Pictures of the Future    Spring 2007

Hybrid Future

^{Erlangen researcher Dr. Friederike Lange studies the corrugated design to be used in a fuel cell power plant (right) that will generate environ-mentally friendly electricity}

Corrugated cardboard has many outstanding properties. It protects fragile materials, and it’s light and inexpensive. But that it would one day symbolize a revolution in power generation is something Albert Jones never could have dreamed of back in 1871, when he registered for a U.S. patent for two layers of paper with a serpentine cardboard layer in between. Still, the device on the desk of Horst Greiner, a fuel cell expert at Siemens Corporate Technology in Erlangen, looks exactly like Jones’ invention, only bigger and not as pliable. Of course, Greiner’s ceramic version isn’t intended for packaging; instead, it will be used for combining hydrogen and air to generate electricity.

Rather than being burned, as in the case of a welding torch, for example, the gases used in fuel cells are converted into water by means of an electrochemical reaction that releases electrons, thereby generating electricity. It’s similar to what occurs in a car battery, but the process utilizes ceramic materials and takes place at temperatures of up to 950 °C (see also "Gentle Revolution" in Pictures of the Future, Spring 2002). "In combination with a gas turbine, a fuel cell can achieve an efficiency of up to 70 %," says Greiner. By way of comparison, the best combined gas and steam-turbine plants feature an efficiency of 58 % ("How to Produce and Distribute Energy Efficiently"). In the future, fuel cell plants producing several megawatts could supply electricity in distributed systems to individual users and small cities with populations of approximately 10,000 residents.

Macaroni or Corrugated Cardboard? Much development work still needs to be done before this becomes reality. To date, the ceramic stack with the corrugated cardboard design has only been operated in a lab, and it probably won’t be ready for use in Siemens power plants before 2012. At the moment, ceramic fuel cell parts look like giant gray pieces of macaroni. Greiner places several of these tubes next to and on top of one another and explains why this is not an optimal shape. "There’s too much empty space in between," he says. Pressing the tubes flat ensures better use of available space, while inserting transverse connections to create a delta shape and setting up several layers inevitably results in a construction similar to corrugated cardboard. This shape offers optimal spatial utilization and maximum space for hydrogen-air exchange. This "delta design" results in more than double the output of a cylinder-shaped cell—and also requires less space. Depending on stack design, power densities up to 600 mW/cm³ can be achieved.

The ceramic tubes have also proved that they can reliably produce electricity. One 100-kW plant currently located in Turin, Italy, has already been operating for 32,000 hours. Other plants have been generating power in the Netherlands for two years, and in Essen, Germany, for six months. "We’ve achieved 99.5 % availability with our facility," reports Dr. Joachim Hoffmann, director of the Stationary Fuel Cell Program at Siemens Power Generation in Nuremberg. That’s not bad for a technology which everybody attests high efficiency but not the highest reliability.

The reliability issue is indeed a serious one, according to Hoffmann, who says many competitors failed with their fuel cells because the units functioned in the lab but not under tough everyday conditions. Some companies have given up—but not Siemens. As early as 40 years ago, fuel cell experts at Westinghouse in Pittsburgh, Pennsylvania (acquired by Siemens in 1997) were studying materials suitable for fuel cells, eventually building the very first solid oxide fuel cell (SOFC) in the late 1970s. "Fuel cell production technology expertise is not easy to come by," says Hoffmann. Other SOFC manufacturers build planar fuel cells with metal interconnects, but all these competitors are now having problems with aging after extended operation. For all of its cells, Siemens uses pure ceramic materials produced at temperatures above 1,500 °C. And regardless of whether they’re later operated at 900 or 1,000 degrees, they are not subject to the dramatic losses of other fuel cell designs.

The Siemens cells lose only 0.1 % of their output per 1,000 operating hours and their efficiency of more than 43 % remains stable across a broad range of temperatures and loads. "We estimate a lifespan of at least 20 years for the delta cells," says Thomas Flower, head of fuel cell activities in Pittsburgh. Flower is convinced that the Siemens concept can be brought to market more quickly than others, even if different fuel cell designs will exist simultaneously for use with different applications in the future.

