Abstract
The device current–voltage (I–V) parameters of single-junction amorphous Si (a-Si) solar cells in natural sunlight at various locations have been investigated over three years. The effective efficiency was compared among testing locations from the latitude of 12.8 degrees to 43.8 degrees. The effective efficiency was varied periodically and the most advantageous performance was obtained in summer at all locations. The increase of output current dominantly contributed to the excellent performance. The output current of single-junction a-Si modules depended not only on module temperature and the annealing effect but also the seasonal variation of the air mass and the atmospheric conditions, such as turbidity and water vapor at each location. The annual performance ratio to initial efficiency measured under standard test conditions reached 82% in Hamamatsu, Japan.