Ocean waves represent a considerable renewable energy resource.
Waves are generated by the wind as it blows across the ocean surface.
They travel great distances without significant losses and so act as an
efficient energy transport mechanism across thousands of kilometres.
Waves generated by a storm in mid-Atlantic will travel all the way to
the coast of Europe without significant loss of energy.

All of the energy is concentrated near the water surface with little
wave action below 50 metres depth. This makes wave power a highly
concentrated energy source with much smaller hourly and day-to-day
variations than other renewable resources such as wind or solar.
Conveniently, the seasonal variation of wave power closely follows the
trend for electricity consumption in Western Europe.

The western seaboard of Europe offers an enormous number of
potential sites. The most promising sites are off the UK, Ireland,
France, Spain, Portugal and Norway.

There is sufficient energy breaking on the UK shoreline to power the
country three times over. However, it is not practical to recover all
of this energy. The economically recoverable resource for the UK alone
has been estimated to be 87TWh per year, or ~25% of current UK demand.

In the past five years there has been a resurgence of activity in
wave energy, as the huge resource potential has been recognised. A
number of developers in different countries have either installed or
are about to install full-scale prototypes with funds in excess of 70
million euros have been committed to these installations.

There are many promising sites around the world; any site on the map
shown with an average wave power level of over 15kW per metre has the
potential to generate wave energy at competitive prices. Many countries
recognise this potential and are seriously looking at how to exploit it.

HOW IT WORKS

The Pelamis is a semi-submerged, articulated structure composed of
cylindrical sections linked by hinged joints. The wave-induced motion
of these joints is resisted by hydraulic rams, which pump high-pressure
oil through hydraulic motors via smoothing accumulators. The hydraulic
motors drive electrical generators to produce electricity. Power from
all the joints is fed down a single umbilical cable to a junction on
the sea bed. Several devices can be connected together and linked to
shore through a single seabed cable.

A novel joint configuration is used to induce a tuneable,
cross-coupled resonant response, which greatly increases power capture
in small seas. Control of the restraint applied to the joints allows
this resonant response to be ‘turned-up’ in small seas where capture
efficiency must be maximised or ‘turned-down’ to limit loads and
motions in survival conditions. The machine is held in position by a
mooring system, for which a patent has been applied for, comprising of
a combination of floats and weights which prevent the mooring cables
becoming taut. It maintains enough restraint to keep the Pelamis
positioned but allows the machine to swing head on to oncoming waves.
Reference is achieved by spanning successive wave crests. The 750kw
full-scale prototype is 120m long and 3.5 m in diameter and will
contain three Power Conversion Module, each rated at 250kW. Each module
contains a complete electro-hydraulic power generation system.

Ideally the Pelamis would be moored in waters approximately 50-60m
in depth (often 5-10km from the shore). This would allow access to the
great potential of the larger swell waves but it would avoid the costs
involved in a longer submarine cable; if the machine was located
further out to sea.

Throughout the construction of the full-scale Pelamis, OPD has been
working closely with WS Atkins who have independently verified the
prototype design according to (DNV) offshore codes and standards.

Click here for an interactive model.
oceanpd.com