3.ocean, geothermal, hydro and biomass energy resources

S.Y.B.Sc. Sem.I Physics Skill Enhancement Course I
Ocean, geothermal, Hydro and Biomass energy resources.
1 Dr. Mrs. Pritee Raotole , MGSM‘s, ASC, College, Chopda
UNIT – 3
Ocean, Geothermal, Hydro and
Biomass Energy Resources.
Syllabus:
a. O c e a n E n e r g y : Ocean Energy Potential against Wind and Solar, Wave
Characteristics and Statistics, Wave Energy Devices.
( 0 3 L , 0 6 M )
Tidal energy,Tide characteristics and Statistics, Tide Energy Technologies, Ocean Thermal
Energy, Osmotic Power. ( 0 2
L , 0 4 M )
b . G e o t h e r m a l E n e r g y : Geothermal Resources, Geothermal
Technologies. ( 0 2 L , 0 4 M )
c . H y d r o E n e r g y : Hydropower resources, hydropower technologies,
environmental impact
of hydro power sources. ( 0 2 L ,
0 4 M )
d . B i o m a s s e n e r g y : biomass, biochemical conversion, biogas generation,
Ocean biomass
( 0 2 L ,
0 4 M )
a. OCEAN ENERGY
3.1a OCEAN ENERGY POTENTIAL AGAINST THE WIND AND
SOLAR:
We have seen previously that Wave Energy is a non-polluting and renewable source of
energy, created by natural transfer of wind energy above the oceans, which itself is created
by the effects of the suns solar energy. As the wind blows across the ocean‘s surface,
moving air particles transfer their energy to the water molecules that they touch.
As the wind continues to blow more and more of its kinetic energy is transferred to the
ocean‘s surface and the waves grow bigger. These larger waves are called gravity waves
because their potential energy is due to the gravitational force of the Earth. There is a lot of

potential energy in the waves generated by the wind, to the point were large storm waves
can lift ships high out of the water.As an ocean wave passes a stationary position the
surface of the sea changes in height, water near the surface moves as it losses its kinetic and
potential energy, which affects the pressure under the surface.
3.2a Ocean wave characteristics and statistics:
Crest = Highest point of the wave
Trough = Lowest point of the wave
Wavelength = Distance from one crest/trough to the next
(m)
Wave Height = Height from trough to crest (m)
Wave steepness = ratio of wave height to wavelength
Amplitude = distance from the centre of wave to the bottom of the trough (m)
Wave Period = time for one full wavelength to pass a given point (s)
These characteristics are important in determining the size of waves, the speed at which
they travel, how they break on shore, and much more. We will refer back to them
throughout the following unit.
Wave Development and Movement
Waves typically propagate from the centre of a storm. These waves combine with pre-
existing waves, creating a confused sea with large and small waves of varying wavelengths
moving in all directions. Some waves will move in the same direction as the storm, and
these will likely grow bigger. Others will head off in the opposite direction, and these will
likely lose energy over time and fade away. The faster waves (i.e. longer wavelength and
shorter wave period) will overtake any smaller waves, and these will be the first waves to
break on distant shores. As the waves continue to disperse from the storm, they settle into
groups of different wave sizes and velocities continuously moving away from the source.
This is known as a wave train.

Fig 3.1a Generation of waves in ocean
Wave energy is associated with a group of waves. Waves in a group are dynamic as they
travel with smaller waves at the leading (front) and trailing (rear) sides of the group, and
larger waves in the middle. Waves move through the group from the rear to the front, first
gaining in size, then shrinking as they approach the front of the group, then disappearing.
Meanwhile, new waves are forming at the rear of the group and moving through the group.
This pattern is due to deep water wave dynamics, which we will not get into here.
The speed at which this one group of waves travels across the water is known as the group
velocity. The apparent speed of each individual wave in the group is known as the phase
velocity. This phase velocity is the speed at which a single phase of a wave (e.g. a crest)
moves across the water and it is typically double the group velocity.

In the simulation below, four groups of waves are shown with the red dot representing the
phase velocity and the green dot representing the group velocity.
Why do we care about group velocity? Because the destructiveness of waves comes from
its energy, and the energy moves with the wave groups, not with the wave crests.
3.2.1a Types of Waves
Wind-generated waves
Wind-waves are a result of wind disturbing the ocean surface and displacing water. Natural
forces, such as the water‘s surface tension (capillarity), or gravity, work to restore the
disturbed water to its calm state, flattening the water‘s surface. Different types of waves are
named for their restoring force. Small winds displace small amounts of water on the
surface, creating very short-wavelength capillary waves. Here, capillarity acts as the
restoring force. Capillary waves are typically only a few cm in length. Larger winds
create gravity waves, for which gravity acts as the restoring force. These waves can be
metres to kilometers long.
Fig 3.2a wind generated waves in ocean
Swell
Waves that you see on the ocean surface on a non-stormy day are not actually formed by
local winds, but instead are formed by winds from distant storms. These waves that arive
from distant sources are known as swell. Swell are gravity waves originating from heavy
winds and are capable of travelling long distances across the ocean with little loss of
energy. Ocean swell is typically generated by storms out at sea (far from shore) and can

carry energy to distant shores where it crashes as breaking waves. Swell with longer
wavelengths tend to have lower wave heights and are less susceptible to decay from surface
winds. They also carry more energy, and are more likely to form large breakers once they
reach the shore.
Swell, like an airplane, takes the shortest distance across the Earth‘s surface as it travels.
These routes are known as Great Circle routes or paths. The shortest distance between two
points on a sphere, like the Earth, is not a straight line but rather a curve. To picture a great-
circle path between two points, it would be the path over a small globe along which an
elastic band would lie if stretched between those two end points.
When out on the water, you may notice different swell coming from different directions.
Depending on the size of the swell and the direction that it‘s travelling in, when it meets
other swell, it can produce diamond-shaped or hatched wave patterns. Add wind waves on
top of the swell and you might be in a confused sea.
If you leave Vancouver in your sailboat and head out into the Strait of Georgia, you will
likely only experience small waves and chop created by local winds and tides. This is
because Vancouver Island lies between the Strait and the open ocean, and protects you
from ocean swell. Incoming swell from distant storms breaks upon the shores of Vancouver
Island and is dispersed as it wraps around the south end of the Island into the Strait. If you
were to take your sailboat around the south end of Vancouver Island and out into the
Pacific, you would immediately notice a difference. Your boat would start to rise and fall
with the incoming ocean swell, which can be quite large at times.
Fig 3.3a demonstrate the swell in ocean

