This file is made by me using different books and different sites. As I forgot to note down the name of the books and sites, so these are not given here. Sorry for this but hope it will be helpful for you.

1. “Heaven’s light is our guide”
RAJSHAHI UNIVERSITY OF ENGINEERING & TECHNOLOGY
DEPARTMENT OF MECHATRONICS ENGNEERING
1st
Year, Even Semester, Session: 2018-2019
Course No: ME 1256
Course Title: Thermodynamics and Heat Transfer Sessional.
Assignment No: 01
Assignment Title: An assignment on Renewable Energy.
SUBMITTED BY:
A. K. M. MOHIBUR RAHMAN
ROLL-1808030
SUBMITTED TO:
Md. Robiul Islam
Lecturer
Department of Mechatronics Engineering
Rajshahi University of Engineering & Technology
Dip Kumar Saha
Lecturer
Department of Mechatronics Engineering
Rajshahi University of Engineering & Technology

2. RENEWABLE ENERGY
Introduction:
Renewable energy is energy from sources that are naturally replenishing but flow-limited;
renewable resources are virtually inexhaustible in duration but limited in the amount of energy
that is available per unit of time.
Renewable energy is the energy that is generated from natural processes those are continuously
replenished. This includes sunlight, geothermal heat, wind, tides, water, and various forms of
biomass. This energy cannot be exhausted and is constantly renewed.
The term renewable energy is used to describe energy that is obtained from natural resources.
Actually it comes from natural resources those do not deplete. It is sustainable and does not
result in a high degree of pollution. Sources of renewable energy include sunlight, wind, water,
biomass, and tides. Renewable energy is used for a variety of industrial and domestic activities.
Many countries have been substituting non-renewable energy for renewable energy due to the
latter’s low environmental impact.
Renewable Energy sources:
The major types of renewable energy sources are
• Hydropower
• Geothermal
• Wind
• Solar
• Ocean
• Biomass
o Wood and wood waste
o Municipal solid waste
o Landfill gas and biogas
o Ethanol
o Biodiesel

3. 1. Hydropower Energy:
Hydropower or water power (from Greek: ὕδωρ, "water") is power derived from the energy
of falling 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.
❖ How hydropower is captured:
A typical hydroelectric plant is a system with three parts: a power plant where the
electricity is produced, a dam that can be opened or closed to control water flow, and a
reservoir where water is stored. The water behind the dam flows through an intake and
pushes against blades in a turbine, causing them to turn. The turbine spins a generator to
produce electricity.
The amount of electricity that can be generated depends on how far the water drops and
how much water moves through the system. The electricity can be transported through
long-distance electric lines to homes, factories, and businesses. Other types of hydropower
plants make use of the flow through a waterway without a dam.
Fig 01: Hydropower Plant.

4. 2. Geothermal Energy:
Geothermal energy is thermal energy generated and stored in the Earth. Thermal energy is
the energy that determines the temperature of matter. The geothermal energy of the Earth's
crust originates from the original formation of the planet and from radioactive decay of
materials (in currently uncertain but possibly roughly equal proportions). The geothermal
gradient, which is the difference in temperature between the core of the planet and its
surface, drives a continuous conduction of thermal energy in the form of heat from the core
to the surface. The adjective “geothermal” originates from the Greek roots “ge”, meaning
earth, and “thermos”, meaning hot.
❖ How geothermal energy is captured
Geothermal springs for power plants. Currently, the most common way of capturing the
energy from geothermal sources is to tap into naturally occurring "hydrothermal
convection" systems, where cooler water seeps into Earth's crust, is heated up, and then
rises to the surface. Once this heated water is forced to the surface, it is a relatively simple
matter to capture that steam and use it to drive electric generators. Geothermal power plants
drill their own holes into the rock to more effectively capture the steam.
Fig 02: Geothermal Plant.

