References
1) Wikipedia. (2008). Standing Wave. [online]
URL: http://en.wikipedia.org/wiki/Standing_waves (28 April 2008)
2) WAVEenergy. (2005). Harvesting the power of the ocean. [online]
URL: http://www.waveenergy.no/ (7 May 2008)
3) AEoogle. (unknown). Wave Power. [online]
URL: http://www.alternative-energy-news.info/technology/hydro/wave-power/ (18 May 2008)
4) The New York Times. (2007). Wave Energy. [online]
URL: http://www.nytimes.com/2007/12/09/magazine/09waveenergy.html?_r=1&oref=slogin
(18 May 2008)
5) Department of Physics, NTNU. (1997). Wave-energy Research. [online]
URL: http://folk.ntnu.no/falnes/w_e/index-e.html (30 May 2008)
6) Energy Resources, Wave Powder. (2008). Wave Power – energy from the wind on the sea. [online] URL: http://home.clara.net/darvill/altenerg/wave.htm (2 June 2008)
7) Earthlink. (2003). Animated Demonstration of Bernoulli’s Principle. [online]
URL: http://home.earthlink.net/~mmc1919/venturi.html
(7 June 2008)
8) Energy Information Administration. (unknown). Ocean Energy. [online]
URL: http://www.eia.doe.gov/kids/energyfacts/sources/renewable/ocean.html
(10 June 2008)
Saturday, May 31, 2008
IT'S REVIEWING TIME
HELLO EVERYONE!
From this day onwards, it will seem as if we are ignoring the existence of this 'PHYSICS SIA 2008' weblog.
Why?
IMPORTANT NOTICE:
We regret to inform the world that from this day onwards, there will be no new posts, therefore we may appear to be hibernating instead of updating the weblog regularly.
BUT, not having new posts DOES NOT mean we're not updating our blog!
As you can see, we have gathered information and collated data (look below!).
However, we will need to carry out a few essential and necessary things, such as..
ASCERTAIN that the information is accurate and true,
EDIT the information,
ADD MORE information,
REVIEW the information,
UNDERSTAND the information well enough to
INSERT OUR OWN OPINIONS, VIEW AND NEW INSIGHTS!
..and so on (:
We appreciate your kind understanding and cooperation.
Yours sincerely,
The authors of this weblog
YCYS!
From this day onwards, it will seem as if we are ignoring the existence of this 'PHYSICS SIA 2008' weblog.
Why?
IMPORTANT NOTICE:
We regret to inform the world that from this day onwards, there will be no new posts, therefore we may appear to be hibernating instead of updating the weblog regularly.
BUT, not having new posts DOES NOT mean we're not updating our blog!
As you can see, we have gathered information and collated data (look below!).
However, we will need to carry out a few essential and necessary things, such as..
ASCERTAIN that the information is accurate and true,
EDIT the information,
ADD MORE information,
REVIEW the information,
UNDERSTAND the information well enough to
INSERT OUR OWN OPINIONS, VIEW AND NEW INSIGHTS!
..and so on (:
We appreciate your kind understanding and cooperation.
Yours sincerely,
The authors of this weblog
YCYS!
Tuesday, May 27, 2008
Case study -- Limpet (Wave power generator) by Wavegen
--
27/05/08
Limpet is a shoreline unit to generate electricity in areas exposed to strong wave energy. It is located on the island of Islay, which is off the west coast of Scotland. The wave power generator was designed and built by Wavegen and researchers from Queen's University in Belfast and has financial backing from the European Union. The current Limpet device is called Limpet 500, which means that it can generate 500 kilowatts of electricity into the island of Islay.
How does Limpet work?
Limpet uses the principle of an oscillating water column (OWC). An oscillating water column is a partially-submerged, hollow structure, either vertically or at an angle, either in shallow water or onshore.
The waves continuously build up crests and troughs in front of the rock face of the power generator. Then, wave power forces seawater to enter the shell chamber. The interior of chamber also follows the sequence of the wave outside the chamber.
