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HEAT ENERGY COLLECTION VIA PARABOLIC SOLAR REFLECTOR
Ritesh Toppo¹, Rahul Tripathi², Rahul Mahamalla³, Er.Dileshwar Kumar Sahu*
¹Undergraduate Bachelor of Engg. Student, Department of Mechanical Engineering, BIT-Raipur, CG India-492001
+91-7587438297
²Undergraduate Bachelor of Engg. Student, Department of Mechanical Engineering, BIT-Raipur, CG India-492001
³Undergraduate Bachelor of Engg. Student, Department of Mechanical Engineering, BIT-Raipur, CG India-492001
*Assistant Professor, Department of Mechanical Engineering, BIT-Raipur, CG India-492001
AbstractThis paper presents the development of a solar parabolic dish collector prototype for rural areas with high solar resource availability in India, which have no access to electricity service or budget resources to purchase a stove (electric or gas). The solar collector prototype proposes a solution to solve these kinds of issues and use sunlight to work it. Through a polished Aluminum parabolic dish, solar radiation is concentrated into a specific area called focus, where thermal energy is generated and is used for cooking or fulfilling a necessity without high investment and helping the environment. To finish, it describes the decisive stages of the prototype implementation, which provides the solar resource analyzed in India, the theoretical analysis, the structural design, the study, and manufacturing materials.. Key words: Focus, Heat losses, solar concentrator, Thermal efficiency, Temperature
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1. INTRODUCTION
Most of the power generated nowadays is produced utilizing fossil fuels, which releases tons of carbon dioxide and other pollutants every second. More importantly, fossil fuel will eventually exhaust. In order to make the development of our civilization sustainable and cause less harm to our environment, people are looking for new source of substitute clean and green energy. Because of the increasing demands in clean energy, the solar energy industry is one of the fastest growing forces in the world. Nowadays there are several major directions for solar technology development. For example, photovoltaic (cells) systems directly convert the solar energy into electrical energy while concentrated solar power systems first convert the solar energy into thermal energy and then further convert it into electrical energy through a thermal engine; it’s a conversion of low grade energy to high grade energy. After a system has been installed, it will be tough task to upgrade the systems or change the operation methods. In order to choose the right solar system for a specific geographic location, we want to understand and compare the basic mechanisms and general operation functions of several solar technologies that are widely studied. This paper not only gives technologies a brief introduction about the fast developing solar technologies industry, but also may help us avoid long term switching cost in the future and make the solar systems performance more efficient, economical and stable.
1.1 Why Solar Energy is one of the forestanding Solution to World Energy Crisis
The sun is the most plentiful and celestial energy source for the earth. All wind, fossil fuel, hydro and biomass energy have their origins in sunlight. Solar energy falls on the surface of the earth at a rate of 120 petawatts, (1 petawatt = 1015 watt). This means all the solar energy received from the sun in one days can fulfill the whole world’s energy demand for more than 20 years.
We are able to calculate the potential for each renewable energy source based on today’s technology. Future advances in technology will lead to higher potential for each energy source. However, the worldwide demand for energy is expected to keep increasing at 5 percent each year. Solar energy is the only choice that can satisfy such a colossal and steadily increasing energy impositions.
There are several applications for solar energy, for instance: electricity generation, solar propulsion, photochemical, solar desalination, and room temperature control. The collection of solar energy and its transfer to electricity energy will have wide application and deep impact on our society, so it has attracted the attention of the researchers and scientists.
1.2 Basics of solar thermal collection/solar concentrating power
The basic principle of solar thermal accumulation is that when solar radiation is incident on a surface (such as that of a black – body) part of this radiation is absorbed, thus increasing the temperature of the surface.
As the temperature of the body increases, the surface loses heat at an increasing rate to the surroundings. Steady state is reached when the rate of the solar heat gain is balanced by the rate of heat loss to the ambient surroundings. Solar concentrators increase the amount of incident energy on the absorber surface as compared to that on the concentrator aperture. The increase is achieved by the use of reflecting surfaces or other optical means which concentrate the incident radiation onto a suitable absorber / receiver.
Electricity is high grade energy. This means it can be easily transferred into other forms like mechanical or heat energy. If we are able to generate economic and plentiful electricity energy, together with the easy transportation electricity energy transmission, the electric power will increase it shares in demand sectors dramatically.
Fig 2: Heliostats Tower
1.3 ENVIROMENTAL CONDITIONS IN RAIPUR CHHATTISGARH
The north westerly hot winds coming from Rajasthan and Madhya Pradesh have led to increase in maximum temperatures in several parts of Chhattisgarh, crossing 46 degrees Celsius.
