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How Does Ocean Wave Power Work?

Ocean waves are both clean and renewable sources of energy with a tremendous worldwide potential of generating electricity. If fully exploited, about 40% of the world's power demand could be supplied by this resource - equivalent to as much as 800 nuclear power plants.

What is Wave Energy?

Some of the kinetic (motional) energy in the wind is transformed into waves once the wind hits the ocean surface. Wind energy ultimately forms due to solar energy and its influence on high and low pressure. This is the reason why wave as well as wind power are considered renewable energy sources.

The density of the energy that is transported under the waves under the ocean surface is about five times higher compared to the wind energy 20 meter (about 65 feet) above. In other words, the amount of energy in a single wave is very high.

How Does Wave Power Work?

In 2001, more than 1000 different methods of utilization of wave energy had been patented by many different wave energy companies, most of which never even made it past the first few stages. Only a few of these projects have been shown to work in reality. The following are the three main methods that look most promising:

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Oscillating Water Column (OWC)
An oscillating water column is partially lowered into water. It is open below the surface line with a hollow upper part filled with air. The water level within the water column increases and decreases with waves coming in resulting in compression and decompression of air. Wells-turbines are ideal for the purpose of converting this into energy, because the turbines rotate the same way independent of the direction of the airflow. A generator converts this mechanical energy into useful electricity.
Surface-following attenuator (Line Absorber)
The point absorber consists of a series of long unit, floating on the surface of the water following the movements of the wave. It is this movement that is harnessed and converted to electricity in the point absorber.

A Scottish company, Pelamis Wave Power (previously known as Ocean Power Delivery), has installed a successful 2.5 MW wave farm Aguçadoura of the coast of Portugal. This wave power plant was opened in September 2008. Below is a picture of one of the Pelamis Wave Energy Converters that is the foundation of Aguçadoura, maybe the most promising device to harness wave energy so far.

This device looks like a sea snake in the water. It consists of a series of joints that generate power as the waves move them up and down through hydraulic rams and a generator. An underwater cable moves the electricity to the shore.
Buoyancy Unit/Point Absorber
The buoyancy unit is floating on the waves or below the water surface, fixed to the bottom, following the vertical movements of the waves up and down. These waves drive a pump that generates electricity.

The power generation of a typical ocean wave energy unit is about 1 MW, but we expect this output to get better along with the wave energy technology.

After several years with low activity around marine energy technologies, the need for renewable energy has pushed the interest for these technologies forward. Some countries have invested more than others when it comes to developing these methods. Britain and Portugal are currently the leading nations when it comes to ocean wave energy conversion, but several other countries are starting to grasp the potential of harnessing wave energy as well.

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How Does Ocean Wave Power Work? - Energy Informative

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Ocean waves are both clean and renewable sources of energy with a tremendous worldwide potential of generating electricity. If fully exploited, about 40% of the world's power demand could be supplied by this resource - equivalent to as much as 800 nuclear power plants. What is Wave Energy?

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Wave energy is as source of power that comes from the endless march of the waves as they roll into the shore then back out again. Humans harness this power along the coastal regions of the United States, Canada, Scotland, and Australia. Energy that comes from the waves in the ocean sounds like a boundless, harmless supply. But is it without its drawbacks? Lets take a look.

Advantages of Wave Energy

1. Renewable: The best thing about wave energy is that it will never run out. There will always be waves crashing upon the shores of nations, near the populated coastal regions. The waves flow back from the shore, but they always return. Unlike fossil fuels, which are running out, in some places in the world, just as quickly as people can discover them. Unlike ethanol, a corn product, waves are not limited by a season. They require no input from man to make their power, and they can always be counted on.

2. Environment Friendly: Also unlike fossil fuels, creating power from waves creates no harmful byproducts such as gas, waste, and pollution. The energy from waves can be taken directly into electricity-producing machinery and used to power generators and power plants nearby. In today's energy-powered world, a source of clean energy is hard to come by.

3. Abundant and Widely Available :Another benefit to using this energy is its nearness to places that can use it. Lots of big cities and harbors are next to the ocean and can harness the power of the waves for their use. Coastal cities tend to be well-populated, so lots of people can get use from wave energy plants.

4. Variety of Ways To Harness : A final benefit is that there are a variety of ways to gather it. Current gathering methods range from installed power plant with hydro turbines to seafaring vessels equipped with massive structures that are laid into the sea to gather the wave energy.

5. Easily Predictable : The biggest advantages of wave power as against most of the other alternative energy sources is that it is easily predictable and can be used to calculate the amount that it can produce. The wave energy is consistent and proves much better than other sources which are dependent on wind or sun exposure.

6. Less Dependency on Foreign Oil Cos : Dependence on foreign companies for fossil fuels can be reduced if energy from wave power can be extracted up to its maximum. Not only it will help to curb air pollution but can also provide green jobs to millions of people.

7. No Damage to Land : Unlike fossil fuels which cause massive damage to land as they can leave large holes while extracting energy from them , wave power does not cause any damage to earth. It is safe, clean and one of the preferred method to extract energy from ocean.

Disadvantages of Wave Energy

But wait, there's- more to it than just a source of clean energy. It has its drawbacks as well.

