This document summarizes the design of a small 500W solar thermal dish Stirling system for use in Thailand. Key aspects include: 1. Thailand has average daily solar insolation of 550W/m2, requiring the system to be designed to operate at lower insolation levels than existing 1000W/m2 systems. 2. The design includes a 2.5m diameter parabolic dish, 4-cylinder gamma type Stirling engine with rotary drive mechanism and regenerator, able to produce 550W of power. 3. Testing of a prototype was conducted at AREF in Bangkok, showing it could produce 550W of power at an operating temperature of 650C and speed of 1200rpm when

1. The Design of Small Solar Thermal Dish Stirling 500 W Stand Alone in
Thailand.
Eng’r. Suravut, Snidvongs*1 and Dr. Sirinuch, Chindaruksa*2
*1 Vice President, Asian Renewable Energy Development and Promotion Foundation, Bangkok, 10400, Thailand ,
airscan@cscoms.com, PhD Students, School of Renewable Energy Technology (SERT), Naresuan University,
Pitsanulok, THAILAND.
*2 Physic Department, Faculty of Science, Naraesuan University, Pitsanulok, THAILAND.
Abstract This can be rearranged as
Thailand has the average insolation of 550 W/m2
daily average which is quite low when compare to the P/(pfVo) = constant (2)
existing system such as SES or Solo, which designed = 0.015
their system for 1000 W/m2, but do not require 1000
W/m2 to operate. Operating the Solar Dish Stirling The equation was found by Bale to be
with medium insolation the system must design with approximately true for all types and sizes of Stirling
proper conditions, such as Increase Dish Diameter, Engines for which data were available including free-
Minimum Power to track the dish, Reduce Piston and piston machines and those with crank mechanism. In
Drive mechanism friction. most instances the engines operated at temperatures of
A purpose of this research is to design a Small 650 ºC and cooler temperatures of 30 ºC [2].
Solar Thermal Dish Stirling 500 W Stand Alone The size of the engine cylinder required may then
System that can operate with lower insolation such as be computed from the Beale number. There is some
Thailand conditions. evidence that the Beale number is conservative for
large engine. Furthermore, in such a high capital cost
1. Introduction application, a sophisticated design with adequate
Insolation in Thailand is varying between in 450 cooling might be expected. Therefore perhaps it would
to 550 W/m2 daily whole year round, and the average be reasonable to double the value of the constant in
value is at 550 W/m2 daily over the year. equation (2) from 0.015 to 0.03. Finally, it is
To operate the Solar Dish Stirling with medium advantageous at this stage to recall, from the aspect of
insolation the system must design to operate with seal, bearing, and piston-ring wear, the attractions of
proper conditions, such as increasing dish diameter, an ‘over square’ engine, i.e. a large bore and short
reduce power to track dish structure, reduce piston and stroke.
drive mechanism friction. From Beale equation considers only the speed,
The rotary drive mechanism seems to be lower volume, mean pressure, and constant. All those
friction than other mechanism such as gear drive, and information can let us find the stroke and piston
whisper tech swash plate system [1]. diameter.
In this research the author will design a Small For the design data we must give the expected
Solar Thermal Dish Stirling 500 W stand alone power output, desire speed, and mean pressure, for the
System that can operate with lower insolation such as example 550 W, 20 hertz (1200 RPM), 1 MPa. For a
Thailand conditions. square engine the piston and stroke ratio usually we
use 1 from equation 1.
2. Solar Stirling Engine Design
The preliminary Stirling Engines designs usually Stroke = D
use the Beale number concept (1). The power output of Vo = ¶ / 4 D2 x D (3)
many Stirling Engines conformed approximately to the P/(pfVo) = 0.03
simple equation: Vo = P/(0.03pf) (4)
D = (4P/(0.03¶pf))1/3 (5)
P = 0.015pfVo (1) = (4*550/(0.03*¶*10*20)) 1/3
D = 4.89 cm
Where P = engine power (watts), Stroke = 4.89 cm
p = mean cycle pressure (bar),
f = cycle frequency or engine speed (hertz), Beale equation can give roughly diameter and
Vo = displacement of power piston (cm3) stroke of power and displacement piston. Beale
Copyright© 2007 by the Japan Society of Mechanical equation cannot give more details on the difference
Engineers. All rights reserved. size of power and displacement piston.
