Fuel Cell a Proven Success in Extensive Field Testing

Posted on April 07, 2003

The "HotModule" fuel cell system from mtu CFC Solutions GmbH is on schedule for series production.
  • Ten "HotModule" fuel cell systems installed to date
  • Environmentally friendly power and heat generation
  • High market potential of the technology
  • Series production start-up planned for 2006
  • Simple operating principle with high development potential

Hanover - The "HotModule" fuel cell system from mtu CFC Solutions GmbH is on schedule for series production. The company, part of the DaimlerChrysler Group, has to date delivered and installed ten field test systems in Europe and in the USA. Eight of these systems are currently undergoing field tests and the remaining two have already completed their tests. Additional systems will be delivered in 2003.

Companies with currently running HotModule systems include the tire manufacturer Michelin, the energy corporation RWE, the Telekom subsidiary DeTeImmobilien as well as various industrial businesses and hospitals. Six of the 250 kW-strong systems were commissioned in 2002 alone. "This was a significant step towards series production of the HotModule", according to Michael Bode, Manager of mtu CFC Solutions.

The HotModule is a technology developed as a decentralized compact power station and which, after ten years of development, is now in the field testing phase, where systems of this type are tested for their day-to-day suitability in various applications.

Environmentally friendly power and heat generation

Although the core business of MTU Friedrichshafen as parent company of mtu CFC Solutions GmbH is the production of diesel engines and drive systems for ships, railway locomotives, heavy vehicles and for decentralized energy generation, developing the HotModule and bringing it up to production standard is part of the company's long-term strategy. As Bode says, "For mtu, fuel cells represent an enhancement to the current product range from a long-term perspective, particularly in the energy systems sector." Above all, the system is well suited to use as a decentralized compact power station because, as well as producing power, it also produces high-temperature heat energy. The heat is required for a number of operating processes, such as generating process vapor for the vulcanization of tires at Michelin and for sterilization and air conditioning in hospitals.

The first commercial HotModule field test system at the University of Bielefeld has already achieved record-breaking results. During its total running time of 16,000 operating hours, the system achieved record figures. It ran longer than any other previous carbonate fuel cell and achieved an electrical efficiency of 47 percent; a value not achieved by any conventional technology in the 250 kilowatt class.

By way of comparison, modern gas engines of the same size work with a mechanical efficiency of maximum 41 percent, which does not even include the conversion of the mechanical energy into power. The current fuel cell systems of mtu achieve even higher values; up to 48 percent in alternating current networks and up to 50 percent in direct current applications, as at DeTeImmobilien.

High market potential of the technology

The markets for stationary fuel cells result from the opportunities presented by this technology within the existing infrastructure. The fuel is basically natural gas, although other gases can also be used. In comparison to conventional combined heat and power plants, the HotModule has significantly higher efficiency and is considerably cleaner. It currently achieves electrical grid power of 230 kilowatts at a cell block output of 270 kilowatts. This also produces some 180 kW of thermal energy. Overall, the HotModule can therefore achieve a utilization rate of more than 90 percent. The emissions that the system produces are so minimal that it can be called "waste air" rather than "waste gas" in accordance with the German Clean Air Act. The waste air consists primarily of hot air and water vapor. Practically no nitrogen oxides or sulfur oxides are emitted. The carbon dioxide emission is also significantly lower than with conventional power stations.

Another technical feature of the HotModule makes it possible to embrace completely new markets beyond the existing markets with this fuel cell. Unlike other fuel cells, the HotModule can be run with other hydrocarbon-based fuels, such as biogas, sewage gas, landfill gas, industrial residue gases and methanol as well as natural gas. "This presents us with completely new possibilities," says Michael Bode. "Currently, much of this gas in industry and agriculture goes completely to waste or at best is used in thermal applications. The HotModule offers a highly efficient possibility to utilize these gases to produce power."

