The document describes a project to operate a Stirling engine using solar energy concentrated by a convex lens. A group of 7 students and their advisor are modifying an existing Stirling engine demonstration to be powered by sunlight rather than gas. Their objectives are to generate electricity using solar power to reduce grid dependence and provide environmentally friendly power. The design changes focus on increasing heat input through the solar concentrator and improving heat transfer to increase efficiency.

2. Group members Roll NO.
Sajjad Ahmed ( Group leader) 26
Ghulam Sarwar 14
Nasir Ali 07
Abdul Baqi 09
Shoaib Ahmed 23
Shafique Rehman 01
Project advisor: Engr. Bashir Ahmed Leghari

3. Overview
 The engine used for the demonstration of Stirling cycle in
the thesis presented in Department of Mechanical
Engineering BUET Khuzdar during 2011 was operated by
CNG/LPG gas. we wanted to operate that with direct solar
radiation using concentrating convex lens.

4. Introduction
 Convex lens is used to converge the solar radiation to a single
point so that high amount of heat energy is obtained.
 This heat energy is used to heat the displacer cylinder of the
stirling engine.
 When the air inside the cylinder is heated its pressure increases
that pushes the displacer. The displacer is connected to the
flywheel by the help of a connecting rod.
 The reciprocating motion of the displacer is converted into
rotational energy of the flywheel by the help of crank.
 This mechanical energy can further be used to produce electric
power.

5. Objective Of the Study
The objective of this project is closely linked to the energy
problem with a specific focus on electricity generation using
solar power
 To reduce the Grid dependence by building a residential
based cost effective and renewable power supply.
 To provide for relief work in disaster affected areas like
earthquake, flood etc.
 To avoid burning of fossil fuel for power generation and
provide a environment friendly power technology.

6. Solar Energy
 Solar energy is the heat energy obtained from the Sun
 In sheer size, solar energy has the potential to supply all
energy needs: electric, thermal, transportation etc
 It is regarded as the solution for reducing the use of fossil
and nuclear fuels and for a cleaner environment.
 Solar energy is very diffuse and is scattered, it therefore,
needs systems and components to capture and concentrate
it efficiently for conversions to any of the uses.

7. Solar-Electric Conversion Systems
There are many different
types of solar energy
systems that will convert the
solar resource into a useful
form of energy.
 CSP systems use lenses or
mirrors and tracking systems
to focus a large area of
sunlight into a small beam.
 PV converts light into
electric current using the
photoelectric effect.

8. Concentrated Solar Power
Concentrated solar power (CSP) technologies use lens or
mirrors to reflect and concentrate sunlight onto receivers.
The receivers collect the concentrated solar energy and
convert it to high-temperature heat that can drive either
 heat engine
 domestic heating
 create steam to drive a turbine
 desalination

9. Different CSP techniques
Solar Parabolic Trough
Fresnel lens
Concentrated Photovoltaic

10. Cont…
 Solar Power Tower  Solar Dish-Engine
Systems

11. Stirling Engine
 A Stirling engine is a heat engine operating by cyclic
compression and expansion of air or other gas. The
working fluid, at different temperature levels such that
there is a net conversion of heat energy to mechanical
work.
 The external combustion aspect enables a Stirling Engine
to operate equally well on multiple types of fuel, such as
natural gas, gasoline, diesel, or even heat from the sun

12. Cont…
 The Stirling engine is noted
for its high efficiency (up to
40%).
 It operates Quietly and the
ease with which it can use
almost any heat source.
 In this case the sun's heat is
used for operating the engine.
 Stirling engine is a closed-cycle
regenerative heat
engine permanently working
on gaseous fluid.

13. Stirling engine configurations
 Alpha engines
It has two pistons in
separate cylinders which are
connected in series by a
heater, regenerator and
cooler.
 Seals are provided on both
the hot and cold pistons to
prevent the escape of gas
from the engine cylinders.

14. Cont…
 Beta Engines
 The Beta engine has both the
displacer and the piston are
in the single cylinder.
A beta Stirling has a single
power piston arranged within
the same cylinder on the
same shaft as a displacer
piston.

15. Cont…
• Gamma Engines
 A gamma Stirling engine
is simply like a beta type
but the power piston is
mounted in a separate cylinder
adjacent to
the displacer piston cylinder.
 both pistons are connected to
the same flywheel.
 The gas in the two cylinders
can flow freely between them.

16. Operation /working cycle
 1-2 const. Volume heating
 2-3 isothermal expansion
of the gas
 3-4 const. Volume cooling
of the gas.
 4-1-Iso thermal
compression of the gas.

