SOLAR STIRLING ENGINE seminar report

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DEPT. OF MECHANICAL ENGINEERING
ACKNOWLEDGEMENT
It is my privilege to express my gratitude to Dr. N PRABHU, Principal,
Kottayam Institute of Technology and Science for providing all technical facilities in the
campus. I thankfully remember all the faculty members and my friends for their valuable
suggestions and kind co-operation.
I also extent my sincere thanks to Mr. NANDHAKUMAR, Head of the
Department of Mechanical Engineering, for giving constant encouragement and valuable
support for completing the seminar successfully.
I would like to express my deepest gratitude to all those who provided me the
possibility to complete the seminar. Foremost, this seminar work would not have been
possible without the guidance of my guide, Mr. SUNIL P VIJAYAN Assistant
Professor, Department of Mechanical Engineering, KITS, who provided the vision,
encouragement and necessary advice for me during the development of seminar.
I express my sincere gratitude to the ALMIGHTY GOD, for giving me the
strength and power to complete the seminar on time.

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ABSTRACT
Electricity has become one of our basic needs of human life today. It plays a vital
role in every sector. But unfortunately, most of the electricity generated today is from
fossil fuels; over 52% in India to be precise. As they are on the brink of extinction, the
search for new source of energies, preferably sustainable ones has long begun. In this run
solar has proven to be one of the most sustainable sources of energy yet it failed to keep
its place in the generation of electricity. It is because the techniques of harvesting solar
energy are limited today. Use of PV panels is the most common technique. But there
exists various methods in generating solar electricity, namely – photovoltaic panels,
concentrated photovoltaic panels, photo – electro – chemical process, dye – synthesized,
thermo electric and solar thermal. Every method uses a unique technique to generate
electricity. But their feasibility in market depends on various factors such as capital
investment, reliability, efficiency and so on. It is essential to explore new methods to
make the most abundant resource a reliable one. Of all the techniques, solar thermal has
proven to be the most effective way to harness solar energy. Its ability to provide thermal
storage makes it all the more interesting. Solar Stirling Generator is a technique that falls
under the category of solar thermal energy. It employs an external combustion engine
known as the Stirling Engine. It is so far the best technology available for electricity
generation from sun light. This has been justified and its manufacturability along with
scope in Indian market has been discussed in this paper.

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TABLE OF CONTENT
TOPIC PAGE NO.
ACKNOWLEDGEMENT I
ABSTRACT II
LIST OF FIGURES VII
CHAPTER 1
INTRODUCTION 01
1.1 BASIC STIRLING ENGINE 01
1 HOT CYLINDER WALL 02
2 COLD CYLINDER WALL 02
3 COOLANT INLET AND OUTLET PIPES 02
4 THERMAL INSULATION 03
5 DISPLACEABLE PISTON 03
6 POWER PISTON 03
7 FLYWHEEL AND LINKAGE CRANK 03
1.2 TYPES OF STIRLING ENGINE 04
1.3 ALPHA CONFIGURATION 04

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1.4 BETA CONFIGURATION 05
1.5 GAMMA CONFIGURATION 06
CHAPTER 2
HISTORY OF STIRLING ENGINE 08
2.1 COMPETITION FROM INTERNAL COMBUSTION 08
2.3 WHY DESIGN A STIRLING ENGINE? 09
2.4 POWER GENERATION TECHONOLOGIES 10
CHAPTER 3
OPERATION OF STIRLING ENGINE 12
3.1 STIRLING ENGINE STAGES 13
3.2 STIRLING ENGINE WITH SOLAR 13
3.3 CONCENTRATING SOLAR PLANTS 14
3.4 CARNOT CYCLE AND STIRLING CYCLE 15
CARNOT CYCLE 16
THE STIRLING CYCLE 16
3.5 EFFICIENCY 17
3.6 TEMPERATURE PROFILE 18

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CHAPTER 4
FEATURES 20
4.1 COMPARISON WITH OTHER TECHNOLOGIES 21
4.2 SCOPE IN INDIAN MARKET 22
1 ON A MEDIUM-LARGE SCALE ELECTRICITY GENERATION 22
2 FOR INDUSTRIES 22
3 ON A SMALL SCALE – FOR HOMES AND BUILDINGS 23
4 IN AGRICULTURE 23
5 RURAL ELECTRIFICATION 23
4.3 HURDLE’S MARKET S IN TODAY 24
4.4 MANUFACTURABILITY 24
4.5 GOVERNMENT REFORMS 25
4.6 ENCOURAGE MANUFACTURING 26
4.7 SMART GRID 26
4.8 PRIVATIZATION 26
4.9 GLOBAL COMPETETIVENESS 27
4.10 DVANTAGESANDDISADVANTAGES 27
4.11 APPLICATIONS 28

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CHAPTER 5
CONCLUSION 29
REFERENCE 30

