NOVELTY - The unit (1) has heat collecting/radiating pipe (4) that is detachably connected to heat medium outlet (2b) for sending heat medium flowing out of heat medium outlet. Downstream connection portion (5) is included with heat medium inlet portion (5a) into which heat medium flowing out of pipe flows, and a heat medium exit portion (5c) to collectively discharge heat medium flowing in from respective heat medium inlet portions. Return pipe (8) is connected to terminal end of heat-medium exit portion to recirculate heat medium flowing out of heat-medium exit portion.    USE - Heat exchange unit buried under earth, or sunk in liquid such as underground water and hot-spring water, used in solar-cell-panel heat absorption and emission system (claimed) such as solar energy power generation system installed in roofs of common house. Can also be used in photovoltaic power generation plant.    ADVANTAGE - The fall of electric power generation efficiency by the temperature rise of solar cell panel can be prevented. The electric power generation efficiency can be improved and stabilized by the solar-cell-panel heat absorption and emission system. By provision of the heat exchanging system which is excellent in design flexibility and versatility, the underground heat can be effectively utilized and excellent efficiency of heat exchange can be attained. The solar cell panel can be cooled easily at many high-temperature seasons, without using the heat source which consumes electric power. The length of heat collection and radiation tube according to underground temperature and required heat amount can be selected and heat exchange unit excellent in design flexibility can be provided.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a solar-cell-panel heat absorption and emission system.    DESCRIPTION OF DRAWING(S) - The drawing shows a side view of the heat exchange unit.    Heat exchange unit (1)    Heat medium outlet (2b)    Heat collecting and radiating pipe (4)    Downstream connection portion (5)    Heat medium inlet portion (5a)    Heat medium exit portion (5c)    Return pipe (8)