Rogue Waves (and Interference)
These are very large waves that form due to wave interference. What is interference? When
two waves run through each other, they can add up or cancel out. This property of waves is
known as interference. If the crest of one wave passes through the trough of another, they
cancel out, which is called destructive interference. The resulting wave is smaller and
carries less energy. Whereas if the crest of one wave passes through with the crest of
another wave, they add up, which is called constructive interference. The resulting wave
is bigger, carries higher energy, but are temporary (short lived). Rogue waves are the
result of constructive interference that causes the wave height to be unusually higher than
the other waves around it, and can catch boaters (and people on the shore) by surprise.
As viewed from the cockpit of your sailboat, a rogue wave would appear to rise out of
nowhere and disappear quickly. You may not see them coming, and often have little or no
time to take action. Large rogue waves can be very dangerous.
Tsunamis
Tsunamis are very long wavelength waves resulting from seismic events, such as
earthquakes, under-water landslides, or volcanic eruptions. Wavelengths can be >200km
with long wave periods. In the open ocean (away from shore) they travel very fast (the
same speed as a jet airliner), but have very small amplitude (cm to a meter or so). Thus,
they have very small wave slopes, and you might not even notice it in the deep ocean,
because the normal wind-waves would catch your attention instead. They may start small-
amplitude out at sea, but when they meet a continental shelf, their wave height increases
dramatically, creating a wall of water approaching the shore.
3.3a WAVE ENERGY DEVICES:
3.3.1a Attenuator
An attenuator is a floating device which operates parallel to the wave direction and
effectively rides the waves. These devices capture energy from the relative motion of the
two arms as the wave passes them.
Fig 3.4a attenuator the wave energy device

3.3.2a Point Absorber
A point absorber is a floating structure which absorbs energy from all directions through its
movements at/near the water surface. It converts the motion of the buoyant top relative to
the base into electrical power. The power take-off system may take a number of forms,
depending on the configuration of displacers/reactors.
Fig. 3.5a point absorber -floating device
3.3.3a Oscillating Wave Surge Converter
Oscillating wave surge converters extract energy from wave surges and the movement of
water particles within them. The arm oscillates as a pendulum mounted on a pivoted joint in
response to the movement of water in the waves.
Fig. 3.6aOscillating wave surge converter
3.3.4a. Oscillating Water Column
An oscillating water column is a partially submerged, hollow structure. It is open to the sea
below the water line, enclosing a column of air on top of a column of water. Waves cause
the water column to rise and fall, which in turn compresses and decompresses the air
column. This trapped air is allowed to flow to and from the atmosphere via a turbine, which
usually has the ability to rotate regardless of the direction of the airflow. The rotation of the
turbine is used to generate electricity.

Fig. 3.7a oscillating water column
3.3.5.a Overtopping/Terminator Device
Overtopping devices capture water as waves break into a storage reservoir. The water is
then returned to the sea passing through a conventional low-head turbine which generates
power. An overtopping device may use ‗collectors‘ to concentrate the wave energy.
Fig. 3.8a Overtoppingi / Terminator device
3.3.6a Submerged Pressure Differential
Submerged pressure differential devices are typically located near shore and attached to the
seabed. The motion of the waves causes the sea level to rise and fall above the device,
inducing a pressure differential in the device. The alternating pressure pumps fluid through
a system to generate electricity.
Fig 3.9a Submerged pressure differential device

3.3.7a Bulge Wave
Bulge wave technology consists of a rubber tube filled with water, moored to the seabed
heading into the waves. The water enters through the stern and the passing wave causes
pressure variations along the length of the tube, creating a ‗bulge‘. As the bulge travels
through the tube it grows, gathering energy which can be used to drive a standard low-head
turbine located at the bow, where the water then returns to the sea.
Fig. 3.10a Bulge wave device
3.3.8a Rotating Mass
Two forms of rotation are used to capture energy by the movement of the device heaving
and swaying in the waves. This motion drives either an eccentric weight or a gyroscope
causes precession. In both cases the movement is attached to an electric generator inside the
device.
Fig. 3.11a Rotating Mass device
3.39.a Other
This covers those devices with a unique and very different design to the more well-
established types of technology or if information on the device‘s characteristics could not

be determined. For example the Wave Rotor, is a form of turbine turned directly by the
waves. Flexible structures have also been suggested, whereby a structure that changes
shape/volume is part of the power take-off system.
3.4a TIDAL ENERGY
Tides are the rise and fall of sea levels caused by the combined effects of
the gravitational forces exerted by the Moon and the Sun, and the rotation of the Earth.
Tidal power or tidal energy is a form of hydropower that converts the energy obtained
from tides into useful forms of power, mainly electricity.
Tidal energy is produced through the use of tidal energy generators. These large underwater
turbines are placed in areas with high tidal movements, and are designed to capture the
kinetic motion of the ebbing and surging of ocean tides in order to produce electricity.
High energy density than other renewable energy forms. It produces no greenhouse gases or
other waste. ... Tidal turbines are 80% efficient, which is higher than solar or
wind energy generators.
3.5a TIDE CHARACTERISTICS AND STATISTICS
 Tides are single waves that stretch across ocean basins.
 They are also shallow-water waves because their wavelengths greatly exceed the
depth of the ocean.
 They occur due to complex interactions of the moon and sun.
 Unlike wind-driven surface waves, tides are cause by two principal factors:
- Gravitational attraction, Centrifugal force
 Two high tides and two low tides occur each day.
 The high tide ―leads‖ the moon slightly due to friction between the water and the
surface.
 Tides are larger at full moon and new moon stages.
Rip current: A relatively small-scale surf-zone current moving away from the beach.
Rip currents form as waves disperse along the beach causing water to become trapped
between the beach and a sandbar or other underwater feature. The water converges into
a narrow, river-like channel moving away from the shore at high speed. A rip current

