Development and control of 5 kW solid oxide fuel cell demonstration unit: Master's thesis

Fuel cells are seen as one of the technologies that are necessary to satisfy the economical and environmental needs of the energy supply in the near future. High temperature solid oxide fuel cells (SOFCs) offer a low-pollution solution to generate power at high efficiencies. This diploma thesis was made during the year 2004 at VTT Technical Research Center of Finland as a part of the FINSOFC project. The scope of this work was to develop an automation and control system for a 5 kWe SOFC demonstration unit. A literature study of the characteristics of solid oxide fuel cells was made to clarify their operational principles. Similarly, a general analysis of the structure of SOFC systems was made using related literature and publications. During this thesis work a SOFC demonstration unit, designed for a 5 kWe class stack, was constructed. The automation system of the demonstration unit was further developed during the construction work and the system was commissioned. Based on both common theoretical knowledge and on features that are unique for the demonstration unit, a control strategy for a SOFC system is presented. A part of this control strategy is validated using the demonstration unit. The SOFC demonstration unit was able to produce 1.4 kWe power with a smaller 1 kWe class stack during commissioning with hydrogen operation. Reformed natural gas, suitable for SOFC fuel, was produced successfully with an ATR unit. Results from these test runs are promising and indicate that the concept of a SOFC CHP plant is technically feasible. Results from this thesis work can be employed to develop the 5 kW SOFC demonstration unit further. The control system layout can also be used in the designing of control systems for SOFC CHP plants. Further research and development efforts are still needed to enable automatic response of the control system to the changing demand of electric and thermal power.