17. Major Components of the Stirling
Engine
 Displacer- To shift the volume of gas from one end of
cylinder to an other.
 Power Piston - The work of the power piston is to
compress the gas at low temperature to expansion space.
 Bush - Used to align the displacer rod and connecting rod.
 Flywheel - It is used to store energy during the
expansion of displacer and provide the same energy
during compression to the power piston.
 Sealing- To reduce leakage of gas and maintaining the
pressure.

18. Cont…
 Regenerator- It captures the heat from the gas after
expansion and provide this heat to the gas when it moves
from cold end to the hot end of the engine.
 Connecting rods- It transmits the mechanical work of the
displacer to the flywheel.
 Cooling fins- Fins are made over the cold end displacer
cylinder for dissipation of heat to the sink.
 Pressure Regulating Screw- It is used to regulate the
pressure.

19. The Solar Concentrator
 It is used to refract light, converging the beam.
 A simple lens consists of a single optical element.
 A compound lens is an array of simple lenses (elements)
with a common axis. The use of multiple elements allows
more optical aberrations to be corrected than is possible
with a single element.

20. Types of simple lenses
 Lenses are classified by the curvature of the two optical
surfaces.

21. Convex Lenses
 Typically made of glass or transparent plastic, a convex
lens has at least one surface that curves outward like the
exterior of a sphere. it is the most commonly used.
 A convex lens is also known as a converging lens. A
converging lens is a lens that converge rays of light that
are traveling parallel to its principal axis

22. Concentration of light through
convex lens

23. Site Characteristic
 This residential based power generation system is
made for the District Khuzdar. The overall direct
normal solar radiation in Pakistan is shown:

24. Geographic location of Khuzdar
 Geographic coordinates of Khuzdar, Pakistan
Latitude: 27.74N , Longitude: 66.64E
Elevation above sea level: 1218 m = 3996 ft

25. Average monthly climate conditions for
The year 2012 in Khuzdar
Months T TM Tm PP V VM
Jan 10.1 17.1 2.4 14.74 2.1 6.7
Feb 11.7 19.6 3.8 0 3.8 9.4
March 19.6 26.1 10.8 13.97 4.5 12.4
April 24.1 29.7 17 27.17 5.2 13.7
May 29.8 36.4 22.6 23.88 5.7 15.1
June 31.5 37.5 24.3 2.03 7.1 17.4
July 32 38.9 24.7 5.33 5.4 15
Aug 32 37.5 25.6 1.02 1.5 12.7
Sep 26.7 32.4 20.7 54.09 3.5 12.8
Oct 22.9 30.5 13.9 0.76 4.9 14.4
Nov 18.1 25.8 9.3 0 4.4 13.4
Dec 12.5 19.4 4.5 25.91 2.7 10.2

26. Solar Parameters
 The solar parameters are taken for 3rd july in
selected site where the maximum temp is 41.5 C
 Labels
HGloCS- Horizontal clear sky Global Radiation
HDifCS- Horizontal clear sky Diffuse Radiation
HBmCS- Horizontal clear sky Beam Radiation
The sum of the diffuse and beam irradiance is
equal to the global irradiance.

27. Legal Time HGloCS W/m2 HDifCS W/m2 HBmCS W/m2
06am 14 11 3
07am 192 43 149
08am 432 69 364
09am 660 90 570
10am 852 107 745
11am 990 119 872
12noon 1067 125 942

28. Legal Time HGloCS W/m2 HDifCS W/m2 HBmCS W/m2
01pm 1076 126 950
02 pm 1016 121 895
03 pm 892 110 782
04 pm 713 95 618
05 pm 492 75 418
06 pm 252 50 201
07 pm 42 20 22

29. Design Specifications
 Our objective is to operate the stirling engine and
produce electric power using solar energy by the
help of convex lens to avoid the use of fossil fuels
and develop a renewable energy technology.
 Since the amount of heat energy produced by a
convex lens is comparatively less than that of fossil
fuels so we had to make the design changed. The
parameters that we worked on are as follows:

30. Data for the Already Existing
Stirling Engine
Dimensions and temperature data
 Inner diameter of displacer cylinder, Di = 32mm
 Length of stroke, l = 36mm
 Temperature of source, T1= 250C0
 Temperature of sink, T2 =100C0
 Swept Volume, Vs=28.95X10-6 m3
 Clearance Volume, Vc = 8.84X10-6 m3
 Compression ratio, r = Vs/Vc = 3.27
 Total Volume, Vt = Vc + Vs
= 37.74X10-6 m3

31. Cont…
 Heat Rejected to Sink, Q4-1=-126.99KJ/Kg
(Compression)
 Heat supplied from hot source, Q2-3 = 177.80 KJ/Kg
 Net work done, Wn= Heat supplied – heat rejected
=50.81 KJ/Kg
 Efficiency, η = 28.6 %
 Minimum Speed (at the start) = 80 r.p.m
 Maximum Speed (at the peak revolutions)
= 422 r.p.m

