But, the solar panels 10 are limited by the present technology, so the solar panels 10 are made to have a large area, and the upper limit of the power generating amount is 300 watts. Then, for satisfying the lower limit requirement of the power generation output of 16.6 kilowatts, at least more than seventeen solar panels 10 are needed so that each of the solar panels 10 has an output of 300 kilowatts under the optimum sunshine condition, to achieve the minimum value. However, the optimum sunshine condition only has 3 to 4 hours per day, so that it is necessary to pave a large number of solar panels 10, so as to simply prolong the power generation output time of the solar panels 10. In addition, the direct-current power of the solar panels 10 have to be converted by an inverter 20 into an alternating-current power to output and supply an electric power. At the same time, the inverter 20 will consume the electric energy, so that the power generation output of the solar panels 10 is reduced (for example: as shown FIG. 1).

But, when the solar panels 10 are arranged largely, the assembly cost is not low. The effective power generation output time of the sunshine is only 3 to 4 hours per day, so that the even power generation output is not steady. The power generation output of the solar panels 10 is reduced by the inverter 20. Thus, it is necessary to think over other method to lift the technology so as to efficiently prolong a steady electric power and to produce a benefit.