PURPOSE: To enhance thermal energy utilizing efficiency, and an efficiency in converting thermal energy into electrical energy, by a method wherein a space between light-transmitting outer and inner pipes is used as a vacuum heat- insulating layer, while a substantially atmospheric gas layer is provided inside the inner pipe, a heat-collecting part is provided in the gas layer, and a solar cell is fitted in the heat-collecting part.

CONSTITUTION: The space between the light-transmitting outer pipe 1 and the light-transmitting inner pipe 3 is maintained in a vacuum condition to constitute the heat-insulating layer 4. A heat-transmitting medium pipe 5 is supported at the center of the inner pipe 3 by a support 6 and an end plate 7. The pipe 5 has a double-pipe construction consisting of an inner pipe 5a and an outer pipe 5b. A flat plate form heat-collecting plate 9 is fitted above the pipe 5, and the solar cell 10 is provided above the plate 9. The energy of the solar cell 10 is taken out through a lead 10a and an electrode 10b. The interior of the inner pipe 3 is set at a gas pressure approximate to the atmospheric pressure. Since the heat absorbed by the solar cell 10 is released into the heat-collecting plate 9, the temperature of the cell itself can be prevented from rising.