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WAVE ENERGY CONVERTERSHydro-elastic perspective

GIRISH DEV KUMAR CHAURASIYA (10NA10011)AVEEK GIRGOSWAMI (10NA30007)

The policy

To utilize the energy in waves to produce electricity

Why offshore? The waves on the open sea have great

energy potential Negligible environmental impacts Minimize the use of fossil fuels in the long

run

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Topics

What causes waves? Wave energy converters Offshore devices Hydroelastic perspective on WECs Advantages/disadvantages

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What causes waves?

The wave energy resource is a concentrated form of solar energy

Winds generated by the differential heating of the earth pass over open bodies of water

The wind pushes surface water particles along with it, setting up a rolling motion in the water and moving the water particles in a vertical, circular path

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Wave energy densities

The power in a wave is proportional to the square of the amplitude and to the period of the motion

Large amplitude (~2 m), long period (~7-10 s) waves have energy fluxes commonly exceeding 40-50 kW/m width of oncoming wave

Wave energy is unevenly distributed over the globe

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Wave energy densities around the globe

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Wave climate in Europe The wave climate along the western coast of

Europe is characterized by particularly high energy. The UK has over half the wave energy potential in Europe, up to 75 kW/m off Ireland and Scotland

Wave climate in the US The West Coast is the most promising area

with wave energy densities in the 25 – 40 kW/m range

Wave energy converters

Four different types of WECs: Oscillating water columns Overtopping devices Point absorbers Surging devices

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Wave energy converters The oscillating water

column Partly submerged

structure with an opening to the sea below the water line

Waves cause the water column to rise and fall, which alternately compresses and depressurizes the air column

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~ This air flows through a turbine which drives an electric generator

Overtopping device mechanism

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Wave energy converters Point absorbers

They provide a heave motion that is converted by mechanical/ hydraulic systems in linear or rotational motion for driving electrical generators

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Wave energy converters

Surging devices Surging devices 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

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Placement of wave energy converters

Three locations Shore Near shore Offshore

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Placement of WECs

Shore/Near shore vs. offshore The potential energy

The power available in the waves is much greater offshore

Near the coastline the average energy intensity of a wave decreases due to interaction with the seabed

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Placement of WECs

Other factors Engineering challenges Construction costs Maintenance and/or installation costs Transmission costs and losses Environmental impacts The scale of electricity production

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Offshore devices

The Pelamis Is a semi-submerged structure composed of

cylindrical sections linked by hinged joints

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Offshore devices

The Pelamis The wave induced motion of these joints is

resisted by hydraulic rams which pump high pressure oil through hydraulic motors via smoothing accumulators

The hydraulic motors drive electrical generators to produce electricity

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Offshore devices The Pelamis

Several devices can be connected together and linked to shore through a single seabed cable

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Offshore devices The Pelamis

A typical 30MW installation would occupy a square kilometer of ocean and provide sufficient electricity for 20,000 homes

Ocean Power Delivery has won a bid for a 750kW project off Islay, Scotland and has recently signed a memorandum of understanding with BC Hydro to develop a 2 MW project off the coast of Vancouver Island, Canada

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Hydro elastic overview

Hydroelastic response of a floating structure can be improved to enhance the safety, serviceabilty, efficiency levels of a wave energy converter.

However, there are some limitations :

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Hydro elastic Limitations

Increasing the structural stiffness. But this approach is not cost effective since larger

structural stiffness translates to need of more and more material.

Surround by breakwaters.Not suitable when the water depth is large.

Disrupted water flow because of the breakwater might result in environmental issues.

Use of air cushion (low frequency incident waves)Sloshing problems might arise because presence of

air columns. Interior space is unnecessarily wasted.

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Reducing hydroelastic response:

Installation of anti motion devicesHowever these devices must have large draft to be

purposeful. They might obstruct incoming ships. Attaching another floating structureExtensive parametric study is reqd. to find

appropriate properties of attachment as well as the connection.

Wave energy converters are usually built by connecting modules of smaller size. So investigation can be done on them to reduce the hydroelastic response.

21Hydro elastic LimitationsReducing hydroelastic response:

In case wave induced response is used to generate electricity which is the case here in our wave energy converter, an increase is response is also desirable

It is important to examine the possibility of maximizing the wave capturing efficiency of the machine by introducing the ability to adjust not only the rotational stiffness(pelamis case) but also the locations connections to the machine.

22Hydro elastic LimitationsIncreasing the hydroelastic response:

Two approaches

First approach objective is to study the effects of length, flexural rigidity and mass of attachments, as well as rotational stiffness of the connections on the hydroelastic response of the main floating structure.

Second approach is to seek for an optimum connection design for a multi-module wave energy converter. This approach will maximize he efficiency of a large floating beam used as a wave energy converter.

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Advantages

Advantages of offshore wave energy Sea waves have high energy densities, the

highest among renewable energy sources Wave energy is generally considered to

provide a clean source of renewable energy with limited negative environmental impacts

It could become a significant source of energy not involving CO2 emissions

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Advantages

The natural seasonal variability of wave energy follows the electricity demand in temperate climates

Negligible demand on land use Could secure energy supplies in remote

regions Large-scale implementation of wave power

technologies will stimulate declining industries, e.g. shipbuilding

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Disadvantages

Disadvantages of offshore wave energy The main wave energy barriers result from

the energy carrier itself: The sea The peak-to-average load ratio in the sea is

very high and difficult to predict The structural loading in the event of

extreme weather conditions, such as hurricanes, may be as high as 100 times the average loading

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Disadvantages

High construction costs induce high power generation costs, thus making the technology uncompetitive 

The incidence of wave power at deep ocean sites is three to eight times the wave power at adjacent coastal sites, but the cost of electricity transmission from deep ocean sites is often prohibitively high

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Environmental impacts

Offshore wave energy devices may be a potential navigation hazard to ships

Near shore devices will have a visual impact Wave energy devices could have an effect on

some forms of recreation Impacts on the marine environment

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Thank You

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