1. Suitable to Certain Locations : The biggest disadvantage to getting your energy from the waves is location. Only power plants and towns near the ocean will benefit directly from it. Because of its source, wave energy is not a viable power source for everyone. Landlocked nations and cities far from the sea have to find alternate sources of power, so wave energy is not the clean energy solution for everyone.

2. Effect on marine Ecosystem : As clean as wave energy is, it still creates hazards for some of the creatures near it. Large machines have to be put near and in the water to gather energy from the waves. These machines disturb the seafloor, change the habitat of near-shore creatures (like crabs and starfish) and create noise that disturbs the sea life around them. There is also a danger of toxic chemicals that are used on wave energy platforms spilling and polluting the water near them.

3. Source of Disturbance for Private and Commercial Vessels : Another downside is that it disturbs commercial and private vessels. Power plants that gather wave energy have to be placed by the coastline to do their job, and they have to be near cities and other populated areas to be of much use to anybody. But these are places that are major thoroughfares for cargo ships, cruise ships, recreational vehicles and beach goers. All of these people and vessels will be disrupted by the installation of a wave energy gathering source. This means that government officials and private companies that want to invest in wave energy sources have to take into account and consider the needs of those they may be disturbing.

4. Wavelength : Wind power is highly dependent on wavelength i.e. wave speed, wave length, wavelength and water density. They require a consistent flow of powerful waves to generate significant amount of wave power. Some areas experience unreliable wave behavior and it becomes unpredictable to forecast accurate wave power and therefore cannot be trusted as reliable energy source.

5. Weak Performance in Rough Weather : The performance of wave power drops significantly during rough weather. They must withstand rough weather.

6. Noise and Visual pollution : Wave energy generators may be unpleasant for some who live close to coastal regions. They look like large machines working in the middle of the ocean and destroy the beauty of the ocean. They also generate noise pollution but the noise is often covered by the noise of waves which is much more than that of wave generators.

None of this is to say that wave energy cannot be useful, but those interested in using it to create power have to look at both sides of the equation. They should consider the positives and negatives of this new energy source and consider who and what they may be disturbing. Who knows what the future holds for this newly-discovered energy source.

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Advantages and Disadvantages Of Wave Energy

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Wave energy is as source of power that comes from the endless march of the waves as they roll into the shore then back out again. Energy that comes from the waves in the ocean sounds like a boundless, harmless supply

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Why Wave Power has Lagged Behind as Energy Source

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Why Wave Power has Lagged Behind as Energy Source

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Innovation

Researchers have long contended that power from ocean waves could make a major contribution as a renewable energy source. But a host of challenges, including the difficulty of designing a device to capture the energy of waves, have stymied efforts to generate electricity from the sea.

It's not difficult to imagine what wind energy looks like - by this point we have all seen the towering turbines dotting the landscape. The same goes for solar power and the panels that are spreading across rooftops worldwide. But there is another form of renewable energy, available in huge quantities, that doesn't really call to mind anything at all: What does wave power technology look like?

Wind and solar power have taken off in the past decade or two, as costs have come down rapidly and threats from climate change have made clear the need to transition away from fossil fuels. Meanwhile, numerous studies have concluded that wave power - and to a lesser extent, tidal power - could contribute massive amounts to the overall energy picture. But while the industry has made halting progress, experts agree that it remains decades behind other forms of renewables, with large amounts of money and research required for it to even begin to catch up.

No commercial-scale wave power operations now exist, although a small-scale installation did operate off the coast of Portugal in 2008 and 2009. In February, U.S. corporate giant Lockheed Martin announced a joint venture to create the world's biggest wave energy project, a 62.5-megawatt installation slated for the coast of Australia that would produce enough power for 10,000 homes. Scotland, surrounded by the rough waters of the Atlantic and the North Sea, has become a hotbed of wave-energy research and development, with the government last year approving a 40-megawatt wave energy installation in the Shetland Islands.

But a central challenge has proven to be the complexity of harnessing wave power, which has led to a host of designs, including writhing snake-like attenuators, bobbing buoys, even devices mounted discreetly on the ocean floor that work by exploiting differences in pressure as a wave passes by. Some devices generate the electricity on the spot and transmit it via undersea cables to shore, while others pass the mechanical energy of the wave along to land before turning it into electrical energy. Which of these drastically divergent concepts might emerge as a winner is far from clear.

"We may not have even invented the best device yet," said Robert Thresher, a research fellow at the National Renewable Energy Laboratory.

From a technical point of view, operating in the ocean is far more difficult than on land; building offshore wind installations, for example, tends to be significantly more expensive than constructing wind farms onshore. Saltwater is a hostile environment for devices, and the waves themselves offer a challenge for energy harvesting as they not only roll past a device but also bob up and down or converge from all sides in confused seas. This provides enticing opportunities for energy capture, but a challenge for optimum design.

"I'd like to be optimistic, but I don't think realistically I can be," said George Hagerman, a research associate in the Virginia Tech University's Advanced Research Institute and a contributor to the U.S. Department of Energy's assessment of wave energy's potential. "You've got all those cost issues of working in the ocean that offshore wind illustrates, and then you've got [an energy] conversion technology that really no one seems to have settled on a design that is robust, reliable, and efficient. With wind, you're harnessing the energy as a function of the speed of the wind. In wave energy, you've not only got the height of the wave, but you've got the period of the wave, so it becomes a more complicated problem."

A theme among wave power experts is that wave energy is where wind energy was three decades ago.

