Atau seperti gelap gulita di lautan yang dalam, yang diliputi oleh ombak, yang di atasnya ombak (pula), di atasnya (lagi) awan; gelap gulita yang tindih-bertindih, apabila dia mengeluarkan tangannya, tiadalah dia dapat melihatnya, (dan) barangsiapa yang tiada diberi cahaya (petunjuk) oleh Allah tiadalah dia mempunyai cahaya sedikitpun. An-Nuur (24) : 40

Kamis, 08 November 2012

Wave power formula

Wave power
Wave power is the transport of energy by ocean surface waves, and the capture of that energy is to do useful work – for example, electricity generationwater desalination, or the pumping of water (into reservoirs). Machinery able to exploit wave power is generally known as a wave energy converter (WEC).

Wave power is distinct from the diurnal flux of tidal power and the steady gyre of ocean currents. Wave-power generation is not currently a widely employed commercial technology, although there have been attempts to use it since at least 1890.[1] In 2008, the first experimental wave farm was opened in Portugal, at the Aguçadoura Wave Park.[2] The major competitor of wave power is offshore wind power.

Physical concepts
Waves are generated by wind passing over the surface of the sea. As long as the waves propagate slower than the wind speed just above the waves, there is an energy transfer from the wind to the waves. Both air pressure differences between the upwind and the lee side of a wave crest, as well as friction on the water surface by the wind, making the water to go into the shear stress causes the growth of the waves.[4]
Wave height is determined by wind speed, the duration of time the wind has been blowing, fetch (the distance over which the wind excites the waves) and by the depth and topography of the seafloor (which can focus or disperse the energy of the waves). A given wind speed has a matching practical limit over which time or distance will not produce larger waves. When this limit has been reached the sea is said to be "fully developed".
In general, larger waves are more powerful but wave power is also determined by wave speed, wavelength, and water density.
Oscillatory motion is highest at the surface and diminishes exponentially with depth. However, for standing waves (clapotis) near a reflecting coast, wave energy is also present as pressure oscillations at great depth, producing microseisms.[4] These pressure fluctuations at greater depth are too small to be interesting from the point of view of wave power.
The waves propagate on the ocean surface, and the wave energy is also transported horizontally with the group velocity. The mean transport rate of the wave energy through a vertical plane of unit width, parallel to a wave crest, is called the wave energy flux (or wave power, which must not be confused with the actual power generated by a wave power device).

Wave power formula
In deep water where the water depth is larger than half the wavelength, the wave energy flux is[a]

with P the wave energy flux per unit of wave-crest length, Hm0 the significant wave height, T the wave period, ρ the water density and g theacceleration by gravity. The above formula states that wave power is proportional to the wave period and to the square of the wave height. When the significant wave height is given in meters, and the wave period in seconds, the result is the wave power in kilowatts (kW) per meter of wavefront length.[5][6][7]
Example: Consider moderate ocean swells, in deep water, a few kilometers off a coastline, with a wave height of 3 meters and a wave period of 8 seconds. Using the formula to solve for power, we get


meaning there are 36 kilowatts of power potential per meter of wave crest.
In major storms, the largest waves offshore are about 15 meters high and have a period of about 15 seconds. According to the above formula, such waves carry about 1.7 MW of power across each meter of wavefront.
An effective wave power device captures as much as possible of the wave energy flux. As a result the waves will be of lower height in the region behind the wave power device.

Wave energy and wave-energy flux
In a sea state, the average energy density per unit area of gravity waves on the water surface is proportional to the wave height squared, according to linear wave theory:[4][8]

where E is the mean wave energy density per unit horizontal area (J/m2), the sum of kinetic and potential energy density per unit horizontal area. The potential energy density is equal to the kinetic energy,[4] both contributing half to the wave energy density E, as can be expected from the equipartition theorem. In ocean waves, surface tension effects are negligible for wavelengths above a few decimetres.
As the waves propagate, their energy is transported. The energy transport velocity is the group velocity. As a result, the wave energy flux, through a vertical plane of unit width perpendicular to the wave propagation direction, is equal to:[10][4]


with cg the group velocity (m/s). Due to the dispersion relation for water waves under the action of gravity, the group velocity depends on the wavelength λ, or equivalently, on the wave period T. Further, the dispersion relation is a function of the water depth h. As a result, the group velocity behaves differently in the limits of deep and shallow water, and at intermediate depths:[4][8]

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Australia’s Waves Could Power the Country

wave energy

It is estimated that harnessing a small portion of marine energy could solve the world’s energy crisis to a great extent, and Australia’s vast coastline alone is estimated to hold the potential to produce four times the nation’s power needs, claims a new report by energy experts GlobalData.

The new report* states that the Southern Ocean is considered one of the most consistent sources of wave energy in the world, and Australia has been busy in the marine energy market over recent years in efforts to benefit from this.

The Renewable Energy Target (RET) set by the Australian government aims to generate 20% (approximately 45,000 GWh) of Australia’s electricity from renewable sources by 2020. Harnessing the power of the oceans can help Australia to reach its targets and meet energy demands more effectively.

The Western Australian state government is offering $10m in grants for the development of sustainable low-emission technologies to reduce Western Australia’s greenhouse gas emissions. Australia’s Renewable Energy Development Program (REDP) has also pledged $435m to accelerate the commercialization and deployment of renewable energy technologies, which include ocean energy.