consists of three parts: the feeder current flowing parallel to the shore inside the
breakers; the neck, where the feeder currents converge and flow through the breakers in
a narrow band or "rip"; and the head, where the current widens and slackens outside the
breaker line. Rip Tide: Rip currents are not rip tides. A distinctly separate type of
current includes both ebb and flood tidal currents that are caused by egress and ingress
of the tide through inlets and the mouths of estuaries, embayments and harbors. These
currents may cause drowning deaths, but these tidal currents or jets are a separate and
distinct phenomenon from rip currents. Recommended terms for this phenomenon
include ebb jet or tidal jet. Undertow: There is spirited discussion and disagreement
among coastal scientists on the existence of a near shore process called "undertow," and
hence there is not an agreed on definition for this word. Undertow is a term often and
incorrectly used for rip currents. The best explanation for what many people attribute to
"undertow" is as follows: After a wave breaks and runs up the beach, most of the water
flows seaward; this "backwash" of water can trip waders, move them seaward, and
make them susceptible to immersion from the next incoming wave; however, there is no
surf zone force that pulls people under the water.
3.6a. TIDE ENERGY TECHNOLOGY:
Tidal power or tidal energy is a form of hydropower that converts the energy obtained
from tides into useful forms of power, mainly electricity. Although not yet widely
used, tidal energy has potential for future electricity generation. Tides are more
predictable than the wind and the sun. the common model for tidal power facilities
involved erecting a tidal dam, or barrage, with a sluice across a narrow bay or estuary.
As the tide flows in or out, creating uneven water levels on either side of the barrage,
the sluice is opened and water flows through low-head hydro turbines to generate
electricity. For a tidal barrage to be feasible, the difference between high and low tides
must be at least 16 feet. La Rance Station in France, the world‘s first and still largest
tidal barrage, has a rated capacity of 260 MW and has operated since 1966. However,
tidal barrages, have several environmental drawbacks, including changes to marine and
shoreline ecosystems, most notably fish populations. Several other models for tidal

facilities have emerged in recent years, including tidal lagoons, tidal fences, and
underwater tidal turbines, but none are commercially operating. Perhaps the most
promising is the underwater tidal turbine. Several tidal power companies have
developed tidal turbines, which are similar in many ways to wind turbines. These
turbines would be placed offshore or in estuaries in strong tidal currents where the tidal
flow spins the turbines, which then generate electricity. Tidal turbines would be
deployed in underwater ‗farms‘ in waters 60-120 feet deep with currents exceeding 5-6
mph. Because water is much denser than air, tidal turbines are smaller than wind
turbines and can produce more electricity in a given area. A pilot-scale tidal turbine
facility – the first in North America – was installed in New York‘s East River in
December 2006. The developer, Verdant Power, hopes to eventually install a 10 MW
tidal farm at the site.
3.7.a OCEAN THERMAL ENERGY:
The ocean cover around 70% of the earth's surface. There are different forms of ocean
energy available like waves, tides and the thermal gradient available in the ocean. In the
OTEC process, the ocean thermal energy is created by solar energy, when the ocean
water absorbs the solar radiation that creates the temperature difference between the
surface water and the bottom water of the ocean. That temperature gradient is used for
the electric power generation.
The Ocean Thermal Energy Conversion (OTEC) is a renewable energy technology that
converts solar radiation into electrical energy. In equatorial areas of earth, the ocean's
surface water temperature, and the deep cold water temperature differ by about 20°C.
The efficiency of the OTEC will be higher if the temperature difference is bigger.
Ocean thermal energy conversion (OTEC)-
Ocean thermal energy conversion (OTEC) is a process or technology for producing
energy by harnessing the temperature differences (thermal gradients) between ocean
surface waters and deep ocean waters.
Energy from the sun heats the surface water of the ocean. In tropical regions, surface
water can be much warmer than deep water. This temperature difference can be used to

produce electricity and to desalinate ocean water. Ocean Thermal Energy Conversion
(OTEC) systems use a temperature difference (of at least 77o
Fahrenheit) to power a
turbine to produce electricity. Warm surface water is pumped through an evaporator
containing a working fluid. The vaporized fluid drives a turbine/generator. The
vaporized fluid is turned back to a liquid in a condenser cooled with cold ocean water
pumped from deeper in the ocean. OTEC systems using seawater as the working fluid
can use the condensed water to produce desalinated water. It having two types-
The first type is known a closed cycle OTEC system- The warmth of the sea water
from the surface causes a liquid with a lower boiling point than water, for example
ammonia, to boil and turn to vapour. This vapour then drives a turbine which turns a
generator, creating electricity. Then the cold sea water from the depths of the ocean is
used to cool the ammonia vapour back into a fluid. It is then recycled back through the
system again.
The second type is known a open cycle OTEC system- In open-cycle OTEC, the sea
water is itself used to generate heat without any kind of intermediate fluid. At the
surface of the ocean, hot sea water is turned to steam by reducing its pressure. The
steam drives a turbine and generates electricity, before being condensed back to water
using cold water piped up from the ocean depths. One of the very interesting byproducts
of this method is that heating and condensing sea water removes its salt and other
impurities, so the water that leaves the OTEC plant is pure and salt-free. That means
open-cycle OTEC plants can double-up as desalination plants, purifying water either for
drinking supplies or for irrigating crops. That's a very useful added benefit in hot,
tropical countries that may be short of fresh water.