A recurring theme among wave power experts is that wave energy is where wind energy was three decades ago. At that time, engineers had not settled on the optimal design for wind turbines, but decades of ensuing research have resulted in highly sophisticated turbine designs. With wave power, some research occurred after the Arab oil embargo of the 1970s, but since then government and commercial research and development into wave power has paled compared to wind and solar energy.

As with any energy source, the fundamental roadblock toward more widespread deployment is cost. So far, the wave energy field is filled with small companies picking off small amounts of government funding where they can. It will likely require the participation of some large companies, such as GE or Siemens (both major manufacturers of wind turbines) before wave power really gets rolling, according to numerous experts. Those companies may be waiting for the technology to sort itself out before investing, a common dilemma in any nascent field.

In spite of the challenges inherent to the medium, the industry is progressing, albeit slowly. There are a few small wave farms and pilot projects in the water, including Pelamis Wave Power's first-ever wave farm off the coast of Northern Portugal. That company has a few megawatt-scale wave farms planned, while others, like Ocean Power Technologies, continue to deploy test devices to improve buoy-based technology.

Australian company Carnegie Wave plans to commission a "commercial scale" installation near Perth later this year, using a fully submerged device that uses wave power to pump water to shore for conversion to electricity. And there are signs that big-company buy-in is starting, as evidenced by Lockheed Martin's Australia project, which will use a buoy technology that generates electricity from the rising and falling of waves.

Another company, M3 Wave, plans to install a new device just off the Oregon coast this summer. M3 will be using a pressure-based device, sitting out of sight on the ocean floor. As a wave passes over it, air inside the device is pushed by pressure changes from one chamber to another, spinning a turbine to generate electricity.

So far, projects producing only a handful of megawatts have actually made it into the water, but experts say the industry needn't settle on one device before substantial progress occurs.

"I wouldn't be surprised if what we eventually find is there will be a device that we use in deeper water, and a device that we use nearer the shore," said Belinda Batten, a professor at Oregon State University and the director of the Northwest National Marine Renewable Energy Center.

The process to refine those technologies is ongoing. The European Marine Energy Centre in Scotland's Orkney Islands allows companies to connect their devices to existing infrastructure and cabling to test their electricity-generating capabilities and identify problems. Batten said her center based at Oregon State is in the permitting and approval process for a counterpart testing center that will enable companies to connect to the existing electricity grid for testing purposes.

The Pacific Northwest and Alaska will likely have a monopoly on the first U.S. wave projects.

The location of those two testing sites is no accident, as they are situated in maritime regions known for energetic waves. The Pacific Northwest and Alaska will likely have a monopoly on the U.S.'s first generation of wave projects, while in Europe the United Kingdom - Scotland in particular - is focusing heavily on wave energy development. The U.K. government says the country could potentially get as much as 75 percent of its energy needs from the waves and tides combined; the U.S. Department of Energy, meanwhile, estimates that wave power in the U.S. could generate as much 1,170 terawatt-hours per year, which is equivalent to more than one quarter of all U.S. electricity consumption.

Thresher of the National Renewable Energy Laboratory says that wave power's first markets may well be in remote places like Alaska, where energy is expensive because of reliance on costly imported fuels like diesel. "There has been an interest in some of the island communities," Thresher said.

With the industry starting to develop larger projects and continuing to test myriad devices in search of the best designs, does that mean wave power could finally be on its way, just as wind was 25 years ago?

Jason Busch, executive director of the Oregon Wave Energy Trust - a non-profit group dedicated to helping advance the industry - said that there are too many variables, such as the price of natural gas or eventual passage of a carbon tax, to apply the experience of wind or solar power to a different technology and time period.

"In my opinion the biggest issue is the failure to price carbon," said Busch. "As long as we refuse to internalize the cost of greenhouse gases, then we're playing on an unlevel playing field."

In spite of the hurdles, though, he thinks that steady technical progress will lead to substantial amounts of grid-connected wave power by 2035. "In the course of 10 years we have gone from having zero wave energy technologies that are even remotely viable to having several in the water, and on the cusp of commercial viability," Busch said. "We're making some really good progress."

Gallery: Click images to enlarge

Dave Levitan is a freelance journalist based in Philadelphia who writes about energy, the environment, and health. His articles have been published by Reuters, SolveClimate, IEEE Spectrum, and Psychology Today. More →

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Why Wave Power Has Lagged Far Behind as Energy Source

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Researchers have long contended that power from ocean waves could make a major contribution as a renewable energy source. But a host of challenges, including the difficulty of designing a device to capture the energy of waves, have stymied efforts to generate electricity from the sea.

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Making Waves: Turning Ocean Power into Electricity

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Making Waves: Turning Ocean Power into Electricity

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Ocean waves have vast energy potential. The Electric Power Research Institute estimates the total wave energy resource along the United States coastline at 2,640 terawatt-hours per year (TWh/yr). One TWh/yr can supply more than 93,000 typical U.S. homes with power annually.

That potential hasn't escaped the notice of ocean engineers, especially Reza Alam, an assistant professor of mechanical engineering at Berkeley since 2011. His research into how muddy seabeds absorb wave energy led him to explore how a mechanical device might convert that energy into electricity.