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LIST OF FIGURE
FIG. 1 BASIC SOLAR STIRLING ENGINE 02
FIG. 2 ALPHA STIRLING ENGINE 04
FIG. 3 BETA STIRLING ENGINE 06
FIG. 4 GAMMA STIRLING ENGINE 07
FIG. 5 STIRLING ENGINE STAGES 13
FIG. 6 CARNOT CYCLE 16
FIG. 7 TEMPERATURE PROFILE 18

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DEPT.OF MECHANICAL ENGINEERING
CHAPTER 1
INTRODUCTION
A Stirling engine is a heat engine operating by cyclic compression and expansion
of air at different temperature levels such that there is a net conversion of heat energy to
mechanical work.
Like the steam engine, the Stirling engine is traditionally classified as an external
combustion engine, as all heat transfers to and from the working fluid take place through
the engine wall. This contrasts with an internal combustion engine where heat input is by
combustion of a fuel.
Engine encloses a fixed quantity of air as is the case with other heat engines, the
general cycle consists of compressing cool gas, heating the gas, expanding the hot gas,
and finally cooling the gas before repeating the cycle. The efficiency of the process is
narrowly restricted by the efficiency of the Carnot cycle, which depends on the
temperature between the hot and cold reservoir.
The Stirling engine is exceptional for of its high efficiency compared to steam
engines, quiet in operation and the ease with which it can use almost any heat source.
This is especially significant as the prices of conventional fuel prices rise in a more
“green cautious” world.
1.1 BASIC STIRLING ENGINE
The engine is designed so that the working gas is generally compressed in the
colder portion of the engine and expanded in the hotter portion resulting in a net
conversion of heat into work. An internal Regenerative heat exchanger increases the
Stirling engine's thermal efficiency compared to simpler hot air engines lacking this
feature. Key components:

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Fig. 1 BASIC SOLAR STIRLING ENGINE
1. Pink – Hot cylinder wall
2. Dark grey – Cold cylinder wall
3. Yellow – Coolant inlet and outlet pipes
4. Dark green – Thermal insulation separating the two cylinder ends
5. Light green – Displacer Piston
6. Dark blue – Power piston
7. Light blue – Linkage crank and flywheel
1. HOT CYLINDER WALL
It is the cylinder through which the external heat source is connected that
provides heat to the gas inside this cylinder in order to expand the gas.
2. COLD CYLINDER WALL
It is the cylinder that provides cooling of the gas by some external means like
cooling system, in order to reuse the gas for another cycle.
3. COOLANT INLET AND OUTLET PIPES
cooling pipes which are connected from power chamber to regenerator, a
cooling chamber disposed around the cooler, and an air pre-heater disposed at a
side of combustion chamber, whereby the operating fluid of engine is cooled by
utilizing the thermoelectric heat pump so that circulation of continuous cooling
water is not required and heat taken out of the operating fluid is made to use for
the pre-heating of the air to be fed to the combustion chamber.

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4. THERMAL INSULATION
The upper portion of the pressure vessel is insulated from the hot surfaces
of the hot heat transfer fluid tubing, hot pistons, hot cylinders, hot heat
exchangers, hot diffusers, and the regenerator canisters. Because the hot-side
temperature is low enough for the hot-side pistons to safely contact their cylinders
while sliding, the hot-side pistons and cylinders operate at the hot-side
temperature. Thus, no insulating caps are used on the hot pistons, eliminating the
pumping loss and the shuttle conduction loss. Because the layout of the 25 kW
Thermo Heart Engine has a clear demarcation between a single hot zone and a
single cold zone, insulating the hot zone has been both more straightforward and
more effective than on previous engines, as evidenced by the long time it takes for
the hot zone to cool down when the engine is stopped.
5. DISPLACER PISTON
The displacer is a special purpose piston, used to move the working gas
back and forth between the hot and cold heat exchangers. Depending on the type
of engine design, the displacer may or may not be sealed to the cylinder, i.e. it is a
loose fit within the cylinder and allows the working gas to pass around it as it
moves to occupy the part of the cylinder beyond.
6. POWER PISTON
This consists of a piston head and connecting rod that slides in an air tight
cylinder. The power piston is responsible for transmission of power from the
working gas to the flywheel. In addition, the power piston compresses the
working fluid on its return stroke, before the heating cycle. Due to the perfect air
tight requirement, it is the most critical part in design and fabrication.
7. FLYWHEEL AND LINKAGE CRANK
The flywheel is connected to the output power of the power piston, and is
used to store energy, and provide momentum for smooth running of the engine. It
is made of heavy material such as steel, for optimum energy storage.

