Development of electrical efficiency measurement techniques for 10 kW-class SOFC system: Part I. Measurement of electrical efficiency

Measurement techniques to estimate electrical efficiency of 10 kW-class SOFC systems fueled by town-gas were developed and demonstrated for a system developed by Kansai Electric Power Company and Mitsubishi Materials Corporation under a NEDO project. Higher heating value of the fuel was evaluated with a transportable gas sampling unit and conventional gas chromatography in AIST laboratory with thermal-conductivity and flame-ionization detectors, leading to mean value 44.69 MJ m−3 on a volumetric base for ideal-gas at the standard state (0 °C, 101.325 kPa). Mass-flow-rate of the fuel was estimated as 33.04 slm with a mass-flow meter for CH4, which was calibrated to correct CH4 flow-rate and effect of sensitivity change and to obtain conversion factor from CH4 to town-gas. Without calibration, systematic effect would occur by 8% in flow-rate measurement in the case for CH4. Power output was measured with a precision power analyzer, a virtual three phase starpoint adapter, and tri-axial shunts. Power of fundamental wave (60 Hz) was estimated as 10.14 kW, considering from total active power, total higher harmonic distortion factor, and power consumption at the starpoint adapter. The electrical efficiency was presumed to be 41.2% (HHV), though this mean value will be complete only when uncertainty estimation is accompanied.