Abstract: An evaporating device comprises sets of solar heating units of a type having an insulated oblong room provided at the top with a slit, a mirror structure mounted on said room and a pipe extending through said room. Pipes from the units of a set form together a vapor pipe. Said evaporating device comprises a regulating valve mounted on each end of said vapor pipe. Said evaporating device comprises liquid supply means, which means comprise supply pipes forming branch pipes, a flow-rate regulating valve mounted on each of said branch pipes and an injecting device mounted on said branch pipes and connecting, near to an end of each unit, to the vapor pipe, said injecting device presenting an injecting opening directed axially in said vapor pipe, in the direction of said unit.