Port MacDonnell in South Australia, Portland, Warrnambool and Philip Island in Victoria, Albany and Geraldton in Western Australia, and parts of the Tasmanian and New South Wales coastlines are optimal sites for wave energy plants in Australia. Most of the projects currently under development are based around Tasmania and Victoria.

Companies in Australia are conducting R&D activities to develop financially viable marine energy technology in order to move close to commercialization, with Oceanlinx and Carnegie Corporation installing demonstration projects in Australia. In Australia, many universities are engaged in developing marine technology, including the Water Research Laboratory in the University of New South Wales, the Australian Maritime College in the University of Tasmania, the University of Wollongong and the University of Sydney.

The kinetic energy of the tides along the Australia coasts has an estimated 678 gigawatt-hours (GWh) of power generation potential, with Western Australia and Queensland ruling with potential 415 GWh and 126 GWh respectively. The waves along the Australian coasts have an estimated 963 GWh of kinetic power generation potential, with Western Australia once again providing the most promise.

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Scotland Unveils Marine Energy Park

Pentland Firth and Orkney Waters

The Pentland Firth and Orkney Waters in the North of Scotland have confirmed their place on the global marine energy map with the launch of the area as a Marine Energy Park.   UK Energy and Climate Change Minister Greg Barker will welcome the launch of the marine park during a visit to Thurso in Caithness, where he is set to address key players from across the marine renewable energy industry.

The Pentland Firth and Orkney Waters Marine Energy Park will incorporate the world-leading European Marine Energy Centre (EMEC) which attracts developers from across the world and where testing of a wide range of wave and tidal energy devices is already under way.

The purpose of the park is to heighten the international profile of the region and its reputation as a world leader in marine energy. The park will build on collaborative partnerships in the region between government on the main land and the Orkney Islands, Highlands and Islands Enterprise(HIE), plus a cluster of local expertise and renewable resource in the area, to help speed up progress of marine power development.

Energy from waves or tides has the potential to generate 27GW of power in the UK alone by 2050, equivalent to the power generated from eight coal fired power stations. A move to marine power can also help cut emissions and tackle climate change.
Energy and Climate Change Minister Greg Barker said:
“It’s great to see Pentland Firth and Orkney Waters confirm their place on the marine power map with the launch of the second of the Coalition Government’s UK Marine Energy Parks. “This area is already a vital part of the marine industry, thanks to its high tidal stream and wave resource. This stretch of water is also home to the European Marine Energy Centre, currently unrivalled anywhere else in the world. This park will help bring together local knowledge and expertise to spur on further development in this exciting industry. “Marine power is a growing green clean source of power which has the potential to sustain thousands of jobs in a sector worth a possible £15bn to the economy by 2050. “The UK is already a world leader in wave and tidal power and we need to really capitalise on this to ensure energy from marine reaches its full potential in our future energy mix.”

Highlands and Islands Enterprise chairman Lorne Crerar said:
“We are delighted that the region’s role in the development of the marine energy sector is being recognised nationally and internationally. “The designation as a marine energy park further promotes the Highlands and Islands of Scotland as a marine energy hub, and will accelerate investment and the industry’s ambition for commercialisation of the technologies being tested here.”

Convener of Orkney Islands Council, Councillor Steven Heddle said:
“The launch of the Marine Energy Park formalises the leading role that the waters around Orkney have already played in the development of marine energy.
“The test sites of the European Marine Energy Centre in Orkney have established it as a world-leading facility in the testing and certification of marine energy devices, allowing a competitive advantage for a new UK industry.
“The development of EMEC, supported by investment from the Orkney Islands Council, has led to the growth of a local supply chain and technical expertise geared towards marine renewables which is second to none.
“Further investment by the Council in piers and onshore facilities with huge growth potential at Lyness, Hatston and Stromness – already rewarded by significant activity and employment – shows our confidence in the successful commercialisation of marine renewables and offshore wind, and in our ability to service these activities.
“We welcome the launch of the Marine Energy Park, and look forward to working with our partners to drive development and economic prosperity for our communities.”
Leader of the Highland Council, Councillor Drew Hendry said:
“The Highland Council has been a key partner in the Pentland Firth & Orkney Waters wave and tidal programme since its earliest days, so we welcome this further recognition of the international significance of the marine resources in the north.
“We are particularly pleased to see the launch of the Marine Energy Park at the new state-of-the-art Engineering, Technology & Energy Centre in Thurso, where the next generation of marine engineers and technicians are already being developed. Together with our partners we continue to support the growth potential of marine energy for the economy of our area.”

The Pentland Firth and Orkney Waters is already a vital part of the UK’s growing marine sector and is home to some of the best wave and tidal resource in the country as well as home grown marine expertise.

This stretch of water is also the site of the world’s first commercial scale leasing round for marine energy. As announced by the Crown Estate (TCE) in 2010, there are 11 successful bidders for sites in Scotland’s Pentland Firth and Orkney waters. Up to 1.6 GW (600 MW from wave and 1000MW from tidal stream) proposed by the developers involved in this leasing round, could, if developed to full capacity, meet the electricity needs of up to three quarters of a million homes.

Scrabster Harbour in Thurso is already expanding its facilities in light of the growing role of offshore energy in the area. Under its “three ports strategy”, Orkney Islands Council is investing in new and upgraded pier and quayside facilities at Lyness, Hatston and Stromness – providing support facilities at key strategic locations for the marine energy industry.

The first UK marine energy park, in South West England, was launched in January this year by Energy and Climate Change Minister Greg Barker.

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