Electricity from Ocean Waves

We can use the bountiful energy in ocean waves to power coastal cities and reduce greenhouse gases. Power companies do not need to crisscross inland regions like ours with electric lines from coal plants, and pipelines from fracking fields, to fuel coastal cities.

The wave industry needs faster reviews, more test sites, and more private investment.

Ocean waves are always there, powerful, out of sight, and near the customers. At night and in calm winds, ocean waves continue. The "technically recoverable wave energy resource is approximately 1,170 terawatt hours (TWh) per year" (DOE), enough electricity for 90% of the households in the US.

"More than 100 pilot and demonstration projects exist throughout the world" (2014,Int'l Renewable Energy Agency).

Wave projects capture energy with floats, turbines, pumps, and generators. All use the motion of surface waves relative to seabed, calm subsurface water, shore, or adjacent parts of the surface water. This article describes some of the designs.

Design Issues for Wave Energy

  • Designs which capture wave motion relative to the seabed or subsurface waters can be used widely. These machines can be anchored far from shore, since long non-corroding cables are a well-developed technology (think ski lifts and weather buoys).
  • Capturing wave motion at shorelines is less practical, since shorelines are scarce, expensive, visible and more turbulent than deep water.
  • Waves can slightly bend hinges between two floats, to generate electricity. However moving hinges in salt water are not a well-developed technology. Pelamis used this approach in Scotland, but could not raise enough money to keep operating.
  • Equipment at sea needs protection from water leaks and corrosion.
  • Taking energy out of waves will reduce movement of sand and sediment. So sites and density matter, to leave the shore alone. A row of wave generators can also be a breakwater, reducing wave damage.s
  • If the moving parts of wave machines move slowly enough, swimming animals can avoid them and benefit from new niches, as happens at shipwrecks.
  • The most well-developed seals for moving parts at sea are propeller shaft seals, which keep water out of ships for years before replacement.
  • Everything in salt water faces corrosion and marine growths (barnacles, seaweeds).
  • Big ships are usually painted steel for weight, cost, design flexibility and high strength, including shocks from storms and docks. They have pumps to address leaks. Drydocks repaint them every few years.
  • Small boats are usually fiberglass for weight, cost, medium strength and low maintenance. They have anti-fouling paint to maintain speed, and pumps to address leaks.
  • Very small boats are usually aluminum or wood and are not kept in salt water year round.

US Government Actions

  • Applicants need years to get permits and licenses, and will often move faster by testing abroad. The US requires more onerous baseline studies for waves than for fracking.
  • There is one ocean test site in Hawaii, which can test four designs per year, and one in Oregon. Each test needs permits from the state, Corps of Engineers, and Coast Guard. "A significant effort is required in face-to-face consultation with stakeholders."
  • The U.S. Department of Energy (DOE) started planning a Prize for wave energy in summer 2012, proposed it to Congress in April 2013, will choose winners in November 2016, and winners will still need more rounds of development. See a list of the semi-finalists below.
  • DOE's Prize is based on performance of 1:50 and 1:20 scale models in tanks. The miniaturized turbines and generators will not work the same as full size machines in the ocean.

Examples of Designs

Note: The DOE also has a list of wave energy conversion (WEC) designs, though most of those designers do not provide enough public information to show how they really work. en.openei.org/wiki/Marine_and_Hydrokinetic_Technology_Database.

 

ACTUALLY OPERATING

 

 

 

1-4 kW

Drakoo-B by Hann-Ocean.com, Singapore.

 

3 tonnes, not all moved by wave

It floats, attached to any floating platform. Valves open and close to let the top of each wave enter. The water drops down and exits at the bottom of the next wave, spinning a turbine. A shaft goes up from the turbine to the generator which sits high and dry above water, capturing 55% of wave energy. A cable takes electricity to shore.

