Low Cost Dual Axis Automated Sunlight Tracker

8/11/2019 Low Cost Dual Axis Automated Sunlight Tracker

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O. A. Babalola & A. B. Alabi

Centrepoint Journal (Science Edition) 2141-3819/2012 $5.00 + 0.00Volume 18, No. 1, pages 19 36 2012 University of Ilorinhttp://www.unilorin.edu.ng/centrepoint

CPJ 2012037/18103

Low Cost Dual Axis Automated Sunlight Tracker

Design for Optimized PV Cell Power Yield

O. A. Babalola* and A. B. Alabi

Department of Physics, University of Ilorin. Ilorin, Nigeria

(Received March 12, 2012; Accepted May 27, 2012)

ABSTRACT: This paper presents a cost efficient heliostat that is able to follow thesun with high accuracy. The main purpose of this work is to design and fabricate a

dualaxis solar tracker with a view to assess the improvement in solar conversionefficiency. A comparative analysis was performed using three systems, i.e.,

DualAxis Tracking, SingleAxis Tracking, and Stationary Modules. An intelligentpositioning design was achieved without the use of microcontrollers, whichsimplifies the tracking algorithm that consists of a closed loop dynamic feedbacksystem acting on four pairs of LDR sensors. The results showed that the use of the

DualAxis Tracking System produced 19% gain on power output, compared with a

SingleAxis Tracking System. The gain of output power with the DualAxisTracking System was much higher (56%) when compared with a stationary systeminclined at 30 to the horizontal.

Keywords: Heliostat, PV Cell, Sunlight Tracking System, Power Optimization, Solar

Energy.

Introduction

A major energy source which has remained relatively untapped is solarenergy. In spite of the wide spread nature and abundance of solar energy, anda well-established technology for converting it to electricity, the bulk ofMankinds energy needs is still sourced from fossil fuels with attendantdeleterious effects on the environment- Hanieh(2009).

*Author to whom all correspondence should be addressed.E-mail: [email protected]


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Centrepoint Journal Volume 18, No. 1 (2012)

Sustainable electrical sources like solar photovoltaic arrays are nowbecoming increasingly important as environmentally friendly alternatives tofossil fuels. But, while theyre nice for the environment, sustainable sourcesarent always easy to apply. These sources are characterized by bothstringent peak-power limitations and use it or lose it availability.Successful application of sustainable energy sources therefore depends on

strict attention to efficiency in both power conversion and energy storage-Davies (1993).

A heliostat is a two axis solar tracking mirror that reflects sunlight onto afixed receiver. Furthermore, in a heliostat, the geometry between the Sun,Mirror, and Receiver are constantly changing throughout the day. In generalthe mirror is aimed normal to the bisector between the sun and receiver."Direct Solar Trackers", such as Dishes, Troughs, and Lenses are notheliostats because they are generally aimed directly at the Sun.

There are many applications for the heliostat, such as in Solar WaterHeating, Lighting, Desalination (Evaporating salt water to make fresh water),Producing Steam to generate electricity and Direct Photovoltaic electricitygeneration- Kreider and Kreith(1981).

A solar panel receives the most sunlight when it is perpendicular to thesuns rays, but the sunlight direction changes regularly with changingseasons and weather. Currently, most solar panels are fixed, i.e., the solararray has a fixed orientation to the sky and does not turn to follow the sun-Harakawa and Tujimoto (2001). To increase the unit area illumination ofsunlight on solar panels, we designed a solar tracking electricity generationsystem. The design mechanism holds the plane mirror and allows the mirrorto perform an approximate 3-dimensional (3-D) hemispheroidal rotation totrack the suns movement during the day and improve the overall electricitygeneration by reflecting the suns radiation to a fixed solar panel. This systemcan achieve the maximum illumination and energy concentration and cut thecost of electricity by without the use of microcontrollers or computer control.

The purpose of this work is to design a simple, cost-effective sunreflecting system that re-directs solar energy to areas that would not naturallyreceive direct sunlight at 90o to its surface. However, unlike current sun-tracking technologies, this work is innovative in that it combines a brainlesscontrol system with solar mirrors to reflect sunlight unto photovoltaic cells.From analyzing the current solar technologies, it was determined that there isa lack of available brainless technology- Davies (1993); current industrystandards all include memory or programming for precise solar tracking. Thisreliance on brains has inflated the cost and accuracy needed for harnessingsolar energy.


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Methodology and Design

The key components of the heliostat system are the reflecting mirror, twomotors, a control system, and a photo sensor system. The photo sensorsystem will provide feedback through the control loop and consequently

orient the mirrors to maximize solar energy intake. The testing and validationof the initial design included a proof-of-concept, physical testing, a thoroughlighting simulation, and several thought experiments. These tests andvalidations yielded a final design that includes the use of apertures tominimize external noise impact.

