A high-pressure wate/steam pilot plant serves experimental investigations of evaporation and condensation processes, which are connected with research on solar direct-evaporation and on thermal energy storage in parabolic channel-solar power plants. The HIPRESS (High Pressure Experiments on Solar Steam) - plant can generate water vapour up to a pressure of 160 bar and a temperature of 450 degrees C in the mass flow range from 15 to 350 kg/h and to supply the test track at nearly any entry conditions of undercooled water along the complete wet steam area right up to superheated steam. In this contribution the requirements on the pilot plant and the system-technical considerations, which led to the circuit concept of the pilot plant, are shown, and the advantages connected with that are explained against the background of the energy turnover of the pilot plant, the necessary plant components and the legal-permission aspects. The apparatus-technical layout, the operative range, and the control-technical concept of the plant are descriped. Finally, first results of the experiments on evaporation processes in inclined, one-sided heated pipes are presented.