3.12a schematic diagram of a)open cycle and b) closed cycle OTEC system
3.8a OSMOTIC POWER:
Osmotic power is the energy derived from the difference in salinity between seawater and
fresh water, which is harnessed to generate electricity.
When fresh water is separated from seawater by a semipermeable membrane, the fresh
water moves by osmosis through the membrane into the seawater. The resulting osmotic
pressure, combined with the permeation flow rate, turns a hydraulic turbine, producing
electricity.
Working
When fresh water is separated from seawater by a semipermeable membrane, the fresh
water moves by osmosis through the membrane into the seawater, raising the pressure on
the seawater side. This is referred to as ―osmotic pressure‖ and is used to drive a turbine.
An osmotic generating station has a limited number of components:
 A semipermeable membrane contained in modules
a)

 Freshwater and seawater filters that optimize membrane performance
 A turbine that generates a driving force based on the osmotic pressure and
permeation flow rate.
 A pressure exchanger that pressurizes the seawater feed required to maintain
high salinity levels downstream from the membrane
Fig. 3.13.a schematic diagram of osmotic generating station
b. Geothermal resources
3.9.b GEOTHERMAL RESOURCES:
Geothermal energy is the heat from the Earth. It's clean and sustainable. Resources of
geothermal energy range from the shallow ground to hot water and hot rock found a few
miles beneath the Earth's surface, and down even deeper to the extremely high temperatures
of molten rock called magma.
3.9.1b Shallow geothermal energy (30 to 400 meters)
From a few meters below the surface of the ground, the temperature of the Earth is constant
all year round. This form of individual geothermal energy, which is the most widespread in
Switzerland, draws energy from the subsoil using one (or more) vertical probe, usually at a
depth of between 120 and 150 meters. At this depth, the soil temperature is between 12°

and 15° Celsius. Liquid is injected into a U-shaped tube. It heats up in contact with the heat
of the subsoil and then rises to the surface. The recovered heat is not sufficient and must be
upgraded by a heat pump to supply radiators or under floor heating. In summer, this low
temperature can be used to cool a home.
3.9.2b Deep geothermal energy (from 400 meters depth)
On the Swiss Plateau, the water temperature between 1 and 4 kilometers deep reaches
between 40° and 130° Celsius. The exploitation in hydrothermal form is one of the
techniques of recovery of this energy.
A pump recovers the water present in the soil using a borehole called
―production‖. Through a heat exchanger, the thermal energy of this water and taken and
injected into another liquid to a remote heating network. If the temperature is not high
enough, it can be increased by means of a heat pump. If the temperature of the geothermal
fluid is sufficient, electricity can be produced. The water from the production hole is
reinjected into the basement or discharged into a stream or lake.
3.9.3b Geothermal energy of great depth (Hot Dry Rock) (from 4,000 to 6,000 meters)
Between 4,000 and 6,000 meters, the temperature of the rock reaches 200° Celsius. The
recovery of this energy makes it possible to produce electricity and heating.
Drilling is done to reach this rock. Then, stimulation is carried out with water under high
pressure to improve the permeability of this rock. Water is injected into this fizzures via a
second borehole, it is heated by contact with the rock, and then pumped to the surface. With
the aid of a heat exchanger, the thermal energy heats up and transforms into a pressurized
gas a working liquid. The latter produces electricity by operating a turbogenerator. The
residual heat is injected into a remote heating network. The pumped water is returned to the
soil after cooling.
3.10.b GEOTHERMAL TECHNOLOGIES:
Geothermal technology harnesses the Earth‘s heat. Just a few feet below the surface, the
Earth maintains a near-constant temperature, in contrast to the summer and winter extremes
of the ambient air above ground. Farther below the surface, the temperature increases at an
average rate of approximately 1°F for every 70 feet in depth. In some regions, tectonic and

volcanic activity can bring higher temperatures and pockets of superheated water and steam
much closer to the surface.
Three main types of technologies take advantage of Earth as a heat source:
Ground source heat pumps
Direct use geothermal
Deep and enhanced geothermal systems
Geothermal energy is considered a renewable resource. Ground source heat pumps and
direct use geothermal technologies serve heating and cooling applications, while deep and
enhanced geothermal technologies generally take advantage of a much deeper, higher
temperature geothermal resource to generate electricity.
3.10.1b Ground Source Heat Pumps
A ground source heat pump takes advantage of the naturally occurring difference between
the above-ground air temperature and the subsurface soil temperature to move heat in
support of end uses such as space heating, space cooling (air conditioning), and even water
heating. A ground source or geoexchange system consists of a heat pump connected to a
series of buried pipes. One can install the pipes either in horizontal trenches just below the
ground surface or in vertical boreholes that go several hundred feet below ground. The heat
pump circulates a heat-conveying fluid, sometimes water, through the pipes to move heat
from point to point.
If the ground temperature is warmer than the ambient air temperature, the heat pump can
move heat from the ground to the building. The heat pump can also operate in reverse,
moving heat from the ambient air in a building into the ground, in effect cooling the
building. Ground source heat pumps require a small amount of electricity to drive the
heating/cooling process. For every unit of electricity used in operating the system, the heat
pump can deliver as much as five times the energy from the ground, resulting in a net
energy benefit. Geothermal heat pump users should be aware that in the absence of using
renewable generated electricity to drive the heating/cooling process (e.g., modes) that
geothermal heat pump systems may not be fully fossil-fuel free (e.g., renewable-based).

