An emerging class of renewable energy technology, the hydrokinetic conversion device (HCD), offers ways to capture the energy of flowing water without the impoundment or diversion of the conventional hydroelectric facilities based on dams and penstocks. Hydrokinetic technologies are designed for deployment in natural streams, like rivers, tidal estuaries, ocean currents, and also in some constructed waterways (e.g. canals). In ocean-energy deployment, hydrokinetic conversion devices can be flexibly arranged into multi-unit arrays, which would extract energy from tidal and marine currents basically in the same way as a wind farm.
This article focuses on recent advances and trends in hydrokinetic system development that may lead to a feasible future scenario for hydrokinetic power. The basic principles of HCDs are explained, and early experiences in the field described. With the help of technical reports, papers, proceedings and websites, we then review existing and emerging technologies in the HCD field. Innovation in mooring, and power transmission systems are also covered.