Elia Zinetti WRIT 340

June 30, 2013

An Ocean of Energy

The energy contained in the ocean’s waves has the potential to become an important

source of renewable energy worldwide. Wave energy converters are very versatile and

have been engineered to function in diverse locations around the Earth’s oceans. Current  

prototypes  of  wave  energy  converters  are  being  studied  in  research  facilities  around  

the  world,  and  the  investments  make  it  plausible  to  assume  that  ocean  waves  could  

become  a  major  source  of  renewable  energy  in  the  near  future.

Introduction

We  live  in  the  twenty-­‐first  century,  where  technology  has  filled  with  commodities  the  lives  

of  an  ever-­‐increasing  number  of  people.  Energy  is  at  the  driving  force  of  this  phenomenon,  

and  the  world,  or  is  demanding  more  of  it.  We  do  not  need  energy  only  for  the  next  fifty,  

sixty  or  even  hundred  years;  we  need  energy  that  will  never  end.  This is why, in recent times,

renewable forms of energy have received increasing attention, not just from scientists and

engineers, but also from governments around the world. One form of renewable energy can be

provided by the waves in the ocean, and even if converting wave energy into electricity is still an

evolving technology, ocean wave energy can play an important role in the renewable energy

market. Moreover,  engineers  have  made  it  possible  to  convert  wave  energy  into  electricity  

in  various  areas  around  the  globe  by  developing  technologies  that  can  function  in  different  

environments. Although wave energy is still in the development phase, this technology is

currently in use in the United States and Europe; furthermore, wave energy has shown the

potential to become an important renewable source of energy.

 

Energy from the Ocean

We  are  familiar  with  the  idea  that  waves  contain  energy.  Simply  spend  a  day  at  the  beach  

and  observe  how  ocean  waves  can  safely  push  to  shore  dozens  of  surfers.  The  intuition  that  

waves  transport  energy  becomes  evident  when  we  see  on  television  images  of  tsunamis  

destroying  entire  harbors  and  villages  near  the  coastline.  However, what is not familiar to

most people is the fact that the energy contained in ocean waves can be harnessed and

transformed into electricity.

Like all other physical waves, ocean waves transport energy. To simply explain how waves are

formed, we have to remember that the sun heats the oceans’ surface unevenly. Above the warmer

spots, the air heats up and floats upward, leaving a space that is filled in by neighboring colder

air. This movement of air masses generates wind. As the wind moves along the surface of the

ocean, friction is produced, causing ripples in the water. The continuous friction between the

wind and ripples causes, in a snowball like effect, larger waves. [1].

Obtaining electricity from the ocean has a history of over 200 years. In 1799, Pierre Girard, a

French engineer, and his son deposited the first patent for a device that could harness power from

the ocean. It was never built, but  Pierre  Girard  was  the  pioneer  of  wave  energy,  and  he  

started  a  movement  of  inventors  who,  throughout  the  following  century,  produced  

sophisticated  machines  able  to  convert  wave  motion  into  electrical  power.  None of these

creations was ever successful in achieving useful amounts of power. Wave energy had a more

funded comeback during the embargo imposed by OPEC in the 1970s. The United Kingdom led

the way and proposed a structure of wave energy converting devices that could generate

approximately 2,000 megawatts of electricity. The plan was deemed too expansive, and was

finally aborted when the oil prices re-entered normality [2]. In recent years the technology has

 

been improved greatly, and wave energy converters have the potential to play an important role

in the renewable energy market.

From Waves to Electricity

The power of ocean waves can be harnessed in different ways, and throughout the past two

centuries, engineers have proposed different solutions to accommodate for different

environments. The major concern in designing a wave energy collector is the location. Devices

positioned on the shoreline, near-shore, or offshore implement different technology in

transforming wave energy into electricity [3]. There are several classifications for wave energy

systems, based on size, location, or working principle. The classification proposed in this article

is based on the three different working principles of wave energy converters:

• Oscillating water column (OWC).

• Oscillating bodies.

• Overtopping.

Oscillating Water Column Devices

The devices that utilize the oscillating water column as their working principle, also known as

first generation systems, are divided into two groups: fixed-structure OWC, and floating-structure

OWC. The optimal location for the fixed-structure OWC collectors is the shoreline, where they

are anchored to the ocean bed. The structure of such devices is simple, which implies easier

installation and less maintenance compared to other devices. The fixed-structure OWC is made of

concrete, and it is partially submerged, shown in Figure1. The submerged section is open at the

bottom, and it encapsulates air above the ocean’s surface.