One of the more recent advents of solar technology has been thedevelopment of solar photovoltaic cells which provide a clean and reliablesource of energy through semi-conductors generating electricity fromsunlight. The photons from the sunlight collide with electrons on the solarcell causing the electrons to jump into a higher energy state and creatingelectricity. The photovoltaic (PV) industry is consistently high-growth,averaging a growth rate of 30% in the past decade Schramek and Mills

(2000).Though PVs have a relatively low payback time (between one and three

years), the initial investment is larger than current residential electricity costsand can be prohibitively costly for residential or small-scale use Schramekand Mills (2004). Solar energy has been used to not only heat and ventilate,but also to air-condition homes. For example, commercial products has beenmade that harnesses energy with PV cells for a complete climate controlsystem for residential use Saxena and Dutta.(1990).

Control Theory

There are two basic forms of control, open and closed loop. Open loop

control does not include feedback mechanisms, while closed loop does.Current solar tracking technologies all use heliostats, which are a form ofopen loop control that predict the suns position based upon a formula for theposition of the sun throughout the year. Because this system predicts wherethe sun will be and bases controls on this, it is referred to as a brainedsystem. This type of system requires a microprocessor which is capable ofcalculating the sun's position for all times of all days throughout the year.Another option is to avoid feedback altogether, and to have a stationarymirror. This presents a very cheap solution, but with its low cost comesextremely low efficiency. This type of system cannot track the sunthroughout the day. A third type of feedback which is not yet employed insolar technology is closed loop feedback. This type of feedback detects the


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positioning of the sun through sensors, and guides motion based upon thelocation of redirected energy relative to the desired direction Konar andMandal(1991). Because this system is not capable of predicting the sunsposition, but rather reacts to where it is measured to be, this will be referredto as a brainless system.

A typical solar tracking PV system must be equipped with two essential

features:

a) Azimuth tracking for adjusting the tilt angle of the surface of the PV arrayduring changing seasons; and

b) Daily solar tracking for maximum solar radiation incidence to the PVarray.

Fig. 1 Variation of the Suns Declination with Day of the Year. According toGCREEDER (2009)

The declination, in degrees for any day of the year (N) can becalculated approximately by the Coopers equation

1

Function Description

The key components of the heliostat system are the reflecting mirror, twomotors, a control system, and a photo sensor system. The photo sensorsystem will provide feedback through the control loop and consequentlyorient the mirrors to maximize solar energy intake. The testing and validation


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of the initial design included a proof-of-concept, physical testing, a thoroughlighting simulation, and several thought experiments. These tests andvalidations yielded a final design that includes the use of apertures tominimize external noise impact.

Control Theory

There are two basic forms of control, open and closed loop. Open loopcontrol does not include feedback mechanisms, while closed loop does.Current solar tracking technologies all use heliostats, which are a form ofopen loop control that predict the suns position based upon a formula for theposition of the sun throughout the year. Because this system predicts wherethe sun will be and bases controls on this, it is referred to as a brainedsystem. This type of system requires a microprocessor which is capable ofcalculating the sun's position for all times of all days throughout the year-Koyuncu and Balasubramanian (1991).

Another option is to avoid feedback altogether, and to have a stationarymirror. This presents a very cheap solution, but with its low cost comes

extremely low efficiency. This type of system cannot track the sunthroughout the day. A third type of feedback which is not yet employedextensively in heliostat technology is the use of the closed loop feedback.This type of feedback detects the positioning of the sun through sensors, andguides motion based upon the location of redirected energy relative to thedesired direction because this system is not capable of predicting the sunsposition, but rather reacts to where it is perceived to be, this will be referredto as a brainless system.

A typical solar tracking PV system must be equipped with two essentialfeatures:

a) Azimuth tracking for adjusting the tilt angle of the surface of the PV array

during changing seasons; and

b) Daily solar tracking for maximum solar radiation incidence to the PVarray.

The block diagram of the solar tracking system and the logic flow of theTracking Control are presented in figures 2 and 3. Presented in figures 8, 9and 10 are the Analogue and the digital hardware implementation of thesystem and the logic.


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Fig. 2: The block diagram of the solar tracking system


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Fig. 3 Tracking Control Flow Chart

Tracking Sensor Design

One of our key modules is the sensor. Because the sensor tracks the solarlight source orientation, selecting the right tracking sensor is very important.CdS sensors are cheap, reliable, and photo-sensitive. In our design, the CdS

sensor provides the major advantage that its photo sensitivity (i.e., spectralcharacteristics) is between 0.4 mm and 0.8 mm, which is close to thewavelength scope of visible solar light (0.38 to 0.76 mm), as shown in Figure4.


