Energy conversion is the process of changing one form of energy into another, a fundamental capability that enables modern civilization to function. It can occur in various ways, from converting the kinetic energy of wind into mechanical power through windmills to transforming solar energy into electrical energy in solar panels. This transformation is essential not just for daily usage but also for harnessing and utilizing natural resources more efficiently. In the context of rural electrification, this process plays a critical role. By converting available local energy resources into electricity, rural communities can access a stable and reliable power supply. This not only improves the quality of life but also supports economic development by powering homes, schools, businesses, and healthcare facilities. Consequently, energy conversion facilitates the broader goal of rural electrification, demonstrating the interconnection between technological innovation and societal advancement.

1. Chapter 9
Ocean and Wave Energy
https://www.alternative-energy-tutorials.com/wave-energy/wave-energy.html
Tesfaye B.

2. Introduction
2

3. Cont..
• The energy from the sea can be obtained mainly in three
forms:
1. Wave energy,
2. Tidal energy and
3. Ocean thermal energy
3

4. 1. Wave energy
• The rise and fall of waves is a renewable source of energy.
• Effective sites for harnessing wave energy need to have
strong waves .
4
The “Limpet” (land-installed
marine-powered energy
transformer) on Islay,
Scotland, is the world’s first
commercial wave energy
device.

5. Cont…
• Wave energy is the transport of energy by ocean surface
waves, and the capture of that energy to do useful work -
for example for electricity generation, water desalination, or
the pumping of water (into reservoirs).
• A machine able to exploit wave power is generally known as a
wave energy converter (WEC).
• Wave power generation is not currently a widely employed
commercial technology although there have been attempts at
using it since at least 1890.
5

6. Physical concept of wave generation
6
Figure: generation of waves via wind blow

7. Cont…
• 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, causes the growth of the
waves.
7

8. Cont.…
• Wave height is determined by wind speed, the duration of
time the wind has been blowing and by the depth and
topography of the seafloor.
8

9. Wave power formula:
9
• Wave power converts the periodic up-and-down
movement of the oceans waves into electricity.
• This takes place 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.

10. Cont..
10
Figure: representation of waves

11. Cont.…
• In deep water where the water depth is larger than half the
wavelength, with P the wave energy flux per unit of
wave-crest length, Hm0 the significant wave height, Te the
wave energy period, ρ the water density and g the
acceleration by gravity.
11

12. Cont.…
• The above formula states that wave power is proportional
to the wave energy 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 wave front length.
12

13. Cont.…
Example 1:
• Consider moderate ocean swells, in deep water, a few km
off a coastline, with a wave height of 3 m and a wave
energy period of 8 seconds.
• Using the formula to solve for power, we get there are 36
kilowatts of power potential per meter of wave crest.
13

14. Cont.…
Example 2:
• 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
1.7MW/m of power across each meter of wave front.
• An effective wave power device captures as much as
possible of the wave energy flux.
14

15. Potential Assessment
• Ocean wave energy is captured directly from surface
waves or from pressure fluctuations below the surface.
• Waves are caused by the wind blowing over the surface of
the ocean.
• The worldwide resource of wave energy has been
estimated to be greater than 2 TW.
15

16. Cont..
• Locations with the most potential for wave power include
the western seaboard of Europe, the northern coast of the
UK, and the Pacific coastlines of North and South
America, Southern Africa, Australia, and New Zealand.
• The north and south temperate zones have the best sites
for capturing wave power.
16

17. Technologies used in Ocean & Wave Energy:
• Wave power devices are generally categorized by the
method used to capture the energy of the waves, by
location and by the power take-off system.
• By Locations are :
Shoreline,
Near shore and
Offshore
17

18. Cont..
• 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.
• Near shore 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).
18

19. Cont..
• 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 (> 30 m
depth).
19

20. Cont..
Types of power take-off include:
• Hydraulic ram, hydroelectric turbine, air turbine, and
linear electrical generator.
20

