The present invention provides methods and systems for facilitating a realty transaction using a computer system including at least one database. Because the relative rotational speed between the inner and outer rotors is twice as great as the rotational speed of the inner rotor or outer rotor, the generator system can produce a relatively large electric power even when the wind speed is low. The fused portion between the tip and the base material has an area of a maximum sectional area portion of a size of not more than 1.