The document discusses wave power and harvesting wave energy through wave farms. It covers the physical concepts behind wave formation, technologies used to capture wave energy like point absorber buoys and oscillating water columns, and locations for wave farms. International examples of wave farms are provided, such as those in Scotland and Portugal. Both the economic and environmental implications of wave farming are addressed.

1. Angshuman Pal
B. Mechanical E. – IV (A-2-2)
001411201048
Jadavpur University
HARVESTING WAVE POWER – WAVE
FARMING

2. Contents
 Introduction
 Physical Concepts
 The Wave Power Formula
 Deep Water
 Sea State
 Technology and Devices Used
 Location and Power Take-off
 Method of Energy Capture
 Economics Implications
 Social Implications
 Environmental Implications
 International Wave Power Farms
 Conclusion
 References

3. Introduction
 We are living in an age where the energy dependency of the
human civilization is increasing with every passing decade.
 The science of energy generation has given rise to technology
capable of producing on a scale of magnitude billions of times
more as compared to earlier days. On the flip side, our
dependence on energy in most cases translates itself into
dependence on natural non-renewable.
 It is time the world focused on alternate means of power
generation. Solar energy, hydel power and wind energy have
long since caught the attention of scientists and active research
is being conducted along those lines.
 One more method of power generation, is the concept of using
wave energy – harvesting the energy available in the natural
cyclic motion of waves.
 Waves proceed in a natural and continuous cycle which is linked
to the geographical and meteorological aspects of the earth
surface. As a result it is non-exhaustive and can be a major
contributor to the power sector considering the long coastlines in
countries like India, China and Russia. Wave farms are a once-
only investment model with very little running costs, similar to

4. Physical Concepts
 Due to the motion of winds passing over the ocean
surfaces, waves and ocean currents are generated.
 Due to the pressure differences caused by differential
heating of the earth surface by the sun over different
longitudes during different parts of the year, oceanic
winds are generated which traverse huge distances
over the seas.
 When these winds propagate at speeds slower than
the speed of the waves below in the ocean surface,
transfer of energy takes place from the wind to the
waves.
 Wave parameters include the wave height, which is a
function of the wind speed, fetch of the wave and the
topography of the seafloor beneath. Larger waves are

5. The Wave Power Formula: Deep
Water
 In deep water, where the water depth is larger than
half the wavelength of the wave, the following
equation holds:
where P is the energy flux in W/m.
 As an example, for moderate ocean swells in deep
water a few kilometres off the coastline, if we have a
wave height of 3m and a wave time period of 8
seconds, we can potentially obtain 36 kW power per
metre of the wavefront. During storms off coasts, the
largest offshore waves are capable of producing up to
1.7 MW/m of wave energy flux.
 As it can be observed, in deep sea the power
generated by a wave is proportional to the square of
the significant wave height, thus indicating the great
importance of utilizing large waves.

6. The Wave Power Formula: Sea State
 Sea state is the condition of the free surface of an ocean
or a sea. When wave power is harvested at sea state, the
following equation holds:
where E is the energy density per unit area in J/m2.
 This includes both the potential and the kinetic energy of
the wave, where both contribute half to the total energy as
per the equipartition theorem. Surface tension is neglected
for larger waves.
 The energy transport velocity or the group velocity (cg) is
responsible for propagation of the energy. As a result, the
energy flux may be expressed as P = E cg where P is in
W/m and cg in m/s.
 Group velocity for a wave depends on the wavelength and
water depth, hence we have different behaviour of group

7. Technology and Devices Used:
Location and Power Take-off
 Location of wave power devices are mainly of
three kinds:
 Shoreline - These remain attached to the shore of
the ocean.
 Near shore - These are a little distance away from
the shore and are generally easily accessible in
small vessels.
 Offshore - These are a considerable distance away
from the shore where effects of the shore upon the
waves are not predominant.
 Modes of power take-off in wave farms include
hydraulic rams, elastomeric hose pumps,
hydroelectric turbines, air turbines, linear

8. Technology and Devices Used:
Method of Energy Capture
 There are four principal technologies used for
capturing energy from waves. These are point
absorber buoys, surface attenuators, oscillating water
columns, and overtopping devices.
 Point Absorber Buoys:
 This is a floating type device held in place by a set of cables
attached to the seabed beneath the buoy. With the rise and fall
of the swell, the buoy experiences periodic vertical oscillations.
This motion is captured to generate electricity using linear
generators or other linear-to-rotary converters. It is also known
as Buoyant Moored Device.
 The EMF within the transmission cables can be hazardous for
aquatic fauna and the acoustics of the devices may render the
location unsuitable for marine habitation. Breeding sites for fish
and marine mammals may get affected and the energy
transmission may adversely affect any nearby shoreline
habitation as well. Due to this, these types of installations are
done far offshore.

9. Technology and Devices Used:
Method of Energy Capture (contd.)
 Surface Attenuators:
 Surface attenuators are similar in construction to Point
Absorber Buoys, but these have multiple floating segments
connected to one another and oriented perpendicularly to the
incoming waves. Flexing motion of the devices due to the swell
results in hydraulic generators generating electricity. It is also
known as Hinged Contour Device.
 An additional hazard for these devices is that the devices may
fail at the joints connecting them due to hostile marine
environment.
 Oscillating Water Columns
 Oscillating water columns contain an air chamber integrated
into the device. The incoming waves compress the air and
force the pressurised air through an air turbine. The air drives
the turbine blades and hence produces electricity.
 This type of device may be used on shore as well as offshore.
Driving of wind through the turbine runner causes production of
immense noise, which may be detrimental to the marine
environment. Marine organisms can also get entrapped into
the air passage.