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2. The Schmidt analysis equation was published by a pure sinusoidal reciprocating motion having a 90
Gustav Schmidt of the German Polytechnic Institute of degree phase difference between the adjacent pistons.
Praque in 1871 [3] in which he obtained closed form
solutions of these equations for the special case of
sinusoidal volume variations of the working spaces.
Schmidt and Simple analysis can give us more
accurate and give the difference size of power piston,
displacement piston, heater area, cooler area, and
regenerator size. The calculation used the math lab
program from Dr. Urieli [4].
p = MR (Vc/Tk + Vk/Tk + (Vrln(Th/Tk))/(Th-Tk)
+ Vh/Th + Vc/Th)-1 (6)
Where p = Mean Pressure bar
M = Mass
R = Gas Constant Figure 2 Compound Gamma type Stirling engine
Vc = Compression Space Volume Source: By author
Vr = Regenerator Space Volume
Vh = Heater Space Volume The advantages of Rotary Drive Mechanism
Vk = Cooler Space Volume Stirling engine are that it is easy staring, smooth
Th = Heater Temperature, K running, and has good low end torque. Rotary Drive
Tk = Cooler Temperature, K Mechanism works well for applying the generator at
the top of a Stirling engine. It easy to installed at the
From Schmidt equations it can give the volume of focal point of a parabolic reflector.
heater and compression volume by this we can get the This Solar Stirling engine was first tested with 700
size of the power and displacer piston. Schmidt W x 4 electric heaters 1 ф 220 V, adjustable power,
equations give us more accurate piston size. and final tested with real solar insolation in Bangkok,
In this prototype engine the author decided to use Thailand at AREF.
4 cylinders gamma type Stirling Engine with internal This Solar Stirling engine was designed by author,
regenerator, Figure 1. This type of engine has the namely “Siam Solar Stirling Engine III”. Don Bosco
advantage of having separate cylinders out weight. Technical School has meanwhile supported the
Gamma type engine can also be compounded into a fabrication work on the Dish Structure, Stirling Engine
compact multiple cylinder configuration, as shown in components, Tracking mechanism and assembly the
Figure 2. engine. The author and his staff have then continued to
do the testing. All tests were done at AREF, Bangkok
in Thailand.
3. Solar Stirling Engine Specification
The Solar Stirling engine was designed as the
following Table 1:
Table 1 Solar Stirling Engine Specification
Type Gamma
Acting Double
Driver Mechanism Negative Rotary
Working Gas Air
Figure 1 Diagram of a simple displacer type gamma
Expansion space Temp 650 C (+/- 5 C)
engine.
Source: www.ent.ohio.edu/~urieli/stirling/engines Compression space Temp 40 – 50 C (+/- 5 C)
Ambient Temperature 40 C (+/-5 C)
This engine is enabling an extremely high specific Thermal Efficiency 60 %
power output. The four cylinders are interconnected Power Control Variable Pressure
(daisy chain), so that the expansion space of one No. of Cylinders 4
cylinder is connected to the compression space of the Means Pressure 0.5 MPa
adjacent cylinder via a series connected heater, Maximum Pressure 1 Mpa
regenerator and cooler. The pistons are typically driven Power Piston Diameter, mm. 48
by a negative swash-plate (Rotary Drum), resulting in Stroke, mm. 40
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3. Power Displacement, cc. 72 x 4
Displacer Diameter, mm. 42
Displacer Length, mm. 150
Heater surface area, cm2 11.40
Cooler surface area, cm2 29.12
Regenerator surface area, cm2 161.60
Expansion swept, cm3 340.00
Compression swept, cm3 220.80
Speed, rpm 500 – 1200
Regenerator Type Tube
Cooling type Ethyl glycol
Electric heater 220 V 700 x 4 W
Mechanical Output Power 215 W @ 20 psi
Mechanical Output Power 550 W @ 80 psi
Source : By Author
4. Rotary Drive Mechanisms
The four pistons gamma type Stirling engine, are
daisy chained together with negative Swash Plate
(Rotary), Figure 3. This is done by driving the Figure 3 Swash Plate Type 2 (Rotary)
displacer via linear drive rods which are attached to the Source : By Author
top of power pistons. The rods pass through a sealed
bulkhead and the displacer cylinders are ported to
power piston cylinders that are phased behind them
90°. This allows an engine that only requires one crank
through per piston where other Stirling engine requires
two.
