Experimental Study on the Performance of an Off-Shore Oscillating Water Column Considering Real Gas Performance

Energy from the ocean has become one of the most promising clean resources for the future. The current challenges of clean energy face a major achievement in increasing the percentage of use from renewable sources. For example, as far as in the case of Europe, the horizon is set to 30% from renewable sources by 2030. In that sense, the available power from ocean waves, with estimates of around 10¹² W when that energy is coast-harvested, increasing to 10¹³ W if that is transformed off-shore, reveals itself as a source to which both scientific and technical efforts must be paid. Not to mention the combined effects of off-shore waves and wind, which can become a reliable focusing for the near future.

In the previous sense, the Oscillating Water Column (hereinafter OWC) represents one of the wave energy conversion technologies to which more research has been devoted during the last decades, with several plants in operation at present. In general terms the OWC consists of a partially submerged air chamber, open to the sea at the bottom and with a power take off usually consisting of a Wells turbine. The wave action induces the compression/expansion of air inside the chamber, and the Wells turbine transform the pneumatic power into electricity to be supplied to the grid. While the expected efficiency for OWC devices usually ranges between 40 and 70 %. Actually, the observed efficiencies take noticeably lower values. Previous research by the authors of this proposal have revealed that implementation of a real gas model to describe the Thermodynamics of the dry air-water vapour mixture inside the chamber helps to explain the deviations in the observed efficiency from expected values. This paper advances in the study of OWC performance from the experimental focus, through the flume test of a simple off-shore OWC device model with a turbine implemented as PTO. The analysis of experimental data is enhanced with the implementation of a real gas hypothesis to describe the compression/expansion cycle inside the chamber, following previous results by the authors. The final goal is to provide with guidelines leading to a more competitive design of the OWC technology, in which the lower efficiency values be balanced by cost-effective deployment, maintenance, repair and replacement.