During crest formation, the level of water in the chamber rises, compressing the entrapped air at the top of the chamber to a value that is slightly above the atmospheric pressure. Thus, the air is forced through a “blowhole” and into “Wells Turbine”, which is designed by Professor Alan Wells of Queen’s University in Belfast.
However, during trough formation, the water inside the chamber recedes, the air is then decompressed to be under atmospheric pressure. This keeps the turbine moving. However, the crest and trough formation of the wave also cause the air to move in two directions. Hence, Wells turbine has been designed to turn successively in only one direction regardless of the direction of the airflow to ensure the efficiency of the harvesting of energy.
The rotation of turbine produced by the constant movement of air is tehn used to drive a generator that converts the energy into electricity.
27/05/08
Limpet is a shoreline unit to generate electricity in areas exposed to strong wave energy. It is located on the island of Islay, which is off the west coast of Scotland. The wave power generator was designed and built by Wavegen and researchers from Queen's University in Belfast and has financial backing from the European Union. The current Limpet device is called Limpet 500, which means that it can generate 500 kilowatts of electricity into the island of Islay.
How does Limpet work?
Limpet uses the principle of an oscillating water column (OWC). An oscillating water column is a partially-submerged, hollow structure, either vertically or at an angle, either in shallow water or onshore.
The waves continuously build up crests and troughs in front of the rock face of the power generator. Then, wave power forces seawater to enter the shell chamber. The interior of chamber also follows the sequence of the wave outside the chamber.
During crest formation, the level of water in the chamber rises, compressing the entrapped air at the top of the chamber to a value that is slightly above the atmospheric pressure. Thus, the air is forced through a “blowhole” and into “Wells Turbine”, which is designed by Professor Alan Wells of Queen’s University in Belfast.
However, during trough formation, the water inside the chamber recedes, the air is then decompressed to be under atmospheric pressure. This keeps the turbine moving. However, the crest and trough formation of the wave also cause the air to move in two directions. Hence, Wells turbine has been designed to turn successively in only one direction regardless of the direction of the airflow to ensure the efficiency of the harvesting of energy.
The rotation of turbine produced by the constant movement of air is tehn used to drive a generator that converts the energy into electricity.
--yingshi
Edited and reviewed by: seokting on 26/06/08
Thursday, May 22, 2008
General advantages and disadvantages/impacts of using wave energy
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22/05/08
ENVIRONMENTAL IMPACTS
Positives:
1) Little to no chemical pollution during operation and little to no land use (Lemonis 2004). These devices would have very low greenhouse gas emissions estimated at 11g of CO2 per kWh for near-shore schemes (Duckers 2004), and 21.67g per kWh for the off-shore Pelamis device (Banjeree et al 2006). This compares to a release of about xx KG of CO2 per kWh for coal-fired electricity production. Environmentally benign and non-polluting: no fuel, no exhaust gases, no noise. Minimal visual impact.
2) As a renewable and highly sustainable non-nuclear source of energy (green energy), wave energy is naturally replenished, in a sense that they cannot 'run-out', is in constant supply over time and that has environmental and social impacts that are generally more benign that that of fossil fuels.
3) Wave power is predictable and dependable, thus humans can be armed with the ability to accurately forecast the wave power spectrum days in advance. This way, they can be well prepared for the next strong currents in order to harness the maximum amount of energy possible and obtain the energy needed for conversions to other forms.
4) There are many ideal locations in Europe, North and South America, Africa, South Pacific Ocean and Asia where high power densities exist close to highly populated areas, therefore there is potential for wave energy to be harnessed and put to efficient, effective use to support many many households, especially when it comes to the generating of electricity.
--cassandra
Negatives:
1) These devices require very high construction costs. From a net energy perspective, the energy required to build the infrastructure may outweigh the small amount of electricity wave projects are capable of producing in the short term. Severe storms have dashed the hopes of some earlier projects, probably before serious energy has been returned.
