17 of the individual reflectors 5 are connected in parallel with one another the preferably liquid heat carrier is delivered by means of a conveyor or feed pump 30 via the tubular conduit or line 19 and a distributor line or conduit arrangement 31 to the conduits or pipes 17 the heat carrier is furthermore collected by means of a collector conduit or pipe arrangement 32 and delivered via the tubular conduit or pipe 21 to a heat exchanger 34 arranged in a heat reservior or storage 33 and is conveyed back from the heat exchanger 34 to the conveyor or feed pump 30 if as schematically indicated in fig1 the reflectors 5 are aligned during the day in accordance with the postion of the sun then the ground 1 at which the plants are being grown is shaded the sun 39 s rays or radiation is not only prevented from reaching the plants rather by means of the solar energy the heat carrier flowing through the conduits 17 is heated and the absorbed thermal energy or heat is delivered by means of the heat exchanger 34 to the heat storage or reservior 33 during the nighttime the switch 28 of the control device 27 is.