 Circulation: The above-ground heat pump moves water or another fluid through a
series of buried pipes or ground loops.
 Heat absorption: As the fluid passes through the ground loop, it absorbs heat from
the warmer soil, rock, or ground water around it.
 Heat exchange and use: The heated fluid returns to the building where it used for
useful purposes, such as space or water heating. The system uses a heat exchanger
to transfer heat into the building‘s existing air handling, distribution, and ventilation
system, or with the addition of a desuperheater it can also heat domestic water.
 Recirculation: Once the fluid transfers its heat to the building, it returns at a lower
temperature to the ground loop to be heated again. This process is repeated, moving
heat from one point to another for the user‘s benefit and comfort.
Fig. 3.14.b Ground Source Heat Pump
The above-ground heat pump is relatively inexpensive, with underground installation of
ground loops (piping) accounting for most of the system‘s cost. Heat pumps can support
space heating and cooling needs in almost any part of the country, and they can also be
used for domestic hot water applications. Increasing the capacity of the piping loops can
scale this technology for larger buildings or locations where space heating and cooling, as
well as water heating, may be needed for most of the year.
3.10.2b Direct use of geothermal

Direct use geothermal systems use groundwater that is heated by natural geological
processes below the Earth‘s surface. This water can be as hot as 200°F or more. Bodies of
hot groundwater can be found in many areas with volcanic or tectonic activity. In locations
such as Yellowstone National Park and Iceland, these groundwater reservoirs can reach the
surface, creating geysers and hot springs. One can pump hot water from the surface or from
underground for a wide range of useful applications.
 Pumping: To tap into hot ground water, a well is drilled. A pumping system may
be installed, although in some cases, hot water or steam may rise up through the
well without active pumping.
 Delivery: Hot water or steam can be used directly in a variety of applications, or it
can be cycled through a heat exchanger.
 Refilling: Depending on the use requirements of the system and the conditions of
the site, the ground water aquifer may need to be replenished with water from the
surface. In some cases, the movement of ground water might refill the aquifer
naturally.

Fig. 3.15.b Direct use geothermal systems
The water from direct geothermal systems is hot enough for many applications, including
large-scale pool heating; space heating, cooling, and on-demand hot water for buildings of
most sizes; district heating (i.e., heat for multiple buildings in a city); heating roads and
sidewalks to melt snow; and some industrial and agricultural processes. Direct use takes
advantage of hot water that may be just a few feet below the surface, and usually less than a
mile deep. The shallow depth means that capital costs are relatively small compared with
deeper geothermal systems, but this technology is limited to regions with natural sources of
hot groundwater at or near the surface.
3.10.3b Deep and Enhanced Geothermal Systems
Deep geothermal systems use steam from far below the Earth‘s surface for applications that
require temperatures of several hundred degrees Fahrenheit. These systems typically inject
water into the ground through one well and bring water or steam to the surface through
another. Other variations can capture steam directly from underground (―dry steam‖).
Unlike ground source heat pumps or direct use geothermal systems, deep geothermal
projects can involve drilling a mile or more below the Earth‘s surface. At these depths, high
pressure keeps the water in a liquid state even at temperatures of several hundred degrees
Fahrenheit.
 Pumping: Hot water or steam is pumped up through a deep well. As the water rises
to the surface, the pressure drops and the water vaporizes into superheated steam
that can be used for high-temperature processes.
 Delivery: The heat from the hot water or steam can be used to heat a secondary
fluid (a ―binary‖ process), or the hot water or steam can be used directly.
 Recirculation: Once the heat is transferred to the delivery system, the now-cooler
water is pumped back underground.
 Dispersal: Unlike ground source heat pumps, used ground water in this case is
simply injected and allowed to disperse back into the ground, rather than being
pumped through a closed loop of pipes.

Deep geothermal sources provide efficient, clean heat for industrial processes and some
large-scale commercial and agricultural uses. In addition, steam can be used to spin a
turbine and generate electricity. Although geothermal steam requires no fuel and low
operational costs, the initial capital costs—especially drilling test wells and production
wells—can be financially challenging. Steam resources that are economical to tap into are
currently limited to regions with high geothermal activity, but research is underway to
develop enhanced geothermal systems with much deeper wells that take advantage of the
Earth‘s natural temperature gradient and can potentially be constructed anywhere.
Enhanced systems can use hydraulic fracturing techniques to engineer subsurface reservoirs
that allow water to be pumped into and through otherwise dry or impermeable rock.
Fig. 3.16.b Deep geothermal systems

c. HYDRO ENERGY
Hydropower or hydroelectricity refers to the conversion of energy from flowing water into
electricity. It is considered a renewable energy source because the water cycle is constantly
renewed by the sun
3.11.c HYDROPOWER RESOURCES
Hydroelectric power comes from water at work, water in motion. Most people do not think
about the initial stages of hydroelectric power. The first step of hydropower is the powers
the hydrologic cycle which in turns gives the earth its water. In the hydrologic cycle,
atmospheric water reaches the earth‘s surface as precipitation. Some of the water
evaporates, but most of the water is absorbed by the ground and becomes surface runoff.
Water from rain and melting snow eventually reaches ponds, lakes, reservoirs, and oceans
where evaporation is constantly occurring. This cycle is a never ending cycle and nature
ensures that water is a renewable resource. The second step is to generate the electricity. To
generate electricity, water must be in motion. When water is in motion, the energy
generated is kinetic energy. When flowing water turns blades in a turbine, the form is
changed to mechanical energy. The turbine turns the generator rotor which then converts
this mechanical energy into another energy form — electricity. Since water is the initial
source of energy, we call this hydroelectric power or hydropower for short.
At hydroelectric power plants, hydropower is generated. Some power plants are located
right on a river or canals but for the plants to work at optimum efficiency with a reliable
water supply, dams are needed. Dams are used to store water and later release it for
purposes such as irrigation, domestic and industrial use, and power generation. The
reservoirs are like rechargeable batteries. The water is stored and when power is needed,
water is released to generate power. The reservoir is then filled back up with rain and
runoff.
Hydropower or water power (from Greek: word "water") is power derived from
the energy of falling water or fast running water, which may be harnessed for useful
purposes. Since ancient times, hydropower from many kinds of watermills has been used as
a renewable energy source for irrigation and the operation of various mechanical devices,

