Pragmatic Approaches in a Commercial Context

Carnegie in its development of CETO wave sites worldwide generally favours the approach of using coarse gridded WWW3 data as a guide to determining general feasibility, then making detailed selections based on deployed tri-axis wave measurement accelerometers, rather than 'gridding in' coarser wave data to finer scales. This approach works in practice because at scales finer than the typical WWW3 grid, the decision about the most suitable site for a wave energy converter is no longer solely dependent on wave resource alone; other considerations such as land and seabed access, and access to onshore grid connections come in to play.

This pragmatic selection of sites, overriding purely wave resource factors, is evidenced in the selection of the Sepia Depression site discussed earlier. Here the site was selected partially for its sheltering ability but mostly for convenience and access.

Another aspect of wave energy converter design that CETO, and indeed all devices, must address is: how adaptable the design is to accommodate the actual dynamic range of wave heights that are expected at locations where they are going to be deployed. The distribution of wave height along with the maximum wave height at a given site must be known in order to match the design to the site. In practice, the gathering of this detailed information could be an expensive and time consuming process if there is not already wave buoy data available at the exact location of deployment, or if surveys and analysis have not already been carried out.

The verification of the operation of CETO at a technical level will involve the comparison of empirical measurement with the convolution output of the device power matrix and the wave matrix for the Sepia Depression site. This process allows the actual capacity factor to be compared with that predicted from the convolution of these two matrices, and is the key to commercial validation.

It is important to note that the tools such as WWW3, while useful for site selection, are not in themselves sufficient to predict the energy output of CETO or of any other wave energy converter for that matter. This is because all wave energy converters around the world have not yet accumulated enough operation data to provide a simple predictor of integrated energy output based on historical or hind-cast wave data statistics. This will emerge over years to come, but for now all wave energy converters will need to demonstrate 'bankability'; that is, a sufficiently high average capacity factor for the particular wave farm to present a favourable return on investment.

Fig. 27.5 Results of wave resource analysis produced by Carnegie and commissioned from RPS METOCEAN for selected locations along the southern Australian coastline

Until sufficient operational data exists, most wave farms, including CETO, will be in this bankability demonstration mode. Furthermore, such demonstration in practice requires a wave buoy on site at the wave farm to correlate the input wave state with the output of the wave energy converter.

Acknowledgments Carnegie acknowledges the spport of the Western Australian government through their LEED funding program, which partially supports this work. RPS METOCEAN is acknowledged for providing the wave data and Mr. Tim Sawyer of Carnegie for the preparation and analysis of the data presented in Figs. 27.4 and 27.5.

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