 

3x2.9x2.4 meters

 

100-400 volts AC

Parts which move or flex: Turbine, generator, bearings, valves

 

electricity is 55% of wave energy

Waterseals: Modest, since generator is above water level

Inertia to be overcome by waves: Water which changes direction slightly, light valves (no inertia from turbine; it turns in constant direction)

Useful life: 20 years, but generator 10y, bearings 2y, valves 1y. 2-year maintenance contract available

 

Must face waves

hann-ocean.com/products/drakoo-wave-energy-converter/principle/

hann-ocean.com/products/drakoo-wave-energy-converter/specifications/

hann-ocean.com/products/drakoo-wave-energy-converter/faq/

 

 

 

 

 

240 kW from 11m diameter

CETO by CarnegieWave.com, Australia

 

30-40¢ per kWh; will drop to 20¢

Buoyant chamber moves up and down  just under the surface waves. The motion drives a pump, sending electricity or water (in a long pipe) to shore. Pumped water drives an electric generator and/or presses against an osmotic membrane to desalinate the water. A return pipe brings the water back to be pumped again.

 

20m, 11 m, 8m diameter, 6 m high.

Anchor drilled 14 m into seabed

 

 

Parts which move or flex: Pump, bearings, generator, tethers, valves

Waterseals: Critical where pump goes up and down at sea bottom

Inertia to be overcome by waves: Float which can be light, since it is not exposed to rough water surface

 

 

Next version will be 1,000 kW for AU$8,000,000 capital cost, not counting development cost

 

Waves any direction

carnegiewave.com/what-is-ceto

youtube.com/watch?t=42&v=ryQ4zQyHeOI

youtube.com/watch?v=wRfBqS0HpFA

carnegiewave.com/ceto-overview/

economist.com/news/science-and-technology/21646176-new-project-coast-australia-may-make-wave-power-reality-looks-swell

 

 

 

 

 

100-300kW

SeaBased, Sweden

 

 

Float moves up/down/sideways on surface. Cable connects to piston on sea floor which drives a linear generator, which generates electricity varying in frequency and voltage. Several connect to one substation, also on sea floor, which converts to DC, then to AC 50 or 60 cycles.

 

 

Parts which move or flex: Piston, bearings, generator, tethers

Waterseals: Critical where piston goes up and down at sea bottom

Inertia to be overcome by waves: Float must be heavy enough to survive storms at the surface.

 

 

They installed 6 in Ghana

 

Waves any direction

seabased.com/en/technology/seabased-wave-energy

tidalenergytoday.com/2015/03/24/seabased-wave-farm-now-in-full-swing/

tidalenergytoday.com/2015/02/10/ghanaian-wave-energy-project-kicks-off/

 

 

 

 

 

0.35-15 kW continuous average

PowerBuoy by Ocean Power Technologies, New Jersey

A permit for Oregon has stalled.

 

15-50kW peak power

Floating buoy moves up and down in waves, relative to a pole which is either driven into the ocean bottom or tethered. They note they have a chain of 5 power conversions, each with efficiency losses: Waves drive the float, which drives a rack+pinion which drives a generator to create "wild Frequency, wild voltage AC power", which they convert to DC, then back to clean AC power. Each unit has a generator, connected to an underwater substation, then to shore.

 

10 tonnes, 13 m high, or

114 t, 34 m high

 

uses 20-250kWh battery to store peak power and provide continuous power

Parts which move or flex: Gears, bearings, generator, tethers

Waterseals: Critical where a moving pole from the float slides in and out of the fixed pole underwater which holds a generator

Inertia to be overcome by waves: Float must be heavy enough to survive storms at the surface

 

Waves any direction

oceanpowertechnologies.com/powerbuoy/

oceanpowertechnologies.com/s/METS2014_OPT-PowerBuoy-System-Level-Design-Development-and-Validation-Methodolog-METS-2014-April-201.pdf

 

 

 

 

 

 

750 kW

Pelamis, Orkney (Bankrupt)

 

1,350 tonnes

Floating tubes, hinged like sausages, flex at joints as waves pass along them. Hinges drive hydraulic pumps which drive generators. A cable takes electricity to shore. The company installed generators in Orkney in 2004 and went into bankruptcy in 2014.

