Energy Engineering
ME 351
by
Atul Singh Rajput
Assistant Professor
National Institute of Technology Karnataka, Surathkal
Curriculum
Credits: (3-0-0) 3
Module 3
Hydel Power Plants
Hydro electric schemes
Wind Energy
Ocean Waves
Ocean Thermal Energy
Geothermal Energy
Ocean energy
Introduction
Wave energy is a renewable energy source that harnesses the power of ocean waves to generate electricity. As a clean,
abundant, and largely untapped resource, it has the potential to play a significant role in the global transition towards
sustainable energy systems. In this section, we will explore the basics of wave energy and its potential across the globe and
provide a brief overview of its history.
The first known patent to extract energy from ocean
waves was in 1799, filed in Paris by Pierre-Simon
Girard and his son.
Pierre-Simon Girard
From 1855 to 1973 there were 340 patents filed in
the UK alone
What Makes Wave
Wind Driven Tidal
Tsunami
What Makes Wave
Ocean Energy
Ocean Thermal Tidal Energy salinity gradient
Energy Conversion
(OTEC)
Ocean Thermal Energy Conversion
Ocean thermal energy conversion produces energy from temperature differences in ocean waters. 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.
Lambert’s Law of absorption K = absorption coefficient
= 0.05 m-1 (clear fresh water)
= 0.27 (turbid freshwater)
= 0.5 m-1 (Very salty water)
Ocean Thermal Energy Conversion
In tropics, the ocean surface temperature often exceeds 25 oC, while 1 km below, the temperature is not usually higher
than 10 oC.
Open cycle OTEC system Closed cycle OTEC system
(Claude cycle) (Anderson cycle)
Ocean Thermal Energy Conversion
Ocean Thermal Energy Conversion
Ocean Thermal Energy Conversion
A closed-cycle Ocean Thermal Energy Conversion (OTEC) system operates between a warm surface seawater
temperature of 27°C and a cold deep seawater temperature of 5°C. The working fluid used in the system is
ammonia, which follows a Rankine cycle.
1.Calculate the maximum possible efficiency (Carnot efficiency) of the system.
2.If the system generates 5 MW of net power output, determine the minimum heat energy absorbed from the
warm seawater.
Ocean Thermal Energy Conversion
A closed-cycle Ocean Thermal Energy Conversion (OTEC) system operates between a warm surface seawater
temperature of 28°C and a cold deep seawater temperature of 4°C. The working fluid is ammonia, which undergoes a
Rankine cycle. The turbine inlet conditions are saturated vapor at 28°C, and the condenser pressure corresponds to
saturated liquid at 4°C.
Given the following data:
•Enthalpy of ammonia at turbine inlet (h₁) = 1430 kJ/kg
•Enthalpy of ammonia at turbine exit (h₂) = 300 kJ/kg
•Enthalpy of ammonia at condenser exit (h₃) = 250 kJ/kg
•Pump work input (h₄ - h₃) = 5 kJ/kg
The mass flow rate of ammonia is 10 kg/s.
Questions:
1.Determine the thermal efficiency of the cycle.
2.Calculate the net power output of the system.
3.Determine the heat absorbed from the warm seawater.
4.Calculate the heat rejected to the cold seawater.
Salinity Gradient
Salinity gradient energy (SGE) is a renewable energy source that's created when two bodies of water with different
salt concentrations mix
Salinity Gradient
Tidal Energy
During the Roman occupation of England, tide mills were built to grind grain and corn
These tide mills operated by storing water behind a dam during high tide. As the tide receded
the water was slowly let out from behind the dam in order to power the mill.
Discovered in 1999 Unveiled was a stone built tidal mill and
evidence of an ancient tidal mill dating back to 787 A.D.
Nendrum Monastic Tidal Site
Tidal Energy: Eling Mill
The mill was included in the Domesday Survey of 1086 Originally milled four tons of flour
each day at maximum output Rebuilt many times, but operates in the same manner.
Tidal Energy: Eling Mill
Tidal Energy
7000
MW
900
200 MW
MW
500
MW
100 100
MW MW
230
MW
100
MW
Tidal Energy
Tidal Barrage Systems
Limitations:
Environmental Impact, High Initial Cost
Limited Locations
Tidal Energy
A newer tidal energy design option is to construct circular retaining walls embedded with turbines that can capture
the potential energy of tides. The tidal lagoon scheme is very similar to the tidal barrage method of using tides to
generate power.
In fact, the only real difference between the two is that the tidal lagoon does not block off an entire estuary, but
rather makes use of only part of it.
During the high tide water level around the lagoon will increase and try to move in the lagoon and during low tide
water will move outside in both direction it will produce electricity
Tidal Lagoon Systems
Limitations:
Environmental Impact, High Initial
Cost, Site-Specific
Tidal Energy
Oscillating
Water Column
Limitations:
Structural Durability,
Limited Efficiency
Tidal Energy
Oscillating Water Column
This type of devices can be located onshore or in
deeper water, offshore, and are characterized by the
presence of an air chamber.
The air in the chamber is compressed by the rising level
of the water due to the waves: the swelling of the water
forces the air through an air turbine in order to create
electricity.