Raipur, Bilaspur and Champa remain hottest in state with heat waves accompanied by dry weather and humidity across state .people prefers remaining indoors as maximum temp. Recorded in morning around 11 am crossed 39 degree Celsius and fluctuates at 45.5 degree Celsius and 35 degree till 10 am.
Some data’s are given below :- ( 3 March 2016)
CONDITIONS COMFORT
TIME
TEMP
WEATHER
WIND HUMIDITY
11.30 33ºC Partly sunny
6Km/h 38%
14.30 35ºC Scattered clouds
7Km/h
33%
17.30
34ºC Partly sunny
4Km/h
35%
20:30
30ºC Passing clouds
No Wind
48%
23:30
27ºC Passing clouds
No Wind
56%
Table 1: Local weather report
Fig 1: Parabolic Solar Reflector
2. DESIGN OF PARABOLIC REFLECTOR
2.1 Prototype design:
The prototype design was carried out contemplates the parabola and focus characteristics, as well as the dimensions adjusted to the estimated budget.
Fig 3: Solar Parabolic Dish
Fig 4: Solar Parabolic Dish
Fig 5: Basic structural Nomenclature of parabolic dish
Fig 6: Real time image of prototype model of solar reflector designed and constructed by authors.
2.2 DESIGN OF PARABOLIC REFLECTOR USING CAD MAX5 SOFTWARE
Fig 7: Wire frame view
Fig 8: Solid 3D view
Fig 9: 3D Back view
Fig 10: Perspective 3D Front view
3. SELECTION OF MATERIAL REQUIRED TO CONSTRUCT SOLAR COLLECTOR
To select the materials, the most relevant aspects were evaluated so they would permit good performance, bearing in mind optical, physical, and thermal factors. The collector’s useful life, optical efficiency, and thermal efficiency depend on these factors to guarantee its operation. Initially, we defined the optical, thermal, and other factors that must be considered to select the materials and, thereafter, we selected the material based on these criteria.
3.1 BASIC DISH MATERIAL AND MANUFACTURING
The basic reflector design consists of the following materials:-
• A parabolic reflector profile built of fiberglass or other suitable metal, mostly aluminum (Al) with a extended steel feed horn and amplifier in its middle.
• A steel actuator device that allow the dish to receive solar energy from sun.
The Manufacturing Process:-
A. To make fiberglass suitable for dish manufacture. A sheet molding compound mixture that includes reflective metallic material and ultraviolet deflecting compositions is mixed with resin of calcium carbonate and a stimulus cure. The mixture forms a paste that is skunked onto a sheet of polyethylene film that has fiberglass added in chopped form. The result is a sheet stratum with the compound paste, fiberglass, and the polyethylene film
B. The sheet is then pressed at 88 degrees Fahrenheit (30 degree Celsius to mature). To shape the sheet into the desired parabolic shape it is pressed at high pressure .The dish is then trimmed cooled and polished and then after it is usable.
C. For metallic dishes that common medium choice is aluminum it can be used by following properties:-
i) Weight
ii) Strength
iii) Linear expansion
iv) Machining Formability
v) Conductivity
Material comparison
The material comparison table values given below are commercially pure metals
Table 2: Material comparison & its properties
Properties Al Fe Cu Zn
Density, g/cm³ 2.7 7.9 8.9 7.1
Melting point, ºC 658 1540
1083 419
Thermal capacity, j/kg, ºC
900 450 390 390
Thermal conductivity, W/m,
ºC
230 75 390 110
Coeff. Of linear expansion x10^-6/ºC
24 12 16 26
EI Conductivity, I.A.C.S
60 16 100 30
EI, resistance x10^
-9 Ωm
70 105 17 58
Modulus of elasticity, GPa
70 220 120 93
3.2 DIAMOND SHAPED GLASSES
In this reflector generally diamond shaped simple glasses are used which have a specific property which are given below on table:-
Chemical Composition:-
Composition Percentage
Sio₂ 80.6%
B₂o₃ 13%
Na₂o₃ 4%
Al₂o₃ 2.3%Miscellaneous
Traces0.1%
Table 3: Chemical properties of mirror
Physical Properties:-
Coefficient of expansion
32.5*10^-7 cm/cm ºC
Strain Point 505 ºCAnneal Point 575 ºCSoften Point 858 ºC
Density 3.23 g/cmYoung’s Mod. 6.4*10000 kg/mm²
Refractive Index
1.474
Temperature Limits
490 ºC -230 ºC
Max Thermal Shock
160 ºC
Table 4: Physical properties of mirror
4. THEORITICAL ANALYSIS OF SOLAR CONCENTRATOR
4.1. Prototype Geometry
The collector’s parabola geometry is fundamental to guarantee proper functioning of the prototype; an error during the geometric calculation would represent deviation of the solar rays; consequently, the absence of temperature at the focal point, which would give way to obtaining low thermal efficiency.