Visiting graduate student Marcus Lehmann joined Alam's Theoretical and Applied Fluid Dynamics Laboratory in 2012. Based on Alam's research, Lehmann began designing a wave energy conversion device, now called the Wave Carpet. Four years later, the Wave Carpet team is moving from theory to practice.

Problem

Harnessing wave power is more complex than the process of converting other renewable energy sources like wind or sun into electricity. Wave heights and frequencies can vary wildly over time and from one shoreline to another. Seawater is highly corrosive. And storms can turn reliable and predictable waves into machinery-destroying battering rams.

The energy market is an equally extreme environment. To survive it, commercial wave energy converters, which the Wave Carpet is on track to become, must produce electricity at a cost equal to, or lower than, that of fossil fuels or more established renewables like solar and wind.

Solution

Alam's research first examined how human-modified sea floors could mimic the ability of muddy shoreline seabeds to dampen and absorb ocean wave energy. Alam then began considering how a synthetic seabed might harness that wave power to produce electricity, and this research led Lehmann to eventually develop the Wave Carpet.

A flexible membrane that runs the length of each Wave Carpet undulates in response to passing waves, absorbing much of their energy, just as muddy sea floors do.

Fastened to the membrane are a series of vertical double-action pumps. When flexed by wave energy, the membrane drives the pumps to pressurize and push seawater through a shared discharge pipe. The water gushing through that pipe powers a shore-based turbine that can generate electricity, drive a desalination plant, or do both.

The Wave Carpet is also designed to survive tough ocean conditions. It's built of corrosion-resistant materials, operates submerged and thus sheltered from storm conditions, and sits far enough below the waterline to eliminate most surface collision danger.

An average device will measure about 30 feet long by 30 feet wide and about 3-10 feet high, depending on local conditions, says Alam. Several devices can also be sited together on one shoreline to power one or more turbines.

Result

The team filed to patent the Wave Carpet in 2012. In 2014, with support from Alam and the CITRIS Foundry, Lehmann led the effort to land a two-year, $500,000 grant - under the name CalWave - from Berkeley Lab's clean energy incubator, Cyclotron Road, to support continued work on the wave energy converter. Alam also arranged support from Berkeley's civil and environmental engineering department, including access to the O'Brien Hall wave tank.

The Wave Carpetters are currently hip-deep in the Department of Energy's prestigious 20-month wave energy design competition. After successfully completing a 1/50-scale tank test of its device in January, the team received the highest score of nine finalists. Finalists receive seed money to develop 1/20-scale models to be tested this summer at the nation's most advanced wave-making facility, the football field-sized Naval Surface Warfare Center's Maneuvering and Seakeeping Basin in Maryland.

Lehmann says the team plans to put a demonstration device in the sea later this year.

Topics: Civil engineering, Design, Devices & inventions, Energy, Environment, Infrastructure

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Making waves: Turning ocean power into electricity

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Ocean waves have vast energy potential. The Electric Power Research Institute estimates the total wave energy resource along the United States coastline at 2,640 terawatt-hours per year (TWh/yr). One TWh/yr can supply more than 93,000 typical U.S. homes with power annually.

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Wave Energy using the Power of the Waves

Wave Energy also known as Ocean Wave Energy, is another type of ocean based renewable energy source that uses the power of the waves to generate electricity. Unlike tidal energy which uses the ebb and flow of the tides, wave energy uses the vertical movement of the surface water that produce tidal waves. Wave power converts the periodic up-and-down movement of the oceans waves into electricity by placing equipment on the surface of the oceans that captures the energy produced by the wave movement and converts this mechanical energy into electrical power.

Wave energy is actually a concentrated form of solar power generated by the action of the wind blowing across the surface of the oceans water which can then be used as a renewable source of energy. As the suns rays strike the Earth's atmosphere, they warm it up. Differences in the temperature of the air masses around the globe causes the air to move from the hotter regions to the cooler regions, resulting in winds.

As the wind passes over the surface of the oceans, a portion of the winds kinetic energy is transferred to the water below, generating waves. In fact, the ocean could be viewed as a vast storage collector of energy transferred by the sun to the oceans, with the waves carrying the transferred kinetic energy across the surface of the oceans. Then we can say that waves are actually a form of energy and it is this energy and not water that moves along the ocean's surface.

These waves can travel (or "propagate") long distances across the open oceans with very little loss in energy, but as they approach the shoreline and the depth of the water becomes shallower, their speed slows down but they increase in size. Finally, the wave crashes onto the shoreline, releasing an enormous amount of kinetic energy which can be used for electricity production. A breaking waves energy potential varies from place to place depending upon its geographic location and time of year, but the two main factors which affect the size of the wave energy are the winds strength and the uninterrupted distance over the sea that the wind can blow.

Then we can say that "Wave Energy" is an indirect form of wind energy that causes movement of the water on the surface of the oceans and by capturing this energy the motion of the waves is converted to mechanical energy and used to drive an electricity generator. In many respects, the technology used for capturing this wave energy is similar to tidal energy or hydroelectric power.

The kinetic energy of the wave turns a turbine attached to a generator, which produces electricity. However, the open oceans can be a stormy and violent environment, resulting in the wave energy machines being destroyed by the very energy they were designed to capture.

