In order to solve the problem of power system for spacecraft, a thermoelectric generator based on organic/inorganic composites is designed. This generator utilizes the temperature difference induced by the sunlight. The power system of a solar array can be improved via thermoelectric generator. The rationality, reliability, economy and advancement of its design principle are explained. Taking n-type polyvinylidene fluoride (PVDF)/Ni nanowire and Cu electricity plate as an example, the results show that when the thermoelement length is short, the contact effect must be considered. Besides, when taking a suitable thermoelement length, a large output power density of the thermoelectric device can be obtained, and the specific power of mass reaches up to 7.21W/kg. Compared with the original solar array, this new design can effectively utilize extra-satellite resources, save costs and provide energy.