Abstract
HYSOLAR is the name of a long-term German-Saudi Arabian cooperative programme for research, development and demonstration of solar hydrogen production as well as utilization of hydrogen as an energy carrier. The programme was started in 1986. Research institutions and universities in both countries are participating. The first phase of HYSOLAR (Ia and Ib), which ended in 1991, focused mainly on investigation, test and improvement of hydrogen production technologies. The participants have reported on their work in more than 90 scientific publications. This paper briefly reviews the most important results and addresses the still open questions and problems. An outlook into the programme's second phase contents, where more emphasis is laid on hydrogen utilization technologies, is also included.