In its simplest terms, an ocean wave is the up-and-down vertical movement of the sea water which varies sinusoidally with time. This sinusoidal wave has high points called crests and low points called troughs. The difference in height of a wave between the crest and the trough is called the peak-to-peak amplitude, then the waves amplitude or height is the centre of these two points and corresponds to the actual sea level when there is no movement of the water, in other words, a calm sea.

The amplitude of an ocean wave depends on the weather conditions at that time, as the amplitude of a smooth wave, or swell, will be small in calm weather but much larger in stormy weather with strong gales as the sea water moves up and down.

As well as the amplitude of the wave, another important characteristic is the distance between each successive crest, or trough, known as the wave period, ( T ). This wave period is the time in seconds between each crest of the wave. Then for a gentle swell this time period may be very long, but for a stormy sea this time period may be very short as each wave crashes onto the one in front.

The reciprocal of this time ( 1/T ) gives us the fundamental frequency of the ocean wave relative to some static point. Smaller periodic waves generated or superimposed onto this fundamental wave such as reflected waves are called harmonic waves. Then the frequency and amplitude characteristics of a wind-generated wave depend on the distance the wind blows over the open water (called the fetch), the length of time the wind blows, the speed of the wind and the water depth.

Waves transport energy from where they were created by storms far out in the ocean to a shoreline. But a typical ocean wave does not resemble a perfect sinusoid, they are more irregular and complex than a simple sinusoidal wave. Only the steady up-and-down movement of a heavy swell resembles a sinusoidal wave much more than the chaotic nature of locally generated wind waves, as real sea waves contain a mixture of waves with different frequencies, wave heights and directions.

Wave Power Devices

Ocean wave energy has many advantages over ocean wind energy in that it is more predictable, less variable and offers higher available energy densities. Depending on the distance between the energy conversion device and the shoreline, wave energy systems can be classified as being either Shoreline devices, Nearshore devices or Offshore devices. So what is the difference between these three types of energy extraction devices.

Shoreline devices are wave energy devices which are fixed to or embedded in the shoreline, that is they are both in and out of the water. Nearshore devices are characterised by being used to extract the wave power directly from the breaker zone and the waters immediately beyond the breaker zone, (i.e. at 20m water depth).

Offshore devices or deep water devices are the farthest out to sea and extend beyond the breaker lines utilising the high-energy densities and higher power wave profiles available in the deep water waves and surges.

One of the advantages of offshore devices is that there is no need for significant coastal earthworks, as there is with onshore devices.

As most of the energy within a wave is contained near the surface and falls off sharply with depth. There is a surprising range of designs available that maximise the energy available for capture. These wave energy devices are either fixed bottom standing designs used in shallow water and which pierce the waters surface, or fully floating devices that are used to capture the kinetic energy content of a waves movement and convert each movement into electricity using a generator.

There are currently four basic "capture" methods:

* Point Absorbers - these are small vertical devices either fixed directly to the ocean floor or tethered via a chain that absorb the waves energy from all directions. These devices generate electricity from the bobbing or pitching action of a floating device. Typical wave energy devices include, floating buoys, floating bags, ducks, and articulated rafts, etc. These devices convert the up-and-down pitching motion of the waves into rotary movements, or oscillatory movements in a variety of devices to generate electricity. One of the advantages of floating devices over fixed devices it that they can be deployed in deeper water, where the wave energy is greater.

* Wave Attenuators - also known as "linear absorbers", are long horizontal semi-submerged snake-like devices that are oriented parallel to the direction of the waves. A wave attenuator is composed of a series of cylindrical sections linked together by flexible hinged joints that allow these individual sections to rotate and yaw relative to each other. The wave-induced motion of the device is used to pressurise a hydraulic piston, called a ram, which forces high pressure oil through smoothing accumulators to turn a hydraulic turbine generator producing electricity. Then wave attenuators convert the oscillating movement of a wave into hydraulic pressure.

* Oscillating Water Column - is a partly submerged chamber fixed directly at the shoreline which converts wave energy into air pressure. The structure could be a natural cave with a blow hole or a man made chamber or duct with an wind turbine generator located at the top well above the waters surface. The structure is built perpendicular to the waves so that the ebbing and flowing motion of the waves force the trapped water inside the chamber to oscillate in the vertical direction.

As the waves enter and exit the chamber, the water column moves up and down and acts like a piston on the air above the surface of the water, pushing it back and forth. This air is compressed and decompressed by this movement and is channelled through a wind turbine generator to produce electricity. The speed of air in the duct can be enhanced by making the cross-sectional area of the duct much less than that of the column.

* Overtopping Devices - also known as "spill-over" devices, are either fixed or floating structures that use ramps and tapered sides positioned perpendicular to the waves. The sea waves are driven up the ramp and over the sides filling-up a small tidal reservoir which is located 2 to 3 metres above sea level. The potential energy of the water trapped inside the reservoir is then extracted by returning the water back to the sea through a low head Kaplan turbine generator to produce electricity.

Then overtopping devices convert the potential energy available in the head of water into mechanical energy. The disadvantage of onshore overtopping schemes is that they have a relatively low power output and are only suitable for sites where there is a deep water shoreline and a low tidal range of less than about a metre.

The idea of harnessing the tremendous power of the oceans waves is not new. Like other forms of hydro power, wave energy does not require the burning of fossil fuels, which can pollute the air, contributing to acid rain and global warming. The energy is entirely clean and endlessly renewable. Wave power has many advantages compared to other forms of renewable energy with its main advantage being that it is predictable.

