Energy considerations for off-grid mines
This article covers infrastructure, strategies and design considerations that can be used to reduce power consumption at a mining operation that is not connected to a major electrical or natural gas grid.
Operating Costs for Remote Mines versus Mines in Central Jurisdictions
Mines in remote, off-grid locations have significantly higher operating costs than operations that are connected to electrical and natural gas grids. Operating expenses for off-grid mines in Canada’s north have been observed to be, on average, 30% to 60% higher than their southern, on-grid counterparts. The majority of a remote mine’s operating expenditure comes from the use of on-site power generation. Typically, fuel is shipped to site and burned in diesel generators to provide electricity and heating for services such as lighting and ventilation. A comparison of various fuel and energy costs for northern locations versus operations within a central jurisdiction is shown in Table 1. An overall operating cost breakdown for precious and base metal mines is shown in Table 2. A reoccurring theme with energy-efficient technologies and strategies are large capital costs, but significant savings over a mine’s life.
|Diesel, $/L||Electricity, $/KWh||Fuel Oil, $/L|
Strategies for Reducing Power Consumption at the Industrial Level
Mining operations can reduce operating expenses by means of detailed, company wide policies and strategies for energy use optimization. A typical energy optimization strategy examines the following six factors :
- Tracking operational energy use in all operations
- Energy conservation whenever possible
- Energy efficient infrastructure and equipment
- Optimization of power generating equipment
- Electrical storage systems
- Renewable energy systems
Energy Tracking and Awareness
Mining companies have the ability to reduce power consumption by simply increasing energy awareness at all levels of the business. Energy awareness is the understanding of energy consumption, and involves the distribution of knowledge surrounding such consumption. This can be achieved through a number of communication pathways such as;
- Company-wide memos or newsletters summarizing energy usage.
- Postings throughout the business in the form of notices or posters illustrating energy usage.
- Monthly meetings held discussing energy usage and possible improvements.
- Workshops by which energy saving techniques are conveyed to all company employees.
- Rewards or incentives for individuals or groups who meet a specified energy-use target.
All of these methods can be summarized by three main awareness techniques; education, incentives, and visibility .
The implementation of energy tracking can create a useful source of data for the communication pathways mentioned above. Historically the tracking of energy use has been an underutilized method due to poor record keeping. There are two general methods for tracking energy consumption, one of which is more intensive than the other. The simplest method to record energy consumption involves the manual maintenance of fuel logs at all energy consuming equipment. A more vigorous approach can be taken with the installation of a real-time monitoring system, known as Energy Management Information Systems (EMIS). These systems track and visually display energy consumption at the source. Such a monitoring system records consumption at a higher accuracy level, however it comes at a higher cost than manual fuel logs. Therefore, companies must prioritize their needs in order to effectively decide between manual and automated tracking .
Case Study – The ISO 50001 strategy at New Afton Mine, BC
The following was adapted from New Gold, 2014 
The New Afton gold and copper mine in British Columbia developed and implemented an energy management initiative with the goal of reducing power consumption and operating expenses associated with the use of propane, fuel oil, diesel and electricity. The initiative covers the requirements of [Iso 50001], which encourages companies to:
- Develop a policy for efficient energy use
- Set goals to meet the policy
- Track and use data to understand energy consumption
- Measure results
- Review policy effectiveness and continually improve energy management
At the New Afton gold mine, this meant cooperation and communication between all employees and executives to identify problem areas. After examining existing data, New Afton identified several areas of major energy inefficiency. The mine plans to improve its air compressors, replace existing processing plant components with more energy efficient options, introduce ventilation on demand , and upgrade all lighting installations both above and underground. Through the use of New Afton’s energy management strategy, the mine expects to see an annual power consumption reduction of 9 Gigawatt hours .
