Wave Resource Assessment

Characterisation of wave energy at project sites and within regions is essential to understanding the viability of wave energy projects and determining the likely cost of energy.

The power that can be produced by Pelamis at a given site depends upon both the characteristics of the machine and the local wave climate. The machine response in a given sea state is known from our sophisticated numerical model of Pelamis that is run in-house and validated against measurements made on scale models and our full-scale machines.

The power output of the machine is thus derived across the full range of sea-states, each defined by the effective height and the period of the waves.

For a given potential wave farm site, the wave climate is established from historical data over a period of several years. Data comes initially from satellite measurements and well established wind-wave numerical models and can then be refined using data from wave-buoys placed in the vicinity.

 

The record of the wave conditions over a representative period builds up a picture of the wave climate, such as its variation with the seasons and from year to year.

The Pelamis simulation and the wave climate data are combined to give the electrical power response over time and from that, its average level and its variability. These in turn will help determine the revenue stream from the sale of that electricity for a wave farm at that location, and therefore its commercial attractiveness. This process is very similar to that used in the wind industry. As more empirical data becomes available from operational machines, the power capture can be defined directly from measurements, although a role will remain for modelling tools in adapting this to improved machine designs and upgrades to control algorithms.

Once the general area of the wave farm site has been determined more work can be done to pick the best site within that area. For example, the mean wave direction and its distribution should be determined. Pelamis is relatively insensitive to changes in wave direction because it ‘weathervanes’ i.e. it swings to face the waves. However, the optimum orientation for the mooring should be aligned to the mean wave direction. A detailed study of the wave climate and the bathymetry may point to a particular location where there is favourable local focusing of waves.

Other essential tasks related to the resource assessment include the calculation of ‘weather windows’ that allow maintenance and other operations, and, of particular importance, the statistical determination of the extreme waves that can be expected at the site over the lifetime of the machine, which the machine is designed to survive.