Rolls-Royce Power Systems is expanding its portfolio of energy systems with the addition of microgrid solutions for mines from MTU Onsite Energy. This means that mine operators will now be offered a sustainable energy supply system that can be operated in remote regions independently of public power grids. The solutions combine renewable energy sources with a battery storage system and both diesel and gas generator sets, in addition to a central controller to ensure that the mine’s entire demand for electricity is made available in a reliable and efficient manner, and one that is friendly to the environment.
Besides diesel and gas generator sets from MTU Onsite Energy, the solutions offered by Rolls-Royce Power Systems also include battery containers combined with photovoltaic and wind power plants in microgrids. The modular designed 40-feet MTUEnergyPack is entirely new on the market. It stores electricity from any source – ready to deliver at the flick of a switch. Peak Power: 2,515 kW (DC)/ 2,475 kVA (AC); Nominal Capacity Range: 700 - 1,260 kWh 
SUSTAINABLE, EFFICIENT AND RELIABLE - ENERGY SUPPLY REQUIREMENTS IN MINES
“For mine operators, energy costs, which account on average for 15 % of the overall operating costs of mine, are a key factor,” Lars Kräft, Vice President Industrial Business at Rolls-Royce Power Systems, explains. “And with a demand for electric power of 50 to 100 MW per mine, sustainability, efficiency and the reliability of the energy supply are now becoming increasingly important in the industry. We have identified our customers’ needs and, with our microgrid systems, are now offering them a solution tailored to their specific requirements,” he adds.

RENEWABLE ENERGIES, BATTERY CONTAINERS, DIESEL AND GAS GENERATOR SETS COMBINED TO PERFECTION
Besides diesel and gas generator sets from MTU Onsite Energy, the solutions offered by Rolls-Royce Power Systems also include battery containers combined with photovoltaic and wind power plants in autonomous power grids. All the components are connected to each other via a smart energy management system, which optimises the way in which the energy is used both technically and commercially. Any excess renewable energy can be stored in the batteries and then made available whenever it is needed. At the same time, fluctuations in power generated from renewable energy sources due to weather conditions and the time of day are compensated for with reliable diesel and gas generator sets, in addition to battery storage systems. The system is thus designed to provide a stable power supply at all times – even when the demand for electric power is high and when systems are required to operate around the clock.

DECARBONISATION AND COST REDUCTION WITH RENEWABLES
Using renewable energies and the associated benefits of carbonisation means that mine operators can make considerable progress in achieving a significantly more sustainable energy supply, which also benefits their stakeholders, such as investors or communities located close to the mine. Due to the integration of renewable energies and the smart networking of all components, there is a significant cost benefit to mine operators. Fuel costs can be reduced for example, in addition to the saving of costs required for connecting mines to the power grids. 

Gas engines are increasingly taking the place of diesels in a range of areas including off-highway applications. Both types of engine deliver similar performance but gas engines emit less CO2 during the combustion process. 
So, what precisely are the differences between the two?
TURBOCHARGERSThe turbochargers used on diesel engines and mobile gas engines are virtually identical. They both feed the engine with the air (and, therefore, oxygen) it needs for combustion. On stationary gas units, the turbocharger has to process both the air and the entire volume of the gas/air mixture and in stationary genset applications, turbochargers are optimized to match full-load conditions because these engines generally operate at full-load.
MIXTURE COOLINGDiesel engines have charge-air coolers that cool the air heated in the compressor before it enters the combustion chamber. On gas engines, this function is performed by the mixture cooler. Depending on the application in question, the gas/air mixture is cooled in two stages to around 50 to 60°С before passing on to the combustion chamber. The thermal energy extracted during the cooling process can be decoupled from the system and fed into a heating system, for example.
FUEL MIXTUREIn diesel engines, air is sucked into the combustion chamber where it is compressed to levels that raise its temperature as high as 700°С. Injectors then introduce diesel fuel that ignites in the hot air. In stationary gas engines, the air is mixed with fuel gas before it passes through the turbocharger and mixture cooler to the combustion chamber. Mobile gas engines utilize multi-point injection systems. Here, air is routed to the cylinder and gas is introduced just before it enters the combustion chamber. This means that the volume of gas can be flexibly regulated dependidng on the power required.
IGNITIONThe most obvious difference between diesel and gas engines can be found in the ignition systems. Diesels are self-igniting engines in which high levels of compression cause the diesel/air mixture to ignite spontaneously. Like gasoline-fueled engines, gas engines use a spark generated by a spark plug to ignite the gas/air mixture (the illustration shows the spark plug connectors and cables leading to the cylinder head cover). Diesel injection systems and extraneous ignition systems on gas engines both need suitable control concepts that determine factors such as, for example, injection timing and duration (diesels) or inginition point and energy (gas).
KNOCK CONTROLDiesel fuels adhere to precise specifications and deliver highly consistent levels of quality for efficient engine set-up. However, the constituents in gaseous fuels vary and this affects combustion. For example, different gases have different methane numbers (similar to octane ratings for gasoline) that indicate the proportional mixture of an equivalent fuel consisting of methane and hydrogen. If the methane number is too low, inefficient spark ignition and other uncontrolled combustion processes can occur in the combustion chamber. These generate `engine knock` and gas engines need to be controlled to deal with the phenomenon. Stationary gas engines use vibration sensors to identify knock whilst pressure sensors do the same on mobile gas engines. Consequently, ignition timing is adjusted as an initial reaction and engine power can be reduced as a second step. In extrem cases, the engine can be shut down to prevent damage.
TROTTLE FLAPSOn both diesels and mobile gas units the formation of the fuel mixture is controlled flexibly for each ignition sequence in order to influence engine power. Stationary gas engines use a premixed gas/air mixture that remains constant and engine power is influenced by using throttle flaps to regulate the flow of the mixture. Mobile gas engines also have throttle flaps but these regulate the pressure of the mixture entering the cylinder.