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1.2 TYPES OF STIRLINGENGINES
There are two major types of Stirling engines that are distinguished by the way
they move the air between the hot and cold sides of the cylinder. The two piston alpha
type design has pistons in independent cylinders, and gas is driven between the hot and
cold spaces.
The displacement type Stirling engines, known as beta and gamma types, use an
insulated mechanical displacer to push the working gas between the hot and cold sides of
the cylinder. The displacer is large enough to insulate the hot and cold sides of the
cylinder thermally and to displace a large quantity of gas. It must have enough of a gap
between the displacer and the cylinder wall to allow gas to flow around the displacer
easily
1.3 ALPHA CONFIGURATION
As shown in figure Alpha Stirling contains two pistons in separate cylinders, one
hot and one cold. The hot cylinder is situated inside the high temperature heat exchanger
and the cold cylinder is situated inside the low temperature heat exchanger. This type of
engine has a high-to power volume ratio but has technical problems due to the usually
high temperature of the hot piston and durability of its seals.
Most of the working gas is in contact with the hot cylinder walls, it has been
heated and expansion has pushed the hot piston to the bottom of its travel in the cylinder.
The expansion continues in the cold cylinder, which is 90° behind the hot piston in its
cycle extracting more work from the hot gas.

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The gas is now at its maximum volume. The hot cylinder piston begins to move
most of the gas into the cold cylinder, where it cools and the pressure drops.
Almost all the gas is now in the cold cylinder and cooling continues. The cold
piston, powered by flywheel momentum other piston pairs on the same shaft) compresses
the remaining part of the gas. The gas reaches its minimum volume, and it will now
expand in the hot cylinder where it will be heated once more, driving the hot piston
power.
1.4 BETA CONFIGURATION
In this section is A Beta Stirling has a single power piston arranged within the
same cylinder on the same shaft as a displacer piston. The displacer piston is a loose fit
and does not extract any power from the expanding gas but only serves to shuttle the
working gas from the hot heat exchanger to the cold heat exchanger. When the working
gas is pushed to the hot end of the cylinder it expands and pushes the power piston. When
it is pushed to the cold end of the cylinder it contracts and the momentum of the machine,
usually enhanced by a flywheel, pushes the power piston the other way to compress the
gas. Unlike the alpha type, the beta type avoids the technical problems of hot moving
seals.

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Power piston (dark grey) has compressed the gas, the displacer piston (light
grey) has moved so that most of the gas is adjacent to the hot heat exchanger.
The heated gas increases in pressure and pushes the power piston to
the farthest limit of the power stroke.
The displacer piston now moves, shunting the gas to the cold end the
cylinder.
The cooled gas is now compressed by the flywheel momentum. This
takes less energy, since when it is cooled its pressure drops.
1.5 GAMMA CONFIGURATION
A gamma Stirling is simply a beta Stirling in which the power piston is mounted
in a separate cylinder alongside the displacer piston cylinder, but still connected to the

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same flywheel. The gas in the two cylinders can flow freely between them and remain a
single body. This configuration produces a lower compression ratio but mechanically
simpler and often used in multi-cylinder Stirling engines as shown in figure.
Fig. 3 GAMMA STIRLING ENGINE

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CHAPTER 2
HISTORY OF STIRLING ENGINE
On September 27, 1816, Church of Scotland minister Robert Stirling applied for a
patent for his economizer in Edinburgh, Scotland. The device was in the form of an
inverted heat engine, and incorporated the characteristic phase shift between the displacer
and piston that we see in all Stirling Engines today.
The engine also featured the cyclic heating and cooling of the internal gas by
means of an external heat source, but the device was not yet known as a Stirling Engine.
That name was coined nearly one hundred years later by Dutch engineer Rolf Meijer to
describe all types of closed cycle regenerative gas engines.
Stirling originally regarded his engine as a perpetual motion machine of the
second kind (i.e. all heat supplied would be converted into work even though his original
hot air engine did not include a cooling system.
Due to the invention of the more powerful internal combustion engine at the
middle of the 19th
century, the Stirling technology was abandoned. But even so, the
Stirling engine had an extra advantage over the steam engine due to its low operating
cost. Also, the steam engine was prone to major failures like explosions. The only major
problem with the Stirling engine was its tendency to fail when the cylinder being heated
became too hot.
Although improvements were made to curb up the problem, stiff competition
from the internal combustion engine forced the hot air engine out of the commercial
scene.
2.1 COMPETITION FROM INTERNAL COMBUSTION
The invention of the internal combustion engine in the 1990’s put the nail on the
coffin for the Stirling type of engine because it generated more power and proved to be
more practical in the automobile industry.

