The next Generation of a Mine’s Power uses a DC Microgrid
The remoteness of many mines throughout the world makes getting power to them a challenge. Mines are often found far from population centers, meaning they are unable to connect to an existing electrical grid. Operations with unsuitable utility power get around this problem by installing “micro-grids”, which are small-scale power grids that can operate independently or together with a standard utility grid.
While a distant coal mine may be fortunate enough to generate its own power by burning coal, other mines must truck large amounts of diesel fuel over many miles of harsh road and terrain. Increasingly, solar and wind are being integrated into mining power infrastructure. However, to date, these alternative energy sources don’t meet the tremendous power requirements of a typical mine, nor are they very cost-efficient. As you will read, Bosch’s DC microgrid is not only suitable for remote mines but every mine, particularly those in high-energy cost areas and those with time-of-day demand metering.
Bosch has developed a solution for mines that employs direct current (DC) microgrids that generate and distribute DC power directly to DC loads, thus avoiding the costly and energy-inefficient alternating current (AC) to DC conversion.
Before getting into the details of DC microgrids, a little background is necessary. Standard utility grids run off AC power, where electrical energy is supplied to homes and companies in the form of 50/60 cycle AC power. Most appliances and HVAC systems use AC, but the electronics within appliances and HVAC require a conversion to DC. The conversion results in a loss of energy and requires additional components that also negatively affect reliability.
Transporting power via AC has an advantage over DC because it can be distributed cost-effectively using transformers that convert voltage levels. However modern semiconductor devices like transistors, microprocessors and LED lights, along with most consumer devices, including TVs and computers, use DC power. Most automation equipment used in factories and mines also runs on DC power.
Avoiding conversion from AC to DC power is made possible by a DC microgrid.
According to microgridprojects.com, as of 2017, over 200 microgrids are being used in communities and industry, but so far all of the mining microgrids are run on AC power. That is something that Bosch is trying to change, through its DC microgrid technology.
“We came to realize that the nature of power and load has changed quite significantly,” said Vinny Matthews, director of technology for Mining and Minerals for Bosch North America. “Now, typically, for a mine, the critical infrastructure, building automation equipment, safety equipment, control equipment, and multi-quadrant electrical drives, are DC.
“So Bosch determined that we could build a DC distribution system, not to replace the AC system, but to complement the AC system – a system that was specifically for DC loads.”
In mines, important infrastructure like fire detection systems, evacuation equipment, emergency call and uninterruptible power supply (UPS) systems, all run on DC power. Electric rope shovels, too, are powered by DC. These machines, used for loading ore into haul trucks, are tethered to the nearest substation by large above-ground cables.
Mines have the option of utilizing a number of power sources for their microgrids. According to a white paper written by Bosch, diesel fuel run through generators remains the most common means of fueling a microgrid, despite costing significantly more than solar or wind – $85 per megawatt hour for solar and $65/MWHr for wind versus up to $250 per MWHr for diesel.
“The reason for [diesel’s] popularity centers around universal availability (diesel fuel is readily available on six continents), convenience (most mines already purchase and store diesel fuel for discontinuous mining equipment) and serviceability (the same maintenance and repair personnel can service diesel engines and diesel-powered generators),” the white paper states.
It also notes that renewable power generation is more expensive to install than diesel and suffers from the intermittency problem, where power is available only when the wind blows or the sun shines. This necessitates a storage system, whose technology is young but rapidly developing in terms of battery efficiency and reduced cost per stored kilowatt.
Yet mines, in their quest to be less dependent on fossil fuels and to improve public perception, are turning to hybrid systems, where solar and wind power, and other interesting combinations, are used in combination with diesel generation.
“The unique and remote nature of mines has pushed the mining industry toward the frontier of microgrid technology. Alternative considerations for microgrid power include fuel cells and the use of inactive mine shafts for hydro power or compressed-air storage. Even modular, microscale nuclear plants are being considered,” according to the white paper.
The DC microgrid by Bosch is well suited to photovoltaic microgrids at mines that are commonly used in sunny climates like the southwest United States.
“What we’re doing is adding onto that, and saying, ‘Okay, look. If you’re generating photovoltaic power as DC, don’t convert it all to AC only to have it be reconverted to DC. Let’s take a portion of that power and distribute it as DC through the mine and we’ll save a lot of money not only on energy use but also in the life cycle of the equipment connected to it,” said Matthews.
Bosch estimates that by eliminating or minimizing conversion of AC to DC power, the cost of the system can be reduced by between 5 and 15 percent. Perhaps even more important, as the AC to DC electronics are either removed completely or replaced with DC/DC devices, system reliability can be increased significantly and the maintenance costs of these devices can be cut by 50 percent over the system’s lifetime.
“You typically would have to have transformers and electrolytic capacitors, which have a relatively short life and, in the electronics world, a relatively high failure rate. So by getting rid of that, you’re not only saving energy, you’re reducing your overall maintenance costs and therefore the total cost of ownership,” Matthews said.
Another added bonus of the DC microgrid is its “smart” functionality. Light fixtures are a ubiquitous feature at mines – both inside and outside – so Bosch began to think of each light fixture as a connectivity interface, capable of supporting security cameras, sensors, etc. Normally all these devices would have to be run through separate wiring, but with a DC microgrid, they all can be powered through a simple two-wire system via power line communication (PLC) protocol.
“The system does not require a separate signal distribution system. So we’re able to use the same wire to not only provide the DC power but also provide a communications interface with all of these sensors and all of these devices that can be distributed throughout the facility,” said Matthews. “It’s really a connectivity advantage – a facilitator for connected industry.”
Put it all together – centralized connectivity, a cost savings in terms of power conversion, increased reliability, a potential halving of maintenance costs over the life of the mine – and the DC microgrid for mines begins to make a lot of sense. Combine these advantages with the decreased use of fossil fuels to power the microgrid and the improved social license as a “green” operator that goes along with that, and the DC microgrid is even more attractive.
“We see it as being highly beneficial to the mining industry. We have started to talk to quite a few mine owners and to quite a few Engineer, procure and construct companies regarding the advantage of this. So we So we expect that these systems are going to grow in popularity,” Matthews concluded.
Read the full whitepaper from Bosch here.