Techno-Commercial Study of Twin Unidirectional Turbine Based Wave Energy Plants

Results from near-shore bottom standing Oscillating Water Column (OWC) based wave energy plants in Japan and India have now been available for about a decade. The most complete and detailed experimental results with near shore OWC plants are possibly from the one at Sakata port, Japan. Experience in Europe is mostly with shoreline devices as evidenced in the LIMPET and other similar plants. The plant in India is the longest standing device since its commissioning in 1991. It is unique in that several power modules with different turbines have been tested. Recently a proposal has been made to use twin unidirectional turbines in lieu of traditional bidirectional turbines promising very significant improvements in the power module efficiency. However, as experience has shown, the overall efficiency is also dependent on matching the power module to the OWC. In this work we review the principal design features that were initially considered for the Indian wave energy plant in the light of recent developments. We suggest methods for optimizing the overall performance in order to design the next generation OWC plant. The work will also be useful for planning newer installations. The influence of the power module on the overall efficiency will be clearly highlighted. As an example we estimate the performance of the Sakata port design with proposed twin unidirectional impulse turbines instead of twin 1.337 m Wells turbines using the experimentally observed hydrodynamic efficiencies. We show the performance of a wave energy plant designed for Indian conditions based on a comparison of the two designs for a plant with an overall width of 10m. The calculation is done for both monsoon and non monsoon conditions and the significant conclusions are highlighted. Cost estimates for two different plant sites, one island and one mainland, are also provided.