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Due to the Rigorous Solar Energy Exploration taking place in the developed
economies, this old technology is being given a newer and fresher approach. In Jordan
scenario, the Stirling engine hopes to offer energy to rural and marginalized areas where
the most common sources of energy include:
Biomass fuel from burning of charcoal, firewood, rice husks, coal, maize cobs
among others.
Biogas - which has become a great use in the rural areas for both cooking and
lighting.
Solar heating - which has made its debut in the rural areas as an alternative means
of cooking energy through use of solar concentrators.
2.3 WHY DESIGN A STIRLING ENGINE?
There are several reasons to use a Stirling Engine
1. One reason is that for this kind of engine it’s almost impossible to explode.
You don’t have to produce steam in a high pressure boiler. And inside the
cylinder there are no explosions needed to run the pistons like in an Otto or
Diesel engine. There are no ignitions, no carburetion because you only need
one kind of gas and no valve train because there are no valves. This was a big
advantage to the steam engines in the days when Stirling invented his engine
because it was much less dangerous to work next to a Sterling Engine than to
a common steam engine.
2. Inside the pistons can be used air, helium, nitrogen or hydrogen and you don’t
have to refill it, because it uses always the same body of gas.
3. To produce heat you can use whatever you want: fuel, oil, gas, nuclear power
and of course renewable energies like solar, biomass or geothermal heat.
4. The external combustion process can be designed as a continuous process, so
the most types of emissions can be reduced.
5. If heat comes from a renewable energy source they produce no emissions.
6. They run very silent and they don’t need any air supply. That’s why they are
used a lot in submarines.

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7. They can be constructed to run very quiet and practically without any
vibration.
8. They can run with a small temperature difference, e.g. with the heat of your
hand or from a cup of hot coffee. They can be used as little engines for work
which needs only low power.
9. They can run for a very long time because the bearings and seals can be
placed at the cool side of the engine they need less lubricant and they don’t
have to be checked very often (longer period between the overhauls).
10. They are extremely flexible. The engine can run as a CHP (combined heat
and power) because the heat which is produced to run it can easily be
collected. Or in summers they can be used as coolers.
2.4 POWER GENERATION TECHONOLOGIES
CHP is the sequential or simultaneous generation of multiple forms of useful
energy (usually mechanical and thermal) in a single, integrated system. CHP systems
consist of a number of individual components prime mover (heat engine), generator, heat
recovery and electrical interconnection configured into an integrated whole.
The type of equipment that drives the overall system (i.e., the prime mover)
typically identifies the CHP system. Prime movers for CHP systems include steam
turbines, gas turbines (also called combustion turbines), spark ignition engines, diesel
engines, micro turbines, and fuel cells.
These prime movers are capable of burning a variety of fuels, including
biomass/biogas, natural gas, or coal to produce shaft power or mechanical energy.
Additional technologies are also used in configuring a complete CHP system, including
boilers, absorption chillers, desiccants, engine-driven chillers, and gasify. Although
mechanical energy from the prime mover is most often used to drive a generator to
produce electricity, it can also be used to drive rotating equipment such as compressors,
pumps, and fans. Thermal energy from the system can be used in direct process
applications or indirectly to produce steam, hot water, hot air for drying, or chilled water
for process cooling.

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The industrial sector currently produces both thermal output and electricity from
biomass in CHP facilities in the paper, chemical, wood products, and food processing
industries. These industries are major users of biomass fuels utilizing the heat and steam
in their processes can improve energy efficiencies by more than 35 percent. In these
applications, the typical CHP system configuration consists of a biomass-fired boiler
whose steam is used to propel a steam turbine in addition to the extraction of steam or
heat for process use.
The following technologies are discussed in this section, with specific respect to
their ability to run on biomass or biogas. A synopsis of key characteristics of each
I. Steam turbines: Convert steam energy from a boiler or waste heat into shaft
power.
II. Gas (combustion) turbines, including micro turbines: Use heat to move turbine
blades that produce electricity.
III. Reciprocating internal combustion (IC) engines: Operate on a wide range of
liquid and gaseous fuels but not solid fuels. The reciprocating shaft power can
produce either electricity through a generator or drive loads directly.
IV. Fuel cells: Produce an electric current and heat from a chemical reaction between
hydrogen and oxygen rather than combustion. They require a clean gas fuel or
methanol with various restrictions on contaminants.
V. Stirling engines Operate on any fuel and can produce either electricity through a
generator or drive loads directly

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CHAPTER 3
OPERATION OF STIRLING ENGINE
Since the Stirling engine is a closed cycle, it contains a fixed mass of gas called
the "working fluid", most commonly air, hydrogen or helium. In normal operation, the
engine is sealed and no gas enters or leaves the engine. The Stirling engine, like most
heat engines, cycles through four main processes: cooling, compression, heating and
expansion. This is accomplished by moving the gas back and forth between hot and cold
heat exchangers, often with a regenerator between the heater and cooler. The hot heat
exchanger is in thermal contact with an external heat source, such as a fuel burner, and
the cold heat exchanger being in thermal contact with an external heat sink, such as air
fins. A change in gas temperature will cause a corresponding change in gas pressure,
while the motion of the piston causes the gas to be alternately expanded and compressed.
The gas follows the behavior described by the gas laws which describe how a gas'
pressure, temperature and volume are related. When the gas is heated, because it is in a
sealed chamber, the pressure rises and this then acts on the power piston to produce a
power stroke. When the gas is cooled the pressure drops and this means that less work
needs to be done by the piston to compress the gas on the return stroke, thus yielding a
net power output.
To summarize, the Stirling engine uses the temperature difference between its hot
end and cold end to establish a cycle of a fixed mass of gas, heated and expanded, and
cooled and compressed, thus converting thermal energy into mechanical energy. The
greater temperature differences the greater thermal efficiency.

