This paper presented performance analysis of solar cells and PVSYST simulation software of polycrystalline silicon and thin film amorphous silicon solar cells under Thailand conditions. The results indicated that performance result based on IEC 61724 standards (Photovoltaic System Performance Monitoring-Guidelines for Measurement, Data Exchange and Analysis) [1] found the average net energy from array (EA,τ) was 11.23 kWh/day. The array yield (YA) was 4.36 h/d and the performance ratio (PR) was 92.54% for Poly-Si solar cells. And the average net energy from array (EA,τ) was 4.22 kWh/day. The array yield (YA) was 4.65 h/d and the performance ratio (PR) was 103.86% for a-Si solar cells. The electrical power of polycrystalline silicon solar cells, the estimated values and the measured values were differed by 4.22% and 17.54% for thin film amorphous silicon solar cells. After applying correction factor based on the relationship of PR, the differed values improve to 10.60%.