10. Technology and Devices Used:
Method of Energy Capture (contd.)
 Overtopping Devices:
 Overtopping devices use the concept of filling a water
reservoir to a greater water depth than the surrounding
ocean. When high waves hit the long structures of
overtopping devices, it creates a head greater than the
datum ocean level. Low head turbines are used to extract
power from the device.
 The mooring system of the device to the seabed can cause
harm to the marine environment. Turbine noise and power
extraction from wave can also cause disruptive effect on the
nearby habitat. These devices may be used either on shore
or floating offshore.

11. Economics Implications
 Even though the potential of wave farming is quite
immense, the economics need to be put in order. At a
nascent stage, huge grants are required to further the
technology adopted by the energy extracting
mechanisms.
 Equipment required to set up a wave farm is also
costly. The reduced possibilities of fishing and other
marine occupations in the vicinity of a wave farm also
create some problems for potential wave farm sites.
Navigation around wave farms is difficult.
 Still, even after considering the high capital costs for
installing a wave farm, the running costs are
considerably low and once established a farm can
yield substantial dividends.

12. Social Implications
 On social grounds, wave farming can affect the
livelihoods of the fishing population who inhabit
coastal areas since their profession will be at risk in
and around wave farms. Tourism spots may also be
affected, with changes in beach patterns and wave
patterns a possible effect of wave farming.
 On the other hand, if farms are integrated along with
harbours and other economic centres, they can create
employment and attract visitors.
 There is the possibility of collaboration with other
offshore installations like oil rigs as well.

13. Environmental Implications
 Although free from the disadvantages like increasing
emissions, carbon footprint, radioactive wastes, etc
which are a derivative of the more conventional
means of energy production, wave farms have their
own set of environmental implications as well.
 The primary one among them is the effect on the
marine environment where the farm is located. It
affects the breeding grounds for fish, ecology of
marine organisms, and also harms coral reefs.
 On the other hand, on shore farms help in reducing
soil erosion, while off shore farms can create artificial
ridges and enhance colonization by marine
organisms.

14. International Wave Power Farms
 The first patent relating to harvesting of wave power
was in 1799 and was filed in Paris. A modern device
was constructed in 1910 by Bochaux-Praceique. The
United Kingdom soon picked up the technology for
harvesting wave power. In the 1940’s, Yoshio Masuda
of Japan used wave energy to power navigation
lights. During the energy crisis in USA in 1973,
renewed interest was observed in this area. Academic
institutions became involved in research on wave
power devices.
 With reduction in oil process in the 1980’s, interest in
wave power waned. In 2003, the European Marine
Energy Centre (EMEC) based in Orkney, Scotland
started development and research on wave power.
Atlantic Ocean waves as high as 19m are used to
generate the power and the generators are connected
to the main grids.

15. International Wave Power Farms
(contd.)
 Scotland is a pioneer when it comes to wave farming, thanks to
the rocky shoreline and rough seas around the British territory. A
£4 fund was granted for a wave farm in 2007, which will be the
largest capacity farm capable of producing 3 MW power
generated by four Pelamis machines.
 A wave farm known as “Wave Hub” has received funding for
establishment of the coast of Cornwall in June 2007. An array of
offshore wave energy generation devices which will keep down
connection costs through a renewable energy project is also on
the cards.
 The USA has planned projects for wave energy on both the West
and East coasts, as well as at Hawaii. But as of now, production
is modest in quantity. The entire US coastline is said to have the
capacity of 252 million MW-hours every year.
 Portugal founded the world’s first experimental wave farm in
2008. The Aguçadoura Wave Farm was the world's first
commercial-scale wave farm. The farm used three Pelamis wave
energy converters totalling to 2.25 MW of total capacity.

16. International Wave Power Farms
(contd.)

17. Conclusion
 In perspective of the ever growing demands for alternative
energy sources, wave farming promises to be a vital
supplement to other renewable energy sources like solar,
wind and nuclear energy.
 It is a clean form of energy which utilises conventional
mechanical turbomachinery to convert the wave energy into
mechanical and electrical energy usable to humans.
 It is still a long time before wave power can take over a
considerable stake in the total energy production of the world,
but research focus should be shifted on it from early stages
itself.
 In a tropical country like with an extensive coastline, there is
considerable scope for tapping the resources of wave power.
The Sundarban delta of Bengal and the Kachchh region in
Gujarat are promising havens for wave farms. Island regions
like Andaman & Nicobar and Lakshwadeep can also

18. References
 Wave Power
http://www.esru.strath.ac.uk/EandE/Web_sites/01-
02/RE_info/wave%20power.htm
 Ingvald Straume
https://commons.wikimedia.org/w/index.php?curid=31768763
 Academic Study: Matching Renewable Electricity Generation with
Demand: Full Report
http://www.gov.scot/Publications/2006/04/24110728/10
 Sundarbans tidal project axed – Indrani Dutta
http://www.thehindu.com/todays-paper/tp-national/sundarbans-tidal-
project-axed/article4590040.ece
 World’s Largest Wave Energy Farm
https://www.engineering.com/ElectronicsDesign/ElectronicsDesignArticl
es/ArticleID/7162/Worlds-Largest-Wave-Energy-Farm.aspx
 Wikipedia
 https://en.wikipedia.org/wiki/Wave_power
 https://en.wikipedia.org/wiki/Wave_farm