Review of current developments in low head, small hydropower

In Europe, the development of hydropower with installed capacities of more than 1 MW and head differences of more than 2 – 3 m is nearly completed. A promising corner of the future hydropower market remains the economical and ecologically acceptable exploitation of smaller hydropower from 100 – 1000 kW with very low head differences of 0.80 up to 2.00 m, where conventional turbines are neither economical nor ecologically undisputed. In response to this situation, a number of novel energy converters, some of which reliant on rather unusual principles, have been proposed and developed. The high efficiencies stated by the inventors are however often neither confirmed by theoretical considerations nor by measurements. Often a positive view of the innovator will valuate the efficiency too high, as well as the specific investment costs as too low, leaving potential investors with a large margin of risk. The most important new technologies were analysed from the view of underlying technical principles and possible efficiency, economy and ecological impact. It was found that most proposed technologies suffer from low efficiencies as well as high investment costs. Only the Rotary Hydraulic Pressure Machine appears to have development potential. The article aims to give an overview over an emerging market in order to give engineers a background for the rational assessment of a variety of new technologies