Miles McIntyre CEE 514 Coastal Engineering Project

Using Coastal Environments to generate energy

1. Abstract

The purpose of this project is to investigate how coastal environments (both offshore and nearshore) can be utilized to harness clean renewable energy and examples will be given of recent projects that use the power of the waves as the technology is still only emerging.

2. Motivation of the Project

I feel this is an important issue to discuss as there is an ever increasing need for mankind to reduce his reliance on using fossil fuels and look to more innovative cleaner sources of energy. Presently renewable energy makes up about 18% of the global energy consumption, with a very small portion of this originating from the ocean. However oceans cover almost 75% of the earth’s surface, holding tremendous amounts of energy and so there is a great potential to capture this and convert into electricity. It has been estimated that if only 0.2% of the ocean energy were harnessed, it could produce enough energy to power the entire world.

3. The Coastal Environment of Targeted Areas and its issues

Waves have the highest power per unit area when compared to wind and solar energies yet only roughly 0.02% of renewable energy generation comes from the ocean. It is a very much underused natural resource that we have in abundance.

Wave power devices extract energy directly from the surface motion of ocean waves or from pressure fluctuations below the surface. However wave power does vary considerably depending on where you are on earth and so isn’t a good idea everywhere. The highest concentration of wind power is found mainly between latitudes 40° and 60° in both northern and southern hemispheres. These regions included Scotland, Northern Canada, Southern Africa, Australia and Northwestern coasts of the United States – locations in nearly virtually every continent.

Power available in waves

Wave energy Flux (in deep water with a depth larger than 0.5L) is calculated using the following equation:

So considering moderate ocean swells, in deep water, a few kilometers offshore, a wave height (H) of 3 meters with a wave period (T) of 8 seconds will produce a wave with a power of 36kW/m.

In major storms, wave heights can easily reach around 15 meters and will have a period of about 15 seconds. These waves will carry approximately 1700kW/m of power per unit width.

Figure 1 -Wind Power Density in the World

(Wind speed U m/s)	(Wave height Hs m)	(Wave period Second)	(Wave Power KW/m)	(Wind Power KW/square meter)
5.1	0.55	3.3	5	0.08
10.3	2.3	6.6	16	0.67
15.4	5.0	9.9	120.2	2.3
20.6	9.0	13.2	520	5.4
25.7	14.0	16.5	1600	10.

Table 1 - Examples of the Wind Power Potential for varies wave conditions

Energy capturing devices can be installed at nearshore, offshore or far offshore locations. Offshore systems are situated in deep water typically more than 40 meters. For nearshore locations aesthetics will be an important issue to consider and are a distance of 12 miles from the coastline is usually considered nearshore. Beyond this is offshore. Other environmental considerations of placing these devices are the impact it has on shipping lanes and the local marine life.

4. Results and Discussions

A variety of technologies have been proposed to capture the energy from waves. Many of these are undergoing demonstration testing at commercial scales and some are still in the research and development stages. Wave power has so far been restricted to only small scale schemes; the main reason for this is that waves are not always constant; they are reliant on a number of different factors like wind speeds.  

Terminator

These extend perpendicular to the direction of wave travel and capture or reflect the power of the wave. These devices are usually found onshore or nearshore, although floating versions have been designed for offshore locations. The oscillating water column is a form of terminator in which water enters through a subsurface opening into a chamber with air trapped above it. The wave action causes the captured water column to move up and down like a piston, forcing the air through an opening connected to a turbine.

Is a floating structure with components that move relative to one another due to the wave action. This relative motion is used to drive an electromechanical or hydraulic energy convertor. The curved, floating canisters, each the size of a house, are connected together and then anchored to the ocean floor. These canisters move relative to one another due to wave action, using hydraulics to convert the rocking motion to rotational motion, which would in turn drive a generator. A single Duck was calculated to be capable of generating 6 megawatts (MW) of electricity—enough to power around 4,000 homes. The plan was to install them in groups of several dozen.

Point absorber

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Attenuators

These are long multisegment floating structures oriented in parallel to the direction of the waves. The differing height of waves along the length of the device causes flexing where the segments connect, and it is this flexing motion that pushed a hydraulic pump. 

Over-topping devices

These consist of reservoirs that are filled by incoming waves to levels above the surrounding ocean. The water is then released and falls back towards the ocean surface. The energy of the falling water under gravity is then used to turn hydro turbines.

