Maximizing the Energy Conversion of a U-Oscillating Water Column in the Low Wave Energy Climate of Gwadar, Pakistan

Abstract

The purpose of this report is to design a wave energy converter, in particular a U-oscillating water column (U-OWC), to maximize energy conversion in the low wave energy environment of Gwadar, Pakistan. At present Pakistan’s 1000km coastline is largely undeveloped and the county is devoid of any wave energy harnessing devices or studies. However, recent years have seen an influx of Chinese investment being made under the China-Pakistan economic corridor agreement, which is stimulus for the near future construction of a large rubble mound breakwater to shelter an assistance vessel basin in the city of Gwadar.

Typically, a WEC is not feasible in low incident wave energy environments because the economic return from minimal energy generation cannot offset the capital cost of the structure. However, the opportunity in Gwadar is unique in the sense that a substantial investment is already envisaged for the creation of a breakwater. Therefore, it is worth investigating if re-designing this structure with vertical caissons embedded with U-OWC chambers is feasible. In this way, the structure can fulfill the dual role of sheltering the assistance vessel basin against wave attack, and produce renewable energy over its design life.

To assist with this task, existing data and methods available in literature along with numerical codes have been utilized. A 10 year SWAN hindcast has been performed, the result of which have been condensed into 60 representative design sea-states on the basis of which the U-OWC chamber geometry
and turbine configuration have been optimized. This was achieved by employing a random sampling technique to determine which combinations produce the most power and by identifying the ideal turbine
operating revolutions for each sea-state.

Next, the approximate cost of the caisson breakwater integrated with U-OWC chambers is calculated and compared against the currently proposed rubble mound design. It is expected that despite an attempt to maximize the energy generation by the device, its levelized cost of energy will be high, given
the low wave energy in the region. Nevertheless, if the design proves cheaper than its rubble mound counterpart, it goes to show that wave energy converter can be deployed in low energy environments provided an opportunity exists where they can be integrated into proposed marine structures. This will
be an important finding, considering that the majority of the global coastline is subjected to moderate to low incident wave energy, and neglected from WEC deployment considerations.