Abstract
Hydropower is a well-established and mature technology that already contributes significantly to the production of renewable electric energy. Large-scale power plants have the most important share in the sector, but there is growing interest in mini- and micro-hydropower because of the chance to take advantage of the unused hydropower potential, which has already been exploited in large water resources. This chapter wants to present the potential of the hydropower sector, with specific attention to the small-scale plants, and to discuss the pros and cons of the main technologies and installation solutions. As the main limiting factors of small hydropower are the environmental impact and the installation cost, a specific focus will be given to the most promising solutions and the novel applications that can overcome these issues. In particular, low-cost and reversible machines will be described and the most interesting research projects on these machines will be presented.