Wave energy is at an early stage of development and is therefore still relatively expensive when compared to other sources of electricity. The House of Commons Science and Technology Committee concluded in 2001 that a true picture of the likely cost of wave power will only be available after the industry has matured and large devices have been operating for some time. However, the cost of wave energy has fallen over the past 10 to 15 years and ongoing technological developments mean the predicted costs of wave energy are continually being reduced.
2) They may also alter coastlines by changing energetic patterns of waves (Lane 2007 may generate various environmental impacts, most of which are unknown. Some wave energy devices may affect the natural flow of sand and other beach sediment and so would require sensitive siting but the installations could also potentially benefit the environment by creating safe havens for fish and helping to reduce coastal erosion.
3) Other potential impacts, such as disruption of marine habitat and fish migration patterns, and sedimentation, are generally agreed to be minimal, but important considerations on an individual project basis.
4) There are also noise impacts due to some devices used to harness wave energy.
5) Though the wave devices have no emissions during generation but the energy associated with the construction of the device does have small associated emissions.
6) There has been some concern about aesthetics and disruption of fishing, shipping, and boating. These impacts would occur in both construction and operation.
--yuwei
Edited and reviewed by yingshi on 19/06/2008
--
11/06/08
Public Perception
Public attitudes toward ocean energy technologies are unknown, but clean energy is generally perceived in a positive light because of its environmental and other benefits. Successful demonstration projects and careful siting practices will help ensure public acceptance of these emerging green energy options.
All new and unfamiliar technologies may initially be viewed with skepticism. In addition, concerns have been expressed over the potential impacts of shoreline and nearshore wave energy devices related to aesthetics as well as sediment transport and other physical processes. These and other technologies may also impact recreational and commercial activities.
OVERCOMING 'negative' point number ONE, which is the only one that can be solved at all
Wave energy is already competitive in niche markets, such as remote islands, which are often reliant on expensive (and environmentally detrimental) diesel generators. The development of wave energy alongside other technologies - fish farms, harbour defences, desalination plants or wind farms could further reduce costs. In addition, there are potentially many opportunities for the wave energy sector to collaborate with the wind power industry, both on joint projects (e.g., combined offshore facilities) and by addressing common problems such as connecting the electricity they generate to the National Grid.
--yuwei
--
17/06/08
Challenges
These are some of the challenges to deploying wave power devices:
Efficiently converting wave motion into electricity; generally speaking, wave power is available in low-speed, high forces, and the motion of forces is not in a single direction. Therefore, it is a challenge to ensure most of the wave energy which acts in different directions to be converted to electrical energy. Besides, as solar energy is converted to wind energy and finally to wave energy, much energy is lost to the surroundings in the process of conversion and hence, it is very important to prevent further loss of energy. Most readily-available electric generators operate at higher speeds, and most readily-available turbines require a constant, steady flow.
Constructing devices that can survive storm damage and saltwater corrosion; likely sources of failure include seized bearings, broken welds, and snapped mooring lines. Knowing this, designers may create prototypes that are so overbuilt that materials costs prohibit affordable production.
High total cost of electricity; wave power will only be competitive when the total cost of generation is reduced. The total cost includes the primary converter, the power takeoff system, the mooring system, installation & maintenance cost, and electricity delivery costs.
--yingshi
Edited and reviewed by the same people who wrote it:
26/06/08
Tuesday, May 13, 2008
Uses of wave energy
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13/05/08
Wave energy has yet to be demonstrated as a possibility for large-scale commercial power generation. However, with the rising costs of fossil fuels and increasing environmental concerns, a competitive wave industry, if developed, could be one of the most environmentally benign of the renewables. The most practical application for wave energy in the short to medium term could be on small, remote islands without easy access to fossil fuel shipments or the need for long transmission lines. The potential for these sorts of small but locally important projects seems highest in the UK, where wave power density is high and much of the research is centered. Ocean Power Delivery, the Scottish company that provided the 2.25 MW installation in Portugal, is planning a 3 MW project in Orkney, the small island systems off the north coast of Scotland (OPD 2007). There has also been research into potential uses for wave energy other than electricity, most notably desalinization and hydrogen generation.
