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Wave Energy in Rarotonga

The regional analysis of the cost of wave energy (See here) concluded that Rarotonga could be suitable to support a wave energy converter. But no location had been identified as a potential wave energy site. This page expands the regional wave energy analysis to the whole of Rarotonga to identify suitable wave energy conversion hotspots.

Finding suitable wave energy sites

Bathymetry consideration

Rarotonga is one of the few countries in the Pacific where the bathymetry would allow the installation of any type of wave energy converters. Wave energy converters can be divided in these three categories: Offshorwe, Nearshore and onshore devices.

• Onshore devices are built and fixed on land. The location may be on the coastline or integrated into structures such as breakwaters. Adjacent depths are typically less than 15 m. These devices are best suited where the shoreline is located on a rock platform with steep bathymetry. These geological features are often raised limestone reefs and lava delta, they are associated with blowholes.

• Nearshore devices are predominantly fixed on the seabed. They capture wave energy nearshore and convert it to electricity in an onshore facility. Depths are typically less than 25 m. These devices generally require a near horizontal (or gently sloping) bathymetry. Rarotonga is one of the few Pacific Countries to have a continental shelf suitable for this type of device.

• Offshore devices are moored to the seabed and transfer the generated electricity using sub-sea cables laid on the seabed. Typical depth are more than 25m but less than 200m as deploying a mooring system in greater depth becomes challenging (and costly). These devices are exposed to larger waves and often more cost effective.

Benchmark device

Wave energy converters come with different cost and efficiency. The cost of operation and maintenance and on the environment can also vary greatly and it can be very hard to decide whether Rarotonga would benefit more from one type of device at a location or another device elsewhere. It is impossible to compare the cost and efficiency of all the wave energy converters because they are not all at the same stage of development. For example, some devices only have a theoretical efficiency while other more advance wave energy converters have a measured (i.e. verified) efficiency. In order to help with decision on what device would be more suitable for Rarotonga, we calculate the cost of energy generation of one wave energy converter, the Pelamis.

From the many wave energy devices developed globally, the Pelamis wave energy converter is one of only two to have reached commercial readiness. Although Pelamis Wave Power Ltd, the firm behind the device, went into administration at the time of writing this report, the milestones reached and the research behind the Pelamis device are unprecedented and unmatched by any other device. Because of the large amount of literature on the Pelamis, it is still a benchmark and, although it is unlikely that more Pelamis devices will ever be built (at least under the same name), the device’s physical characteristics and cost evaluation can be used to probe the economic feasibility of wave energy.

Pelamis costs

Wave Power and energy cost for pre-selected sites

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