The bronze bushing sealed bulkhead was replaced
with guide bearing with rubber seal, and replace the
Mitter gear with Rotary Drum. This could call
Negative Swash plate. It also added more bearing and
universal joint. The rotation, Clock-wise or counter
clock-wise, can be done by adjust a little phase angle,
positive or negative, different.
This engine stands a height of 60 cm. The surface
area of the heating side is 11.40 cm2. The total weight
when mostly made of aluminum casting is around 20
kgs. The working piston diameter is 4.8 cm, the
restrictor piston diameter is 5.00 cm, and the stroke is
4.00 cm. The engine was designed with pressured air
as working fluid at an operating pressure of up to 1
MPa (147 Psi). The method of heating it arbitrary
since it is a Striling engine, but the prototype was
heated with 700 x 4 W electric heater, adjustable
power, each cylinder the engine produces 130 W
mechanical work.
The maximum heat input is 2800 W which is more Figure 4 Swash Plate Type 2 (Rotary)
than the estimated heat input from the concentrating Source : By Author
dish, 2,000 W at solar insolation 550 W/m2, average
daily Thailand insolation. The engine was circulating 5. Calculation results
with Ethyl Glycol to cool the engine. The engine is
estimated to have the thermal efficiency of 60 % and 5.1 Engine data
mechanical efficiency of 30 %. Comp clearance vols 4.0 cm3
The engine starts running at 200 °C and produces Comp swept vols 72.0 cm3
550 W power output when near the max temperature Exp clearance vols 3.0 cm3
of 650 °C. The ideal speed is approximately 1200 rpm Exp swept vols 69.0 cm3
and the torque output is 10.4 Nm. Expansion phase angle advance 90.0 deg
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4. 5.2 Annular heat exchanger Cooler data 5.9 Heater Simple analysis
Void vols 137.22 cm3 Average Reynolds number 1841.00
Free flow area 0.13 cm2 Maximum Reynolds number 3323.90
Wetted area 3.43 cm2 Heat transfer coefficient 202.79 W/m2*K
Hydraulic diameter 16.00 mm Heater wall/gas temperatures Twh 923.00 K
Cooler length 10.50 cm Tgh 892.00 K
5.3 Tubular regenerator housing with stacked wire 5.10 Cooler Simple analysis
mesh matrix Average Reynolds number 4110.70
Matrix porosity 0.160 Maximum Reynolds number 7135.40
Matrix wire dia 0.130 mm Heat transfer coefficient 38.94 W/m2*K
Hydraulic dia 0.024 mm Heater wall/gas temperatures Twh 313.00 K
Total wetted area 0.0542 m2 Tgh 374.50 K
Regenerator length 148.0 mm
Void vols 0.24 cm3 5.11 Converged heater and cooler mean temperatures
heater wall/gas temperatures Twh 923.00 K
5.4 Annular gap heat exchanger heater data Th 892.00 K
Void vols 21.44 cm3 cooler wall/gas temperatures Twk 313.00 K
Free flow area 0.02 cm2 Tk 374.50 K
Wetted area 2.86 cm2
Hydraulic dia 3.00 mm 5.12 Regenerator Simple Analysis
Heater length 10.00 cm Average Reynolds number 18.100
5.5 Operating parameters Maximum Reynolds number 32.800
Gas Type Air Stanton number (Average Re) 0.203
Mean pressure 4,200 kPa Number of transfer units 2,487.000
Cold sink temperature 313.0 K Regenerator effectiveness 1.000
Hot source temperature 923.0 K Regenerator net enthalpy loss 0.500 W
Effective regenerator temperature 546.1 K Regenerator wall heat leakage 13.900 W
Operating frequency 20.0 Hz
Pressure phase angle beta 18.0 deg 5.13 Pressure Drop Simple Analysis
Total mass of gas 0.991 gms Pressure drop available work loss 26,946.7 W
