Offshore Wave Energy
Lars Espevik
The policy
 To utilize the energy in waves to
produce electricity
 Why offshore?
~ The waves on the open sea have
great energy potential
~ Negligible environmental impacts
Problems addressed
 Increase the amount of electricity
that originates from renewables
 Minimize the use of fossil fuels in
the long run
 Address climate change problems
 Make wave energy economically
feasible
Conclusions
 Wave energy has great potential
 Offshore wave energy is just in its
starting phase
 Many scientific and economic
obstacles remain
 The problem of transportation and
storing
Topics
 History of wave energy
 What causes waves?
 Wave energy converters
 Offshore devices
 Advantages/disadvantages
 Legal/economic incentives
 The future of wave energy
History of wave energy
 Before 1973
~ First ideas patented in 1799
~ Between 1855 and 1973 there were
340 patents
~ Several configurations of wave
energy converters were designed and
tested at model scale and some have
been operated at sea
History
 After 1973
~ In Europe, intensive research and
development study of wave energy
conversion began after the dramatic
increase in oil prices in 1973
~ Several research programs with
government and private support
started mainly in the UK, Portugal,
Ireland, Norway, Sweden and
Denmark
History
History
~ In the early 1980s the UK government
put a stop to the funding of wave
energy projects
~ The increased focus on climate
change from the mid 1990s led to
increased interest in renewables
~ Also, the recent increases in the oil
price has improved the attractiveness
of emerging renewable technologies
such as wave energy
History
~ International conferences in wave energy
were held in Edinburgh, UK, 1993, Lisbon,
Portugal, 1995, Patras, Greece, 1998 and
Aalborg, Denmark, 2000
~ At present there are more than 1,000
patents held worldwide related to wave
energy
~ Some commercial plants have been
deployed
~At present the world-installed capacity is
about 2 MW
What causes waves?
 The wave energy resource is a
concentrated form of solar energy
 Winds generated by the differential
heating of the earth pass over open
bodies of water
 The wind pushes surface water particles
along with it, setting up a rolling motion
in the water and moving the water
particles in a vertical, circular path
What causes waves?
Wave energy densities
 The power in a wave is proportional to
the square of the amplitude and to the
period of the motion
 Large amplitude (~2 m), long period
(~7-10 s) waves have energy fluxes
commonly exceeding 40-50 kW/m width
of oncoming wave
 Wave energy is unevenly distributed
over the globe
Wave energy densities
around the globe
Numbers in kW/m
Wave energy densities
around the globe
 Wave climate in Europe
~ The wave climate along the western coast
of Europe is characterized by particularly
high energy. The UK has over half the
wave energy potential in Europe, up to
75 kW/m off Ireland and Scotland
 Wave climate in the US
~ The West Coast is the most promising area
with wave energy densities in the
25 – 40 kW/m range
Wave energy converters
 Four different types of WECs:
~ Oscillating water columns
~ Overtopping devices
~ Point absorbers
~ Surging devices
Wave energy converters
 The oscillating water
column
~ Partly submerged
structure with an
opening to the sea
below the water line
~ Waves cause the
water column to rise
and fall, which
alternately
compresses and
depressurizes the air
column
~This air flows through a
turbine which drives an
electric generator
Wave energy converters
 Point absorbers
~ They provide a heave motion that is
converted by mechanical/ hydraulic
systems in linear or rotational motion
for driving electrical generators
Wave energy converters
 Surging devices
~ Surging devices
exploit the
horizontal particle
velocity in a wave
to drive a
deflector or to
generate pumping
effect of a flexible
bag facing the
wave front
Placement of wave energy
converters
 Three locations
~ Shore
~ Near shore
~ Offshore
Placement of WECs
 Shore/Near shore vs. offshore
~ The potential energy
- The power available in the waves is
much greater offshore
- Nearer the coastline the average energy
intensity of a wave decreases due to
interaction with the seabed
Placement of WECs
~ Other factors
-
Engineering challenges
Construction costs
Maintenance and/or installation costs
Transmission costs and losses
Environmental impacts
The scale of electricity production
Offshore devices
 The Archimedes Wave Swing
~ An underwater buoy of which the upper
part (floater) moves up and down in the
wave while the lower part stays in position
~ The floater is pushed down under a wave
top and moves up under a wave trough
Offshore devices
Offshore devices
 The Archimedes Wave Swing
~ The interior of the system is pressurized
with air and serves as an air spring
~ The mechanical power is converted into
electrical power by means of a Power Take
Off system (PTO)
~ The PTO consists of a linear electrical
generator and a nitrogen filled damping
cylinder
~ Problems installing the 2 MW system off