5. 3. Wind Energy:
Wind is a form of solar energy. Winds are caused by the uneven heating of the atmosphere
by the sun, the irregularities of the earth's surface, and rotation of the earth. Wind flow
patterns are modified by the earth's terrain, bodies of water, and vegetative cover. This
wind flow, or motion energy, when "harvested" by modern wind turbines, can be used to
generate electricity. Wind power is a sustainable and renewable energy, and has a much
smaller impact on the environment compared to burning fossil fuels.
❖ How wind energy is captured:
The terms "wind energy" or "wind power" describe the process by which the wind is used
to generate mechanical power or electricity. Wind turbines convert the kinetic energy in
the wind into mechanical power. This mechanical power can be used for specific tasks
(such as grinding grain or pumping water) or a generator can convert this mechanical power
into electricity to power homes, businesses, schools, and the like.
Wind turbines, like aircraft propeller blades, turn in the moving air and power an electric
generator that supplies an electric current. Simply stated, a wind turbine is the opposite of
a fan. Instead of using electricity to make wind, like a fan, wind turbines use wind to make
electricity. The wind turns the blades, which spin a shaft, which connects to a generator
and makes electricity.
Fig 03: Wind Mill.

6. 4. Solar Energy:
Solar energy, radiation from the Sun capable of producing heat, causing chemical reactions,
or generating electricity. The total amount of solar energy incident on Earth is vastly in
excess of the world’s current and anticipated energy requirements. If suitably harnessed,
this highly diffused source has the potential to satisfy all future energy needs. In the 21st
century solar energy is expected to become increasingly attractive as a renewable energy
source because of its inexhaustible supply and its nonpolluting character, in stark contrast
to the finite fossil fuels coal, petroleum, and natural gas.
❖ How solar energy is captured:
Solar radiation may be converted directly into electricity by solar cells (photovoltaic cells).
In such cells, a small electric voltage is generated when light strikes the junction between
a metal and a semiconductor (such as silicon) or the junction between two different
semiconductors. The power generated by a single photovoltaic cell is typically only about
two watts. By connecting large numbers of individual cells together, however, as in solar-
panel arrays, hundreds or even thousands of kilowatts of electric power can be generated
in a solar electric plant or in a large household array. The energy efficiency of most present-
day photovoltaic cells is only about 15 to 20 percent, and, since the intensity of solar
radiation is low to begin with, large and costly assemblies of such cells are required to
produce even moderate amounts of power.
Fig 04: Solar Plant.

7. ❖ How captured solar energy is converted into household works:
Fig 05: Capturing Solar Energy.

8. 5. Ocean Energy:
Ocean energy refers to the energy carried by ocean waves, tides, salinity, and ocean
temperature differences. The movement of water in the world’s oceans creates a vast store
of kinetic energy, or energy in motion. Some of this energy can be harnessed to generate
electricity to power homes, transport and industries.
The term ocean energy encompasses both wave power i.e. power from surface waves, and
tidal power i.e. obtained from the kinetic energy of large bodies of moving water. Offshore
wind power is not a form of ocean energy, as wind power is derived from the wind, even
if the wind turbines are placed over water.
The oceans have a tremendous amount of energy and are close to many if not most
concentrated populations. Ocean energy has the potential of providing a substantial amount
of new renewable energy around the world.
❖ How wave energy is captured:
• Using Wave Profile Devices:
The pitching and heaving of the waves causes a relative motion between an absorber and
reaction point. The left hand wave energy device above, uses a heavy ballast plate
suspended below the floating buoy. The buoy is prevented from floating away by a mooring
line attached to a sea-floor anchor. This mooring line allows the point absorber to operate
offshore in deeper waters.
As the buoy bobs up-and-down in the waves, a oscillatory mutual force reaction is
generated between the freely moving absorber and the heavy plate causing a hydraulic
pump in between to rotate a generator producing electricity. The middle wave energy
device operates in a similar manner to the previous floating buoy device. The difference
this time is that the freely heaving buoy reacts against a fixed reaction point such as a fixed
dead-weight on the ocean floor. As this type of point absorber is bottom mounted, it is
operated in shallower near shore locations.
Fig 06: Wave Profile Devices.

