Here is a compilation of essays on ‘Wave Energy’ for class 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Wave Energy’ especially written for school and college students.
Essay on Wave Energy
Essay Contents:
- Essay on the Introduction to Wave Energy
- Essay on the Mechanism of Wave Motion
- Essay on Power from Wave Energy
- Essay on the Wave Energy Conversion by Floats
- Essay on the Wave Energy Conversion Devices
- Essay on the Advantages of Wave Energy
- Essay on the Disadvantages of Wave Energy
Essay # 1. Introduction to Wave Energy:
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Ocean and sea waves are caused indirectly by solar energy uneven solar heating and subsequent cooling of the earth’s crust causes winds which along with rotation of the earth cause waves. Wave energy when active is very concentrated; therefore wave energy conversion into useful energy can be carried out at high power densities. A large variety of devices have been developed for harvesting of wave energy but these are complicated and fragile in the face of gigantic power of ocean storms.
Essay # 2. Mechanism of Wave Motion:
A progressive wave has a free surface and is acted upon by gravity and is shown in Fig. 10.1.
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It has the following parameters:
λ = Wavelength [m] = Cτ
a = amplitude [m]
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2a = height (from crest to trough) [m]
τ = period [s]
f = 1/τ frequency [s–1]
c = Wave propagation velocity [m/s] = λ/τ
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n – Phase rate [s–1]
= 2π/τ
The period t and wave velocity c depend upon the wave-length and the depth of water.
The relationship between wavelength and period can be approximated as:
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λ = 1.56 τ2
Where λ is in metres and τ in seconds.
Figure 10.1 shows the cross-sections of the wave at time 0 and θ.
The sinusoidal simple harmonic wave can be expressed by:
Or
Where,
y = height of wave above mean level [m]
θ = time, [s]
m = 2π/λ [m-1]
(mx – nθ) = 2π(x/λ – θ/τ) = phase angle [dimensionless]
The wave profile at time θ has the same shape as at time 0. It is displaced from it by a distance x = θ/τ = θ(n/m)
When θ = τ, x = λ. The wave profile assumes its original position. The wave motion is continually lateral, i.e., in the x direction with a speed of propagation c = λ/τ.
The motion of water does not follow the wave motion. A given particle of water rotates in place in an elliptical path in the plane of wave propagation. A wave, therefore, possesses potential energy and kinetic energy.
Essay # 3. Power from Wave Energy:
The total energy of a wave is the sum of its potential energy and kinetic energy.
i. Potential Energy:
The potential energy is due to elevation of water above the mean level (y = 0). Consider a differential volume y d × (see Fig. 10.1). It has a mean height of y/2.
The potential energy,
where,
m = mass of liquid in volume y dx [kg]
g = gravitational acceleration = 9.81 m/s2
gc = conversion factor = 1 kg.m/Ns2
ρ = Water density [kg/m3]
L = arbitrary width of the two-dimensional wave perpendicular to the direction of wave propagation [m]
ii. Kinetic Energy:
The kinetic energy of the wave is the energy of the liquid between two vertical planes perpendicular to the direction of wave propagation x and placed one wavelength apart. From hydro dynamic theory,
iii. Total Energy and Power:
The potential energy and kinetic energy of a progressive sine wave are identical. Therefore, total energy
Example 1:
A 2m wave has a 6s period and occurs at the surface of water 100m deep. Find the energy and power densities of the wave. Take water density – 1025 kg/m3.
Essay # 4. Wave Energy Conversion by Floats:
The wave motion is horizontal and motion of water is primarily vertical. The water motion is converted into mechanical power by the use of floats. A large float is driven up and down by water within stationary guides. This reciprocating motion is converted to mechanical and then to electrical power.
i. Float Wave-Power Machine:
Figure 10.2 shows Martin’s float wave-power machine. A square float moves up and down with the water. Four vertical manifolds that are part of a platform guide the float. A piston is attached to the float which compresses air in a cylinder which is stationary with the platform. The piston-cylinder arrangement acts as a reciprocating air compressor. The downward motion of the piston draws air into the cylinder via inlet check valve.
