The daily watt-hour efficiency (eta(Wh)) and daily integrated output power (P-Wh) of the a-Si and poly-Si module have been used to examine the performances of both modules on the basis of two years＇ data accumulated at outdoor conditions. Results from the analysis of experimental data taken under incident solar energy higher than 3.0 k Wh/m(2) per day show that the annual average of eta(Wh) of the a-Si module is about 95% and 92.5% of its efficiency at STC condition at the first and second year, respectively, while the values are nearly unchanged at about 89% for the poly-Si module. During a one year period, the average P-Wh of the a-Si and poly-Si module was about 60% and 56%, respectively, of their calculated output power at STC condition, so that the P-Wh for each watt-peak (W-p) of the maximum power of a-Si module is about 11% higher than that of the poly-Si module.