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3.1 STIRLING ENGINE STAGES
Fig. 3 STIRLING ENGINE STAGES
3.2 STIRLING ENGINE WITH SOLAR
Solar energy is one of the more attractive renewable energy sources that can be
used as an input energy source for heat engines. In fact, any heat energy source can be
used with the Stirling engine. The solar radiation can be focused onto the displacer hot-
end of the Stirling engine, thereby creating a solar – powered prime mover. The direct
conversion of solar power into mechanical power reduces both the cost and complexity of
the prime mover. In theory, the principal advantages of Stirling engines are their use of
an external heat source and their high efficiency. Stirling engines are able to use solar
energy that is a cheap source of energy.

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A solar powered stirling engine was patented by Roelf J Meijer in 1987. His
invention relates a heat engine, such as a Stirling cycle engine, with a solar dish collector
in order to produce electricity. This apparatus consists of a large dish aimed at the sun to
reflect the rays into the focus point, which is located at the center of the dish. Solar
energy is now collected in the form of heat to fuel in a Stirling cycle engine. Which
operates by letting heat flow from a hot source to a cold sink in order to do work. The
work output of the stirling cycle is then used to drive a generator and create electric
power.
Placed at the focus of a parabolic mirror a Stirling engine can convert solar
Energy to electricity with efficiency better than non – concentrated photovoltaic cells.
In 2005, it is created a 1 KW Stirling generator with a solar concentrator, this was
a herald of the coming of a revolutionary solar, now days it generates electricity much
more efficiently and economically than Photovoltaic (PV) systems with technology called
concentrated solar power (CPS). Nowadays the company Infant Applications has
development a 3 KW Solar Stirling product.
By a mirror to focus the sun’s rays on the receiver end of a Stirling engine. The
internal side of the receiver then heats hydrogen gas, which expands. The pressure
created by the expanding gas drives a piston, crank shaft, and drive shaft assembly much
like those found in internal combustion engines but without igniting the gas. The drive
shaft is connected to a small electricity generator.
Generally concentration solar power (CSP) and is significant potential grid for
water pump in or electrification.
3.3 CONCENTRATING SOLAR PLANTS
Concentrating solar power plants uses parabolic trough collectors or central tower
concentration arrangement. In parabolic trough system a parabolic shaped concentrator of
aluminum is used. In the Centre the receiver is placed. The temperatures at the Centre
point are of 232 degree calcium. In the central tower system many number of Helios
tastes are arranged in pattern such that the entire reflection of each heliostat towards a
central tower. The central tower acts as a receiver. Generally molten salt is used as a
working fuel to exchange the heat. Sun catcher technology is also same as parabolic

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trough but with some modifications. In the solar stirling scheme instead of using external
gas turbines direct stirling engine is used besides heat exchange media.
Fig. 4 TYPICAL EFFICENCY COMPARISON OF CPC AND FLAT PLATE COLLECTORS FOR
1000WM2
SOLAR INSOLATION
3.4 CARNOT CYCLE AND STIRLING CYCLE
The Carnot cycle has a low mean effective pressure because of its very low work
output. Hence, one of the modified forms of the cycle to produce higher mean effective
pressure whilst theoretically achieving full Carnot cycle efficiency is the Stirling cycle.
Similar to Carnot cycle stirling engine cycle also uses the liquid or gaseous heat exchange
medium.
The Ideal Gas Law describes the relationship between pressure, volume and
temperature of gas in a closed system. It is written P·V = n·R·T
Where n is the number of moles of gas and R is a constant associated with the
particular gas or mix of gasses in the engine. R and n will both be constants for a given
engine, and so their product, nR will be a constant.

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CARNOT CYCLE
Carnot, a French Scientist showed that the most efficient possible cycle is one in
which all the heat supplied is at one fixed temperature, and all the heat rejected is rejected
at a lower temperature. The cycle therefore consists of two isothermal processes joined
by two adiabatic processes. Since all processes are reversible, then the adiabatic
processes in the cycle are also isentropic. The cycle is most conveniently represented on a
T-S diagram as shown below
Fig. 5 THE CARNOT CYCLE ON A T-S DIAGRAM
THE STIRLING CYCLE
The Stirling cycle comes closest to the Carnot cycle efficiency while having a
higher work ratio.
Despite the fact that the efficiency may not be practical in real fabrication and
testing, the Stirling engine gives the best output.
Fig. 6 STIRLING CYCLE

