Background Report: Fuel Cell on the Way to Series Production

• New record reached in terms of efficiency
• Great Market Potential for the Technology
• Low-cost construction with potential for further cost savings
• Simple operating principle

Munich - The HotModule is a carbonate fuel cell which has been developed as a distributed small-scale power plant and which, after more than ten years of development work, is presently undergoing practical trials involving the testing of systems of this type in a variety of applications in order to determine their suitability for everyday use.

While MTU Friedrichshafen, the parent company of mtu CFC Solutions GmbH, has its core business in the manufacture of diesel engines and drive systems for ships, railroad applications, heavy vehicles and distributed energy-supply systems, the company is engaged in developing the HotModule and readying it for series production as part of a long-term strategy, because, for the company, the fuel cell represents an addition to the present-day range of products, especially in the field of energy-supply systems.

The HotModule is particularly environment-friendly, its pollutant emissions being virtually zero. It helps to conserve natural resources, because it requires significantly less fuel than comparable conventional power plants in order to generate the same quantity of electricity. The system is especially suitable as a distributed small-scale power plant because, in addition to electrical power, it also generates high-temperature heat, which is required for a multiplicity of industrial processes.

New record reached in terms of efficiency

By contrast with other fuel-cell technologies, the HotModule is already today a comparatively mature technology with relatively low production costs thanks to its design and construction. This also explains why series production of the HotModule is in sight, says Michael Bode, President of the board of management of mtu CFC Solutions GmbH: "With each new system, we gather important experience which is taken into account in the further development of the product, above all with regard to readying it for series production. The target we have set ourselves is 2006, when we plan to start series production."

The previously installed HotModule systems achieve electrical efficiencies of almost 50 percent, a value which is not reached by any conventional technology in the 250-kilowatt class. For the purposes of comparison, modern gas engines of the same size class have a mechanical efficiency of around 40 percent, which does not include the conversion of the mechanical energy into electrical power.

Great Market Potential for the Technology

The results from the first field trials of the HotModule have aroused great interest among potential users. In 2002 alone, five systems were taken into service. "This was an important step toward readying the HotModule for series production," explains Michael Bode. The systems were installed at, among others, DeTeImmobilien in Munich, IPF in Magdeburg, RWE in Essen and IZAR in Cartagena, Spain.

The HotModule also boasts a particular technical feature which opens up the way to a range of entirely new applications in addition to the known markets: In contrast to other fuel cells, the HotModule can be operated not only on natural gas, but also on a variety of other fuels containing hydrocarbons, such as biogas, sewer gas, landfill gas and industrial waste gases. At present, many of these gases produced in industry and agriculture are lost or, at best, converted into heat. The HotModule allows such gases to be used to generate electrical power.

Low-cost construction with potential for further cost savings

The HotModule, like other types of fuel cell, is still undergoing development and readying for series production. The most important step on the way to series production is to further simplify the construction of the system in order to reduce the cost of production. The company's medium-term goal for its fuel cell is to arrive at a cost of 1200 to 1500 euros per kilowatt of output in order to make the system economically attractive. The aim is to simplify not only the cell itself, but also the preparation and treatment of the fuel gas. In addition, mtu engineers are working to increase the energy density of the cell and to extend its service life. The output from each of the individual cells, presently at 0.7 kW, is to be increased in future to 1 kW. The greatest savings potential, however, lies in series production. "At present, each HotModule is still produced by hand at a cost which cannot be compared with that of series-manufactured products, such as engines," says Bode. "When we get the HotModule to the stage where it is ready for series production, there will be further potential cost savings of 50 percent, allowing us to achieve our cost target.“

Simple operating principle

The HotModule is of very simple construction. The entire system consists of three separate parts: a central steel boiler with the fuel cell stack – this is the actual HotModule, which gives the overall system its name –, a front-end gas treatment section and an electrical part, which converts the generated DC into AC current and also houses the control system.

The HotModule is a carbonate fuel cell with its interior at a temperature of 650 degrees Celsius. The high temperature makes it possible to forgo the use of expensive precious-metal catalysts. Nickel is sufficient for initiating the fuel-cell reaction. At 650 degrees Celsius, there is also another effect which is obtained: When natural gas and water are brought together inside the fuel cell, this releases hydrogen, which is precisely the fuel required for the operation of fuel cells and which, in low-temperature fuel cells, has to be produced at great expense in bulky reforming plants. The most welcome side-effect, however, is to be found in the exhaust air from the HotModule: heat at a temperature of 400 degrees Celsius, which can be used to produce high-pressure steam, which, in turn, is required for many industrial processes.

The actual core of the system is composed of some 350 individual cells which are arranged in tandem and held together by tie rods. They together form the cell stack. The individual cells are in the form of flat sandwiches, two electrodes (anode and cathode) enclosing a carrier foil which is filled with the electrolyte lithium-potassium carbonate. When the hydrogen flows over one electrode and air flows over the other one, a process is started at 650 degrees Celsius which generates electricity. This process employs low flow velocities at atmospheric pressure. The high temperature melts the electrolyte and permits the exchange of electrons. The carbonate ions discharge on the anode side and release an oxygen atom which combines with the passing hydrogen to form water (H2O). The remaining carbon dioxide (CO2) returns to the cathode side, where it picks up two electrons and one oxygen atom from the passing air and thus returns to the process as a carbonate ion (CO32-).

Technical data of the HotModule

Fuel	Natural gas, biogas, sewer gas, landfill gas, industrial waste gases, methanol
Electrical output of cell block	270 kW
Electrical mains output	245 kW
Thermal output	180 kW
Electrical efficiency of cell block	Around 56 %
Overall efficiency	> 90 %
Number of cells	Around 350
Exhaust-air temperature for use as heat	Around 400° C