To solve the following problem: when selling a photovoltaic power generation system, there has not been an effective method for finding a candidate destination thereof, business efficiency is bad, and a power generation amount and power generation efficiency desired by a customer cannot be obtained, so that there is many cases that business negotiations are not concluded because sunlight condition is bad, for example, a roof direction does not have a proper angle to sunlight, a roof area is insufficient, a roof shape is special, or an obstacle causes shade, even if receiving an inquiry of installation from the customer and actually visiting to investigate the roof shape, the roof direction, the sunlight conditions or the like.

In this method, image information including the rooftop shape of a building or a house, the roof area, and the roof direction is read from an aerial photograph or a satellite photograph together with a land form, a hopeful house or a hopeful building satisfying a prescribed criterion is selected from the image information, the hopeful house or the hopeful building are collated with a map, its address, and its possessor or the like are specified to produce a hopeful customer list, and efficient sales activity for the photovoltaic power generation system is performed by direct mail or the like.