# waves

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```					The Viability of Wave Energy

Applicability for the Pacific
Northwest?
Visual Impact Comparison
Relative Strength of Wave Energy

   Best sites are a) North Atlantic b) Gulf of
More Continuous Data
Wave Resource Map
Conceptual Difficulties
   In a wave, the energy content is
distributed throughout the wave
   Therefore, one needs to build a device to
focus or collimate that distributed energy
   Design challenge then becomes a) how big
of device is needed and b) what is the
efficiency of converting wave mechanical
energy into electricity?
   Wave energy is variable hourly and
seasonaly but is continous over 24 hours
Three Basic Kinds of Systems
 Offshore (so your dealing with swell energy
not breaking waves)
 Near Shore (maximum wave amplitude)
 Embedded devices (built into shoreline to
receive breaking wave – but energy loss is
occurring while the wave is breaking)
Some Physics
 Ocean waves are irregular and are not
easily characterized by an average height
 Relevant parameter is A, or amplitude of
the wave (above mean sea level)
More Physics
   Power per meter is the product of the energy density and
the wave front velocity (inverse of period)

On the PNW coast, values for average wave amplitude
and for wave period are such that wave power is in the
30-50 kw/m area.
So potential yield along the Oregon Coast, assuming
10% efficiency is:
40 kw/m x 1000 m/km x 600 km = 24000 MW 
equivalent to PNW Hydro
Devices 1: The Air Piston

Incoming wave pushes
water level up to
basically compress air in
a piston to turn the crank
on a generator. When
water recedes, air
comes back into the
chamber.
This device is known as
the oscillating water
column (OSC).
OSC Continued

Note: Red Line is
average sea level
– front wall must
be located below
that line to make a
seal so that the air
doesn’t rush out –
tidal variations are
therefore important

In principle, one could modify extant coastal headline
topography to build these devices.
Difficulties with OWC approach
• Initial cost of barrier wall is high – due to lack of
• Zoning regulations protect most coastal
• Rich marine life is often found there
• Device must withstand potentially big storms
Unit Capacity of OWC

• Physics is similar to that of a wind turbine but wave
power is more dense
• Yield depends on total square meters of rotor area but
efficiencies are very difficult to calculate
• Near Shore anchored devices capture highest amount
of wave energy but sensitive to local mean sea level
• Reliability of waves is about 2 times higher than wind
Unit Capacity/Footprint
• Based on existing ON shore facility in India
(operational around 1993)
• 50 KW plant requires
• 100 square meter footprint and 3000 tons of
concrete
• Scaling up to 100 MW implies 2000 individual
100 square meter installations or roughly 5 per
mile along Oregon coastline and this is just for
100 MW
 Shoreline installations probably don’t make
sense – even if previous calculation is
wrong by a factor of 10 (which is unlikely)
 Therefore, look towards large installations
in near shore  but that could be
expensive
Ocean Power Technologies Claim

• The footprint of a 100MW conventional
power plant, including surrounding
settling ponds, and additional facilities can
be up to 2 sq miles (not true on average).
A comparable OPT power plant would
occupy less than 1 square mile of unused
ocean surface out for sight from the shore
(okay?)
The Tapered Channel Device
• Works like a hydroelectric dam

Waves rush in to fill reservoir which then drains through a
turbine system back into the ocean. Simple idea really.
Power depends on total volume of water.
Pros and Cons of TAPCHAN
• Could incorporate this into new kinds of
seawall/jetty/harbor protection projects
• Average wave energy must be high in order to
push all the water into the reservoir
• Reservoir needs to stay full and can’t drain at
low tides
• Significant capital cost and large coastal
footprint per MW because the depth of the
reservoir is shallow
• Likely not practical in most locations
The Power Buoy
• Video explanation
Power Buoy Continued
   Unit capacities are small (20KW) so you
need a large network – possibly subject to
catastrophic failure in severe weather
An Offshore Buoy Farm

Current
Problem is
that unit
capacity is
only 50
Watts for a
12 foot
cylinder –
need
millions
Principle Advantage: Can Withstand severe Weather
Power Buoy Footprint

80 MW per
square KM 
this is good

Don’t need to be anchored to sea floor
But Material Footprint is large

• Hard to find real technical data from the
vendor
• Can scale a couple of known cases
• OPT 20KW buy weighs 17 tons
• That’s 850 tons of material per MW 
much more material intensive than wind
turbines
The Overtopping Device

Similar to TAPCHAN idea but can easily be
installed near short instead of on shore.
Power basically depends on incoming wave
amplitude (height above mean sea level)
Focus Mechanism
The Wave Dragon Project
 Ambitious  project to harvest up to 10
Gigawatts of Power in the North Atlantic
 Floating sea monsters
Pros and Cons of Wave Dragon
 In principle this could actually work
 Unit capacity appears to be 16
Turbine 4 MW individual dragon
 25,000 then gives you 10 GW of
power
 Principle challenge is then “grid
connection” but scale of project does
not seem formidable
Hinged Devices
 A large Sea Snake  length is important
to generate high unit capacities
 Material/production scheme similar to wind
turbine main shafts
UK Pelamis Project

Unit Capacity is 750 KW; Power is generated at each
of the hinged locations essentially through a device
that converts pressure wave energy into electrical
current.
Each tube is 150 meters long and 3.5 meters wide
UK project employs 7 tubes to generate 5.25 MW
Biggest potential problem (besides grid connection) is
durability
The Pelamis Project

To set the scale of the
devices
The Future Sea Snake Farm ?
 Footprint argument is favorable: 30MW
facility would occupy 1 sq km of ocean.
 Look to the UK to seriously develop this
resource if initial prototypes prove succesful
New Idea  Use Bottom Waves

 Wave Roller device  anchored to the sea
floor (obviously near the cost)
 Easiest to build electricit export
infrastructure
 But energy density is lower; still prototypes
are being developed
Summary
 There is much potential in worldwide wave
energy; 1000 TerraWatts available
 Capturing wave energy and converting that
into electricity is difficult  but this allows for
innovate devices to be designed
 Large scale projects very capital intensive
 Optimum technology not yet discovered so
best to experiment
 Surface sea snakes may be best option
Potential Local Projects
 OPT facility at off shore from Reedsport
 Oregon State wave energy research facility
at newport
 Tidal power project in Tacoma Narrows

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 views: 5 posted: 11/11/2011 language: English pages: 34
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