High Efficiency, Energy Saving Equipment and Infrastructure
Mines in remote locations resort to independent means of generating electricity and are burdened with the expense of transporting fuels such as diesel. To improve project feasibility and reduce operating expenditure, it may be beneficial to use energy efficient equipment and infrastructure. However. It may be difficult to incorporate high efficiency solutions as they often come with higher capital costs and longer payback periods.
The objective of ventilation in underground mining is to provide sufficient airflow quality and quantity to control the concentration of pollutants such as gases, dusts, heat and humidity . Well ventilated mine workings may improve the efficiency of machines and operators – increasing production. Ventilation systems are a noteworthy portion of an underground mine’s operating expenditure. Ventilation accounts for 25% to 40% of total energy costs and 40% to 50% of the energy consumed at an operation. Furthermore, it is believed a large number of ventilation systems have efficiencies of 65% or lower . During the engineering design phase of a project, suitable ventilation design can reduce capital expenditure and electricity requirements for an underground mine. Besides initial design, operational advances such as ventilation on demand and on/off peak timing can reduce energy requirements as well as operating expenditure.
Remote mines power most of their infrastructure and camps with electricity. Traditionally, diesel generators have been responsible for supplying the electricity. In recent years however, renewable forms of energy are gaining ground, as well as renewable-hybrid systems. Nevertheless, well-selected generators and battery energy storage systems may reduce a mines operating costs. The downside is this typically leads to higher capital costs.
Diesel generators have evolved as a technology through decades of use. Other types of generators include gasoline, natural gas and propane. Some benefits of diesel generators over the other types may include:
- No spark plugs to replace
- Less fuel burned to do same work
- Low volatility of diesel (less likely to ignite)
Industrial diesel generators are amongst the world’s largest generators, and may approach ratings of several megawatts. For example, the Caterpillar model 3616 diesel generator  is rated at over three megawatts. Remote mines will employ banks of generators  to power their infrastructure. Having banks of generators of varying size with on/off capability may be more beneficial than several larger generators as diesel generators are most efficient when operating at or above 80% of their total capacity . The electrical load required by the mine may vary over a working day, so having a bank of generators allows the mine to limit the amount of generators that are active to maximize efficiency (thus reducing diesel consumption).
Some considerations when selecting high efficiency diesel generators for a remote mining operation may include :
- Generator operating and maintenance costs are significantly higher than their capital cost.
- Generators should be used in parallel for adjustment to various power loads (peak, low) as well as easy integration for potential future expansions.
- Cycle charging through the combination of a generator, battery storage, and inverter system can be useful, especially for camp settings.For example, a camp’s energy requirements may spike during mealtimes and shift change, but drop during sleep periods.
Remote Mine Power Generation Battery Energy Storage Case Study
The following case study was adapted from Janzen et al., 2013 .
Generators typically operate at 80% to 85% of their power rating to deal with load fluctuations. Operating at near-maximum power ratings improves efficiency, but may be impractical with traditional generator infrastructure seen at producing mines. By incorporating a Battery Energy Storage System (BESS), electricity costs (diesel consumption) may be reduced.
A remote mine in Northern Canada has a power plant capacity of 30MW. The power is sourced exclusively from a bank of diesel generators. The figure that follows illustrates a simplification of the configuration.
Over a period of one month power data was recorded. It was found power demand was consistent, with the exception of drops during upset conditions or maintenance periods. The addition of a 3.6 MW/1.7 MWh BESS was simulated. The cost of such a unit was assumed to be $2M. It was also assumed there would be a reduction in maintenance costs.
The simulated system was modeled for one year. The simulation and subsequent financial analysis suggested:
- $330,000 reduction in annual operational expenditure
- 6-year Payback period
- BESS life estimate of 20 years
The results of the study suggest the mine would benefit from a BESS if mine life extended 6 years beyond implementation of such a system.
Example of a Remote Site: Voisey’s Bay
Vale’s Voisey’s Bay open pit mine in Northern Labrador relies on diesel generators to supply 15 MW of power . Vale is planning an expansion which would see the mining method switch to underground. To address increased demand for electricity, the site would require additional diesel power generators and diesel fuel storage . It is important the engineering design maximize the efficiency of generators to minimize operating costs.