such as gristmills, sawmills, textile mills, trip hammers, dock cranes, domestic lifts,
and ore mills. A trompe, which produces compressed air from falling water, is sometimes
used to power other machinery at a distance. Hydropower is the most efficient way to
generate electricity. Modern hydro turbines can convert as much as 90% of the available
energy into electricity. The best fossil fuel plants are only about 50% efficient. In the U.S.,
hydropower is produced for an average of 0.85 cents per kilowatt-hour (kwh).
3.12.c HYDROPOWER TECHNOLOGIES
Hydropower has been used by mankind since ancient times. The energy of falling
water was used by the Greeks to turn waterwheels that transferred their mechanical energy
to a grinding stone to turn wheat into flour more than 2000 years ago. In the 1700s,
mechanical hydropower was used extensively for milling and pumping.
The modern era of hydropower development began in 1870 when the first hydroelectric
power plant was installed in Cragside, England. The commercial use of hydropower started
in 1880 in Grand Rapids, Michigan, where a dynamo driven by a water turbine was used to
provide theatre and store front lighting (IPCC, 2011). These early hydropower plants had
small capacities by today's standards but pioneered the development of the modern
hydropower industry.
Hydropower schemes range in size from just a few watts for pico-hydro to several GW or
more for large-scale projects. Larger projects will usually contain a number of turbines, but
smaller projects may rely on just one turbine. The two largest hydropower projects in the
world are the 14 GW Itaipu project in Braziland the Three Gorges project in China with
22.4 GW. These two projects alone produce 80 to 100 TWh/year (IPCC, 2011).
Large hydropower systems tend to be connected to centralised grids in order to ensure that
there is enough demand to meet their generation capacity. Small hydropower plants can be,
and often are, used in isolated areas off-grid or in mini-grids. In isolated grid systems, if
large reservoirs are not possible, natural seasonal flow variations might require that
hydropower plants be combined with other generation sources in order to ensure continuous
supply during dry periods.

Hydropower transforms the potential energy of a mass of water flowing in a river or stream
with a certain vertical fall (termed the "head"). The potential annual power generation of a
hydropower project is proportional to the head and flow of water. Hydropower plants use a
relatively simple concept to convert the energy potential of the flowing water to turn a
turbine, which, in turn, provides the mechanical energy required to drive a generator and
produce electricity (Figure).
The main components of a conventional hydropower plant are:
» Dam: Most hydropower plants rely on a dam that holds back water, creating a large water
reservoir that can be used as storage. There may also be a de-silter to cope with sediment
build-up behind the dam.
» Intake, penstock and surge chamber: Gates on the dam open and gravity conducts the
water through the penstock (a cavity or pipeline) to the turbine. There is sometimes a head
race before the penstock. A surge chamber or tank is used to reduce surges in water
pressure that could potentially damage or lead to increased stresses on the turbine.
» Turbine: The water strikes the turbine blades and turns the turbine, which is attached to a
generator by a shaft. There is a range of configurations possible with the generator above or
next to the turbine. The most common type of turbine for hydropower plants in use today is
the Francis Turbine, which allows a side-by-side configuration with the generator.
» Generators: As the turbine blades turn, the rotor inside the generator also turns and
electric current is produced as magnets rotate inside the fixed-coil generator to produce
alternating current (AC).
» Transformer: The transformer inside the powerhouse takes the AC voltage and converts it
into higher-voltage current for more efficient (lower losses) long-distance transport.
» Transmission lines: Send the electricity generated to a grid-connection point, or to a large
industrial consumer directly, where the electricity is converted back to a lower-voltage
current and fed into the distribution network. In remote areas, new transmission lines can
represent a considerable planning hurdle and expense.

Fig 3.17.c: Typical "Low Head" Hydrofower Plant With Storage
» Outflow: Finally, the used water is carried out through pipelines, called tailraces, and re-
enters the river downstream. The outflow system may also include "spillways" which allow
the water to bypass the generation system and be "spilled" in times of flood or very high
inflows and reservoir levels.
Hydropower plants usually have very long lifetimes and, depending on the particular
component, are in the range 30 to 80 years. There are many examples of hydropower plants
that have been in operation for more than 100 years with regular upgrading of electrical and
mechanical systems but no major upgrades of the most expensive civil structures (dams,
tunnels) (IPCC, 2011).
The water used to drive hydropower turbines is not "consumed" but is returned to the river
system. This may not be immediately in front of the dam and can be several kilometres or
further downstream, with a not insignificant impact on the river system in that area.
However, in many cases, a hydropower system can facilitate the use of the water for other
purposes or provide other services such as irrigation, flood control and/or more stable

