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Why nearshore?

22 Sep 11 - Paddy O'Kane, Chief Technical Officer

At Aquamarine Power we strive to think differently. And also to apply science and reason to develop our technology in an optimum manner. So while most other wave technology manufacturers have opted to develop deepwater or shoreline devices we have opted for an area characterised as 'nearshore'. We classify nearshore as an area where the water depth is 10-20m.

Unique characterisitics

Our choice of location is not arbitrary. We have carefully selected this area to make best use of its unique set of characteristics. These characteristics were first defined by Professor Trevor Whittaker and Dr. Matt Folley following an EPSRC funded project at Queen's University Belfast.

Their research investigated the key performance drivers of wave energy converters in the nearshore and shoreline areas and identified a number of compelling items about this previously unexploited region. When considered collectively, it became clear that the team had found a niche area for development of a highly efficient wave energy device. The duo discovered that the nearshore environment offered:

Amplified wave force in the surge direction due to 'shoaling'. Orbital particle motion in deep water is largely circular. However, this motion is distorted in the nearshore region due to sea bed interaction. This results in an amplification of forces by up to 50% in the surge (beach) direction in the nearshore area as illustrated in the diagram above.

Filtering of the largest ocean waves. The largest storm and rogue waves are filtered out before reaching the nearshore area, largely due to the action of wave breaking. Therefore extreme forces on a wave energy converter are significantly reduced in the nearshore area enhancing survivability of the device and reducing manufacturing costs.

Narrower directional spread. While waves in deep water are omni-directional, waves in the nearshore region are largely directed in a beach-ward direction with a tight directional spread. This characteristic facilitates efficient energy capture from a device that reacts to a directional surge force such as Oyster.

High net power capture capability. While it has been previously acknowledged that the level of gross wave energy is less in the nearshore area, no-one had previously quantified the ratio of 'exploitable wave energy' versus gross energy in the two regions, i.e. the level of energy that can reasonably be extracted from the waves.  The team calculated that the average exploitable resource was typically only 10-20% less at 10m when compared to a 50m water depth.

Lower power transmission losses. A typical nearshore site with a 10-15m water depth is only 500m from the shore when compared to several km for a typical deep water (50m) site. This means that transmission losses are less for an equivalent nearshore site.

A 'sweet spot'

What the team identified was a 'sweet spot' in the nearshore area; a more benign and accessible environment, just beyond the area of predominant wave breaking that still offered excellent energy capture. It is these characteristics that each Oyster device has been designed to exploit.

 
 
 

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