Active Control Systems
With advancements in instrumentation and communication systems, next-generation monitoring systems can actively control mine systems and services to minimize waste and operational costs. For mines near the end of their mine life, it may be difficult to justify the placement of instrumentation. Young mines and projects in the early-design phase may benefit from control system instrumentation. However, experience has shown excessive instrumentation may make control systems overly complex, unreliable, and difficult to maintain. A more practical approach may involve strategic placement of instrumentation in zones and nodes deemed critical .
Ventilation on Demand
The general practice in underground mining is to ventilate the entirety of the mine, all the time. However, this practice is extremely wasteful as a limited portion of the mine will be occupied at any instance . Ventilation on demand is a concept that seeks to minimize wastefulness by only ventilating active or soon to be active regions of a mine.
The following case study was adapted from Gundersen et al., 2005 . Consider an underground mining operation that breaks 150 kt of rock (ore and waste) per month. Stope mucking is done with a 200 kW LHD and a 295 kW truck. Active stopes require 45 m3/s of fresh air and inactive stopes require 20 m3/s of fresh air (to cover the minimum required for the passing of equipment such as supervisor trucks). The mine layout dictates that stopes operate in pairs, with 18 stopes (9 pairs) required for drilling/preparation, blasting, or clearing. However, at any one time, only 5 stopes need to be active (mucking after blast). Since stopes are configured in pairs, 5 pairs (10 stopes) require some degree of ventilation. Consider the following three scenarios:
- 18 stopes (9 pairs), each ventilated at 45 m3/s
- 10 stopes (5 pairs), each ventilated at 45 m3/s
- 10 stopes (5 pairs), active stopes ventilated at 45 m3/s, inactive stopes ventilated at 20 m3/s
The first scenario can be considered the worst case, where every stope regardless of activity is ventilated as if it were an active stope. The total airflow required would be 810 m3/s (45 m3/s x 18 stopes).
The second scenario simulates a case where ventilation can be controlled “on” or “off’ for each pairing. Since only 5 pairs (10 stopes) require some degree of ventilation, the remaining 4 pairs (8 stopes) are unventilated. However, the 5 pairs comprising 10 stopes will be fed at 45 m3/s as there is no control between stopes in a pair and the active stope must be fed at least 45 m3/s. The total airflow required for the second scenario would be 450 m3/s (45 m3/s x 10 stopes).
The final scenario simulates a case where ventilation can be controlled for each individual stope. This may involve an automatic system that would track vehicle movement and accordingly switch fans and regulators as the equipment moves through the mine. Active stopes would have total airflow of 225 m3/s (45 m3/s x 5 stopes) and inactive stopes would have total airflow of 100 m3/s (20 m3/s x 5 stopes). The final scenario’s overall airflow would be 325 m3/s. In summary, the three scenarios have airflow requirements of 810 m3/s, 450 m3/s, and 325 m3/s respectively.
From observing the airflow requirements of the three different cases, one may deduce more control leads to greater cost savings. This is not necessarily the case, as operational savings may not exceed additional capital expenditure required to purchase additional fans and control instrumentation.
Lighting on Demand
To conserve energy, inactive mine drifts should not be illuminated. Manual or automated control of such drifts will provide some cost savings. Unlike other on demand systems (e.g. ventilation), lighting on demand is near-immediate. Very little lead time is required to illuminate a drift with controlled lighting.
Renewable Energy Sources and Hybrid Power Generation
Renewable energy producing systems exist within the industry today in the forms of wind turbines, hydroelectric dams on nearby rivers, and solar farms . Due to the extreme power demands of mining operations, renewable energy sources cannot completely replace diesel generators at the present time. However, for remote mining operations, the use of hybrid renewable-diesel power generation systems can reduce power costs up to 70% . Existing proof-of-concept projects, such as the 3 MW wind turbine installed at the Raglan mine in northern Quebec, demonstrate the viability of hybrid designs . Hybrid systems can improve efficiency while still utilizing existing infrastructure (such as diesel generators). Further cost reduction can be achieved by using battery power storage in tandem with hybrid systems.