Tidal Energy
Oscillating Wave Energy Converter
These devices are typically characterized by structure
fixed on the seabed, and an oscillating part connected
to the structure. Energy is collected from the relative
motion of the oscillating part respect to the fixed
structure. The oscillating part can be constituted by
oats, aps or membranes.
Tidal Energy
Overtopping Device
These type of devices are characterized by a long
structure that uses waves to fill a water reservoir which
is located to a higher position respect to the sea level.
The potential energy of the water contained in the
reservoir is then exploited by low-head turbines.
This class of devices can be found either onshore or
offshore.
Tidal Energy
Overtopping Device
These type of devices are characterized by a long
structure that uses waves to fill a water reservoir which
is located to a higher position respect to the sea level.
The potential energy of the water contained in the
reservoir is then exploited by low-head turbines.
This class of devices can be found either onshore or
offshore.
Tidal Energy
Submerged Pressure Differential
These devices use flexible membranes in order to exploit the
difference of pressure at different locations below a wave. This
pressure differential is then utilized in a closed power take-off (PTO)
fluid system, producing a fluid flow that drives a turbine and then an
electrical generator. The membranes are then used as a surface
between the ocean and the PTO system. These membranes are
characterized by a large rigidity and a low mass, allowing the
frequency content of the waves to be fully transferred to the fluid of
the PTO system.
A submerged converter of this type can be placed both in midwater
or on the seafloor, where the influence of the waves is attenuated.
It is possible to observe two possible configurations of this wide class
of devices:
the first (1st) presents a fixed structure tethered to the seabed and an
oscillating part that exploits the difference of pressure generated by
the travelling waves;
Tidal Energy
Submerged Pressure Differential
the second (2nd) presents a long flexible conducts on
which the differential of pressure generated by the
wave causes a water flux that passes through a low-
head turbine on the bow of the device. This second
type of device is also called Bulge Wave.
Tidal Energy
Notional Heaving Point Absorber Near-Shore Point Absorber
Tidal Energy
Surface Attenuator
These devices behave similarly to floating point
absorbers, but are constituted by a number of floating
bodies connected to one another. This chain of
floating bodies orients itself to the same direction of
the incoming wave, and a flexing motion is generated
by the waves on the system.
This motion drives hydraulic pumps, ultimately
generating electricity.
Tidal Energy
Rotating Mass Generator
These device are usually floating and are constituted by
a vessel in which one or more rotating masses are
found. The coupling between the rotation of the mass
and the movement of the hull produced by the waves
lead to the generation of a gyroscopic torque, which is
used by a rotary PTO to extract energy.
A clear example of a rotating mass generator is our
project called ISWEC (Inertial Sea Wave Energy
Converter). This system transform the wave-induced
rocking motion of a buoy into electrical power by
means of the gyroscopic effects produced from a
spinning flywheel carried inside the buoy.
Tidal Energy
PeWEC
PeWEC, acronym of Pendulum Wave Energy
Converter, in which the assigned system to the energy
generation consists by a group of pendulums that
through their oscillating motion, determined by hull’s
dynamic, transmit a force to PTO, who generates
electric energy.
PeWEC is initially aiming at lower energetic closed seas
with lower-period waves (e.g., the Mediterranean Sea).
When the device is moved by the waves, a relative
motion between the hull and the internal pendulum is
obtained, mostly due to the pitching motion.
Tidal Energy
River Current
Turbines
Tidal Stream
Dynamic
(In-Stream)
Tidal
Turbines
Power
Limitations:
Maintenance, Limitations:
Variable Energy Experimental Stage,
Output, High Cost and Limitations:
Installation Challenges Engineering Environmental Impact,
Complexity Maintenance
Questions
A tidal barrage operates with a tidal range of 6 meters. The area of the basin behind the barrage is 5 km². The density of
seawater is 1025 kg/m³.
(a) Calculate the total potential energy available per tidal cycle.
(b) If the tidal cycle occurs twice a day, what is the daily energy output?
A tidal stream turbine operates in water moving at 2.5 m/s. The turbine has a blade radius of 10 meters and a power
coefficient (Cp) of 0.4. The density of seawater is 1025 kg/m³.
•Calculate the power generated by the turbine.
A tidal power plant generates 50 MW of power. If the theoretical energy potential is 120 MW, determine the efficiency
of the plant.
A tidal turbine produces 200 kW at a water velocity of 3 m/s. Assuming the power varies with the cube of velocity,
estimate the power output if the velocity drops to 2 m/s.
Questions
A wind turbine operates in an area with:
•Wind velocity = 8 m/s
•Rotor diameter = 20 m
•Air density = 1.225 kg/m³
(a) Calculate the total available wind power in the swept area.
(b) Find the maximum power extractable based on Betz’s limit.
A wind turbine has the following data:
•Wind velocity = 10 m/s
•Rotor radius = 15 m
•Air density = 1.225 kg/m³
•Actual power output = 250 kW
(a) Calculate the theoretical maximum power using Betz’s law.
(b) Determine the power coefficient (Cp), which represents the efficiency of the turbine.
A wind turbine generates 100 kW when the wind speed is 6 m/s. Assuming the power extracted is proportional to the
cube of wind velocity, calculate the expected power output when:
(a) Wind speed increases to 9 m/s
(b) Wind speed decreases to 4 m/s
35
Atul Singh Rajput
Email ID: atulsingh@nitk.edu.in
