Expansion of a processing plant in Mali gave B2Gold the opportunity to reduce both operating costs and emissions by adding a solar plant to its Fekola operation

B2Gold Corp. is building a $38 million hybrid solar/heavy fuel oil plant at its Fekola mine in Mali, and expecting to save $9 million in energy costs per year.

Banking on the sun

Although construction on B2Gold’s solar plant in Mali is currently on hold, the company is committed to the alternative energy source

By Lynn Greiner

Building on the success of the solar project at its Otjikoto mine in Namibia, B2Gold’s Fekola mine in Mali will eventually be home to one of the largest off-grid hybrid solar/heavy fuel oil (HFO) plants in the world.

Originally slated for completion in the third quarter of this year, construction has been temporarily suspended due to issues related to COVID-19 (it is expected to be finished within six months of restarting). When commissioned, the plant will provide 30 megawatts of power in addition to the existing 64 megawatt HFO and diesel capacity. The solar plant will also have a 15.4 megawatt hour battery component with up to 17.3 megawatts of discharge power.

Why solar?

B2Gold originally began processing ore at Fekola in September 2017, but within a year the company wanted to expand its operations and increase its throughput from six million tonnes per annum to 7.5 million. Eight CAT 16CM32 HFO generators and four CAT 3516B diesel generators (totalling an installed capacity of approximately 64MW) powered the plant, but the expansion provided an opportunity for B2Gold to reduce some operating costs while reducing the company’s carbon footprint. An additional source of power wasn’t strictly needed – after the expansion is completed, the power demand will be 40 megawatts, an amount the existing HFO plant can meet – but adding in another energy source makes more engines available for maintenance.

“At the time we were making [the original] construction decision for Fekola, we looked at a number of sources of energy,” said Dennis Stansbury, senior vice-president of engineering and project evaluations at Vancouver-based B2Gold. “We’re a long way from the grid in Mali, and the amount of power available on the grid was in question, so we had to do something standalone and made the decision to construct the HFO plant.

“When we later looked at upgrading the power plant, we looked at wind generation, but there are insufficient sustained winds, and the combination of a flat countryside and a river that dries up for part of the year meant that hydro power was out. That left solar as the best option to combine with our existing power plant.

“When we ran the numbers with all the current information, it has about a four-year payback,” Stansbury said. “And so my question… wasn’t, ‘well, why did you do solar?’ It was ‘why would you not do solar?’ It’s has a very short payback and that’s why we went so big and chose a 30 megawatt plant.”

Reasons for the switch

Money, for starters. Based on our study assumptions, total estimated cost savings will be about $9 million per year; the mine’s life has now been extended to 2030, with B2Gold expecting “significant estimated increases in average annual gold production to over 550,000 ounces per year during the five-year period 2020–2024 and over 400,000 ounces per year over the life of mine” working on the estimate of 81 per cent indicated and 19 per cent inferred mineral resources.

The solar plant, with a capital cost of $38 million, will reduce processing costs by more than seven per cent, and save at least

13.1 million litres of HFO per year. The environment wins too – CO2 emissions will shrink by about 39,000 tonnes per year, and on a sunny day the solar power will allow at least three of the HFO generators to be shut down for maintenance during the day without affecting production.

The icing on the cake, Stansbury said, is that by using batteries, the operation will be able to almost entirely dispense with the use of the diesel generators, which are currently used only in situations that require emergency power such as taking a mill down and quickly restarting it, as they are able to spin up power rapidly to meet spikes in demand. (HFO generators, which produce power at about two-thirds the cost of diesel generators, are not as efficient for quick-start or emergency situations in the same way as diesel ones, as they take longer to bring on line, and run most efficiently The seven megawatt solar power plant at B2Gold’s Otjikoto Mine is serving as a model for the one at Fekola. when used at 85 per cent of their nominal capacity). B2Gold is considering omitting diesel generators therefore how much solar power, to expect on any given day. It from future plant designs, even those without solar, and using even includes cloud detection capabilities. on-demand battery power to take up the slack when necessary “If you have a day, [when] you’ve got some sunshine and then and then recharging the batteries with excess HFO (or solar) you’ve got some clouds, and you’re trying to produce a significapacity. cant amount of your power with solar, you have to keep what we

The solar installation at Fekola will consist of 92,736 mono- call spinning reserve online,” Stansbury explained. “What that crystalline passivated emitter and rear cell (PERC) solar mod- means is if the cloud bank thickens a little bit, the production ules (385/390 watt-peak capacity) from Canadian Solar from your solar panels is going to drop. You have to make sure arranged in 3,312 strings over 69.4 hectares, connected to 276 that you have enough HFO generators online that they can pick inverters. The arrays use a single-axis tracking system from up that difference. So, on a cloudy day, let’s say you really need Array Technologies that tips the panels up to maximize the two generators running at 85 per cent efficiency – that’s kind of amount of solar radiation they receive at any given time of day. the sweet spot – and your solar is picking up the rest of it. But if A dual-axis tracking system that also turns panels from side to you’ve got a cloudy day, you probably have to run three engines side was evaluated, but it was determined that the additional because you need that spinning reserve to pick up any drop that complexity and capital cost associated with this could not be you might have in the solar production because of clouds or any justified. other interruptions.

Everything is pulled together and controlled by an integrated “With the battery system, you don’t need to do that, you just control system that is being developed to combine Wärtsilä’s run the two engines you need. If there’s a period of time where GEMS system with the existing supervisory control and data additional power is required, the battery supplies that power, so acquisition (SCADA) system being used to currently run the HFO it allows you to run your fuel engines much more efficiently plant. This integrated control system counters power spikes, because you have the batteries as part of your system.” allows startup of milling equipment without firing up additional That saves a lot of money since the HFO engines do not run engines, and permits operations to maximize the time HFO efficiently at 60 to 65 per cent capacity. It is harder on them, as engines are down. The system also allows for remote monitoring they do not achieve complete combustion of the fuel. Running of the power station. As solar output increases in the morning, them at a fairly high load minimizes the amount of fuel congenerators can be shut down, minimizing wear and fuel con- sumed per kilowatt hour and is easier on them from a maintesumption. The automated system compensates for issues with nance point of view. The batteries recharge once requirements generators, even in the middle of the night, feeding battery abate using excess output from either the solar or HFO generapower to keep production running uninterrupted. tors, as it is available.

B2Gold relied on two German renewable energy companies B2 Gold is developing several other deposits near the Fekola Suntrace (which was the project lead) and BayWa r.e. to do the operation. With the addition of solar power at Fekola, it may be project analysis, engineering designs, layouts, final cost esti- possible to power other smaller processing plants from the cenmate, and procurement evaluations. As the project progresses, tralized Fekola power installation and do so at a lower cost than their employees will also assist with site installation, commis- other power supply options. “The logic of keeping [all of the sioning and training of the solar plant operators. power generation capacity] in one plant makes a tremendous amount of sense. So we’re looking at ways that we can expand Tracking the weather the solar component and probably expand the battery compo-

The final piece is a weather forecasting system by Reuniwatt nent to the plant if we were to add additional production facilithat allows operators to figure out how much sunshine, and ties in the area,” said Stansbury. CIM