9. • Using Oscillating Water Column:
As the incident waves outside enter and exit the chamber, changes in wave movement on
the opening cause the water level within the enclosure to oscillate up and down acting like
a giant piston on the air above the surface of the water, pushing it back and forth. This air
is compressed and decompressed by this movement every cycle. The air is channeled
through a wind turbine generator to produce electricity as shown.
The type of wind turbine generator used in an oscillating water column design is the key
element to its conversion efficiency. The air inside the chamber is constantly reversing
direction with every up-and-down movement of the sea water producing a sucking and
blowing effect through the turbine. If a conventional turbine was used to drive the attached
generator, this too would be constantly changing direction in unison with the air flow. To
overcome this problem the type of wind turbine used in oscillating water column schemes
is called a Wells Turbine.
Fig 07: Oscillating Water Column.
• Using Wave Capture Device:
The basic impoundment structure can be either fixed or a floating structure tethered to the
sea bed. The wave overtopping device uses a ramp design on the device to elevate part of
the incoming waves above their natural height.
As the waves hit the structure they flow up a ramp and over the top (hence the name
“overtopping”), into a raised water impoundment reservoir on the device in order to fill it.
Once captured, the potential energy of the trapped water in the reservoir is extracted using
gravity as the water returns to the sea via a low-head Kaplan turbine generator located at
the bottom of the wave capture device.

10. Fig 08: Wave Capture Device.
❖ How tidal energy is captured:
• Using Tidal Barrage:
A Tidal Barrage is a type of tidal power generation that involves the construction of a fairly
low dam wall, known as a “barrage” and hence its name, across the entrance of a tidal inlet
or basin creating a tidal reservoir. This dam has a number of underwater tunnels cut into
its width allowing sea water to flow through them in a controllable way using “sluice
gates”. Fixed within the tunnels are huge water turbine generators that spin as the water
rushes past them generating tidal electricity.
Tidal barrages generate electricity using the difference in the vertical height between the
incoming high tides and the outgoing low tides. As the tide ebbs and flows, sea water is
allowed to flow in or out of the reservoir through a one way underwater tunnel system.
This flow of tidal water back and forth causes the water turbine generators located within
the tunnels to rotate producing tidal energy with special generators used to produce
electricity on both the incoming and the outgoing tides.
Fig 09: Tidal Barrage.

11. • Using Tidal Stream:
A Tidal Stream Generation system reduces some of the environmental effects of tidal
barrages by using turbine generators beneath the surface of the water. Major tidal flows
and ocean currents, like the Gulf Stream, can be exploited to extract its tidal energy using
underwater rotors and turbines.
Tidal stream generation is very similar in principal to wind power generation, except this
time water currents flow across a turbines rotor blades which rotates the turbine, much like
how wind currents turn the blades for wind power turbines. In fact, tidal stream generation
areas on the sea bed can look just like underwater wind farms.
Fig 10: Tidal Stream.

