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| Fuel cell focus


serves as an electrolyte, allows only protons – the positively charged atomic nucleus of hydrogen – to pass from anode to cathode. The water content of the membrane required for this ion conduction is responsible for limiting the operating temperature to a maximum of 100°C. The amount of precious metal (eg, platinum) required for the catalyst has been steadily reduced in recent years. This has already led to a significant reduction in costs and remains the focus of development efforts.


For Rolls-Royce Power Systems applications, the PEM fuel cell is ideal thanks to the high- power density, high scalability, modular design capability and resultant flexibility. Fuel cells can, for example, be built directly into battery- powered or electrified energy systems. The cell achieves high electrical efficiency (around 50%) and high current density, and is also very safe to use. This makes it suitable not just as a source for stationary power– say in the form of an emergency generator or UPS – but also ticks all the boxes for mobile use aboard ships. To increase the power density even further, today’s fuel cell systems sometimes feature air compressors or even electric turbochargers. As with internal combustion engines, the compressors or turbochargers pump air into the air system at a pressure of 2 to 3 bar. Several individual fuel cells can be connected in series to form a stack, thus increasing the voltage. To achieve more performance, the stacks can also be connected in parallel. This increases the amount of current generated to multiples of that achieved by serial connection. In developing and applying fuel cell technology, Rolls-Royce Power Systems draws on years of experience. Between 1999 and 2011, 26 high-temperature fuel cell systems – molten carbonate fuel cells (MCFCs) – were installed and successfully operated in various areas of application.


The combination of electricity and pressurised steam is used in a wide range of processes in industry and in the health sector. The systems have run for an average of about 22 000 operating hours, and performance data has been recorded and analysed. While market conditions and the general framework at that time did not support full production of MCFCs, all lights are now green for introducing PEM fuel cells into mass-market settings as an alternative source of drive power and the PEM fuel cell is now seen as the appropriate technology for Rolls-Royce Power Systems’ applications.


The key advantages of PEM over molten carbonate include its technical and market maturity, its power density and faster transient response. The latter advantages are particularly important because they allow PEM to serve a wider range of applications.


Potential applications for PEM FC


Data centres, emergency power and alternatives to diesel


Their characteristic features mean PEM fuel cells are suited to various applications currently


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Above: Fuel cell technology can provide climate neutral power supply


powered by combustion engines. Among other things, fuel cells could play a key role in zero- carbon data centres.


Data centres are part of the worldwide safety- critical infrastructure, which includes hospitals, airports and telecommunications, and it is essential that it operates absolutely trouble- free. In the event of a power failure, the current solution is usually for diesel generator sets to supply power to the data centre until normal operation is restored. mtu emergency power gensets meet the highest exhaust emission standards and offer maximum reliability with minimum maintenance, yet the combustion of fossil fuel (diesel) inevitably results in exhaust gas emissions.


If fuel cells are used for backup power supply – be it in the form of an uninterruptible power supply (UPS) or a mains backup system (MBS) – the only things given off are heat and humid spent air.


The fuel cell system has no moving parts, which minimises mechanical maintenance The fuel cell also wins on efficiency. Whereas, with a combustion engine, mechanical energy has to be converted into electricity using an additional generator, the fuel cell supplies electricity without any extra equipment. A further advantage is that it can be scaled with ease. More modules mean more power, and fuel cell systems can easily be added later and grow with the data centre. This makes fuel cell systems a long-term, future-proof investment.


In future, the basic power requirements of a data centre could be covered by solar and wind power plants. If sufficient “green” electricity were available, hydrogen could be produced from water by electrolysis and stored on site. Alternatively, the hydrogen requirement for powering the fuel cell could be covered by a future H2


supply network. In the event of a power failure, it would immediately


step in to supply the data centre and avoid infrastructure outages.


Rolls-Royce Power Systems will make fuel cell technology available to its customers in future. To provide a zero-carbon, pollutant-free standby power solution, up to six modules will be integrated into a fuel cell system. The modules will consist of stacks featuring several hundred fuel cells and the supply lines for air, hydrogen and cooling. The modular design will make it possible to adapt output to requirements. Up to 24 modules can be installed in one FC container. Rolls-Royce Power Systems is aiming to offer an integrated, fully-featured emergency power solution. This will include the fuel cell system, a UPS system, batteries and the hydrogen infrastructure. The technology will be black- start-capable, ie, able to resume generation without intervention, and deliver more than two MW of power.


The cost-effectiveness of the fuel cell can be increased in future by storing the surplus electricity produced and using it at peak load times. An alternative option is to feed 20% to 30% of the electricity generated into the grid and thus benefit from the distributed feed-in tariff. In addition to the economic benefit, this will relieve pressure on the overall grid and reduce power peaks.


Rolls-Royce Power Systems is planning to co- operate with Cellcentric, the fuel cell joint venture between Daimler and Volvo, to develop a range of fuel cell power generation technologies, primarily back-up power solutions for environmentally friendly data centres. These are intended to offer emission-free alternatives to diesel engines, which have so far been used as emergency power generators or for covering peak loads.


Demand response


A high degree of flexibility is required to accommodate the increasing use of renewable


www.modernpowersystems.com | July/August 2021 | 15


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