Analysis and research on
converging-type solar power collecting
systems
Jen-Yu. Shieh1, Chu Shan. Chen2, Yueh Hsun. Li3, Kun Hsien. Lin3
Abstract –This paper uses optical design software CODE V to design optic non-spherical
Fresnel len and using non-optic simulation software LightTools to conduct light ray tracing
and analysis of light energy. Optic software has optimization function to design the best
optic non-spherical Fresnel lens; through this research analysis and simulation evaluation
of optical systems, design miscalculations and risks of failure can be lowered as well as
verifying laboratory results. Research and development are also performed on optic
Fresnel lenses made with a hybrid material, which involves using molding methods to
combine glass and silicon. During experiments, it was discovered that Fresnel lenses made
with white glass and silicon have an average penetration of 92% within infrared
wavelength perimeters; those made with PC materials had average penetration of only 76%.
The lifespan of silicon Fresnel lenses are also much longer than other plastic materials.
Therefore the application of silicon materials on converging-type solar power collecting
systems would likely become the best option in the future.
Keywords: converging-type solar power battery, Fresnel lens, silicon
1. Introduction
Photoelectric effect is turning solar energy into
electrical energy; it is a simple and effective method.
However, to-date the efficiency of power generation has
been less than desirable, and the high costs prove to be
inconsistent with economic efficiency. This direct and clean
method of electricity generation has a high development
potential and is an important item in developing green
alternative energy sources of the future. Fresnel lenses[1][2]
are a key element in converging-type solar batteries; due to
excellent converging properties of the Fresnel lens[3], solar
batteries can reach higher levels of electricity generation[4]
Currently, requirements of converging lenses in
converging-type solar power batteries are: UV resistance,
heat resistance, weatherproof, long lifespan. Although
glass materials are durable and heat-resistant, it is not easy
to process or mass-produce; it is also heavy and costly.
Plastics are easy to process and mass-produce, and it is
also cheap; however, it is not durable and cannot tolerate
heat. Therefore there is a need to develop a material that is
appropriate for converging-type solar power batteries[5].
Required
characteristics
Glass
PMMA
PC
COP
Silicone
Refractive index
◎
○
○
○
○
This experiment uses hybrid silicon Fresnel lenses created
with molding methods. The Fresnel lenses produced by
this method is heat-resistant, weather-resistant with no
problems with yellowing; it has a long lifespan, which
cuts back on the cost of replacing the lens. Figure 1 shows
hybrid Fresnel lenses to be advantageous.
Fig 1 Cost comparison between PC materials and hybrid Fresnel lenses
2. Experiment methods
Figure 2 is the developmental flowchart of the Fresnel
lens. The best Fresnel lens can be designed through every
step of the flowchart.
Material
Complex
refractive index
◎
Penetration
◎
○
×
○
○
Optical design
◎
○
○
○
Light ray tracing
UV resistance
◎
ᇞ
×
×
◎
Model design
Heat resistance
◎
×
ᇞ
ᇞ
Model
◎
NG
Hardness
◎
○
○
○
△
Absorption
◎
×
×
○
△
Processability
×
◎
◎
○
○
Price
×
◎
◎
○
△
Molding
NG
Surface profile
OK
NG
Power generation
test
◎:excellent ○:average ᇞ:poor ×:very poor
NG
Table 1. Characteristics comparisons of average optical lens material
Table 1 is a comparison chart of characteristics of
average optical lens materials. Silicon materials can be
processed by molding techniques; it is lightweight, easy to
process, can be mass-produced, weatherproof
and heatproof. However, it is expensive. Compared with
glass and plastic materials, silicon has many advantages.
Reliability test
Completion
Fig 2 Fresnel lens developmental flowchart
2.1 Material selection
Silicon material[6] was the main focus of this
experiment. The material of the lens determined the
lifespan and costs of the lens. After selecting appropriate
silicon material to undergo optical design[7] and molding,
a hybrid Fresnel lens of glass and silicon was created. A
surface profiler was used to confirm whether the surface
shape fit design criteria, and then the power generation
efficiency testing and reliability testing were conducted
before confirming whether differences in the efficiency of
power generation will exist.
Table 3. Results of various solar converging lens designs
Table 2. Property comparisons between silicon gel and generic optical
lens material
From Table 2 we can see that silicon gel is
heat-resistant; optical-grade silicon materials are
UV-resistant and does not become discolored (yellow)
easily.
2.2 Optical Design
The refractive index of lens material n1, refractive
index of air 1, and the radius of lens curvature R1 and R2
respectively. The relationship between the focus size and
radius of lens curvature is as follows in the lens maker's
equation[8].