drinking water supplies. It can also improve conditions for navigation, fishing, tourism or
leisure activities.
The components of a hydropower project that require the most time and construction effort
are the dam, water intake, head race, surge chamber, penstock, tailrace and powerhouse.
The penstock conveys water under pressure to the turbine and can be made of, or lined
with, steel, iron, plastics, concrete or wood. The penstock is sometimes created by
tunnelling through rock, where it may be lined or unlined.
The powerhouse contains most of the mechanical and electrical equipment and is made of
conventional building materials although in some cases this maybe underground. The
primary mechanical and electrical components of a small hydropower plant are the turbines
and generators.
Turbines are devices that convert the energy from falling water into rotating shaft power.
There are two main turbine categories: "reactionary" and "impulse". Impulse turbines
extract the energy from the momentum of the flowing water, as opposed to the weight of
the water. Reaction turbines extract energy from the pressure of the water head.
The most suitable and efficient turbine for a hydropower project will depend on the site and
hydropower scheme design, with the key considerations being the head and flow rate. The
Francis turbine is a reactionary turbine and is the most widely used hydropower turbine in
existence. Francis turbines are highly efficient and can be used for a wide range of head and
flow rates. The Kaplan reactionary turbine was derived from the Francis turbine but allows
efficient hydropower production at heads between 10 and 70 metres, much lower than for a
Francis turbine. Impulse turbines such as Pelton, Turgo and cross-flow (sometimes referred
to as Banki-Michell or Ossberger) are also available. The Pelton turbine is the most
commonly used turbine with high heads. Banki-Michell or Ossberger turbines have lower
efficiencies but are less dependent on discharge and have lower maintenance requirements.
3.13.c ENVIRONMENTAL IMPACTS OF HYDROELECTRIC POWER

Land Use
The size of the reservoir created by a hydroelectric project can vary widely, depending
largely on the size of the hydroelectric generators and the topography of the land.
Hydroelectric plants in flat areas tend to require much more land than those in hilly areas or
canyons where deeper reservoirs can hold more volume of water in a smaller space.
At one extreme, the large Balbina hydroelectric plant, which was built in a flat area of
Brazil, flooded 2,360 square kilometers—an area the size of Delaware—and it only
provides 250 MW of power generating capacity (equal to more than 2,000 acres per MW).
In contrast, a small 10 MW run-of-the-river plant in a hilly location can use as little 2.5
acres (equal to a quarter of an acre per MW).
Flooding land for a hydroelectric reservoir has an extreme environmental impact: it
destroys forest, wildlife habitat, agricultural land, and scenic lands. In many instances, such
as the Three Gorges Dam in China, entire communities have also had to be relocated to
make way for reservoirs
Wildlife Impacts
Dammed reservoirs are used for multiple purposes, such as agricultural irrigation, flood
control, and recreation, so not all wildlife impacts associated with dams can be directly
attributed to hydroelectric power. However, hydroelectric facilities can still have a major
impact on aquatic ecosystems. For example, though there are a variety of methods to
minimize the impact (including fish ladders and in-take screens), fish and other organisms
can be injured and killed by turbine blades. Apart from direct contact, there can also be
wildlife impacts both within the dammed reservoirs and downstream from the facility.
Reservoir water is usually more stagnant than normal river water. As a result, the reservoir
will have higher than normal amounts of sediments and nutrients, which can cultivate
an excess of algae and other aquatic weeds. These weeds can crowd out other river animal
and plant-life, and they must be controlled through manual harvesting or by introducing
fish that eat these plants . In addition, water is lost through evaporation in dammed
reservoirs at a much higher rate than in flowing rivers.

In addition, if too much water is stored behind the reservoir, segments of the river
downstream from the reservoir can dry out. Thus, most hydroelectric operators are required
to release a minimum amount of water at certain times of year. If not released
appropriately, water levels downstream will drop and animal and plant life can be harmed.
In addition, reservoir water is typically low in dissolved oxygen and colder than normal
river water. When this water is released, it could have negative impacts on downstream
plants and animals. To mitigate these impacts, aerating turbines can be installed to increase
dissolved oxygen and multi-level water intakes can help ensure that water released from
the reservoir comes from all levels of the reservoir, rather than just the bottom (which is the
coldest and has the lowest dissolved oxygen).
Life-cycle Global Warming Emissions
Global warming emissions are produced during the installation and dismantling of
hydroelectric power plants, but recent research suggests that emissions during a facility‘s
operation can also be significant. Such emissions vary greatly depending on the size of the
reservoir and the nature of the land that was flooded by the reservoir.
Small run-of-the-river plants emit between 0.01 and 0.03 pounds of carbon dioxide
equivalent per kilowatt-hour. Life-cycle emissions from large-scale hydroelectric plants
built in semi-arid regions are also modest: approximately 0.06 pounds of carbon dioxide
equivalent per kilowatt-hour. However, estimates for life-cycle global warming emissions
from hydroelectric plants built in tropical areas or temperate peatlands are much higher.
After the area is flooded, the vegetation and soil in these areas decomposes and releases
both carbon dioxide and methane. The exact amount of emissions depends greatly on site-
specific characteristics. However, current estimates suggest that life-cycle emissions can be
over 0.5 pounds of carbon dioxide equivalent per kilowatt-hour.
To put this into context, estimates of life-cycle global warming emissions for natural gas
generated electricity are between 0.6 and 2 pounds of carbon dioxide equivalent per
kilowatt-hour and estimates for coal-generated electricity are 1.4 and 3.6 pounds of carbon
dioxide equivalent per kilowatt-hour.

d. BIOMASS
3.14.d BIOMASS:
Biomass is a renewable energy source that is derived from living or recently living
organisms. Biomass includes biological material Including trees, plants, plant fiber, and
animal wastes, not organic material like coal. Biomass is any organic matter. Energy
derived from biomass is mostly used to generate electricity or to produce heat. Thermal
energy is extracted by means of combustion, gasification, pyrolysis, and fermentation.
Biomass can be chemically and biochemically treated to convert it to a energy-rich fuel.
Biomass resources include primary, secondary, and tertiary sources of biomass.
Primary biomass resources are produced directly by photosynthesis and are taken
directly from the land. They include perennial short-rotation woody crops and
herbaceous crops, the seeds of oil crops, and residues resulting from the harvesting of
agricultural crops and forest trees (e.g., wheat straw, corn stover, and the tops, limbs,
and bark from trees).
Secondary biomass resources result from the processing of primary biomass
resources either physically (e.g., the production of sawdust in mills), chemically (e.g.,
black liquor from pulping processes), or biologically (e.g., manure production by
animals). Tertiary biomass resources are post-consumer residue streams including
animal fats and greases, used vegetable oils, packaging wastes, and construction and
demolition debris.There are various conversion technologies that can convert biomass
resources into power, heat, and fuels for potential use.
3.15.d BIOCHEMICAL CONVERSION:
In biochemical process the bacteria and micro organisms used to transform the raw
biomass in o useful energy like methane and ethane gas. Following organic treatment
are given to biomass-
 Fermentation of biomass (aerobic digestion)
 Anaerobic digestion of biomass

