment constraints to ensure gridreliability and high engine efficiency. Load forecasting integrates thedifferent trends and patterns that are detectable in historic data as well as satellitebased solar forecasting to provide a holistic approach to dispatching power. TheFekola site has a sky imager, or cloud tracking camera with a fisheye lens, thatprovides solar forecasts for the next half hour in high temporal resolution.

To ensurethat operators really understand the platform, and have visibility over theadvanced controls, the UI provides probability distributions of the solarforecast. Tracking the forecast errors enables operators to see whether thesolar is overproducing or underproducing what the forecast was expecting at thetime and provides visibility to the operators on the key performance indicators.This feedback is an important part of the machine/human interface and providesoperators with insight if an engine is required to be turned on at shortnotice.

Automatedcurtailment enables the optimization of the system providing a reactivity thatpeople 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 exceedssome spinning reserve requirement. For example, if a large, unexpected cloudarrives, the battery is dispatched to fill the gap while the engines ramp up. Oncethe cloud disappears however, the engines remain committed to operating for afew hours, and the solar power is transferred to recharge the battery.

Over time,as load patterns shift, the load forecasting algorithm will also be dynamicallyupdating to match the changing realities of the load. As mining equipment hitslayers of harder rock, increasing the power load, the system will adjust anddispatch the engines accordingly.

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

The Fekolamine project incorporates the largest off-grid hybrid power solution in theworld, demonstrating the growing case for clean energy and its sustainable andeconomic potential for mines in Africa and beyond.

As the costof batteries and solar panels continues to become more competitive, hybridsolutions are proving to be a realistic and effective means for increasingenergy reliability and lowering operating costs in any context, thus freeing upresources to improve the human condition; whether through cheaper materials andgainful employment, or by providing broader access to reliable electricity forhealthcare, education, and improved quality of life. 

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