"Small hydropower with very low head or pressure differences below 2.5 m and hydraulic power ratings of 50 to 1000 kW is a significant renewable resource, with an estimated unused potential in rivers alone of e.g. 600 to 1000 MW in the UK and more than 500 MW in Germany. The economically and ecologically efficient utilisation of this hydropower bracket still constitutes an unsolved problem since c ...