The goal of the research project DUKE is the development and demonstration of the once-through concept for parabolic trough plants with direct steam generation (DSG). Solar fields with DSG generate the steam for a steam turbine directly in the solar field piping, whereas other solar field concepts need an additional heat transfer fluid, like synthetic oil. By that, DSG is more efficient and higher temperatures are possible. Plataforma Solar de Almería is owned by the Spanish research centre CIEMAT.