 

The oscillating motion of the waves moves the trapped column of air upward, and thorough a

turbine driving the electrical generator [4].

Figure 1: Cross section of a fixed-structure OWC [5].

The largest fixed-structure OWC prototype ever built was named OSPREY. It was located along

the coast of Scotland and its maximum power output was 2 megawatts. The sea destroyed the

OSPREY prototype in 1995 [4].

The floating-structure OWC shares the same working principle of the fixed-structure OWC; the

main difference is that the structure of these devices is allowed to freely float, thanks to air

chambers, instead of being anchored to the ocean’s bed. The floating-structure OWC is held in

place by a cable anchored to the ocean’s bed. An example of a floating structure is the Backward

Bent Duck Buoy or BBDB [4], shown in Figure 2.

 

 

Air  

Air  

 

Figure 2: Cross section of a BBDB floating-structure OWC [4].

Similarly to the fixed-structure OWC, the waves induce an oscillation in the structure of the

buoy, which in turn generates the upward motion of the mass of air trapped between the water

and the air turbine. The air movement finally drives the turbine, which is connected to a generator

producing electricity. A 12 meter long Bent Duck Buoy, about 1/4th of the actual dimensions, is

being tested in Ireland since 2006 in preparation for a full-scale deployment [4].

Oscillating Body Devices

Oscillating body devices are considered second generation systems, and are located offshore

where they take advantage of more powerful waves. An example of an oscillating body device,

shown in Figure 3, has been recently been developed in Oregon at Oregon State University [4].

The prototype is composed of a heavy buoy that is free to move upward and downward along a

spar, which is anchored to the ocean bed by a cable. The buoy’s relative motion with respect to

the spar activates a magnetic generator, which converts the motion into electricity. The prototype

Figure  3:  Oscillating  body  device  developed  at  the  Oregon  State  University  [4].

Spar

Generator

Buoy

Cable

 

is a scaled down version of the final product and with a buoy’s radius of 3.5 m, and it produces a

power of 10 kilowatts [4].

A second example of an oscillating body device is the Pelamis, shown in Figure 4.

 

Figure  4:  Pelamis  [6]  

The shape of the Pelamis resembles a sea snake, and the structure is oriented in the direction of

the waves. The three joints, connecting the four cylindrical sections of the Pelamis, are the key in

understanding the operations of this device. The waves in the ocean cause an oscillatory motion

in the joints. This motion is resisted by hydraulic rams that pump oil into hydraulic motors

connected to electric generators [3]. Each Pelamis is 140 m long and at peak output it generates

2.25 megawatts. This technology is at work in Portugal, where each Pelamis powers about 1,500

homes [7].

 

Overtopping Devices

The overtopping converters are essentially different from the two previously described classes of

wave energy converters. Overtopping converters transform the kinetic energy in the waves in

potential energy by filling a reservoir slightly above the average ocean level. An example, shown

in Figure 5, is the Tapchan, which was built in Norway in the 1980s [4].

 

The constantly decreasing width of the collector in the Tapchan concentrates the incoming

waves, which increase in height, allowing water to spill into the reservoir. The reservoir is

designed to be wide enough to minimize oscillations on the surface of the water. Once the water

is filled up, it provides a constant source of water for the turbine adjacent to it. The power output

of this Norwegian prototype was of 350 kilowatts [4].

A Glimpse into the Future

The devices described above are just a few amongst the technologies currently available to

convert the kinetic energy of ocean waves into electricity. One of the major experimentations

around the world is happening in Oregon, and it is being carefully observed in the U.S.

government because the U.S. have the potential to generate vast amounts of electricity by

extracting the energy of waves. In fact, the total wave energy that could be collected in the United

States’ territories is estimated to be 1,170 terawatts per year [9], or 3.49 quads. Considering that

the energy consumed in 2011 in the United States was 97 quads [10], wave energy could provide

approximately 3.6 % of the entire U.S. energy requirement. To put this percentage in prospective

Figure  5:  the  Tapachan  [8].