Wave energy conversion device for DESALINIZATION
An impulse-type “wave motor” employs a seabed-mounted or supported structure mounting a wave energy absorbing panel on a hinged lever arm for reciprocation motion to obtain optimal absorption of wave energy from wave motion in the sea. For deepwater wavelengths of L, the panel is optimally positioned in a region within L/2 depth from the sea surface. The panel motion is coupled by a connecting rod to a fluid pump which generates a high-pressure fluid output that may be used to drive a reverse osmosis desalination unit or to produce other useful work. Seawater or brackish water may be desalinated through reverse osmosis membranes to produce water quality for consumption, agricultural, or other uses. The submerged operating environment of the device in a region of one-half the design wavelength provides the maximum available energy flux and forced oscillations. The pump may be of the positive-displacement piston type, plunger type, or multi-staging driver type, or a variable volume pump.
(Offshore electrolysis-hydrogen generation unit)
In future commercial applications, hydrogen could be produced offshore at the point of energy generation in a co-located facility, or it could be produced at an onshore location, utilizing the energy generated at the offshore power generation facility. Because all four alternative energy sources under analysis in the OCS Alternative Energy Programmatic EIS are capable of producing electricity, electrolysis is currently the most viable means of producing hydrogen from any of the four alternative energy sources. Electrolysis involves the dissociation of water into hydrogen and oxygen by passing a current through an electrochemical cell, and has been available commercially for decades.
Otherwise, the generated electricity may also be supplied to households in order to power appliances used in daily life, as well as effectively reduce the already large amount of carbon emissions that the particular country is giving out. This an effort to reduce the harm we are doing on Mother Earth can help save up to 10,000 tonnes of carbon dioxide each year.
13/05/08
Wave energy has yet to be demonstrated as a possibility for large-scale commercial power generation. However, with the rising costs of fossil fuels and increasing environmental concerns, a competitive wave industry, if developed, could be one of the most environmentally benign of the renewables. The most practical application for wave energy in the short to medium term could be on small, remote islands without easy access to fossil fuel shipments or the need for long transmission lines. The potential for these sorts of small but locally important projects seems highest in the UK, where wave power density is high and much of the research is centered. Ocean Power Delivery, the Scottish company that provided the 2.25 MW installation in Portugal, is planning a 3 MW project in Orkney, the small island systems off the north coast of Scotland (OPD 2007). There has also been research into potential uses for wave energy other than electricity, most notably desalinization and hydrogen generation.
Wave energy conversion device for DESALINIZATION
An impulse-type “wave motor” employs a seabed-mounted or supported structure mounting a wave energy absorbing panel on a hinged lever arm for reciprocation motion to obtain optimal absorption of wave energy from wave motion in the sea. For deepwater wavelengths of L, the panel is optimally positioned in a region within L/2 depth from the sea surface. The panel motion is coupled by a connecting rod to a fluid pump which generates a high-pressure fluid output that may be used to drive a reverse osmosis desalination unit or to produce other useful work. Seawater or brackish water may be desalinated through reverse osmosis membranes to produce water quality for consumption, agricultural, or other uses. The submerged operating environment of the device in a region of one-half the design wavelength provides the maximum available energy flux and forced oscillations. The pump may be of the positive-displacement piston type, plunger type, or multi-staging driver type, or a variable volume pump.
--seokting
--
13/05/08
Storing and Transporting Energy as HYDROGEN (hydrogen generation)
Offshore wind, solar, and wave energy do not always produce energy at the time at which it is needed. In addition, the energy produced at remote offshore locations using these technologies and ocean current technology must typically be brought to onshore consumers. To address the sporadic nature of energy production from these sources at offshore locations, feasible methods for storing excess energy until it can be used and for transporting it must be developed. Currently, the most attractive approach is the use of hydrogen as a storage medium. Hydrogen can be generated on location on a variety of scales, and it can be stored and transmitted for later consumption in fuel cells in vehicles or converted into electricity. At this time, however, hydrogen is not being used to store or transport energy produced with ocean energy technologies in commercial applications.