Actual power from simple analysis -26,848.8 W
5.6 Schmidt Analysis Actual heat power in from simple 193.9 W
Work 5.067 J analysis
Power 101.3 W Actual efficiency from simple -13,845.0 %
Qexp 7.667 J analysis
Qcom -2.600 J
Indicated efficiency 0.661 6. Dish specifications
5.7 Ideal Adiabatic Analysis Table 2. Dish Specification
Heat transferred to the cooler -59.73 W Dish Type Parabolic
Net heat transferred to the regenerator 0.00 W Structure Type Space Truss
Heat transferred to the heater 160.67 W Dish Diameter, m 2.50
Total power output 101.34 W Dish Focus, m 1.56
Thermal efficiency 0.631 Depth. m 0.25
Total height, m 3.20
5.8 Simple Analysis Aperture area, m2 4.90
Heat transferred to the cooler -82.11 W
Reflective, % 90
Net heat transferred to the regenerator 0.00 W
Power at receiver, W 2,000
Heat transferred to the heater 179.48 W
Tracking sensor H bridge LED
Total power output 97.85 W
Thermal efficiency 0.545 Tracking power, W 10 x 2
Source : By Author
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5. 9. Conclusions
The “Siam Solar Stirling Engine System III (SSES
III) prototype” was designed to meet Thailand’s
weather environment (such as humidity, solar
insolation, soft land, and wind load, etc.).
The Dish structure and Solar Stirling engine
components were fabricated by the Don Bosco
Technical School under the author’s supervision. The
system is now under testing for reliability and
endurance.
Figure 3 shows the SSESIII. This engine stands a
Figure 5 Parabolic Dish Structure at AREF, Bangkok, height of 60 cm. The surface area of the heating side is
Thailand. Basic engineering and calculation for steel 11.40 cm2. The total weight when mostly made of
structure and foundation was created by the author. aluminum casting is around 20 kgs. The working
Steel fabrication work was built by the Don Bosco piston diameter is 4.8 cm, the restrictor piston diameter
Technical School. Erection and Installation work was is 5.00 cm, and the stroke is 4.00 cm. The engine was
also created by the author and the AREF staffs as well designed with pressured air as working fluid at an
as controllers system, Solar Tracker mechanism, the operating pressure of up to 0.5 MPa (72 Psi). The
circuit design and assembly work. method of heating it arbitrary since it is a Striling
Source : By author engine, but the prototype was heated with 700 x 4 W
electric heaters, adjustable power, each cylinder the
Delta Truss Support Structure made from steel. engine produces 130 W mechanical work. The
The Delta Ring attached to the top of Delta Truss maximum heat input is 2,800 W which is more than
Support Column. The dish structure made from GRP, the estimated heat input from the concentrating dish,
12 panels. The acrylic mirror was glued to the GRP 2,000 W at solar insolation 550 W/m2, daily average
dish. The reflector attach to the Delta Ring with Thailand solar insolation. The engine was circulating
adjustable screw. The Solar Stirling engine install at with Ethyl Glycol to cool the engine. The engine is
the center of focus point. The temperature at the focus estimated to have the total efficiency of 31 %. The
is around 650 °C. engine starts running at 200 °C and produces 550 W
power output when near the max temperature of 650
7. Performance °C. The ideal speed is approximately 1200 rpm and the
torque output is 10.4 Nm.