However, like many other forms of renewable energy, ocean wave energy also has its disadvantages such as its inflexible generation times dependant upon the tides, the visual impact of wave devices on the seas surface, as well as the threat of collision to shipping and navigation.

Here are some of the main advantages and disadvantages of wave energy.

Wave Energy Advantages

Wave energy is an abundant and renewable energy resource as the waves are generated by the wind.

Pollution free as wave energy generates little or no pollution to the environment compared to other green energies.

Reduces dependency on fossil fuels as wave energy consumes no fossil fuels during operation.

Wave energy is relatively consistent and predictable as waves can be accurately forecast several days in advance.

Wave energy devices are modular and easily sited with additional wave energy devices added as needed.

Dissipates the waves energy protecting the shoreline from coastal erosion.

Presents no barriers or difficulty to migrating fish and aquatic animals.

Wave Energy Disadvantages

Visual impact of wave energy conversion devices on the shoreline and offshore floating buoys or platforms.

Wave energy conversion devices are location dependent requiring suitable sites were the waves are consistently strong.

Intermittent power generation as the waves come in intervals and does not generate power during calm periods.

Offshore wave energy devices can be a threat to navigation that cannot see or detect them by radar.

High power distribution costs to send the generated power from offshore devices to the land using long underwater cables.

They must be able to withstand forces of nature resulting in high capital, construction and maintenance costs.

Wave Energy Summary

We have seen that there is a wide variety of wave energy conversion devices which can be used to harness the energy captured by a wave power generating system. Some of the wave energy devices mentioned above are built on the shoreline, making the engineering and construction of these schemes much easier, eliminating the need for long underwater cables runs. But the power density of waves is much less than is available some distance offshore. However, this can be partly compensated for by the concentration of the wave energy.

Offshore devices are situated in much deeper water, with typical depths of more than 30 metres. The wave power available at these deep ocean sites is about three to eight times the wave power available at shoreline sites with a range of completely submerged wave energy conversion devices available for offshore use. The type of wave energy conversion device used in a particular location, depends on the type of device and its distance from the shoreline.

In the next tutorial about Wave Energy, we will look in detail at some of the more common Wave Energy Devices currently being used to generate electricity from the sea.

For more information about "Wave Energy" and how to generate your own electricity using the power of the sea, or obtain more tidal energy information about the various tidal energy systems available, or to explore the advantages and disadvantages of wave power, then Click Here to order your copy from Amazon today about ocean, tidal and wave energy, the energy revolution from the sea.

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Wave Energy and how wave energy creates electricity

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Wave Energy also known as Ocean Wave Energy, is another type of ocean based renewable energy source that uses the power of the waves to generate electricity. Unlike tidal energy which uses the ebb and flow of the tides, wave energy uses the vertical movement of the surface water that produce tidal waves.

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Energy Source: Ocean waves

Energy Type Converted: Varied, mostly kinetic and potential

U.S. Theoretical Energy Potential: 1,500 TWh/year (varies with water depth)

Power Density: 2 - 100 W/m² (est.) (varies with water depth and wave height)

Device Types: Point Absorbers, Terminators, Attenuators, and Oscillating Wave Surge Converters

A wave energy converter (WEC) is defined as a device that converts the kinetic and potential energy associated with a moving wave into useful mechanical or electrical energy. There are a bunch of Wave Energy Converter (WEC) devices out there; a quick search on Google Patents returns over 7,400 results. I know you'd love for me to provide a SWOT analysis on each and every single one, but let's stick to the basics. This page will hopefully introduce you to general ideas and principals for how most WECs operate.

Wave energy converters can generally be classified into one of six different categories: point absorbers, terminators, attenuators, oscillating wave surge, submerged pressure differential, and rotating mass devices. Some might fall into a couple different categories, but by and large these classifiers work for most of what you'll come across in the industry. The industry has not yet settled on a single device type, everything is still on the table. However, once the industry settles on a design like the wind industry did for the three blade horizontal-axis turbine we'll see rapid advances.

Six Degrees of Freedom.
Source: http://officerincharge.blogspot.com

Before we dive-in, take a look at the image above that depicts the six degrees of freedom that a floating body can experience, you'll probably want to reference this as you read about these different devices.

Point Absorbers

Point absorbers are floating structures that have a small horizontal dimension compared with their vertical dimension and utilize the wave action at a single point. Most designs for point absorbers resemble a typical buoy, at least from the surface. Generally one end of the absorber is fixed (or relatively fixed compared to the water surface) while the other moves in a vertical motion, the resulting reciprocating action is used to pump a fluid or drive a linear generator, which in turn can provide usable power. Referencing our six degrees of freedom above, this device takes advantage of the heaving motion. Point absorbers are one of the most common design types in the industry today and PowerBuoy (shown above) is just one such example.

Overtopping or Terminator Devices

Overtopping wave energy converters, sometimes called terminators, utilize a difference in potential energy to generate useful energy. These devices recreate a similar wave action that you'll find on the beach. Floating outstretched arms focus waves so that they build in height. The waves are then directed towards an artificial beach where the water will run up a ramp and into a storage reservoir which is at a higher elevation than the surrounding sea level. From here the fluid is drained from the higher elevation and the flow is used to power a turbine. These devices are more likely to be found near shore, but some have been converted for offshore use, such as the Wave Dragon for example. This type of WEC must adjust itself to the height of the oncoming waves for best efficiency, so a pressurized air system is used to adjust the floating height.

