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.
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
• 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
• 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.