Fermentation of biomass (aerobic digestion) – It is process of decomposition of
complex molecules of the organic compound under the influence of microorganism
(ferment) such as yeast, bacteria, enzymes etc..
The example of fermentation process is conversion of grains and sugar crops into
ethanol and co2 in presence of yeast.
Anaerobic digestion of biomass- It is Anaerobic Fermentation process involves
conversion of decaying wet biomass animal waste in to biogas through decomposition
process by the action of anaerobic bacteria. The most useful biomass for production of
biogas are animal and human waste, plant residue and other organic waste amterial with
high moisture content.
3.16d BIOGAS GENERATION:
Biogas obtained by anaerobic digestion of cattle dung and other loose & leafy organic
matters/ biomass wastes can be used as an energy source for various applications
namely, cooking, heating, space cooling/ refrigeration, electricity generation and
gaseous fuel for vehicular application. Based on the availability of cattle dung alone
from about 304 million cattle, there exists an estimated potential of about 18,240
million cubic meter of biogas generation annually. India is implementing one of the
World‘s largest programme in renewable energy. Biogas can be produced from a vast
variety of raw materials (feedstocks). The biggest role in the biogas production process
is played by microbes feeding on the biomass.
Biogas is produced using well-established technology in a process involving several
stages:
 Biowaste is crushed into smaller pieces and slurrified to prepare it for the
anaerobic digestion process. Slurrifying means adding liquid to the biowaste to
make it easier to process.
 Microbes need warm conditions, so the biowaste is heated to around 37 °C.
 The actual biogas production takes place through anaerobic digestion in large
tanks for about three weeks.

 In the final stage, the gas is purified (upgraded) by removing impurities and
carbon dioxide.
Fig 3.18.d: Biogas plant
After this, the biogas is ready for use by enterprises and consumers, for example in a
liquefied form or following injection into the gas pipeline network. Biogas comprises of
60-65% methane, 35-40% carbon dioxide, 0.5-1.0% hydrogen sulphide, rests of water
vapors etc. Biogas is non-toxic, color less and flammable gas. It has an ignition
temperature of 650 - 7500C.
3.17.d Ocean biomass:
Ocean or marine biomass, in a reversal of terrestrial biomass, can increase at higher
trophic levels. In the ocean, the food chain typically starts with phytoplankton, and
follows the course:
Phytoplankton → zooplankton → predatory zooplankton → filter feeders → predatory
fish
Phytoplankton are the main primary producers at the bottom of the marine food chain.
Phytoplankton use photosynthesis to convert inorganic carbon into protoplasm. They
are then consumed by microscopic animals called zooplankton.

Zooplankton comprise the second level in the food chain, and includes
small crustaceans, such as copepods and krill, and the larva of fish, squid, lobsters and
crabs.
In turn, small zooplankton are consumed by both larger predatory zooplankters, such
as krill, and by forage fish, which are small, schooling, filter-feeding fish. This makes
up the third level in the food chain.
The fourth trophic level consists of predatory fish, marine mammals and seabirds
that consume forage fish. Examples are swordfish, seals and gannets.Apex predators,
such as orcas, which can consume seals, and shortfin mako sharks, which can consume
swordfish, make up the fifth trophic level. Baleen whales can consume zooplankton and
krill directly, leading to a food chain with only three or four trophic levels.
Marine environments can have inverted biomass pyramids. In particular, the biomass of
consumers (copepods, krill, shrimp, forage fish) is larger than the biomass of primary
producers. This happens because the ocean's primary producers are tiny phytoplankton
that grow and reproduce rapidly, so a small mass can have a fast rate of primary
production. In contrast, terrestrial primary producers grow and reproduce slowly.
There is an exception with cyanobacteria. Marine cyanobacteria are the smallest
known photosynthetic organisms; the smallest of all, Prochlorococcus, is just 0.5 to 0.8
micrometres across. Prochlorococcus is possibly the most plentiful species on Earth: a
single millilitre of surface seawater may contain 100,000 cells or more. Worldwide,
there are estimated to be several octillion (~1027
) individuals. Prochlorococcus is
ubiquitous between 40°N and 40°S and dominates in the oligotrophic (nutrient poor)
regions of the oceans. The bacterium accounts for an estimated 20% of the oxygen in
the Earth's atmosphere, and forms part of the base of the ocean food chain.

Questions
Questions for (02) Marks
1. Define Tidal energy.
2. What is Osmotic Power?
3. Define Geothermal Energy.
4. What is Hydro Energy?
5. What is biomass?
1. write note on Ocean biomass
2. Write note on Geothermal Resources,
3. Write short note on Ocean Energy Potential against Wind and Solar,
4. State the Tide characteristics and Statistics.
5. Write note on Ocean Thermal Energy.
6. Write note on Hydropower resources.
1. Describe the open and closed OTEC system
2. Broadly explain hydropower technologies,
3. Explain Tide Energy Technologies
4. Explain biogas generation.
5. Explain broadly Wave Energy Devices.
6. Write note on biochemical conversion of biomass.
7. Explain in detail Wave Characteristics and Statistics.
8. Explain the Geothermal Technologies in detail
************

3.ocean, geothermal, hydro and biomass energy resources

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