1
1 1
= ( n1 −1)( − )
f
R1 R 2
(1)
f : known focus
R1: radius of lens curvature on the first side
n1 : lens refractive index
R2: radius of lens curvature on the second side
First, plano-convex lenses underwent initial design.
The material was BK7 with refractive index (nd) of 1.5 and
focal distance of 100mm. Inserting these numbers into the
lens maker’s equation, a radius of 50mm was achieved
After completing spherical design, these data were
entered into the CODE V optical design software to
determine settings for non-spherical and Fresnel lens values.
Lastly, optimization was conducted, and the best optical
design values can be achieved.
Comparisons between plastic and silicon materials
were conducted. The Fresnel lens was thinner (at 3mm)
than lenses of other types but still maintained excellent
converging effects[9].as shown in Table 3 From this it can
be concluded that Fresnel lens can be thinner, lighter, and
lower the amount of material used.
2.3 Light ray tracing
This experiment used LightTools[10] to conduct
light ray tracing. It is imported in SAT file form then
constructed and edited based on item material, size, shape,
and curvature; light source and number were then selected
and light ray tracing performed and simulated. The system
will indicate light ray distribution of various trajectories,
and after setting up simulation models in LightTools,
photometric simulation can then be conducted. The
plausibility of design can be confirmed through the results.
Resulting data include: illuminance, intensity, and
luminance. This thesis uses illuminance as data most
indicative of converging characteristic and uses it to
calculate the area of convergence and size of focal power.
LightTools light ray tracing system will read the file
before constructing and editing item material, size, shape,
and curvature. Then light source and number are selected
before conducting light ray tracing and simulation of
various light trajectory and distribution[11], as in Figure 3.
After analysis, radiation illuminance could be derived, as in
Figure 4 and 5; illuminance distribution above the receiver
is uniform and even. Figure 5 shows the illuminance
distribution of Fresnel lens converging light ray on top of
the receiver. Plano-convex lenses are arranged in series
before undergoing light ray tracing and illuminance
analysis, as in Figure 6; the result of the analysis shows that
the illuminance distribution is broader and of lower value,
as in Figure 7. Fresnel lenses area also arranged in series, as
in Figure 8; the resulting illuminance distribution is more
centered and have higher value, as in Figure 9. Using a
surface profiler, the height and relative positioning values
of the surface of the Fresnel lens can be measured; these
values can be converted to derive a graph of the surface
profile. Comparisons between results and model profile
will show the difference between the two[12], as in Figure
10.
Fig 6. Light ray tracing of spherical lens arranged in series
Fig 7. Analysis of radiation and light illuminance of spherical lens
Fig 3. LightTools light ray tracing
Fig 8. Light ray tracing conducted in series formation
Fig 4. Analysis results of Fresnel lens illuminance
Fig 9. Analysis diagram of radiation and light illuminance of Fresnel lens
Fig 5. Analysis results of Fresnel lens illuminance
distribution in the mold cavity. After curing the mold
silicone, then the top of the body to leave the products out
of the top surface of the movable side mold, products
removes, the complete extrusion forming. During the
molding process, the amount of pressure would determine
the results of molding; the greater the pressure, the more
complete in shape would be the Fresnel lens, and the greater
power-generating efficacy,
Fig 10. Comparison between silicon Fresnel lens and model profile
3. Experiment Results
During optical design, four models of various
specifications were designed and compared; the four
specifications were: spherical bi-convex lens, non-spherical
bi-convex lens, non-spherical plano-convex lens, and
Fresnel lens. From the designing results, Fresnel lens was
the thinnest (3mm); non-spherical bi-convex lens had the
smallest focal point (0.0148). Due to its material, the
Fresnel lens had the best penetration (92%) within broad,
long wavelength perimeters and the best actual
convergence rate (382).
During the process of laboratory research, several
influential factors were identified; each was then analyzed
and experimented with to increase the power-generating
efficacy, as in Table 4.
(1) Lathe tool value R was changed from 0.1 to 0.05,
causing an increase of 7.2%
(2) draft angle was changed from 5° to 3°, increasing
power-generating efficacy 3.6%
(3) after non-spherical data were corrected to change
the precision of the surface profile, the power-generating
efficacy of green glass material can be increased 9.6%
Table 4. Analysis values of various improvement strategies and
comparison of actual efficacies
As in Figure.11.Mold ready state. The glass placed in
the fixed side of the type, injected into silicone mold
movable side center, mold clamping action, due to silicone
by squeezing of mold inside, thus the uniform flow and
Fig 11. Mold structure
Power-generating efficacy can be increased from the
original 25.2% to 55.8%, as in Table 5.