To calculate the parabola, a mathematical analysis was performed to find the values that satisfy the design criteria, like: diameter, aperture angle, and concentration ratio.
Fig 11: Reflector prototype geometry
4.2 Dimensions of the solar collector parabolic dish
Nomenclature Value DescriptionDa 1.5 Diameter of aperture (m)F 0.42 Focus (m)A 0.015 Radius of the cylinder
receptor
Table 5: Dimensions of the solar collector parabolic dish
4.3 The diameter of aperture and the maximum angle that defines it are related by equation (1)
∅ = 2𝑎𝑟𝑐𝑡𝑔𝐷𝑎4𝑓 = 83.521°………. (1)
Another important parameter to adequately define the geometry of the solar collector parabolic dish is the edge radius or maximum distance value existing between the focal point and the paraboloid extreme. Equation (2) defines said value as the following:
𝑟𝑟 = 2𝑓1+𝑐𝑜𝑠∅ = 0.7548 mts………… (2)
An indicator to bear in mind in solar collector systems is the concentration index or concentration ratio; the higher the concentration ratio, the higher the temperature to be reached with the solar concentrator system. Parabolic dish collectors are characterized for having a higher concentration ratio than the rest of the solar collector system. The concentration index is defined as the ratio between the aperture area and receiver area.
𝐶 = 𝐴𝑎*𝐴𝑟……….. (3)
The aperture area can be calculated through the following ratio:
𝐴𝑎 = 𝜋𝐷𝑎24 = 1.7671 𝑚²…………….. (4)
To find the area of the receiver, it is necessary to consider the aperture angle, the radius of the receiver, the radius of the edge, and the angle supported by the sun seen from the earth. This last constant is because the rays from the sun are not parallel to each other, given that the sun has a finite radius. From the earth, the sun is seen as a circular dish that subtends a 32' or 0.53° α angle. It is known that a=0.015 m, c is the hypotenuse formed between the focus and point B and Ø=83.521°. According to the aforementioned, we have:
𝑐 = 𝑎𝑠i𝑛∅ = 0.015096429 m…………… (5)
Now, point B would be equal to:
𝑏 = 𝑟𝑟−𝑐 = 0.739725………………….. (6)
Where Rr is the receptor radius. According to the previous equation, we obtain:
𝑅𝑟 = 𝑏𝑠in (𝛼2) = 1.72131x10³־ m……………. (7)
Upon observing Figure 10, the following geometric ratio is noted among points BCE: Where h/2 is ha lf the contact surface of the receiver cylinder. With the equation, we obtain the angle formed between h/2 and Rr.
Θ = 90+α2……………….. (8)
We also find half the contact surface of the receiver cylinder, as noted in equation (9):
ℎ² = 𝑅𝑟cos (𝜃−∅) = 0.00206 m…… (9)
Calculated area of receiver is, h = 387.92mm²
With values Aa, Rr and applying equation (3), we proceed to calculate the concentration ratio of the solar collector parabolic dish:
C=1.7671 m², 0.0003879 m²=4555.671……………… (11)
The calculated concentration ratio corresponds to the maximum concentration obtained within a parabolic concentrator with a flat receptor; however, equation 11 does not consider the angular dispersion in the receptor. The main causes of said dispersion are: inappropriate solar monitoring, poor quality in the polish of the reflector surface, and inadequate curvature on the concentrator surface.
Bearing in mind the angular dispersion and considering that all the specular radiation reflected is on an angular cone with (0.53 ° + δ).
Where: δ is the specular deviation, which has a theoretical value of 3 degrees. Finding the value of h1, the actual maximum concentration ratio is 35
4.4 Necessary values to calculate temperature in the receiver
Parameter Nomenclature Value(unit)
Environmental
Temperature
T-amb 20 ºC or 291016
K
Approximate
temp.of the sun
T-asol 5726.84 ºC or
6000 K
Emissivity del
receiver
e 0.5
Maximum
efficiency range
of solar collector
(40%-60%)
n 0.4
Table 6: Necessary values to calculate temperature in the receiver
5. FINAL DESIGN OF MODEL WITH DIMENSIONS
Fig 12: Model with design and dimensions
6. REAL TIME OBSERVATIONS
Sr.No Noticed
Time
Ambient
temperature
Output
temperat
ure
01 8:00 am 23 ºC 90 ºC
02 9:00 am 28 ºC 140 ºC
03 10:00 am 33 ºC 190 ºC
04 11:00 am 38 ºC 240 ºC
05 1:00 pm 45 ºC 295 ºC
7. CONCLUSION
The work presented in the paper is an attempt of designing a solar reflector of selected dimensional parameters. Extensive literature review was carried out to elucubrate the various perspective and application of solar reflectors. A suitable designing procedure and software was chosen from the available method to design different parts of solar reflector. 3D max cad software is used extensively for making parts.