21. Cont..
21
Fig: General lay out of ocean wave energy conversion process

22. Cont..
• When evaluating wave energy as a technology type, it is
important to distinguish between the four most common
approaches:
Point absorber buoys
Surface attenuators
Ooscillating water columns and
Overtopping devices.
22

23. Cont..
i. Point absorber buoy
• This device floats on the surface of the water, held in
place by cables connected to the seabed. Buoys use the
rise and fall of swells to drive hydraulic pumps and
generate electricity.
23
Ocean Power Technology's (OPT) - Power
buoy wave generation system

24. Cont..
ii. Surface attenuator
• These devices act similarly to point absorber buoys, with
multiple floating segments connected to one another and
are oriented perpendicular to incoming waves.
• A flexing motion is created by swells that drive hydraulic
pumps to generate electricity. Eg. Pelamis Wave Energy
Converter, Portugal
24

25. Cont..
iii. Oscillating water column
• Oscillating water column devices can be located on shore
or in deeper waters offshore. With an air chamber
integrated into the device, swells compress air in the
chambers forcing air through an air turbine to create
electricity.
25

26. Cont..
26
Fig: Oscillating water column wave energy convertor

27. Cont..
iv. Overtopping Devices
• Overtopping devices have reservoirs that are filled by
incoming waves, causing a slight buildup of water
pressure like a dam.
• The water is then released, and gravity causes it to flow
back into the ocean.
• The energy of the falling water is used to turn hydro
turbines to generate power.
27

28. Cont..
• Specially built floating platforms can also create electricity
by funneling waves through internal turbines and then
back into the sea.
28

29. 2. Tidal power/energy
• Tidal power, also called tidal energy, is a form of
hydropower that converts the energy of tides into
electricity or other useful forms of power.
• Tidal energy is generated by the relative motion of the
Earth, Sun and the Moon, which interact via gravitational
forces. explain how?
• Tides are more predictable than wind energy and solar
power.
Tide: The alternate rising and falling of the sea due to the attraction of the
moon and sun (oxford English dictionary). 29

30. Generation of tidal energy
• Tidal energy is extracted from the relative motion of
large bodies of water, periodic changes of water levels,
and associated tidal currents, are due to the gravitational
attraction of the Sun and Moon as explained.
• There are two ways of getting tidal energy. These are by:
• Tidal stream and
• Tidal barrages
30

31. Tidal stream generator
• Tidal stream generators (or TSGs) make use of the
kinetic energy of moving water to power turbines, in a
similar way to wind turbines that use moving air.
• This method is gaining in popularity because of the
lower cost and lower ecological impact compared to tidal
barrages.
• System work best where there are very strong tidal
zones(Norwegian and British coastlines)
31

32. Fig: Tidal stream generator 32

33. Cont.…
• A tidal stream generator(TSG) is a machine that extracts
energy from moving masses of water, or tides.
• These machines function very much like underwater
wind turbines, hence are also sometimes referred to as
tidal turbines.
• TSGs are the cheapest and the leas ecologically damaging
among the three main forms of tidal power generation.
33

34. Tidal barrage
• Tidal barrages make use of the potential energy in the
difference in height (or head) between high and low tides.
• Barrages are essentially dams across the full width of a
tidal estuary, and suffer from very high civil infrastructure
costs, a worldwide shortage of viable sites and
environmental issues.
34

35. Cont..
.
35

36. Cont…
• Tidal power is a predictable and reliable source of
electricity.
• However, the difference between high and low tides
needs to be at least 5 metres to generate practical
amounts of electricity.
36
 Worldwide, only around 20 sites
have been identified as suitable
for tidal power stations.
 The UK has eight possible sites.

37. 3. Ocean thermal energy conversion
• Ocean thermal energy conversion uses the temperature
difference between cooler deep and warmer shallow or
surface seawaters to run a heat engine and produce useful
work, usually in the form of electricity.
37

38. Cont...
38

39. Thank you !