Entering new terrain in power station construction

One of the greatest available sources of energy lies in further increasing energy efficiency. This also applies to power station construction. Researchers from the DLR want to improve the use of natural gas by combining gas turbines and fuel cells. Industry has also shown a strong interest and companies have come on board. Whenever Axel Widenhorn turns on the gas turbine in his lab, he's looking to get more out of the utilized fuel than is the case at present. "Power stations in the lower megawatt range currently use much less than half the energy they have been fed with to produce electricity," explains the engineer from the DLR Institute of Combustion Technology in Stuttgart. Widenhorn heads a young group there that is developing the combustion technology for a power station that combines gas turbine and fuel cell to create a hybrid technology. He aims to raise the electrical efficiency level to 60 per cent. Although large central power stations use the energy similarly efficiently for generating electricity, the remaining 40 per cent is lost as waste heat released into the air. By contrast, a small, decentralised power station that only has one hundredth of the capacity is able to use this waste thermal energy to heat flats and buildings. So, a hybrid power station would be efficient both in power generation and in using the residual heat. "In a hybrid power station, the gas turbine and the fuel cell support each other," explains Axel Widenhorn, "which enables us to raise the efficiency level." The fuel cell not only generates electricity but also the 800°C hot waste gases used to drive the gas turbine. In turn, the gas turbine produces electricity plus compressed air which is fed into the fuel cell along with the fuel. This means squaring the circle. The result is that the electrical efficiency rate increases by up to 15 percentage points over that of the fuel cell, the best individual component.

That this project promises success can be seen in the interest that industrial partners are showing in the Helmholtz Virtual Institute "Hybrid power station: gas turbine, SOFC fuel cell, and system regulation." In addition to Axel Widenhorn's group, the DLR Institute of Technical Thermodynamics and the Institute of Aircraft Propulsion Systems at the University of Stuttgart, Siemens Fuel Cells and Energie Baden-Württemberg are also working on the project. The Virtual Institute forms the basis for structured cooperation between the partners. The core engineering competencies needed in the field of gas turbines, high-temperature fuel cells and regulators for successful implementation are strategically joined together, thereby concentrating the specific strengths of the partner institutes.

Scientists at the Virtual Institute organise the cooperation practically like a real-life institute. They have a coordinator and regular team meetings. Furthermore, researchers also take on external responsibilities, for example, to raise additional external funds. "When I switch on my computer, I can immediately see which colleagues are available, even if they are not working in the same building," enthuses Widenhorn. The engineers are entering new terrain in numerous areas. They have to develop innovative plant and operational concepts for the hybrid power station. The combustion processes and air-fuel mixtures that occur in the hybrid power station have not yet been studied in detail. In fact, regulation of the hybrid power station still presents the scientists with a number of major challenges. After being switched on, the fuel cell needs hours before it reaches full load. While the gas turbine starts up within a few seconds. This means that after the power station is activated, the gas turbine initially has to run without its symbiotic partner, the "fuel cell". Engineers first of all design the regulator on the computer using a virtual power station.

"We do this to develop control concepts for each individual phase. Not only for switching it on, for example, but also for switching it off, for load changes and, of course, for emergency stop situations," explains Axel Widenhorn. In the next step, he and his colleagues test the regulator in the lab system. If the research power station works in the lab, Energie Baden-Württemberg plans to build a demonstrator using the new technology in five years' time. With a capacity of some four megawatts, it would be able to provide a small town of 4,000 inhabitants with electricity and some heating.