Series production start-up planned for 2006

Compared with other fuel cell technologies, the HotModule is already comparatively advanced and relatively economical to produce due to its design and construction. This is one reason why series production of the HotModule is imminent, according to Bode: "With every new system we gain valuable experience, which we incorporate during further development, above all with regard to preparation for series production. The preliminary target for us is 2006, when we envisage the start-up of series production."

The HotModule is already relatively economical compared with other fuel cells. With the HotModule, the company could halve costs per kilowatt output within a few years. However, Michael Bode believes the price still needs to fall further: "The standard in the market is high. At less than EUR 1,000 per kilowatt, gas engine systems now represent the target, although they are considerably less efficient than our HotModule."

In the medium-term, mtu CFC Solutions intends to achieve between EUR 1,200 and EUR 1,500 per kilowatt of installed output with its fuel cell, in order to make the HotModule commercially attractive. The company is therefore focusing on further reducing the costs of producing the system. This includes treating combustion gas far more cost effectively in future than at present through technical simplifications. mtu technicians are also reexamining the actual cells in detail. The intention is to further simplify their composition, save materials, increase the output of the cells and reduce the number of necessary steps in cell production. However, the greatest saving potential is in series production. "At present, each HotModule is still a handmade single unit that cannot be compared with series-produced products, such as engines, in terms of costs," says Bode. "If the HotModule goes into series production, this would mean a further 50 percent cost saving, thus making this cost target attainable".

Simple operating principle with high development potential

The composition of the HotModule is very simple. The entire system consists of three separate components, namely a central steel container with the fuel cell stack - this is the actual HotModule that gave the entire system its name - upstream gas treatment and an electric part, in which the generated direct current is converted into alternating current and the system control is housed.

The HotModule is a carbonate fuel cell, inside which the temperature is 650 degrees. The high temperature eliminates the need for expensive catalytic converters made of precious metal. Nickel is sufficient to initiate the fuel cell reaction. At 650 degrees, yet another effect becomes apparent: combining natural gas and water within the fuel cell results in dehydrogenation. Hydrogen is the fuel that is required to run fuel cells, and it can only be obtained at great expense in the case of low-temperature fuel cells in bulky reformation systems. However, the most welcome of side effects can be found in the waste air emitted by the HotModule: 400 degree heat, with which high-pressure steam can be produced, which in turn is required for many industrial processes.

The actual nucleus of the system is some 350 individual cells, which mtu at present purchases from its US partner company Fuel Cell Energy Inc. They are installed in sequence and are held together by anchor bars, thus creating the cell stack. The individual cells are constructed as flat sandwiches. Here, two electrodes (anode and cathode) surround a carrier film, which is filled with the electrolyte lithium potassium carbonate. If the hydrogen coats one electrode and air coats the other, this results in an energy-producing process at 650 degrees Celsius. This process is pressureless and with low flow rates. As a result of the high temperature, the electrolyte melts and facilitates the exchange of ions: The carbonate ions discharge at the anode side and give off an oxygen atom that combines with the hydrogen flowing past to form water (H2O). The remaining carbon dioxide (CO2) returns to the cathode side, where it takes two electrons and an oxygen atom from the air flowing past and thus returns to the process as a carbonate ion (CO32-).

Like other fuel cell types, the development of the HotModule is not yet complete. There are various aspects of the HotModule where there is room for development. With this in mind, mtu technicians are working on increasing the energy density of the cell and extending its service life. The individual cells that currently produce 0.7 kW are set to generate 1 kW of power each in future. mtu engineers are also in the process of making the HotModule even more flexible. It should be in a position to continue to generate power independently in the event of problems with the power supply system, even in the event of total power failure.

Technical data of the HotModule

Fuel Natural gas, biogas, sewer gas, landfill gas, residual gases (from industry), methyl alcohol
Electrical output of cell block 270 kW
Electrical mains output Approx. 230 kW
Thermal output 180 kW
Electrical efficiency of cell block Approx. 56 %
Total utilization efficiency > 90 %
Number of cells Approx. 350
Used-air temperature for heating purposes Approx. 400° C