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The idealized stirlining cycle consists of four thermodynamic process acting on
network of the fluid
1-2: Constant volume heat addition: the gas passes back through the regenerator
where it recovers much of the heat transferred in (2) above, heating up on its way to the
expansion space.
2-3: Isothermal expansion: the expansion space and associated heat exchanger
are maintained at a constant high temperature and the gas undergoes isothermal
expansion absorbing heat from the heat source.
3-4: Constant volume heat removal: the gas is passed through a regenerator
where it cools transferring heat to the regenerator for use in the next cycle.
4-1: Isothermal compression: the compression space and associated heat
exchanger are maintained at a constant low temperature so that the gas undergoes
isothermal compression, rejecting heat to the cold sink.
3.5 EFFICIENCY
Stirling cycle is a practical Carnot Cycle. It has a theoretical efficiency equivalent
to that of Carnot efficiency. But, the regenerator losses are to be considered. Over all, the
conversion efficiency of single unit ranges from 24% - 36% where as that of a PV system
is hardly 12%.
Where
W is the work done by the system (energy exiting the system as work),
QH is the heat put in to the system (heat energy entering the system),
Tc Is the absolute temperature of the cold reservoir, and TH is the absolute temperature of
the hot reservoir.

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Fig. 7 Comparison of Different Cycle Efficiency with Different Operating Temperatures
Solar energy is focused on the Solar Receiver that is converted to 25KW of
electricity for a peak conversion efficiency of approximately 31.25%. SES (stirling
energy systems) holds the world record of 31.25% efficiency for solar isolation to grid
commercial power.
3.6 TEMPERATURE PROFILE
Spain is the leading country in production of solar electricity through
concentrated solar power, producing over 3200 MW. In spite of its rich temperature
distribution, India possesses the installed capacities sum-up to only 800 MW. The
temperature profiles of India and Spain are compared below. It is estimated that the
potential of India would be nearly 10 times than that of Spain’s when utilized effectively.
The temperature profiles of both countries are display below.
Fig. 8 TEMPERATURE PROFILE IN INDIA AND SPAIN

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Be taken huge advantage. Stirling engines can work on temperature diffential as low as
even 7 . However, for an efficient conversion of sunlight to electricity, a temperature
difference (difference between hot end and cold end temperature) has to be ranging from
95℃ - 120 . In places where the concentrated temperature is not so high, the cold end
temperature may be varied and also the working fluid or regenerator design. It is the temperature
difference that really matters. It is to be noted that maintaining a lower temperature is
accompanied by a not so attractive price tag.

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CHAPTER 4
FEATURES
Though this technology is new, it is becoming the future of solar energy. It’s the
features of the Solar Stirling Generator that has made them star of Solar Electricity. Some
of the key features are listed below:
a. Environmental friendly: No gasses are released into atmosphere.
b. Quiet operation: As there are no turbines or heavy machinery, these tend to be very
quiet. Perhaps even quieter than an internal combustion engine.
b) No need of new transmission lines: As the power generated is AC.
c) Lesser payback period: Which is only 6 months or a large scale which in case of PV is a
minimum of 2 years.
d) Comparatively longer life time: PV panels produce electricity by self-destruction at
slower rate, which means they eventually die. They need to be replaced after the cell life
is down by 15 or 20 %. But the Stirling engines can run years and years. As there is no
explosion inside the cylinder just like internal combustion engine, the life of Stirling
engine is more than a traditional internal combustion engine.
e) Cheap electricity generation: The cost of electricity produces on a larger scale with a
plant efficiency of 32% would be about 7 rupees per KWH.
f) Minimum maintenance: When compared to a stem, hydro or nuclear power plant, the
maintenance is quiet easy.
g) Digital display: Every individual unit can be provided with a digital display to determine
the electricity generated by each unit.
h) Easy to implement: The barrier of being impractical is being shattered at un-imaginable
speeds.
i) More utilization of sunlight due to the solar tracker.
j) Hybridization: All that a Stirling engine needs is a source of heat. It provides the
versatility of employing various fuels such as either geothermal, biogas or any other. A
hybrid solar Stirling generator is the best possible way to harvest electricity to harvest all
year long.

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4.1 COMPARISON WITH OTHER TECHNOLOGIES
The various technologies in harvesting solar electricity are mentioned below and
are compared with certain characteristics.
CONC – PV* = CONCENTRATED PHOTO VOLTAIC PANELS.
CHARACTERISTICS PV
CONC-
PV*
PARABOLIC
TROUGH
SOLAR
TOWER
SOLAR STIRLING
GENERATOR
Base load capacity     
Competitive cost of
electricity generated
    
Maxed conversion
efficiency
    
Hybridization     
Thermal storage     
Longer life time     
AC output     
Least area required
per KWH
    