Solar reflector technology is non conventional system and attracting wide attention due to their varied applications. Development of a sophisticated engineering product like solar reflector smooth surface is a continuous process.
A lot of work is yet to be done on the design aspects before the solar reflectors readied for market consumption. The design algorithm has to take into various other parameters to make to suitable for practical applications. Also, manufacturing of such complex shapes of parabola profile is another ongoing investigation work.
Further research work is needed to carry so the design and manufacture process would result in development of even better and more efficient solar reflector panels.
8. ABBREVIATIONS
Symbol Description Unit
Aa Aperture area m²
Ar Receiver area m³
D Distance between
Sun and earth
Km
ET Equation of Time
Minute
hͭͭ Radiation heat transfer
coefficient
W/m² K
I Beam solar radiation
W/m²
K Thermal Conductivity
W/m K
Table 8: Symbols and their usual meanings
Table 7: Experimental observations
9. REFERENCES
1. [Becker, 2000] M. Becker, W. Meinecke, M. Geyer, F. Trieb, M. Blanco, M. Romero, and A. Ferrière, Solar Thermal Power Plants, EUREC-Agency, May 03, 2000.
2. [Elsayed, 1994] Elsayed, Moustafa M. Ibrahim S. Taba, and Jaffar A. Sabbagh, Design of Solar Thermal Systems, Scientific Publishing Center, King Abdulaziz University, Saudi Arabia, 1994 AD (1414 AH) ISBN : 2-001-06-9960
3. [Jackson, 2008] S. Jackson. Overview of Solar Thermal Technologies. US Department of Energy (DOE). DOE/EPRI Technology Characterization. Global Solar Thermal Energy Council, (2008). Web address of document: http://www.solarthermalworld.org/node/30
4. [Morin, 2012] Gabriel Morin, Jürgen Dersch, Werner Platzer, Markus Eck, Andreas Häberle, Comparison of Linear Fresnel and Parabolic Trough Collector power plants, Solar Energy, Volume 86, Issue 1, Pages 1-12 (January 2012).
5.[NREL,2003] National Renewable Energy Laboratory(NREL) staff members, Concentrated Solar Power (CSP) Resource Potential, Figure 12, US Department of Energy (DOE), National Renewable Energy Laboratory(NREL). (Apr 29 2003). Web address of document: http://www.eia.doe.gov/cneaf/solar.renewables/ilands/fig12.html
6.[NREL,1994] National Renewable Energy Laboratory(NREL) staff members, Concentrated Solar Power (CSP) Resource Potential, Figure 12, US Department of Energy (DOE), National Renewable Energy Laboratory(NREL). (Apr 29 2003). Web address of document: http://www.eia.doe.gov/cneaf/solar.renewables/ilands/fig12.html
7. [Pilkington, 1996] Pilkington. Status Report on Solar Trough Power Plants. Cologne, Germany, Chapter 3.1, (1996).
8. [Pitz-Paal, 2012] Robert Pitz-Paal et al., Concentrating Solar Power in Europe, the Middle East and North Africa: A Review of Development Issues and Potential to 2050, Journal of Solar Energy Engineering. 134, 024501 (2012).
9. [Rabl, 1985] Ari Rabl, Active Solar Collectors and Their Applications, Oxford University Press, ch. 7.2.3, 1985
10. [Reddy, 1987] Reddy, T. Agami ,The Design and Sizing of Active Solar Thermal Systems, Oxford University Press, USA (September 3, 1987) ISBN-10: 0198590164 | ISBN-13: 978-0198590163
11. [Reif, 2010] John H Reif and Katie L. Reif, "Solar Concentrator System for Solar Energy Plants", US Patent Application 12/889,313. Filed Sept 23, 2010 with the US Patent Office and assigned to Eagle Eye Research, Inc
12. [Sargent, 2003] Sargent and Lundy LLC Consulting Group, Assessment of Parabolic Trough and Power Tower
Solar Technology Cost and Performance Forecasts. National Renewable Energy Laboratory, Chicago, Illinois, (October 2003).
13. [Zaibel, 1995] R. Zaibel et al., An astigmatism corrected target-aligned heliostat for high concentration, Solar Energy Materials and Solar Cells 37, pp. 191-202, 1995
