Using only a low head drop in a river or tidal flows to create electricity may provide a renewable energy source that will have a minimal impact on the environment.
Generating significant power from low-head locations using conventional technologies typically requires large volumes of water.
Due to the low rotational speeds produced, gearboxes are required to efficiently drive generators, which can result in large and expensive equipment and civil infrastructure.
Low-head pumped seawater storage: Currently at very low TRL levels but in the coming decade these technologies could become part of the energy system.
Although a dam-like structure is required, no area is enclosed, and therefore most of the benefits of 'damless hydro' are retained, while providing for vast amounts of power generation.
Low-head hydro is not to be confused with "free flow" or "stream" technologies, which work solely with the kinetic energy and the velocity of the water.
Turbines suitable for use in very-low-head applications are different from the Francis, propeller, Kaplan, or Pelton types used in more conventional large hydro.
Different types of low-head turbines are: A number of concerns have been raised about the environmental impacts of river current and tidal devices.
Where large sites aren't cleared “the vegetation overwhelmed by the rising water decays to form methane – a far worse greenhouse gas than carbon dioxide”, particularly in the tropics.