Affordable investment     
Less hassle     

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4.2 SCOPE IN INDIAN MARKET
The Scope of concentrated solar power in sun-blessed regions like India is
immense. Electricity is one of the building blocks of every developing nation. There are
five major areas of applications for the solar Stirling.
Generator namely:-
1. On a medium-large scale electricity generation
2. For industries
3. On a small scale- For homes and buildings
4. In Agriculture
5. Rural electrification
1. ON A MEDIUM-LARGE SCALE ELECTRICITY GENERATION
On a large scale, SSG have recorded highest efficiency that can be
obtained on commercial, practical solar electricity technologies with reasonable
area and investment. Also, the cost of electricity generated is cheapest when
compared to other solar techniques. The output electricity generated is AC. Hence
there is no need of another setup as in case of PV panels where the generated DC
has to be converted into AC for further applications. There is no need for new
transmission lines. The existing ones would very well suffice.
2. FOR INDUSTRIES
Power crisis is one of the most unmanageable macro-economic challenges
faced by Indian Industries. It creates a vulnerable situation where few already
started shutting down. During summer, it gets even worse. Most of the places
suffer power cuts of at least 6 hours. The possible solution could be companies
becoming power independent, thus resulting Green Industries. The industries
run on green and clean power. The solar Stirling generators are so versatile. Each
unit can generate from 10KW or even lower up to 1MW!! The area required per
KW depend on various factors, such as the temperature profile of region,

KITS SEMINAR REPORT
23
specifications of engine. Each individual unit is capable of producing electricity.
There is no processing at various stations as in a thermal power station where the
steam generation, turbine containment, condensers, cooling towers and all the
other processes are necessary for power generation. An industrial area can be
given its own power generation instead of each company as on larger scale, the
systems are cost effective.
3. ON A SMALL SCALE- FOR HOMES AND BUILDINGS
These systems are not very effective on smaller scale, but are sure better
than PV systems. Gated communities, municipalities etc can have them set up
where the original power lines may just be taken as the backup ones. 24 hour
electricity guarantee is an attractive feature to put up.
4. IN AGRICULTURE
The latest break-through is solar Stirling water pumps. It is ironic that one
strives for food in their entire life and yet agriculture is one of the most neglected
sectors. With proper strategies, dependence of agriculture on monsoon can be
reduced. One such strategy would include the setting up of solar pump in fields.
They are so compact hence can be shared by various fields. Proper water supply
system would be much handy. Government initiatives will be appreciated.
5. RURAL ELECTRIFICATION
India is a nation of villages. Almost 2/3rd
of its population lives country
side. But unfortunately, only less than a 30% of rural population is accustomed to
electricity. The major problem behind rural electrification is the transmission
losses, which are accounted to appalling 30 %. Villages are offset from the cities,
often at very large distances. Setting up of new power lines would cost a fortune.
The nation doesn’t have enough power to feed industrial sector and cities. Where

KITS SEMINAR REPORT
24
comes the question of villages? Hence the villages are often left un-electrified.
The Solar Stirling Generators can be set up in the village premises itself. Single
plant can be used for various surrounding villages. Biogas could be best hybrid
fuel. This is a major step towards the development of villages. Villages do
deserve a chance to develop alongside with the cities, which determines the true
development of nation, as quoted by many leaders including honorable Prime
Minister, Sri. Narendra Modi.
4.3 HURDLE’S MARKET S IN TODAY
Though this is a very potential technology, we don’t find this in market today.
The major drawback is that, it is a very new technology. It takes a little while to creep
into the markets. Apart from this, there are few other challenges faces, as mentioned
below:
 Rapidly reducing costs of PV modules
 Well established PV market
 Few manufacturing challenges
 Known for being impractical
 Comparatively higher investment
4.4 MANUFACTURABILITY
The components of this system are not relatively simpler, but the raw materials
are all abundant in India. The machining processes required are also quite simpler when
compared to that of an internal combustion engine. Manufacturing of curved glass is
done by making a mould of mild steel first. Then the mould is pre heated and later a glass
plank of required dimensions is placed in that. The entire setup is heated together and
cooled in a process called annealing. It particularly requires skilled labor. The
manufacturing can be either done all in house, i.e. all the components manufactured
individually in a single factory or by adopting revolutionary techniques such as JIT (Just
in Time), lean manufacturing etc. The later ones have proved to be very beneficial as they
increase the productivity. Few required components are to be brought from various other
allied industries and then are assembled. This also reduces the capital investment
significantly.

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The following chart explains the manufacturability-
Component Sub-component Material Manufacturing process
Collector
i) Dish PVC Injection molding
ii) Curved glass
surface
Glass Special technique
Stirling
Engine
i) Hot end Lens (biconcave) Available in market
ii) Cooling system Radiator Available in market
iii) Cylinder lining
Available in market
iv) Connecting rods
v) pistons
vi) valves
vii) Housing
Cast iron/
Aluminum
Casted / welded
ix) Working fluid
Helium/ nitrogen
/air/other
Available in market
Electricals
and
Electronics
i) GPS tracking ----- Available in market
ii) Alternator ----- Available in market
iii) wirings ----- Available in market
Support
structure
i) Frame work S.S. , PVC ,
ii) Stand S.S, Aluminum Welding
4.5 GOVERNMENT REFORMS
Government policies should encourage growth of renewable energy segment. This
may involve tax benefits, assured power purchase agreements for power generated from
these segments, privatization etc.

