The aim of the study is to investigate the location and design of a medium scale (0.5 to 1 MW) shoreline oscillating-water-column (OWC) pilot plant for wave energy conversion. In particular, the pilot plant is intended to serve as a European platform for research into aspects of wave energy devices at practical scale, namely in problems associated with constructional methods, air turbines, primary control systems, grid interactions, etc.
A study was made of the use and limitations of frequency and time domain approaches in modelling oscillating water column (OWC) devices. The existing gap between knowledge on device hydrodynamics, power equipment and wave resource and the procedures which apparently were followed in the design of existing OWC prototypes was also examined. Furthermore, a statistical approach to the overall design of OWC power plants was developed which highlights the relevance of wave to wave statistics. The use of by pass valves in parallel with the turbine was examined and particular attention was given to the problem of estimating short term energy storage requirements, in order to smooth out electricity production in wave groups and periods of calmness.
An experimental investigation was made of the aerodynamic performance of a high solidity Wells turbine for a wave power plant. A monoplane turbine of 0.6 m rotor diameter with guide vanes was built and tested. The tests were conducted in unidirectional steady air flow. Measurements taken include flow rate, pressure drop, torque and rotational speed, as well as velocity and pressure distributions.
A remarkable difference was found in flow rate coefficient prior to stalling for 2 similar rotors having slightly different blade profiles. This indicates that a judicious choice of the blade profile, using accurate modelling of the viscous flow around the turbine blades (90 degree stagger angle cascades), is required to enlarge the range of flow rates for which the turbine can perform with good efficiency).
Kinetic energy losses measured at the turbine exit are substantially smaller than viscous losses at the rotor. However, the use of guide vanes to remove flow swirl at the exit can result in a considerable improvement in efficiency, which, for the constant thickness NACA 0015 rotor considered in the study was found to attain 17.1%.
The results indicated that the use of stator blades produced a nonnegligible reduction of the value in the ratio of flow rates, which means a less extended range of flow rates for which the turbine performs efficiently.
Research has been carried out concerning the selection of a site and the preliminary design for medium scale shoreline oscillating water column pilot plant to serve as a European platform for research into aspects of wave energy devices at practical scale.
One site on Islay and one on Pico have been proposed for the construction of 2 European Pilot Plants. The plant on Islay will demonstrate the 'designer gully' method of construction in which the water column structure is built in a man made recess in an otherwise straight length of coastline. The plant on Pico will utilize a natural rock gully and will demonstrate a more advanced form of the construction techniques used in small plant built on Islay in 1988.
If shoreline wave energy is to have wider applications in the European Community and worldwide. It will be necessary to develop modular systems which can possibly be transported to site in sections or even prefabricated close to the site, but beyond the splash zone, even in storm conditions.
It will also be necessary to standardize the design of components in the Wells turbine generator module so that machines can be readily assembled to suit a range of pneumatic wave power devices.
To avoid the development of site specific designs it would be better not to select a single site for the demonstration plant. The plant should also form part of an overall programme of work including a large element of fundamental generic research.
Funding SchemeCSC - Cost-sharing contracts