HYDROGEN PRODUCTION
(Offshore electrolysis-hydrogen generation unit)
In future commercial applications, hydrogen could be produced offshore at the point of energy generation in a co-located facility, or it could be produced at an onshore location, utilizing the energy generated at the offshore power generation facility. Because all four alternative energy sources under analysis in the OCS Alternative Energy Programmatic EIS are capable of producing electricity, electrolysis is currently the most viable means of producing hydrogen from any of the four alternative energy sources. Electrolysis involves the dissociation of water into hydrogen and oxygen by passing a current through an electrochemical cell, and has been available commercially for decades.
--cassandra
--
06/06/08
But of course, after all that, we still have to come back to the most essential and prominent use of wave energy: the conversion of this kinetic energy into electrical energy!
CONVERSION TO ELECTRICAL ENERGY
During the next 20 years, experts foresee a need for 1500 GW. of additional power supply to meet new demand. This equals to 15000 power plants that are 100 MW each and 59 million barrels of oil consumed in each day. The world Bank estimates that the developing countries alone will need to spend $100 billion each year for the next 30 years installing new power plants most of which will be in the equatorial Zone. These are astronomical figures that could mean enormous quantities of fossil fuel and 2.2 billion tons of CO2 release to the atmosphere per year. Hence, an urgent need to switch to alternate energy. Among the alternate energy resources, wave energy is considered as one of the promising alternate energy resources that has high availability factor (day & night) compare with other resources such as Wind energy or Solar energy.
It has been estimated that if less than 0.1% of the renewable energy available within the oceans could be converted into electricity, it would satisfy the present world demand for energy more than five times over.
Therefore, it is important and worthwhile to conduct experiments on wave energy harnessing techniques to tap the wave power to generate electricity.
The electricity generated in this way (using 'green' energy / renewable sources of energy) is usually used to run large factories and companies, which may otherwise cause the depletion of fossil fuels that are non-renwable. This, therefore, facilitates the progress made by
Otherwise, the generated electricity may also be supplied to households in order to power appliances used in daily life, as well as effectively reduce the already large amount of carbon emissions that the particular country is giving out. This an effort to reduce the harm we are doing on Mother Earth can help save up to 10,000 tonnes of carbon dioxide each year.
--yuwei
Edited and reviewed by the people who wrote it:
21/06/08
Friday, May 2, 2008
Ocean Wave Energy Technologies / Devices used to harness wave energy and often, convert into electrical energy
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02/05/08
A variety of technologies have been proposed to capture the energy from waves. Some of the more promising designs are undergoing demonstration testing at commercial scales.
Wave technologies have been designed to be installed in nearshore, offshore, and far offshore locations. The OCS Alternative Energy Programmatic EIS is concerned primarily with offshore and far offshore wave technologies. Offshore systems are situated in deep water, typically of more than 40 meters (131 feet).
While all wave energy technologies are intended to be installed at or near the water's surface, they differ in their orientation to the waves with which they are interacting and in the manner in which they convert the energy of the waves into other energy forms, usually electricity. The following wave technologies have been the target of recent development.
Terminator devices extend perpendicular to the direction of wave travel and capture or reflect the power of the wave. These devices are typically onshore or nearshore; however, floating versions have been designed for offshore applications. 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 to force the air though an opening connected to a turbine. Oscillating Water Columns are partially submerged, hollow structures open to the seabed below the water line. The heave motion of the sea surface alternatively pressurizes and depressurizes the air inside the structure generating a reciprocating flow through a turbine installed beneath the roof of the device.
A point absorber is a floating structure with components that move relative to each other due to wave action (e.g., a floating buoy inside a fixed cylinder). The relative motion is used to drive electromechanical or hydraulic energy converters.