12. 6. Biomass Energy:
Biomass energy is any kind of energy that uses a biological organism (plant or animal) as
its source.
Because the definition of biomass is so broad, fuels that can be considered "biomass"
include a wide variety of items and researchers are discovering new biomass energy
sources all the time. Animal manure, landfill waste, wood pellets, vegetable oil, algae,
crops like corn, sugar, switch grass, and other plant material—even paper and household
garbage—can be used as a biomass fuel source.
Biomass fuel can be converted directly into heat energy through combustion, like the
burning of a log in a fireplace. In other cases, biomass is converted into another fuel source;
examples include ethanol gasoline made from corn or methane gas derived from animal
waste.
❖ How to produce Biomass energy:
All biomass energy production methods ultimately rely on the process of photosynthesis
in plants, where plants capture sunlight, carbon dioxide from the air, and water and use
them to produce carbohydrates. These plant-based carbohydrates are the materials that are
used to produce biomass energy.
In general, the two methods for producing biomass energy are by burning the biomass
directly and through the gasification of biomass.
• Direct burning of biomass materials: The biomass materials are burned and the
heat that is produced is used to heat water into steam. The steam is then sent through
a steam turbine, which generates electricity.
• Gasification: Wet biomass, such as manure or food waste, undergoes fermentation
in a special tank, producing methane. Dry biomass, such as agricultural waste, is
subjected to high temperatures in the absence of oxygen, producing synthesis gas
(syngas). The gas produced through either process is then burned to produce
electricity in a gas engine or a gas turbine.
• Fuel Cells: If the syngas is pure, it can be utilized in fuel cells for electricity
production. This is not yet a commercially-available technology.

13. ❖ Cycle of Biomass:
The Figure below shows how Biomass is cycle is continuing day by day:
Fig 11: Cycle of Biomass.

14. Renewable Energy at a glance:
Fig 12: A Village of Renewable Energy.
Advantage and Disadvantage of different renewable energy
sources:
Fig 13: Advantages & Disadvantages.

15. Advantages of Renewable Energy
1. Renewable energy is eco-friendly:
It is a clean source of energy, meaning, it has low or zero carbon and greenhouse emission.
Fossil fuels emit high levels of greenhouse gas and carbon dioxide, which are greatly
responsible for global warming, climate change, and degradation of air quality. Fossil fuels
also contribute to sulfur emission to the atmosphere leading to acid rains. Acid rains can cause
damage to buildings. Solar and wind power are considered eco-friendly because they emit zero
toxic gases to the environment. The use of renewable energy dramatically reduces the
dependence on fossil fuel as a source of energy, hence, cutting back on air pollution.
2. It’s a renewable resource:
This implies that they do not deplete over a lifetime and there is zero possibility that they will
run out (sustainable source of energy). Sources of energy like fossil fuels (oil, gas, and coal)
are considered limited resources and there is strong possibility that they will run out in the
future. Renewable energy can help developing countries from over-reliance on fossil fuels.
Powerful winds, heat emanating from beneath the earth, sunshine and moving water can
guarantee a huge and steady energy supply to a nation for many years.
3. Renewable energy is a reliable source of energy:
In the previous few decades, the use of fossil fuel has sharply increased. This over-reliance on
fossil fuels has led to our security being threatened. Fossils fuels are prone to trade disputes,
political instabilities, spike in energy prices and unnecessary wars. These variables affect a lot
more than a nation’s energy policies; they can significantly drain a county’s economy.
Although most argue that solar and wind energy are unreliable, a solid infrastructure puts this
argument to rest. If solar and wind plants are distributed over a large geographical location,
there can be minimal electricity generation interruption because weather disruptions in one
location cannot be the same in other locations.
4. Leads to job creation:
Renewable energy makes real economic sense because it is a cheaper alternative to most
traditional sources of energy. Since the inception of renewable energy, new and stable jobs
have been added to most world economies. For, instance, in Germany and UK, many jobs have
already been created thanks to their relentless efforts to develop and encourage the use of
renewable forms of energy. Experts project that with the ongoing rigorous campaigns to
embrace renewable energy, thousands of stable jobs will be created.
5. Renewable energy has stabilized global energy prices:
Change up to renewable sources of energy means stability of energy prices across the globe.
This is because the cost of renewable energy depends on the initial cost of installation of
renewable energy technologies as opposed to fossil fuels, which increase and decrease

