Page 149 - Fundamentals of Ocean Renewable Energy Generating Electricity From The Sea

Wave Energy Chapter | 5 139

resources exhibit strong seasonal and interannual variability, the extremes in
the theoretical resource (e.g. regularly over 500 kW/m) are capped by the
device characteristics, rated at 750 kW. Out of interest, the capacity factor (see
Section 1.5) for the Pelamis device at this location over a decade of simulation is
22%, which is fairly encouraging compared with other renewable technologies
(e.g. Table 1.5).
Finally, the practical resource is the portion of the technical resource that is
available after considering all constraints such as socioeconomic and environ-
mental factors. The practical resource excludes regions of low power density,
regions that are distant from electricity infrastructure, navigation channels,
marine protected areas, etc.

5.5.2 Survivability and Maintenance

WECs operating on the water surface are exposed to storms and other extreme
events. In particular, high and steep waves, especially breaking waves, are likely
to damage WECs. Further, a particular WEC is designed to operate, and convert
energy efficiently, over a limited range of conditions (e.g. see the Pelamis power
matrix in Fig. 5.17), usually tuned to the most frequent wave conditions that
occur at a particular site: extreme waves are not usually within this range.
Therefore, it is necessary for most wave devices to have a survival mode; for
example, a device could be sunk to a particular depth where wave orbital motion
will be reduced (e.g. related to the wave length), or to relax the load on a turbine
in an OWC device.
At the other end of the scale, prolonged periods of low wave energy provide
opportunities for device maintenance. A site that is consistently energetic
may be desirable from theoretical and technical resource perspectives, but is
undesirable from a practical resource perspective.

REFERENCES

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[3] M.R. Hashemi, S.T. Grilli, S.P. Neill, A simplified method to estimate tidal current effects on
the ocean wave power resource, Renew. Energy 96 (2016) 257–269.
[4] M. Benoit, F. Marcos, F. Becq, Development of a third generation shallow-water wave model
with unstructured spatial meshing, in: Coastal Engineering 1996, 1997, pp. 465–478.
[5] J.M. Smith, A.R. Sherlock, D.T. Resio, STWAVE: Steady-State Spectral Wave Model User’s
Manual for STWAVE, Version 3.0, Engineer Research and Development Center, Coastal and
Hydraulics Lab, Vicksburg, MS, 2001.
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Cambridge, 2010.
[7] J.-F. Filipot, F. Ardhuin, A.V. Babanin, A unified deep-to-shallow water wave-breaking
probability parameterization, J. Geophys. Res. Oceans 115 (C4) (2010) C04022.