Onshore Devices – extract the energy in breaking waves

The oscillating water column consists of a partially submerged concrete or steel structure that has an opening to the sea below the waterline. It encloses a column of air above a column of water. As waves enter the air column, they cause the water column to rise and fall. This alternately compresses and depressurizes the air column. As the wave retreats, the air is drawn back through the turbine as a result of the reduced air pressure on the ocean side of the turbine.

Oscillating water column

The Tapchan, or tapered channel system, consists of a tapered channel, which feeds into a reservoir constructed on cliffs above sea level. The narrowing of the channel causes the waves to increase in height as they move toward the cliff face. The waves spill over the walls of the channel into the reservoir and the stored water is then fed through a turbine.

Tapchan

Pendulor device

The Pendulor wave-power device consists of a rectangular box, which is open to the sea at one end. A flap is hinged over the opening and the action of the waves causes the flap to swing back and forth. The motion powers a hydraulic pump and a generator.

Ideas still in development (testing in a lab)

Anaconda Tube

This is a large distensible tube, made out of rubber, closed at both ends and filled with water. The Anaconda tube is designed to be anchored just below the sea’s surface, with one of its ends facing the oncoming waves.

This works when a wave hits the tube’s end, compressing it forming a bulge (pressure) wave inside the rubber tube that oscillates the fluid back and forth. As the bulge wave moves down the tube, the wave that caused it runs along the outside at the same speed - making the bulge wave inside grow even bigger. This action turns a power-generating turbine at Anaconda's far end. A full-scale 100-tonne Anaconda will be 200 meters long and 7 meters in diameter. It will produce 1 megawatt (enough for 2,000 homes) at a cost of 6p (4 cents) or less per kilowatt hour.

A device called CETO, currently being tested off the coast of Western Australia, consists of a single piston pump attached to the sea bed, with a float tethered to the piston. Waves cause the float to rise and fall, generating pressurized water that drives hydraulic generators to run reverse osmosis desalination.

While other sources of renewable energy - such as wind and solar - have been widely adopted in recent years, wave energy has been slow to take off. Wave and tidal power are primarily in the prototype and experimental stage, but several companies are ramping up prototypes and test vehicles

Conclusion

Wave power has the potential to play an important part in the long term goal of switching to renewable sources for generating energy. The deployment to such schemes around the world has brought recognition to the technology available. This interest will stimulate the growth of the industry allowing other technologies to advance and realize their full potential. However much still needs to be done. Until the devices become more economically viable and more competitive with other renewable such as wind, it is likely that wave powered electricity will still only be used to supply small communities or for individual commercial plants. There are some efforts underway, but they pale in comparison to the amount of money being poured into wind and solar projects, leaving this area an interesting opportunity for the right kind of investor

The problems the industry faces are not the ideas themselves, but the technology itself that make the exploration of wave power a challenge. The British government’s decision back in the 1970’s to shut its wave-energy research program and with so many wave energy companies originating from the UK, the field was set back by nearly two decades. However the good news is that interest in wave power has revived earlier this decade, but many problems still exist like, designing the devices to withstand the power of the oceans, the costs improved in implementing these schemes, and obtaining the vessels for transporting the equipment out to location. Another practical problem is the lack of infrastructure to connect wave-energy generators to the power grid.

However there are signs of change. Big utilities are starting to take the technology available to them seriously and are teaming up with smaller wave-energy companies, so the industry has many opportunities ahead that with the right investments could easily take off and dominant in future energy production.

The world’s first commercial wave farm, consisting of three Pelamis Machines (snake-like tubes) was installed off the coast of Portugal in October 2007, with many more planned for the future.

Current Projects include a wave farm that is set to be built off the coast of California due for completion in 2012 and a commercial wave-power park in Oregon. There are many companies out there that already have and are currently developing the technology and devices to convert the power of the oceans into useful energy.

5. References

http://www.guardian.co.uk/technology/2008/aug/07/research.waveandtidalpower

http://apps1.eere.energy.gov/consumer/renewable_energy/ocean/index.cfm/mytopic=50009

http://en.wikipedia.org/wiki/Wave_power

http://business.timesonline.co.uk/tol/business/industry_sectors/utilities/article4449287.ece

http://news.bbc.co.uk/1/hi/technology/6410839.stm