32. Design Specifications
 Hot side temperature T1
 Cold End temperature T2
 Swept Volume Vs
 Clearance volume Vc
 Compression ratio r
 Heat rejected to the sink
Q4-1
 Heat supplied to the hot end,
Q2-3
 Reduce Losses ( Leakage,
conduction and convection)

33. Cont…
Hot side temperature ( T1)
 Since T1 depends on heat energy supplied from the
source. It depends on the solar concentrator (lens).
Like:
 Area of the lens
 No of lens
 Concentration ratio

34. Cont…
Cold end temperature (T2)
 The cold end temperature is reduced by increasing the fin
surface area and number of fins to increase the heat
dissipation.
Swept Volume (Vs)
Vs =(π/4) D2l
D = inner diameter of the displacer cylinder
l = length of stroke
Increased swept volume by increasing the Diameter of displacer and length
of stoke.

35. Cont…
Clearance volume (Vc)
Vc =(π/4) D2 l1
l1= clearance length
By reducing the clearance length l1 we reduced the
clearance volume.
Heat supplied to the hot side
(Q2-3)
Q2-3 = R T1 ln ( Vs/Vc)
By increasing T1, Vs and decreasing Vc the amount of heat
energy supplied is increased.

36. Reduce Losses
 Leakage losses- Air leakage is a big problem at the
heating section. To prevent leakage we used O-Rings
between support collar and expansion cylinder.
 Conduction losses
To reduce conduction losses the heat cap and the
displacer cylinder is made as thin as possible.
 Convection losses
Convection from hot side to the surrounding is very
difficult to stop but by placing the engine in a certain
area where the natural air circulation is comparatively
low the convection loss of heat is prevented.

37. Modified design specification
Inner diameter of the displacer cylinder, Di = 48.5mm
Length of stroke, l = 38 mm
Clearance length , l1 = 10 mm
Hot end Temperature, T1 = 200C
Cold end temperature, T2 = 50C
Swept volume, Vs = 70.2x10-6 m3
Clearance volume, Vc = 18.5x10-6 m3
Total volume, Vt = 88.7x10-6
Compression ratio, r = Vs/Vc = 3.80
Heat supplied to hot end Q2-3 =180.8 KJ/Kg
Then heat rejected to the sink, Q4-1= -123.7 KJ/Kg
Net Work done Wn = 57.1 KJ/Kg
Thermal Efficiency of the engine η =31.7%

38. Solar concentrator
For concentrating the solar energy onto the receiving section of the
stirling engine to heat it up we used convex lens. Parameters for the
convex lens are given below:
Type of lens used is biconvex
Diameter of the lens, d= 130 mm
Focal length, L = 20cm
Area of lens, A= (π/4) d2
= 0.0153m2
Diameter of the beam at the focal point, di = 10 mm
Concentration ratio, C = d/di
= 130/10 = 13

39. Cont…
In our site selected ( Khuzdar) the average horizontal clear sky Global irradiance
from 7.am to 6.pm is calculated to be
=720 W/m2
The amount of solar radiation intensity that can strike our lens is:
= 720x area of the lens
=720x0.0153
= 11.01 W/ lens
Since the concentration ratio is,
C= 13
then the amount of solar energy produced by the lens at the focal point is
=11.01x13
= 143.2 W/lens

40. Test Results
Time HGloCS W/m2
Temperature at hot
end (C0)
Angular Speed
(RPM)
Thermal
effiiency
7:00 am 192 17 0 0
8:00 am 432 20 0 0
9:00 am 660 72 150 6.3%
10:00 am 852 180 180 28.6%
11:00 am 990 191 262 30.0%
12:00 pm 1067 195 280 30.9%
1:00 pm 1076 199 303 31.5%
2:00 pm 1016 197 250 31%
3:00 pm 892 194 230 30.7%
4:00 pm 713 140 175 21.7%
5:00 pm 492 124 65 18.6%
6:00 pm 252 65 0 4.43%

41. Test Results

42. Test Results

43. Conclusion
Old Design Modified Design
 Source of energy input
Fossil fuel
 Net work done
Wn = 50.81 KJ/Kg
 Thermal efficiency
η = 28.6 %
 Source of energy input
Direct solar thermal energy (
convex lens)
 Net work done
Wn = 57.1 KJ/Kg
 Thermal efficiency
η = 0.317 = 31.7%

44. Future Recommendation
The following recommendations are given for future
work:-
 That the Fresnel lens which is made of plastic can be more
successful.
 That it is also recommended that helium gas is used
instead of air due to its better thermodynamic properties.
 The overall efficiency can be improved, if increase the size
of the lens used in the system.
 The efficiency of the system can be improved by using
automatic tracking.