A vision of all-electric mines is closer to reality than ever before

Reducing carbon (CO2) emissions during open-pit operations is now a major driver for mining companies globally. Trolley assist systems are being employed to limit diesel fuel usage and lower costs, while at the same time boosting speed-on-grade. 

A new generation of diesel-electric trucks has emerged. These have an electrical system on board, which makes attaching them to a trolley line relatively straightforward. This concept is becoming a commercially viable way of moving towards all-electric mines in the future. 

One of the key challenges of reducing diesel fuel usage is cycle times. There is no technology today that enables miners to fill a truck’s tank and complete a shift without stopping. Instead, there is a choice of increasing the speed of the mobile equipment or the size the fleet itself – both of which have a direct impact on capital expenditure.

Enter trolley assist 

Trolley assist systems have returned to the market over the last three years, in locations including North and South America, Africa and Turkey. This is mainly due to CO2 emissions taxes, the removal of tax advantages from diesel, and premiums offered by energy suppliers to incentivise companies to use electricity. Trolley lines offer huge benefits in terms of CO2 reduction. 

Mining trucks regularly carry 3,000 to 5,000 litres of diesel and consume around 300 to 400 litres per hour while travelling up a 17km ramp in half an hour. By going electric, the vehicles on-trolley only use around 30 to 50 litres an hour, saving as much as 350 litres an hour and making operations much more CO2 efficient.  

In addition, the speed of the trucks will increase, meaning a higher throughput at the mine. This allows operators to think about parking some of their fleet, resulting in better planning around vehicle maintenance, availability and longevity. 

One example of the trolley assist systems revival is at the Aitik open pit copper mine in Sweden. Boliden, ABB and partners trialled the electrification of four haulage trucks on a 700m trolley line, with the goal of reducing annual diesel usage by 800,000 litres and carrying 70 million tons of ore every year at the mine without using fossil fuel. 

Reduced diesel consumption at Boliden mines  

Boliden has now moved on from the 700m trolley line trial at Aitik to confirming it will install an additional 3km of trolley line at the mine, plus 1.8km at Kevitsa (in addition to the accompanying conversion of diesel-electric haul trucks). By doing so Boliden says it will reduce its diesel consumption by 5,500 cu.m/y when its investment is complete. 

Aitik is currently the only mine in an arctic climate where electric trolley has been installed. Overall, with the further 3km of electric trolley line, greenhouse gas emissions from transportation over the life of mine are reduced by nearly 15 percent. 

In Kevitsa, 13 mining trucks have been converted for electric trolley lines at the same time as the 1.8km electric trolley line is being built. The investment means that greenhouse gas emissions over the life of this mine are reduced by 9 percent. 

Modern mine management  

Diesel-electric trucks have an electrical powertrain in the wheels, meaning they can be driven fully electric. They have an electrical genset on board, so they generate electricity as they go. However, due to the limitations of existing battery technologies, it is not possible to manage large payload trucks of 280–400 tons fully battery equipped. Companies are therefore trying to close the gap between the trolley and the loading or the dumping point using battery packs and other solutions. 

The transformation from diesel to electric is bringing new advantages in terms of CO2 reduction but also new constraints in terms of mine planning and fleet management. Energy costs represent almost one third of a mining company’s total cost base; helping industry to manage these costs is therefore key.