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4.6 ENCOURAGE MANUFACTURING
India is generally a trader oriented economy. Any industry strives to make 7-9%
of profit on any product. But the trades instead make 20% profits easily, which is not a
very good sign for developing countries, such as India. This encourages the foreign goods
to be just brought by traders and selling them at desired profits. It distorts the nation’s
economy. To avoid this, traders’ licenses are to be imposed with certain limitations, fair
enough thought to promote equivalent profits.
4.7 SMART GRID
Smart grid’s represent the energy internet of the future, it is central to reduce
T&D losses in Indian power distribution Sector. Smart grid is an electrical grid that uses
information and communications technology to gather and act information, such as
information about the behaviors of suppliers and consumers. It presents some primary
benefits including lower operating and maintenance costs, lower peak demand, increased
reliability and power quality, reduction in power theft and resultant revenue losses,
reduction in carbon emissions and expansion of access to electricity. Smart grids through
demand response and load management reduce per unit production cost. A smart grid can
reduce the need for additional transmission lines by reducing peak demand. Learning
from European nations, USA & China, who have firm steps in this direction, India should
aim to bring reforms in this direction at earliest.
4.8 PRIVATIZATION
Most of the electricity generation firms are owned by government itself as they
require really huge investment as in case of nuclear or thermal. Manufacturing of Solar
Stirling Generators is possible with minimum hassle. Industries in private sector can
manufacture these and market not only within the nation, but also abroad. Private sectors
find maximum scope in this field.

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4.9 GLOBAL COMPETETIVENESS
Once the quality constraint is maintained, these can be sold globally. India faces
various challenges in Global Competitiveness today. To conquer global markets, the
following are to be considered:
 Quality
 Reliability
 Attractive price tag
 Marketing strategies
 Logistic s
It is important to note that it is not the price that is to be reduced, instead the value
has to be increased which is a basis for Value Engineering.
4.10 ADVANTAGES AND DISADVANTAGES
 Inside the pistons can be used air, helium, nitrogen or hydrogen and won’t
have to refillable because it uses always the same body of gas.
 To produce heat we can use whatever we want: fuel, oil, gas, nuclear
power and of course renewable energies slice solar, biomass or geothermal
heat.
 The external combustion process can be designed as a continuous process,
so the most types of emissions can be reduced.
 If heat comes from renewable energy source they produce no emissions.
 They run very silent and they don’t need any air supply. That’s why they
are used lot in submarines.
 They can run for a very long time because the bearings and seals can be
placed at the cool side of the engine → they need less lubricant and they
don’t have to be checked very often (longer period between the
overhauls).

KITS SEMINAR REPORT
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At the same time solar stirling engine suffers from discontinuous operation. Thus
most of the plants designed as hybrid system that uses other source to continue power
generation during non-availability of solar power.
4.11 APPLICATIONS
Applications of the Stirling engine range from heating and cooling to under water power
systems. A Stirling engine can function in reverse as a heat pump for heating or cooling. Other
uses include: combined heat and power, solar power generation, Stirling cry coolers, heat pump,
marine engines, and low temperature difference engines.
The Stirling engine is noted for its high efficiency compared to steam engines, quiet
operation, and the ease with which it can use almost any heat source. This compatibility with
alternative and renewable energy sources has become increasingly significant.

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CHAPTER 5
CONCLUSION
Today, Stirling engine are used some very specialized applications, like in
submarines or auxiliary power generators, where quiet operation is important. Stirling
engines are unique heat engines because their theoretical efficiency is nearly equal to
their theoretical maximum efficiency, known as the Carnot Cycle efficiency.
The best (and presumably most expensive) of current practical photovoltaic
systems convert about 22% of the available solar energy in to electricity. This mechanical
system claims 24%, and all using ordinary low-environmental-impact materials and
manufacturing techniques. Unlike fancy semiconductor solar panels.
The new era in harvesting solar energy has begun. It is just a matter of time before
these engines become a very potential source of solar electricity. Many countries have
already invested in this technology and are reaping the twin benefits of nation
development and environmental fortification. The solar thermal potential of India
remains undiscovered. Few estimates state that it might even be few Giga-watts. After 2
centuries of their invention, Stirling engines are now put to their full-fledged applications.

KITS SEMINAR REPORT
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REFERENCES
1. Keerthi Sirisha Nomula, Scope and manufacturability of solar stirling engine
generator in India, October 2015.
2. Rakesh K Bumataria and Nikul K Patel, Review of Stirling engines for pumping
water using solar energy as a source of power, January 2013.
3. Anish Saini, Sivam Kohli and Ajesh J Pillai, Solar powered stirling engine driven
water pump, November 2013.

SOLAR STIRLING ENGINE seminar report

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