This 2007 research paper explains how solar thermal could be used in the production of renewable hydrogen. It acknowledges that for achieving a hydrogen economy in the first place, the basis will be the use of fossil fuels. However, a further step would be that the conventional production processes will have to be substituted by renewable technologies.
The paper explains the technical aspects and steps that are needed to achieve this. By using water as feedstock and by applying solar energy as the driving energy for its decomposition, the production of hydrogen becomes free of emissions and free of the consumption of fossil fuels.