There are many different ways in which the sun’s energy can be harvested to provide electricity on earth, the two most common being concentrated solar power and photovoltaic cells. Concentrated solar power uses collected radiation from the sun to heat water in various ways (for instance, through reflection onto a central focal point or through individual solar panels), effectively creating a steam generator that can be used for a variety of applications . Another method to capture the sun’s energy is through the use of photovoltaic cells, which take advantage of the photovoltaic effect, a property held by certain materials that allows them to convert radiation directly into electricity by releasing electrons when photons come into contact with the cell . However, photovoltaic cells are unable to efficiently store energy (as electricity is much more difficult to store than heat), meaning they are only effective when the sun is shining . Despite this, photovoltaic cells are more widely used worldwide, as shown in Figure 3 below:
Currently, solar energy is the most cost-effective renewable energy source per unit of electricity produced. This makes it an excellent candidate to replace fossil fuels as a feasible energy source, and it is even less expensive than natural gas . Prices can range between $8-$34 per kilowatt-hour generated per month, depending on the size of the panel, as shown in Table 3 .
|System Size (Watts)||Monthly Output (KWh)||Cost Range ($)|
|200-600||29-75||1,000 - 1,750|
|1,000 - 1,500||130 - 200||3,500 - 6,750|
|2,000 - 3,000||300 - 400||7,500 - 8,500|
|4,250 - 5,750||300 - 400||7,500 - 8,500|
|6,000 +||1,950 - 2,600||16,000+|
Table 3 shows the price range of various solar panels based on their output 
Difficulties Associated With Solar Energy Systems
Incorporating solar power generation has many challenges. First and foremost, the fact that power generation is limited to daytime hours is a huge obstacle that often makes solar power an unfeasible option for many regions. This is especially troublesome for remote mines in northern Canada, which experience far less sunlight in the winter months than the rest of the world. On top of this, weather can severely impact solar energy production. Clouds blocking the sun, snow covering panels, and fog can prevent panels from effectively producing electricity. It is estimated that fog can reduce solar panel effectiveness by up to 95% .
Improper positioning of the panels relative to the sun can reduce the effectiveness of energy production. The sun only occupies half a degree of space in the sky, making it difficult to absorb all of its energy unless panels are perfectly positioned to face the sun directly. Coupled with the movement of the sun, efficiency is reduced further . Lastly, solar panels occupy a large area, though remote areas will not usually have the same constraints as urban areas .
Solar Power Plant Case Study
While solar power generation is not feasible for operations in northern climates, it is an attractive option for off-grid mines in warm, arid and sunny environments, such as Australia or South Africa. Photovoltaic cells have even been used as a hybrid power source with diesel by [Cronimet Mining Power Solutions] at a chromium mine in South Africa, as well as [Rio Tinto]'s Weipa Mine in Australia. Plans have been announced to begin development on a 10.6 MW project on [Sandfire’s Degrussa Mine] in Australia . At the Cronimet mine, a 1.8 GWh solar power plant has reduced the operations diesel CO2 emissions by more than 10,000 tonnes per year. Since implementing the solar power generating plant, the mine has been able to reduce annual diesel consumption by more than 50% . It is important to note that these solar plants are not capable of powering the entire mine on their own, and are being used in tandem with existing diesel generators.
Wind energy is a relatively cheap-to-operate and space-efficient source of power that is currently used across Canada and 90 countries worldwide . By harvesting wind through turbines or sails, energy can be produced in large quantities. In addition to this, some mines in northern Canada have used or planned to use local wind turbines to provide electricity to their operations and surrounding communities.