Table 3 Solar Stirling Engine Performance SSESIII can be rotate Clock-wise or counter
Cost USD 1,280.00 clock-wise by adjust a little phase angle, positive or
Mean Time Between Fail (hrs) 18,000 negative, different.
Maintenance Time (hrs) 3,500 The Negative Swash Plate Drive Mechanism
Torque (N-m) 10.4 (Rotary Drive), all piston rods install with guide
Thermal Eff. % 60 bearing on both side to reduce the friction. This type of
Mechanical Eff. % 31 Mechanism needs very accurate workmanship to
Source : By Author make. It is very quite during the operation. The Stirling
engine can be rotate clockwise or counter clockwise by
8. Results adjust a little phase angle, positive or negative,
different. The maintenance time are high, 18,000 hrs.
Figure 6 show the friction test for this rotary
Rotary Drive Friction Test
mechanism.
12
As the weight of Rotary drum is in balance so this
10 type of mechanism create much lower vibration than
V
other system. This type of Drive Mechanism has fewer
8
A parts than Daisy Chain Gear Drive but complicate to
6 W make. The cost of the system is medium high. The
4
friction is about 6.1 W. The engine torque 10.4 N-m is
quite good. Thermal efficiency is 60 %. and
2 Mechanical Efficiency is 31 %. The Rotary Drive
- Mechanism can be improved mechanical efficiency up
500 700 900 1100 1300 1500 1700 1900 to 31 %. SSESIII required power to track only 10 x 2
W.
Figure 6 Daisy Chain Rotary, Friction Test By increasing dish diameter, reduce power to
Source : By Author track, enlarge displacer piston, reduce friction for drive
5

6. mechanism, and reduce power piston friction make the
SSESIII operate with Thailand conditions.
Friction of Stirling engine may not have direct
effect to the insolation, but if the Stirling engine has
less friction, Stirling engine will require less power to
overcome the friction. This will gain the performance
of the Stirling engine up. Thus, with medium
insolation as Thailand, average 550 W/m2 daily,
Stirling engine could perform better.
ACKNOWLEDGMENTS
This research was prepared by Mr. Suravut
SNIDVONGS, Vice President, Asian Renewable
Energy Development and Promotion Foundation, EIT
member, a PhD Student, School of Renewable Energy
Technology, Naraesuan University, Pitsanulok,
Thailand. The author would like to acknowledge the
assistance and guidance of Asian Renewable Energy
Development and Promotion Foundation Dr. Sub.Lt.
Prapas Limpabandhu Deputy Minister of Foreign
Affair, Mr. Sutas AROONPAIROJ and staffs, the
Engineering Institute of Thailand members who
provided a critical review of this research through its
various stages, including Asist. Prof. Dr. Sirinuch,
Chindaruksa, Physic Department, Faculty of Science
Naraesuan University, as Advisor, Dr. Vichit,
Yamboonrung, Assoc. Prof. Dr. Wattanapong
Rakwichien, Asist. Prof. Dr. Mathanee
Sanugansermsri, as Co-Advisor and the Naraesuan
University Staffs, Pitsanulok, Thailand. Especially the
Don Bosco Technical School staffs for their
fabrication and construction work on the prototype.
Finally, the author would like to thank the numerous
industries to provide information for this research.
References
[1] Suravut, Snidvongs, The comparison for
different type of drive mechanism for small solar
stirling engine 500 w in Thailand, 2007. ISEC 2007,
24-26 September, 2007. Tokyo, JAPAN.
[2] Ronald J. Steele, The Stirling Steele Engine
drawing, 1994. U.S.A
[3] G.Walker, Stirling Engines, Claarendon
Press, Oxford, 1980, p.73.
[4] Schmidt G 1871 The Theory of Lehmann’s
Calorimetric Machine Z. ver. Dtsch. Ing. 15 part
[5] http://www.ent.ohio.edu/~ureli/stirling/
[6] Chris Newton, Team Solaris, Final Design,
Fall 2003.
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