24/05/08
• Heaving devices (floating or submerged), which provide a heave motion that is converted by mechanical and hydraulic systems in linear or rotational motion for driving electrical generators.
• Pitching devices that consist of a number of floating bodies, hinged together across their beams. The relative motions between the floating bodies are used to pump high-pressure oil through hydraulic motors, which drive electrical generators.
• Surging devices that 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.
An economically viable design with a simple geometrical construction but strong enough to withstand against the waves with different heights and different wave periods and directions is essential. The design would usually consist of a rectangular chamber and a pyramidal top which is installed on top of the chamber. A conical duct is erected on the pyramidal top to reciprocally move the air from the chamber and into the chamber during the process of wave approach and wave leaves the chamber. A turbine which is mounted on top of the duct is subjected to turn in one direction as the airflow moves bi-directional. A generator is coupled to the turbine that produces electricity by rotating it's armature shaft which is coupled with the turbine shaft.
02/05/08
A variety of technologies have been proposed to capture the energy from waves. Some of the more promising designs are undergoing demonstration testing at commercial scales.
Wave technologies have been designed to be installed in nearshore, offshore, and far offshore locations. The OCS Alternative Energy Programmatic EIS is concerned primarily with offshore and far offshore wave technologies. Offshore systems are situated in deep water, typically of more than 40 meters (131 feet).
While all wave energy technologies are intended to be installed at or near the water's surface, they differ in their orientation to the waves with which they are interacting and in the manner in which they convert the energy of the waves into other energy forms, usually electricity. The following wave technologies have been the target of recent development.
Terminator devices extend perpendicular to the direction of wave travel and capture or reflect the power of the wave. These devices are typically onshore or nearshore; however, floating versions have been designed for offshore applications. 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 to force the air though an opening connected to a turbine. Oscillating Water Columns are partially submerged, hollow structures open to the seabed below the water line. The heave motion of the sea surface alternatively pressurizes and depressurizes the air inside the structure generating a reciprocating flow through a turbine installed beneath the roof of the device.
A point absorber is a floating structure with components that move relative to each other due to wave action (e.g., a floating buoy inside a fixed cylinder). The relative motion is used to drive electromechanical or hydraulic energy converters.
..
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Attenuators are long multisegment floating structures oriented parallel to the direction of the waves. The differing heights of waves along the length of the device causes flexing where the segments connect, and this flexing is connected to hydraulic pumps or other converters.
Overtopping devices have reservoirs that are filled by incoming waves to levels above the average surrounding ocean. The water is then released, and gravity causes it to fall back toward the ocean surface. The energy of the falling water is used to turn hydro turbines. Specially built seagoing vessels can also capture the energy of offshore waves. These floating platforms create electricity by funneling waves through internal turbines and then back into the sea.
--seokting
Edited and reviewed by: yuwei, 15/06/08
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24/05/08
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There are many wave energy conversion techniques patented worldwide. Some main concepts for wave energy converters can be classified within a few basic types:
• Heaving devices (floating or submerged), which provide a heave motion that is converted by mechanical and hydraulic systems in linear or rotational motion for driving electrical generators.
• Pitching devices that consist of a number of floating bodies, hinged together across their beams. The relative motions between the floating bodies are used to pump high-pressure oil through hydraulic motors, which drive electrical generators.
• Surging devices that 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.
An economically viable design with a simple geometrical construction but strong enough to withstand against the waves with different heights and different wave periods and directions is essential. The design would usually consist of a rectangular chamber and a pyramidal top which is installed on top of the chamber. A conical duct is erected on the pyramidal top to reciprocally move the air from the chamber and into the chamber during the process of wave approach and wave leaves the chamber. A turbine which is mounted on top of the duct is subjected to turn in one direction as the airflow moves bi-directional. A generator is coupled to the turbine that produces electricity by rotating it's armature shaft which is coupled with the turbine shaft.
--yuwei
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