Hybrid Fresnel lens made from a base of white glass
has very high optical efficiency within a 350~2000nm
wavelength perimeter; the average penetration is 92%
compared to only 76% of PC Fresnel lens. In this aspect, the
hybrid Fresnel lens made with white glass base has good
optical efficiency and therefore a converging advantage.
The greater the circumference of the Fresnel lens, the
greater its power-generating efficacy[13-15]; this needs to
considered alongside chip specifications and lifespan, as in
Table 6.
Table 5. The effects of molding pressure on power-generating efficacy
[6] S.P Yeh, The study of a high efficiency and uniformity solar
concentrator for III-V solar cells, M.S. dissertation, Dept. Optics and
Photonics., National Central Univ., Taoyuan.,Taiwan.,2007.
[7] Y.S Chen, Design of Surface Structures on Fresnel Lens Used for
Solar Energy Concentration, M.S. dissertation, Dept. Aeronautics and
Astronautics .,National Cheng Kung Univ., Tainan., Taiwan., 2009.
[8] F.L.Pedrotti, L.S.Pedrotti, Introduction to Optics, 3th edition,
Addison-Wesley, 2006.
[9] C.Y. Hu, Design and analysis of Fresnel-lens solar concentrator, M.S.
dissertation, Dept. Electro-Optical Engineering., National Chiao Tung
Univ., Hsinchu., Taiwan., Sep, 2006.
[10]Ching-Nien Wang, CODE V and LightTools introduce, Terasoft.
Table 6. Comparison of power-generating efficacy of different types of
Fresnel lenses
4. Conclusion
1. Hybrid silicon Fresnel lenses are UV-resistant and
heat-resistant; they have long lifespans and not easily
discolored. They are malleable and have high
Processability; they can be mass-produced and have
great potential in market competition.
2. The thickness can be reduced from the 26mm of
plano-convex lenses to the 3mm of Fresnel lenses,
saving material usage and decreasing production
costs greatly.
3. The hybrid Fresnel lens made with white glass base
and the PC Fresnel lens have good optical efficiency
and in comparison with other materials a converging
advantage.
4. The amount of pressure would determine the results
of molding; the greater the pressure, the greater
power-generating efficacy. Power-generating
efficacy can be increased from the original 25.2% to
55.8%.
5. The circumference of the Fresnel lens is limited by
the specification of the non-spherical processing
machine; the greater the circumference the greater
the power-generating efficacy.
6. Optical design follows trends; the main point of
discussion during design planning will determine the
emphasis in characteristics of optical component.
5. Reference
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6. Authors Information
Jen-Yu. Shieh1 received the B.S. degree in
electrical enginerring from Feng-Chia
University, Taichung, Taiwan, in 1984 and the
M.E. degree in computer engineering and
Ph.D. degree in electrical engineering from
Florida Atlantic University, Boca Raton, in
1989 and 1992, respectively. While
completing graduate degrees at FAU, he was
an associate professor of Department of
Electro-Optics Engineering at National
Formosa University, Huwei, Taiwan. Since
February 2010, he has been an professor. His current research interests
include innovation and consumer products. He also has 47 patents and 4
consumer products.
Chu Shan. Chen2 was born in Changhua,
Taiwan, on November 20, 1971. He was a
student of graduate institute of Electro-Optical
and Materials Science, National Formosa
University of Huwei, Yun Lin, Taiwan,in 2008
to 2010. In optoelectronics and materials
science research. Currently working in the
optical industry, in optical components and the
Plastic lens production process has been 16
years work experience.
Yueh Hsun. Li3 was born on November
4th,1988 in Taichung, Taiwan. In 2010, he
graduated from National Formosa University of
Optical-Electro department in Yunlin,Taiwan.
He researches in biotechnology and
Electro-Optical and Materials Science in
graduate institute from 2011 in National Formosa University. Mr. Li is
one of members in Electro-Optical Application Laboratory and
Biological Optical Materials and protein applications Engineering
Laboratory.
Kun Hsien. Lin3 was born in Yun Lin, Taiwan,
on March 28, 1988. He received the degree in
Optical-Electro from the University of
Taiwan, in 2010. He is a student of graduate
institute of Electro-Optical and Materials
Science, National Formosa University of
Huwei, Yun Lin, Taiwan. He is engaged in
researches on Electro-Optical and Materials
Science. Mr. Lin is a member of
National Formosa University.