Performance characteristics of water wheels

Abstract

During the eighteenth, nineteenth and the first half of the twentieth century, water wheels were important hydraulic energy converters. It is estimated that in England 25,000–30,000 wheels were in operation around 1850; in Germany 33,500 water wheels were recorded as late as 1925. Today, only very few water wheels are still in use. Low head hydropower is seldom exploited, since cost-effective energy converters for these conditions are not available. A small number of companies are currently again manufacturing apparently economically attractive over- and undershot water wheels; the performance characteristics of these wheels are however unclear so that the assessment of the potential of a site as well as their design and efficient operation relies on estimates. A number of engineering textbooks and three detailed experimental studies of water wheel design and performance were published between 1850 and 1935, but nowadays appear to be virtually unknown. A detailed study of these reports was conducted, and the performance characteristics of overshot water wheels were analysed in order to assess the application of such wheels for electricity generation. It was found that water wheels have to be designed for a given flow rate, head difference and intended operating regime. Properly designed overshot wheels have an efficiency of 85%, undershot wheels of approximately 75% for 0.2 < Q/Q_max < 1.0, making this type of energy converter suitable for the exploitation of highly variable flows.Water wheels must, however, be operated within certain parameter ranges in order to be able to perform efficiently; they appear to offer an efficient and cost-effective solution for the exploitation of low head hydropower sources.