Power Production Analysis of the OE Buoy WEC for the CORES Project

John Lavelle, Jens Peter Kofoed

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Abstract

This report describes the analysis performed on the OE Buoy for the CORES project by the wave energy group at Aalborg University, Denmark. OE Buoy is a type of Oscillating Water Column (OWC) wave energy converter as part of the CORES project. This type of device is one of the most developed to extract energy from the ocean (1). Typically, a Wells turbine is used for the Power Take Off (PTO) for OWCs. The Wells turbine has the advantage that it is self-rectifying – with the ability to operate with either direction of airflow, which changes during each cycle of the wave. This type of turbine, however, suffers from the occurrence of sudden stops (2). Another type of self-rectifying turbine, an impulse turbine, was used in place of a Wells turbine to, in refit of the OE Buoy, in order to compare the two types.OE Buoy was deployed in Galway Bay, Ireland during March, April and May of 2011, during which a total of 39 hours of power production data was collected. A data acquisition system was used to sample the sensors on board and the generator shaft power time-series data was used in the analysis here. A wave-rider buoy, located at the site of OE Buoy and operated by the Marine Institute Ireland, was used to determine the wave statistics for the sea conditions which coincided with the OE Buoy device data, in order to estimate the efficiency of the device as a function of the sea state (for example as a function of the mean zero down period, Tz, and, significant wave height, Hs) as described below. This may then be used to estimate the yearly power production of the device at the test site location or another location, by using the long-term wave statistics for the given site. Additionally, the power production for a given scale of device may be estimated by applying the appropriate scaling to the efficiency function. With sea trails – unlike wave tank testing – we are limited to testing in the sea states that happen to occur when the device is operational during deployment period. This can mean that efficiency data is sporadically distributed as a function of Tz and Hs, making it difficult to determine the efficiency function. The Equimar project deliverable 4.2 (3) describes a method for analysing and presenting the power production data in order to determine the yearly power production of the device at a given location and quantify its uncertainty. The limited amount of power production data meant that it was not possible to fully implement the method, as the efficiency data was too sparsely distributed as a function of Tz and Hs, but the method used here is based on the Equimar protocol to give an approximate estimate of the yearly power production.
Original languageEnglish
Place of PublicationAalborg
PublisherDepartment of Civil Engineering, Aalborg University
Number of pages18
Commissioning bodyThe CORES EU Project
Publication statusPublished - 2011
SeriesDCE Technical reports
Number119

Keywords

  • OE Buoy
  • Oscillating Water Column
  • OWC
  • Wave Energy Converter
  • Wells Turbine
  • Power Top Off
  • PTO

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    Lavelle, J., & Kofoed, J. P. (2011). Power Production Analysis of the OE Buoy WEC for the CORES Project. Department of Civil Engineering, Aalborg University. DCE Technical reports, No. 119