 

120-180 m long, 4 m diameter

 

 

Parts which move or flex: Pumps, bearings, generators, tethers, hinges

Waterseals: Critical on hinges

Inertia to be overcome by waves: Entire mass of system, which must be heavy enough to survive storms at the surface

 

 

bbc.com/news/uk-scotland-scotland-business-30560980

emec.org.uk/about-us/wave-clients/pelamis-wave-power/

 

 

 

 

 


 

 

DESIGN PHASE

 

 

500 kW

Spindrift by SpindriftEnergy.com, California

2 ¢/kWh

150' tube hangs from a float. Waves lift the tube through still water below, spinning a turbine in mid-tube. The tube narrows at the turbine (Venturi tube) to speed the water Power is proportional to the cube of water speed, and Venturi tube accelerates low speed waves to create high speed water flow, unlike other designs. A shaft goes up from the turbine to the generator which sits high and dry above water. A cable takes electricity to shore.

150 feet high, needs area 140'x140'

$400,000 capital cost each

Parts which move or flex: Turbine, generator, bearings, tethers

Waterseals: Modest, since generator is above water level

Inertia to be overcome by waves: Entire mass of system: float must be heavy enough to survive storms at sea. They plan tube in heavy concrete, but it could be light plastic, since it is not exposed to surface storms.

Waves any direction

youtube.com/watch?v=AZSc7llHJUI

spindriftenergy.com/faq.html

spindriftenergy.com/faq1.html

 

 

 

300kW

Protean by ProteanWaveEnergy.com.au, Australia, owned by mining company (Stonehenge)

13 ¢/kWh

Float tethered to bottom moves up/down/sideways in surface waves. Cables from bottom go over pulleys in float to counterweights. Pulley shafts drive pumps or generators.

18 t = 3t float+15 t weight

 

Parts which move or flex: Cables, pulleys, bearings, generators, tether

Waterseals: Critical since cables constantly slide from water in and out of buoy which holds generator

Inertia to be overcome by waves: Cables, pulleys, float, which must be heavy enough to survive storms at sea.

Waves any direction

https://2718f7c0-a-578fcc8e-s-sites.googlegroups.com/a/proteanwaveenergy.com.au/www2/Stonehenge%20Company%20Presentation%20-%20Protean%20Acquisition%2003092014.pdf

 

 

 

>500 kW

SeaRay by ColumbiaPwr.com, Oregon + Virginia

 

A big float with a stabilizing pole below it, and 2 small floats on sides which waves move up/down relative to the big float, turning generators in the big float.

 

Parts which move or flex: Bearings, generators, tethers

Waterseals: Critical, since hinges are on water surface, so alternately wet and dry

Inertia to be overcome by waves: Side floats, which must be heavy enough to survive storms at sea.

Self-aligns to face waves

columbiapwr.com/ray-series/

 

 

 

 

Wave Carpet at TafLab.berkeley.edu, California, to be commercial in 2024

 

Flexible plastic surface in water about 60' deep will move up and down in bottom waves caused by surface waves. Motion drives pistons to pump water which would be piped to generate electricity. At 1:25 minutes into their video, they show a trickle of water pumped by a prototype 2 feet below the surface.

 

Parts which move or flex: Carpet, bearings, pumps, generator, tethers

Waterseals: Critical where pistons go in and out

Inertia to be overcome by waves: Modest mass of carpet, pistons, and water being pumped

Waves any direction

newscenter.berkeley.edu/2014/01/28/seafloor-carpet-catches-waves-to-harness-energy/

taflab.berkeley.edu/uc-berkeley-ocean-wave-energy-converter/

youtube.com/watch?t=86&v=INEGcJ7AGGQ

calwave.org

Semi-finalists in the DOE Contest

We apologize for the jargon from the DOE contest site. When we could find clearer explanations on the designers' own sites we added them here.