Things haven’t always gone so smoothly for Siemens/Westinghouse. For example, plans originally called for a fuel cell to be coupled with a gas turbine ten years ago. The idea was to burn the residual hydrogen fuel in the exhaust gas to generate electricity in the turbine. The turbine was also supposed to supply compressed air, warm it with its waste heat, and force it into the cells under high pressure. "That would have generated practically no heat, but plenty of electricity," says Greiner. Nothing came of it, however, and in 2002, Siemens and the EnBW energy company decided to shelve the joint project for the time being. "We wanted to build a nearly market-ready demonstration plant, but that wasn’t possible at the time," says Dr. Wolfram Münch, head of Research, Development and Demonstrations at EnBW in Karlsruhe, Germany.

Pilot Plant. The biggest problem was the gas turbine. In the low-output category of 200–300 kW, there was no suitable model on the market at the time, and developing a new turbine would have cost about 15 mill. €. So it was a stroke of luck two years ago when the German Aerospace Center (DLR)—in cooperation with the Institute for Aviation Drive Systems at the University of Stuttgart—offered to enhance the control system for coupling gas turbines with fuel cells on the basis of a 100-kW micro gas turbine from an Italian manufacturer. The only condition was that a fuel cell manufacturer and a power supply company participate in the project.

"We contacted Siemens again and quickly agreed that we should join forces," Münch recalls. EnBW plans to use the efficient power plant especially to help industrial companies and local utilities generate electricity for their own needs, with EnBW operating the plants and acting as an energy services provider.

The new schedule is tight. DLR plans to conduct a simulation in 2008 to determine if the fuel cells and gas turbine work well in tandem before linking the components in 2009. The system will then be optimized, and EnBW will put a demonstration plant into operation in its network in 2012. That plant will produce two to four megawatts of electricity, with the fuel cell accounting for about 75 % of that total. It’s still too soon to say if the 70-% electrical efficiency target will be realized with the combination, but ceramic cells with the corrugated design will be used for the project.

Power for Pittsburgh’s Botanic Gardens. Experience has shown that trying to achieve too many fuel cell advances simultaneously is a flawed approach. That’s why Siemens also plans to build smaller fuel cell plants without gas turbines to gain additional operational experience. Three such plants, each with an output of 125 kW, will go on line in 2007. One has already been built in Hanover, through a partnership with local utility and the energy supplier E.ON; the other two will be used in Tokyo and Fairbanks, Alaska. At the Siemens subsidiary TurboCare in Turin, Italy, a next-generation power plant will be built in 2008.

There, the material to be used will be more conductive. It will generate 150 kW of power at over 47-% efficiency and be just as compact as the other units. In parallel, selected customers will be using small units producing five kilowatts each. Two supply electricity to Deutsche Telekom buildings in Steinfurt and Bonn; three are in operation in the U.S., including one at the Pittsburgh Botanic Gardens, where a unit is supplying power for regulating the temperature in the Tropical Rain Forest House.

Also on the agenda are alternative fuel cells that use biogas and sewage gas, free byproducts from water treatment facilities. Hybrid fuel cell power plants can be operated with a variety of fuels. A current project in the U.S., for example, involves a hybrid plant that will run on coal gas, whereby the carbon dioxide will be separated from the coal before it is burned. Siemens engineers say this CO₂ separation will lead to only a 5-% loss in efficiency; the same process in a conventional coal-fired plant would decrease efficiency by around 10 %.

Financial Hurdles. "If a hybrid plant is economical and functions reliably from a technical standpoint, then its technology has a good chance of making it to market," says Münch. Customers are interested in distributed systems with a high electricity output and low emissions, but the decisive factor is cost.

The fuel cell sector is getting a big boost from the Fuel Cell Initiative, which includes all major German energy suppliers and fuel cell manufacturers, as well as the German Energy Agency. Long-term funding has also been provided by the German Ministry of Economics and the EU. Siemens has invested 30 mill. € of its own funds and external funding in fuel cell research in Erlangen. This sum doesn’t include Siemens’ activities in Pittsburgh supported by the U.S. Department of Energy.

If preliminary work is successful, hybrid fuel cell technology could be on the market ten years earlier than expected. Competitors in this field have erred in the past by launching very costly systems before they were ready. Indeed, today a fuel cell plant from Siemens would also be too expensive now; the manufacturing processes, such as those for cell production, still aren’t cost-optimized. And there’s still lots of precision work to be done, which continues to drive up costs, says Hoffmann. Nevertheless, automated production should bring costs down to a reasonable level by 2012. Hoffmann is optimistic. "The general trend toward consistently rising energy prices plays right into our hands," he says.
                                                                                                                 Bernd Müller