16. depending on the current inflation and availability of the resource. Respective governments
would only need to cater to the initial costs and that’s it.
6. Less maintenance of facilities:
Once infrastructure for the harnessing of the renewable resource is laid down, there is low to
zero maintenance required. This means that the owners of the facilities will reap big profits
while providing cheap electricity to the population.
7. Boosts public health:
This is a no-brainer. If governments took upon themselves to build more renewable energy
facilities, the population would enjoy the health benefits. According to a study by the U.S.
Environmental Protection Agency, Americans spend approximately $361.7 to $886.5 billion
every year on overall health of the population. A big chunk of this budget goes to mitigate and
cure diseases related to fossils fuel use like heart diseases, cancer, and neurological disorders.
Greenhouse, carbon and sulfur compounds emitted by fossils fuels are risky to our health if
inhaled over time. This is reason enough to consider renewable energy moving forward.
8. Empowering of people in the countryside:
Renewable energy generation mainly takes place in remote settings. This means that local
towns would get a fair share of power generated, ultimately, catalyzing the regeneration of
those depressed areas both socially and economically. Electrification of those areas will open
up untapped opportunities for development through the advancement of greenhouses using
geothermal power, district heating of towns and communities through hot water generated by
the energy exploitation of forestry and agricultural biomass.
Disadvantages of Renewable Energy
1. Not every form of renewable energy is commercially viable:
Many forms of renewable energy must be collected at a specific location, which means
distribution networks must be setup to take advantage of the power that can be generated.
These networks require a massive fossil fuel investment that can take generations to neutralize
with the use of renewable energy. From tidal power to geothermal, the commercial viability of
many renewable energy resources is not available right now.
2. Many forms of renewable energy are location-specific:
Even solar energy has limited potential in some locations. In Seattle, Washington, just 71 days
per year are classified as “sunny,” or having a cloud cover that is less than 30%. Northern cities
may go prolonged periods without any sunlight during the winter months. Because renewable
energy is often location-specific, it may not be available for every community to use.

17. 3. Many forms of renewable energy require storage capabilities:
With traditional power resources, a home or business is connected to a local distribution grid
so that it can be accessed 24/7. When using a renewable energy resource, back-up and storage
resources must be included with the power generation opportunity. Sunlight doesn’t happen at
night. Wind speeds are not always consistent. The storage capabilities that are required can
push the cost of a new renewable energy system beyond what the average person or community
can afford.
4. Pollution is still generated with renewable energy:
Renewable energies are cleaner than most fossil fuels, but “cleaner” and “clean” are very
different terms. A resource like biomass still burns waste products and puts pollution into the
atmosphere. This includes carbon and methane, which are classified as greenhouse gases. The
technologies and facilities that are used to build renewable energy resources require fossil
fuels, as do the transportation and distribution networks. In many instances, renewable energy
relies on fossil fuels, whereas fossil fuels do not rely on renewables.
5. Renewables often require subsidies to make them affordable:
In the United States, an emphasis on biofuels and renewable energies led to the creation of
ethanol as a crude oil replacement. Despite taxpayer-funded subsidies in place for this corn-
based fuel, only 430,000 barrels per day were produced in 2007. That was enough to replace
2% of the oil that was being consumed while corn prices skyrocketed because of the crops
being funneled into this renewable fuel.
6. Some forms of renewable energy require a massive amount of space:
To produce 20 megawatts of energy, current solar technologies require 100 acres of space. In
comparison, the footprint for a nuclear power plant is 1 square mile to produce 1,000
megawatts of energy. Solar is therefore 45 times less space efficient compared to nuclear
power. Solar is even worse, requiring up to 360 square miles to produce the same energy as
one nuclear power plant.
7. Low-efficiency levels:
Renewable energy technologies are still significantly new to the market, meaning, they still
lack the much-needed efficiency. This poses forecast problems and investors may shy away
from investing their money for fear of not getting returns pretty quick.
Conclusion:
The advantages and disadvantages of renewable energy show us that this technology has great
potential. We have yet to realize its full potential, however, because of certain limitations that
come with renewables, with more investments into this technology, prices can be lowered, jobs
can be created, and the transition toward the consumption of fewer fossil fuels can happen.