Collector  

 

we can compare it to the percentage of energy provided by wind energy. The entire wind

production in 2011 was 1.17 quads [11] or roughly 1.2 % of the entire energy consumed by the

U. S., and only one third of the estimated power that could be generated by wave energy alone.

Oregon’s government and universities are currently studying a long-term plan that would start a

competitive wave energy industry. In the last months of 2012, Oregon announced that the final

projects would include 10 buoys, shown in Figure 6, capable of producing 1.5 megawatts, or

enough electricity to satisfy the demand of 1,000 homes [12]. The buoys that will be utilized in

Oregon are called PowerBuoy [13], and according to the previous classification they are

oscillating body devices of second generation.

 

Figure  6:  Oregon's  PowerBuoys  compared  to  the  size  of  a  person  [13].  

 

Conclusion

Wave energy conversion is a technology that has been around for quite some time, 214 years to

be exact. Currently start up cost is the main issue with the slow expansion of this technology.

Despite the two centuries of history, ocean wave conversion can still be considered new, and

engineers are utilizing different prototypes to test real life situations and to obtain results that can

convince the government to invest in this form of renewable energy. However, states like Oregon

 

are betting on the huge potential estimated for wave energy, and are investing in long term plans

to utilize ocean waves as significant energy source. Oregon is a good step forward in the

development of wave energy conversion, and with the investment of individuals or organizations

as equally enterprising, ocean waves could be an important renewable energy source in the near

future.

 

References

[1] J. McGrath. (2008, July 15). How Wave energy Works [Online]. Available:

http://science.howstuffworks.com/environmental/earth/oceanography/wave-energy1.htm

[2] E. Callaway. (2007, November 7). Energy: To catch a wave (Nature 450, 156-159.)

[Online]. Available: http://www.nature.com/news/2007/071107/full/450156a.html

[3] W. B. Wan Nik, O. O. SUlaiman, R. Rosliza, Y. Prawoto, A. M. Muzathik. (2011). Wave

energy resource assessment and review of the technologies [Online]. Available FTP:

IJEE.IEEFoundation.org Directory: vol2/issue6 File: IJEE_11_v2n6.pdf

[4] F. António, O. Falcão. (2010). Wave energy utilization: A review of the technologies.

[Online]. Available FTP: http://mhk.pnnl.gov Directory: wiki/images/5/58 File:

Wave_Energy_Utilization.pdf

[5] Y. M. C. Delauré. (2003, February 2003). 3D hydrodynamic modeling of fixed oscillating

water column wave power plant by boundary element methods [Online]. Available:

http://www.sciencedirect.com/science/article/pii/S002980180200032X

[6] Center for Climate and energy Solution. (2011, August). Hydrokinetic Electric Power

Generation [Online]. Available: http://www.c2es.org/technology/factsheet/Hydrokinetic

[7] A. Jha. (2008, September 24). ‘Wave snakes’ switch on to harness ocean’s power (The

Guardian Environment). [Online]. Available:

http://www.guardian.co.uk/environment/2008/sep/24/renewable.wave.energy.portugal

[8] National energy education Development Project. [Online]. Available: http://need-

media.smugmug.com/Graphics/Graphics/17024036_Bdmf8C/1289371669_KpV99ff#!i=1

289371669&k=KpV99ff

[9] P. Jacobson. (2011). Mapping and Assessment of the United States Ocean Wave energy

Resource [Online]. Available FTP: http://www1.eere.energy.gov Directory: water/pdfs

File: mappingandassessment.pdf

 

[10] U.S. Energy Information Administration. (2012). Annual Energy Review 2011 [Online].

Available FTP: http://www.eia.gov Directory: totalenergy/data/annual/pdf File: aer.pdf

[11] A. M. Stark. (2012, October 24). Americans use more efficient and renewable energy

technologies [Online]. Available: https://www.llnl.gov/news/newsreleases/2012/Oct/NR-

12-10-08.html

[12] D. Ferris. (2012, October 3). Oregon Races To Catch Up To Europe In Wave Energy

[Online]. Available: http://www.forbes.com/sites/davidferris/2012/10/03/in-wave-energy-

oregon-races-to-catch-up-to-europe/

[13] J. Barnard. (2012, August 22). Oregon wave power project gets green light to go forward

[Online]. Available: http://www.katu.com/news/local/Wave-power-project-off-Oregon-

gets-federal-permit-to-go-forward-167132545.html