Diesel – Wind Hybrid System Case Study
Diavik Diamond Mines Inc. (a subsidiary of Rio Tinto plc) installed a $33 million, 9.2 MW wind farm to reduce energy costs when wind speed and direction meets requirements. It is estimated that the wind farm will reduce energy costs by $5-6 million per year. The project was completed in September 2012 and continues to power parts of the mine today . Additionally, Glencore Xstrata recently installed a wind turbine at their Raglan Nickel-Copper project on the Ungava Peninsula. It features a 3 MW turbine connected to the current diesel grid and has been running for over a year, saving 2.4 million liters in diesel fuel. The project cost just under $19 million . Although initial capital costs can be very high, renewable power sources pay for these costs in diesel savings. However, both these projects operate only when conditions are near-ideal; mines are forced to rely on diesel energy for the majority of their energy needs. This is because, like solar energy, wind power is heavily affected by weather conditions. In addition to this, wind turbines pose a threat to wildlife as rotating blades have been known to strike and kill birds .
Large-scale hydroelectric power plants are usually at the heart of power grids. Small-scale (100kW-30MW), micro (5kW-100kW), and pico (<5kW) hydroelectric production are typically not central to power grids, but are based on the same principles as larger dams. Smaller hydroelectric operations usually consist of small barricades on pools or small lakes that divert water to a power generation station through pipes or canals. These systems can produce constant power around the clock when the water is running, which makes it advantageous compared to solar or wind energy . However, micro hydroelectric operations often do not produce enough energy to sustain a mine unless several power stations are used, which could possibly drive the cost to power the mine to undesirable levels  . In terms of scale, a 30MW hydroelectric plant could power some small mines, though others require far more power.
Difficulties Associated With Hydroelectricity
Hydroelectric power generation relies on nearby water sources to operate, which might not be present and could freeze over in the winter with off-grid mines in northern Canada. Furthermore, it is estimated that the construction of these dams can cost around $3.2 million (for small installations of around 500kW) and up to $89 million in some cases (without accounting for installation in remote areas), making it a capital-intensive option  . In addition to this, the construction of a dam or diversion canal could have large impacts on local ecosystems, which, when coupled with the high capital costs and permitting necessary, could make hydroelectricity an unfeasible option at the scale necessary to power a mine. As a result, smaller dams could be used in combination with other power sources (such as diesel) in order to reduce fuel costs and reduce the mine’s carbon footprint.
Geothermal energy is a clean and renewable energy source that involves drilling into the earth to take advantage of the naturally high temperatures deep in the crust. Water exposed to the earth’s high temperatures is then converted to steam, which can then spin a turbine, generating relatively constant electricity . According to the United States Office of Energy Efficiency and Renewable Energy, the construction of a geothermal power plant producing less than one megawatt can range from $3000 to $5000 per kilowatt of electricity, which suggest a 1 MW geothermal power plant may cost $3-$5 million dollars . However, some power plants with even larger capacities can cost tens of millions of dollars, with a 50 MW plant costing an estimated $130-140 million . Like hydroelectricity, this high capital cost will likely be too much for a mine to afford. In addition to this, geothermal power generation has potential to cause earthquakes, which can endanger miners if power plants are stationed nearby .
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- ↑ Steel International, “Global Mining Industry Eyes Off-Grid Solar Power”, Steel International Contracting Company ltd., Berlin, Ger. 2015.
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- ↑ Ground Truth Trekking. (2014, October) Ground Truth Trekking. [Online]. http://www.groundtruthtrekking.org/Issues/MetalsMining/Powering-Large-Mines-In-Alaska.html
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- ↑ Newfoundland and Labrador Department of Natural Resources. (2012, November) Power in Our Hands. [Online]. http://www.powerinourhands.ca/pdf/Labrador_Mining.pdf
- ↑ Renewables First. Renewables First. [Online]. https://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/how-much-do-hydropower-systems-cost-to-build/
- ↑ Canadian Geothermal Energy Association. (2016) Canadian Geothermal Energy Association. [Online]. http://www.cangea.ca/about-geothermal.html
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