Advanced Ocean Energy @ Virginia Tech, Blacksburg and Hampton, VA

"floating [cylinder], with single-acting power take-off (PTO) units incorporated into flexible tethers connecting the [float] to a fully submerged reaction plate."

AquaHarmonics, Portland, OR

"concept is a point absorber with latching/de-clutching control."

Atlas Ocean Systems, Houston, TX, atlasoceansystems.com

"Point absorber with suspended oscillating ballast driving pneumatic bladder."

CalWave, Berkeley, CA, calwave.org

"submerged pressure differential device" A more detailed description is with the other descriptions above.

Float Inc.- BergerABAM, San Diego, CA, abam.com

"Impedance-Matched, Optimized Multi-Band Oscillating Water Column Terminator... to remediate winter storm sea-states on the [Columbia River Bar] to a degree that eliminates the need for navigation channel closures... system of WEC-breakwaters must perform by absorbing, rather than reflecting, wave energy – and thereby producing electric power as a salable product.

IOwec, Cambridge, MA

"Floating point absorber with eccentric gyroscopic system... simplicity and: no articulation or moving parts in direct contact with water; the main system components taken individually are well proven, highly reliable and mature technologies"

M3 Wave, Salem, OR, m3wave.com/

"Submerged mid-column pressure differential harvester... The open ocean eats puny man-made things for breakfast. Survivability is the key to cost-effective energy harvesting." Crest passes over chamber A, raising its pressure, driving air out through turbine (generator) into chamber B. Then crest passes over B, driving air back through bidirectional turbine to A.

Mocean Energy, Annapolis, MD, moceanenergy.com/

 

"Point absorber with cross-coupled pitch, heave and flex "

response." "a hinged raft. Wave forcing and the bodies’ dynamic responses leads to a motion about the hinge (called flex), which drives a power take-off mechanism that converts the kinetic energy into electricity. It has 7 degrees of freedom. The innovation of the Mocean WEC is in the design of the shapes of the bodies, which dramatically improves its dynamics and thus power absorption."

Oscilla Power, Seattle, WA

"high-force, low-displacement... a two-body, multi-mode point absorber."

Principle Power, Berkeley, CA, principlepowerinc.com/

"Floating Barge with Inter-connected Oscillating Water Columns"

RTI Wave Power, York, ME

"Wave terminator using floodable/submergable elongated wave front parallel float."

Sea Potential, Bristol, RI, seapotential.com

"A multi-mode power capture point absorber called DUO."

SEWEC, Redwood City, CA

"Floating Oscillating Water column WEC with internal turbine generator."

< a target="_blank" href=" http://waveenergyprize.org/teams/super-watt-wave-catcher-barge-team">Super Watt Wave Catcher Barge,Houston, TX, marineenergycorp.com

"Point Absorber Barge Whose Mooring System Turns Onboard Generators"

"barges are the worst behaving vessels which attract the most wave forces because of their large flat bottoms. They also know that barges are the lowest cost per ton hull. They know that barges are easy to tow to site and easy to moor. They know that using the high mooring system loads to turn generators in normal sea conditions is feasible. They know that barges and their mooring systems are regularly designed to survive extreme storm conditions"

Wave Energy Conversion Corporation of America (WECCA), North Bethesda, MD, weccamerica.com

"Articulated Barge"

"without the use of environmentally hazardous fluids. With simple linear electrical generators"

"by submerging the WEC device to 20 meters below the surface, wave motion is attenuated to 37% of surface motion. A simple idea which can revolutionize the longevity"

Wavefront Power (Team Flapper), Research Triangle Park, NC

"Combined OWSC and Heaving Device"

Waveswing America, Sacramento, CA, awsocean.com

"Sub-sea pressure-differential point-absorber... linear generator"

"reacts to changes in sub-sea water pressure caused by passing waves and converts the resulting motion to electricity via a direct-drive generator."