The upward motion compresses the air and sends it through an outlet check valve to the four underwater floatation tanks via the four manifolds. The four floatation tanks serve the dual purpose of buoyancy and air storage tanks and four manifolds serve the purpose of float guides and discharge air pipes.
The compressed air in the buoyancy-storage tanks is used to drive an air turbine that drives an electric generator. The electric current is transmitted to the shore via an underwater cable.
ii. Working Air Cycle:
The air enters the compressor at atmospheric pressure, volume and temperature p0, v0 and T0. It leaves the cylinder at p1, v1 and T1. The air is cooled in the storage tanks back to T0. Therefore, compression can be assumed as isothermal process.
The air expands in the turbine by adiabatic process.
The turbine work:
iii. Limitations:
i. It would take kilometers of linear arrays to produce 100 MW.
ii. Waves not perfectly sinusoidal.
iii. Aspiration of water into intake system and submersion by large waves.
iv. Water entering turbine.
v. Problems of cost and corrosion. Molded plastic should be used.
vi. Design to withstand storms.
vii. Marine growth.
viii. Power transmission to shore.
Essay # 5. Wave Energy Conversion Devices:
There are a number of wave energy conversion devices developed and experimented.
i. Hydraulic Accumulator Wave Machine:
The machine consists of the following main components:
1. Pressure Amplifier:
The waves enter the cylinder of pressure amplifier at the bottom and move the main piston. The pressure of the closed loop fluid is amplified to about 5 bars.
2. Hydraulic Accumulator:
The high-pressure fluid is conducted through a one-way up valve to a hydraulic accumulator. The accumulator has air cushions on the top which helps to maintain a constant pressure.
3. Pelton Turbine:
Part of high-pressure fluid flows through a Pelton wheel or Francis hydraulic turbine that drives an electrical generator .On the trough of the wave, the composite piston is pushed downward by the high fluid pressure. The exhaust water is sucked via return valve. The capacity of hydraulic accumulator is large enough to permit continuous turbine operation though the waves are cyclic.
ii. High-Level Reservoir Wave Machine:
It also consists of pressure amplifier which sends high pressure water to a high level reservoir on a shore line. The potential energy of water in the reservoir is used to run a water turbine.
iii. The Dolphin-Type Wave-Power Machine:
The major components of the system are a dolphin, a float, a connecting rod and two electrical generators Fig. 10.6.
The float has two motions. The rolling motion about its own fulcrum with the connecting rod is amplified and converted into continuous rotary motion with the help of gears. The electrical generator is driven. The other vertical motion is also amplified and converted into rotary motion to drive the gears.
iv. Dam-Atoll Wave Machine:
The waves wrap themselves around the atolls (small volcanic islands) from all sides, creating a spiral in the centre. A turbine is driven when water is discharged radially outward.
Essay # 6. Advantages of Wave Energy:
The main advantages of power from wave energy are:
i. It is a free and renewable energy source.
ii. Wave-power devices do not require large land masses.
iii. It is relatively pollution free.
iv. After removal of power, the waves are in placid state.
v. A string of devices have to be used wherever there is large wave activity. In addition to producing electricity, the system protects coast lines from the destructive action of large waves, minimize erosion and help create artificial harbour.
Essay # 7. Disadvantages of Wave Energy:
There are several disadvantages also:
i. Waves lack dependability.
ii. There is relative scarcity of accessible sites of large wave activity.
iii. The conversion devices are relatively complicated in construction.
iv. The devices have to withstand the enormous power of stormy seas.
v. There are unfavourable economic factors such as large capital investment and costs of repair, replacement and maintenance.
vi. Problems of biological growth of marine organisms are relatively unknown.
Arabian Sea off India and Pakistan has suitable sites for wave energy harvesting.