Oscillating Water Column (OWC)

Oscillating Water Column Design Source: OceanLinx

In an OWC the incoming wave is used to generate a reciprocating motion of a fluid, which can then drive a turbine. The device works buy first trapping a chamber of air above the water level, kind of like being under an upturned boat. On top of the air chamber is an air duct that allows flow through a bi-directional turbine. When a wave passes across the device the water level will naturally rise and fall. As the water level drops, a slight vacuum is created, drawing in air from the outside. When the water level rises, the air is forced back out. This back and forth motion is used to drive a turbine generator to produce electricity. OceanLinx is well known for this type of device.

Attenuators

Attenuators are wave energy converters that are oriented parallel to the direction of wave travel. They are usually (but not always) modular in design and rely on the flexing of joints to generate power. Think of two barges linked together. Referencing our six degrees-of-freedom diagram, these devices try to capitalize on several different translations of motion; such as surge, sway, and heave as examples.

The most popular example of this type of WEC is Pelamis, manufactured by Pelamis Wave Power. Pelamis is a semi-submerged, articulated structure composed of cylindrical sections connected with hinged joints. The wave-induced motion of the joints is resisted by hydraulic rams that pump high-pressure fluid to drive hydraulic motors, which in turn power electrical generators to produce electricity.

Oscillating Wave Surge Converters (OWSC)

This class of device is fairly self-explanatory: they use the surge motion of ocean waves. These devices are usually submerged or on the seafloor in shallow water. The most simple design is a pendulum arm flap that pivots on a hinged joint as wave motion acts on it, causing it to oscillate back and forth. The movement of the flap acts like a large lever arm which can be mechanically linked to drive a generator or pressurize a fluid.

Submerged Pressure Differential

This class of wave energy converter comes in two different flavors. In one type, the device rests on or near the seafloor and relies on pressure fluctuations as a wave passes overhead to flex a pliable material such as a air bladder and squeeze a fluid to drive a turbine or some other power take-off unit. The other type is similar to a point absorber, but the submerged, like that shown above. In this type, a buoyant, submerged float is actuated by passing waves and this reciprocating motion is converted to energy with a linear generator.

Rotating Mass

Rotating mass wave energy converters are generally surface riders that use an internal weight rotating about a fixed point to drive a rotational alternator. The motion of ocean waves cause the hull's center of buoyancy and center of gravity to shift, and the rotating mass thus rotates about its axis to find its new center point. Since waves keep the device constantly rolling and swaying, the mass is constantly rotating about trying to reach equilibrium.

As we can see there are numerous methods for harnessing wave power; in fact that's part of the reason that wave energy hasn't grown as rapidly as wind or solar. The most efficient and cost effective way to capture wave energy is still not obvious. As the industry matures, expect to see one or two of these device types become more common, what's referred to as technology convergence. It's perfectly possible that the best design hasn't been discovered yet, perhaps it uses some advanced material like electroactive polymers. What is for certain is that more of these devices need to get out in the water to test, iterate, and improve so that the industry can mature.

References: The European Marine Energy Center, Ocean Wave Energy Conversion, Ocean Power Technologies, Bureau of Ocean Energy Management, Wave Dragon, Wind and Water Power Program

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Wave Energy Converters - The Liquid Grid

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Wave Power Overview Energy Source: Ocean waves Energy Type Converted: Varied, mostly kinetic and potential U.S. Theoretical Energy Potential: 1,500 TWh/year (varies with water depth) Power Density: 2 - 100 W/m2 (est.) (varies with water depth and wave height) Device Types:...

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How do we get power from the tides?

There are also three main ways that tidal energy is harnessed:

Tidal Barrages - A tidal barrage works like a dam. When the tide goes high, the reservoir fills up. When the tide drops, the dam lets the water out. In both directions the moving water can spin the blades of turbines to create electricity.

Tidal Fences - These are smaller structures than a barrage. A number of vertical turbines form a fence between two land masses. When the tide moves in or out, the turbines spin and generate electricity.

Tidal Turbines - These are individual turbines placed anywhere there is a strong tidal flow.

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Environment for Kids: Wave and Tidal Energy

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Kids learn about wave and tidal energy and how this renewable power can help the environment. Teach students about this new technology.

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Wave energy (or wave power) is the transport and capture of energy by ocean surface waves. The energy captured is then used for all different kinds of useful work, including electricity generation, water desalination, and pumping of water. Wave energy is also a type of renewable energy and is the largest estimated global resource form of ocean energy.

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https://www.conserve-energy-future.com/waveenergy.php

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How are Ocean Waves Converted to Energy?

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How are Ocean Waves Converted to Energy?

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How are Ocean Waves Converted to Electricity?

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5 steps to convert ocean waves to electricity, and it all starts with the sun.

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Wave of Discovery: Harnessing the Ocean's Power

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Wave of Discovery: Harnessing the Ocean's Power

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Wave energy research swells

Capturing the power of ocean waves could become an important part of the world's renewable energy portfolio. But capturing that clean energy is not just the vision of 21st century scientists.

"There are patents going back to 1799," says Annette von Jouanne, professor of electrical engineering and computer science at Oregon State University, and a world leader in wave energy research.

