We are developing I kW class solid oxide fuel cell (SOFC) system for residential power generation (RPG) application supported by Korean Government. Anode-supported single cells with thin electrolyte layer of YSZ (yttria- stabilized zirconia) or ScSZ (scandia-stabilized zirconia) for intermediate temperature operation (650-750 degrees C), respectively, were fabricated and small stacks were built and evaluated. The LSCF/ScSZ/Ni-YSZ single cell showed performance of 543 MW cm(-2) at 650 degrees C and 1680 MW cm(-2) at 750 degrees C. The voltage of 15-cell stack based on 5 cm x 5 cm single cell (LSM/YSZ/Ni-YSZ) at 150 mW was 12.5 V in hydrogen as fuel of 120 sccm per cell at 750 C and decreased to about 10.9 V at 500 h operation time. A 5-cell stack based on the LSCF/YSZ/FL/Ni-YSZ showed the maximum power density of 30 W, 25 W and 20 W at 750 degrees C, 700 degrees C and 650 degrees C, respectively. LSCF/ScSZ/Ni-YSZ-based stack showed better performance than LSCF/YSZ/Ni-YSZ stack from the experiment temperature range. I-V characteristics by using hydrogen gas and reformate gas of methane as fuel were investigated at 750 degrees C in LSCF/ScSZ/FL/Ni-YSZ-based 5-cell stack. (C) 2007 Elsevier B.V. All rights reserved.