the coast of Portugal
Offshore devices
 The Floating Wave
Power Vessel
~ Consists of a floating
basin supported by
ballast tanks in four
sections
~ A patented anchor
system allows the
orientation of the
vessel to the most
energetic wave
direction
~ A 1.5 mW vessel is
planned to be
deployed at 50–80 m
depth 500 m offshore
Shetland
Offshore devices
 The Wave dragon
~ Is an overtopping device,
which elevates ocean
waves to a reservoir
above sea level
~ Water is let out through a
number of turbines and in
this way transformed into
electricity
~ The prototype is
deployed in Nissum
Bredning, an inlet in the
northern part of Denmark
Offshore devices
 The McCabe Wave Pump
Offshore devices
 The McCabe Wave Pump
~ The device consists of three
rectangular steel pontoons, which are
hinged together across their beam
Offshore devices
 The McCabe Wave Pump
~ The MWP was primarily designed to
produce potable water although it can
also be used to produce electricity
~ A 40 m long prototype was deployed
in 1996 off the coast of Kilbaha,
County Clare, Ireland
Offshore devices
 The Mighty Whale
~ Is an OWC based
device for offshore
operation
~ A 120 kW prototype
with 3 OWCs in a
row has been
operating since 1998
1.5 km off Nansei
Town, Japan
at 40 m depth
Offshore devices
 PowerBuoy
~ Developed in the US by Ocean Power
Technologies
~ It is a wave generation system that
uses a buoy to capture and convert
wave energy into a controlled
mechanical force which drives an
electrical generator
Offshore devices
Offshore devices
 PowerBuoy
~ The PowerBuoy is enhanced with sensors,
which continuously monitor the
performance of the various subsystems
and surrounding ocean environment. In the
event of very large oncoming waves, the
system automatically disconnects
~ In 2002 the company received funding of
$ 4,300,000 from the US Navy’s Office of
Naval Research for the first major phase of
a wave power project in Hawaii
Offshore devices
 The Pelamis
~ Is a semi-submerged structure
composed of cylindrical sections
linked by hinged joints
Offshore devices
 The Pelamis
~ 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
Offshore devices
 The Pelamis
~ Several devices can be connected
together and linked to shore through
a single seabed cable
Offshore devices
 The Pelamis
~ A typical 30MW installation would occupy a
square kilometre of ocean and provide
sufficient electricity for 20,000 homes
~ Ocean Power Delivery has won a bid for a
750kW project off Islay, Scotland and has
recently signed a memorandum of
understanding with BC Hydro to develop a
2 MW project off the coast of Vancouver
Island, Canada
Advantages
 Advantages of offshore wave energy
~ Sea waves have high energy densities, the
highest among renewable energy sources
~ Wave energy is generally considered to
provide a clean source of renewable
energy with limited negative environmental
impacts
~ It could become a significant source of
energy not involving CO2 emissions
Advantages
~ The natural seasonal variability of
wave energy follows the electricity
demand in temperate climates
~ Negligible demand on land use
~ Could secure energy supplies in
remote regions
~ Large-scale implementation of wave
power technologies will stimulate
declining industries, e.g. shipbuilding
Disadvantages
 Disadvantages of offshore wave
energy
~ The main wave energy barriers result
from the energy carrier itself: The sea
~ The peak-to-average load ratio in the
sea is very high and difficult to predict
~ The structural loading in the event of
extreme weather conditions, such as
hurricanes, may be as high as 100
times the average loading
Disadvantages
~ High construction costs induce high
power generation costs, thus making
the technology uncompetitive
~ The incidence of wave power at deep
ocean sites is three to eight times the
wave power at adjacent coastal sites,
but the cost of electricity transmission
from deep ocean sites is often
prohibitively high
Environmental impacts
 Offshore wave energy devices may
be a potential navigation hazard to
ships
 Near shore devices will have a
visual impact
 Wave energy devices could have
an effect on some forms of
recreation
 Impacts on the marine environment
Legal incentives
 Public Utility Regulatory Policy Act
(PURPA)
 State goals for renewable energy
 Renewable Portfolio Standards
(RPS)
 System Benefit Charges
Government funding
 Research and development efforts are
being sponsored by government
agencies in Europe and Scandinavia
 In the US there is little research due to
lack of funding. The Navy, through its
Office of Naval Research SBIR
program, has provided some research
funds. Generally, the funding level is not
adequate for demonstration projects
The future
 Need of technology improvements
~ Wave energy conversion technologies
have significantly advanced during recent
years, especially in Europe
~ Most devices are still in the prototypephase
~ The survivability/reliability of devices for
offshore operation has still to be
demonstrated
~ Combination of offshore wind and wave
energy devices?
The future?