Interest and support of this technology has not been consistent. There was enthusiasm after the 1970s oil embargo, but it dropped when oil prices stabilized.

"There have been ebbs and swells of interest," says Ted Brekken, assistant professor of energy systems at Oregon State, "but a lot of people would agree that we have passed a turning point, and I think the interest level now is here to stay."

The cavernous Wallace Energy Systems and Renewables Facility (WESRF) in Corvallis, Ore., is where von Jouanne and Brekken work on wave energy systems. There is support now from federal and state governments, as well as some power companies, but that has not always been the case.

"In 1998 when I was writing these proposals, people were saying 'she's crazy--we're not going to be able to harness energy from the ocean, it's just too harsh of an environment,' and so it took a lot of persistence," says von Jouanne. "Some of my first proposals awarded were through the National Science Foundation (NSF). And that really was the seed money that helped this wave energy program grow."
Engineering challenge
The same constant motion of waves that provides the energy is also continuously battering the hardware that is capturing it. So the engineering challenge is making that hardware strong and simple.

"When you look at reliability and maintainability, you want devices out there that won't need regular maintenance, which would require people to go out there in vessels," adds von Jouanne, "because that factors into the cost."

In September 2008, Oregon State, working with Columbia Power Technologies and the U.S. Navy, deployed its eleventh wave energy prototype--a permanent magnet linear generator that creates power with few moving parts.

"A float heaves up and down with the waves. Underneath the float is a magnet assembly, and as that magnet assembly heaves up and down, it creates a changing magnetic field," explains von Jouanne. "The coils in the spar experience that changing magnetic field and that induces voltage, and creates electricity."

The concept for a wave energy installation would be an array of these buoys. They would have a power takeoff cable going down to the sea floor, coming together at a central junction box. From that central junction box would be a subsea cable back to shore and onto the electrical grid.
Protecting wildlife
While there is great promise with this technology, there is also concern for the wildlife that will share the ocean with these energy devices. So the teams putting together the wave energy plans at OSU asked marine mammal specialists to be involved from the very beginning.

About 18,000 North Pacific gray whales migrate yearly between Alaska and Mexico, and often travel very close to shore. Their journey will take them near wave energy devices, which are expected to be anchored about two and a half miles off the Oregon coast.

"We're trying to be ready if issues develop. What we're looking at now is some testing of a potential mitigation measure, an acoustic deterrent, if it becomes necessary to keep whales away from the early test units," says Bruce Mate, fisheries and wildlife professor and director of the Marine Mammal Institute at Oregon State.

The cabling that will bring the energy from the buoys to the grid has to be designed to prevent entanglements. Thousands of whales, dolphins, turtles and other sea creatures are killed each year because they are caught in fishing gear.

"These animals weigh about 30 tons, and they're traveling at three to four knots," (up to 4.6 miles per hour), "so hitting something solid could constitute a problem," notes Mate.
Testing and deployment
So how close is wave energy to actually putting electricity onto the grid? Worldwide, the western sides of large land masses are optimal for capturing wave energy, because of the prevailing west to east winds. For that reason, the United Kingdom (UK) are leaders in wave research in Europe, with deployments planned off of Portugal. In the United States, Reedsport, Ore., is going to be a wave energy test and demonstration facility starting next year.

"We do have some companies like Ocean Power Technologies in the United States, and their timeline for deploying buoys off the Oregon coast is the summer of 2010 when they plan to deploy one 150 kilowatt buoy (enough to power between 60-150 homes), and in 2011, they plan to deploy nine more," says von Jouanne.

The Electric Power Research Institute (EPRI), along with the Bonneville Power Administration (BPA), determined that Reedsport would be an ideal site for a wave energy test site, because of its good wave action, existing marine access and terrestrial electric transmission lines.

While research in wave energy is 15-20 years behind renewables such as wind power, waves are far more reliable as an energy source. While solar power is only available about 50 percent of the time; and winds are not constant, waves are, and experts say wave energy might one day provide up to six percent of the electricity needs of the United States.

"One of the beauties of wave energy is that it is highly forecastable, up to 48 hours in advance," says Chris Haller, an OSU engineering graduate student. The National Oceanic and Atmospheric Administration (NOAA) maintains a huge network of data collecting buoys, so power companies would know with great accuracy how much energy the waves would be putting onto the grid.
Making an impact
Both von Jouanne and Brekken say many of their students are drawn to renewable energy research both by the engineering challenges and the desire to help solve the world's energy problems. They also say it can be a lot of fun.

"Something I try to stress to my students is there are a lot of creative opportunities for engineers and mathematicians. I often will sit at home, or on my bike ride to work, and think, oh, that would be cool, let's try that," says Brekken.

"I love helping students develop those skills to help them springboard into industry, and be successful in an area like renewable energy. They're making a significant impact on the energy future of their region of the country, and the world. And it's very exciting to be part of that process," adds von Jouanne.

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Wave Energy - Science Nation | NSF - National Science Foundation

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Wave energy research swells Capturing the power of ocean waves could become an important part of the world's renewable energy portfolio. But capturing that clean energy is not just the vision of 21st century scientists. "There are patents going back to 1799," says Annette von Jouanne, professor of electrical engineering and computer science at Oregon State University, and a world leader in wave energy research.