European wave energy pilot plant on the island of Pico, Azores, Portugal

Research has been carried out with respect to the optimal phase control of an oscillating water column (OWC) equipped with a linear air turbine. The theory is based on Pontryaguin's Maximum Principle, and takes into account the air compressibility as well as turbine losses. Numerical results were computed for an OWC, of 2-dimensional idealized geometry, for which analytical expressions are available for the hydrodynamic coefficient of radiation. Numerical results were computed and shown to illustrate the advantages of phase controlling an OWC device in both regular and irregular waves. Due to numerical difficulties, a closely related problem rather than the original problem was solved, which gives a suboptimal solution. It was found that the most adequate turbine for a phase controlled device does not necessarily maximize the energy produced if the device is not controlled.

Following several years of research and development on wave energy a project to build a oscillating water column (OWC) wave power plant was started in the Islands of Azores. The first step in the project was to choose the site location. After some preliminary work, Porto Cachorro in the Island of Pico, was chosen due to a combination of favourable coastline morphology, good exposure to the most energetic wave direction and electric energy demand. Tank testing of a 1/35 scale model of a shoreline OWC power plant has been undertaken using both in site and JONSWAP spectra. Difficulties in the reproduction of spectra namely the shift of peak frequency and the presence of secondary peaks have been detected. Despite these difficulties it was possible to optimize the chamber geometry using 17 different JONSWAP spectra, leading to a full scale result for root mean square absorbed power of 360 kW for a chamber with 129 m{2} area.

A novel type of self rectifying air turbine incorporating aerofoil blades has been developed. This turbine offers the possibility for varying the flow duct area to maintain the air velocities as the wave driven flow rate changes. This is particularly suitable for wave energy conversion as wave power levels vary considerably from day to day. A small model of this turbine has been constructed and initial testing has been carried out in unidirectional flow. Further testing of the concept is required to prove the viability and determine actual efficiencies for the machine. The present model could be tested in a facility with air blower capability larger than is available in Cork.

Spectral measurements and spectral data have long been used for describing the wave climate at specific sites, and as tools for dimensioning coastal structures plus, recently, wave power devices. Although the spectral approach will continue to be important, an ever growing number of time dependent problems have arisen in recent years, thus spurring the interest for the stochastic modelling of wave related time series. A method to build wave climate simulation models has been presented and applied to 74 months of 3-hourly Waverider spectra, measured off Figueira da Foz, Portugal. The stochastic models used are based on previous works by Medina et al (Proceedings of the IAMR Conference, Madrid, 1991) who used 6-hour data for the coast of Oregon. Despite its simplicity, the method presented has been found to work well. The synthetic time series for significant wave height, wave energy and upward 0-crossing periods, and peak spectral frequency, seems to reproduce most of the features of the mean observed monthly average and variance trends, autocorrelations, and cross correlations with significant wave height. The main weaknesses of the model seems to lie in the emulation of interannual variability. Preliminary analysis under way raise hopes that a change in the type of parameterisation (eg by average monthly values, instead of by month number) will produce better models, while preserving the simplicity and speed of the current methodology.

The project concerned the design andpartial construction of a wave energypower plant of the oscillating watercolumn type on the Portuguese islandof Pico, Azores. By the end of the sec-ondrelated project the finished powerplant will contribute to the local powergrid of the island of Pico, and simulta-neouslyserve as a permanent test bedfor new wave energy technologies andequipment. The data collected on theoperational performance of the plantwill then allow the overall design meth-odology,the structural design of thechamber, the design and adequacy ofthe various items of equipment, andmethods for predicting energy produc-tion,to be validated.

The objective of this project is the utilization of sea wave energy. The project is framed within the scope of the JOULE program, and includes the basic design of a pilot plant of industrial size, and the detailed design and construction of the concrete structure of the power plant. The device is of the oscillating water column type (OWC) and is equipped with a Wells air turbine, a variable speed electrical generator and a controlled bypass relief valve. This is the first wave energy plant to be built in Portugal (and one of the first worlwide), and will supply a small isolated electrical grid.