Much power demand would be required now at the power system because of the use of various home appliances such as air conditioner, refrigerator, etc The present power demand of the utility is faced to weaken the allowable reserve margin in Korea because most large power loads such as air conditioner are used in summer especially at midday for one day The peak power demand of the utility usually occurs at 2 or 3 o'clock in the afternoon [I] This time almost coincides with the time when the amount of the sunshine becomes the highest, and thus the maximum solar power could be obtained This urgent problem could be solved by the use of Photovoltaic (PV) systems which have the merits of green energy source without pollution, and free choices in power generation scale, and the use of dead space such as rooftop