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Fig 4. CdS Stereogram and Sensitivity Scope compared with CdSeand Cd(S,Se) Sensor According to Hanieh(2009).

One of our key modules is the sensor module. Because the sensor tracksthe solar light sources orientation, selecting the right tracking sensor is veryimportant. CdS sensors (see Figure 4) are cheap, reliable, and photo-sensitive. In our design, the CdS sensor provides the following advantages:

Without polarity (ohmic structure), the CdS sensor is easy to use.

CdS sensors have a photo-variable resistor in which the internalimpedance changes with the intensity of light energy.

When the ambient light brightens, the CdS sensors internal impedancereduces.

The CdS sensors photo sensitivity (i.e., spectral characteristics) is 0.4 to0.8 mm, which is close to the wavelength scope of visible solar light(0.38 to 0.76 mm).


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The Light Sensor Unit

The tracking sensor is composed of eight units of similar CdS sensors,which are located at the east, west, south, and north to detect the light sourceintensity in the four orientations. The eight sensors are divided into twogroups, east/west and north/south. In the east/west group, the east and west

CdS sensors compare the intensity of received light in the east and westcoordinates while the north/south group of CdS sensors compare the intensityof received light in the north and south coordinate as shown in Figure 5. Eachof these has two LDRs for coarse/wide angle tracking and two LDRs forlocking the heliostats position when the sun rays pass through them.At the CdS sensor positions, brackets isolate the light from other orientations

to achieve a wide-angle search and quickly determine the suns position asshown in Figure 6.

Fig. 5 Transverse Cross-Section of the Light Sensor Unit emphasizing theeast-west group of LDRs


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The brackets are designed to have an aperture of approximately =15oeach for the wide angle-tracking mode and less that =0.1ofor the lockingmode. The design is such that the brackets have a depth of x such that

2

and a width of y which was designed to be about 40 mm. The locking

aperture was designed to have a depth L such that

3

where d the diameter of the tube was designed to be approximately 12 mm.

Fig. 6. Longitudinal Cross-Section of the Light Sensor Unit

Overall, the tracking error was designed to be given by the equation

4

where X is the distance between the light sensor unit and the heliostat and Yis the distance between the Sun(light source) and the vertically placed solarpanel. The arrangement is shown in figure 7 for tacking in the east-westdirection.


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Fig. 7 East to West Solar Track with respect to Heliostat-Solar PanelPosition

Fig. 8 Light intensity Comparator Circuit


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Fig. 9 Digital logical Circuit

Fig. 10 H-Bridge Driver Circuit


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Results and Discussion

We compared the Relative Performance of the fixed Solar Panel tilted at

30o to the Horizontal (Stationary Module ) with the SingleAxis Tracking

System and also with the DualAxis Tracking System at Ilorin (0830'N,

0435'E), Nigeria in the month of October, 2010. A seven-day average of the

power obtained from a fixed solar cell of 60 W rating was obtained for three

sets of identical solar cells. A 10 , 100 W resistor each was used as the load

to each resistor for the 16 V solar panels. The single axis tracking was done

with the Heliostats mirror tilted at 30o to the Horizontal so that its

performance can be accurately compared with the directly irradiated fixed

solar panel. The result of the power obtained for the load resistor between

8:00 am and 7:00 pm is presented in Table 1.


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Table 1. Seven-day Average Result for the Fixed, Single Axis and Dual Axis Operated Solar Cells

Seven-day Average Result (October 2010)

Stationary Module

SingleAxis Tracker D

Time Voltage (V) Current (A) Power (W) Voltage (V) Current (A) Power (W) Vo

8:00 6.17 0.03 0.16 6.55 0.07 0.46 7.0

9:00 8.64 0.8 6.95 10.39 2.15 22.33 15

10:00 16 1.6 25.63 17.9 1.99 35.6 19

11:00 16.4 1.86 30.57 19.85 1.77 35.12 19

12:00 17.54 1.6 28 18.4 2.42 44.46 20

13:00 18.13 1.79 32.44 18.45 2.37 43.75 19

14:00 15.73 1.48 23.26 19.68 1.76 34.54 20

15:00 17.33 1.58 27.3 18.03 1.77 31.97 18

16:00 13.56 1.18 15.94 17.3 1.77 30.58 17

17:00 6.47 0.8 5.17 14.19 2.27 32.16 17

18:00 6.02 0.51 3.05 6.68 1.8 12.04 9

19:00 5.84 0.01 0.05 6.31 0.02 0.12 6.3


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The result show that the peak output voltage of the loaded solar panelsobtained to be approximately 18V occurred at about12:00 to 13:00 for thefixed solar panel, whereas for the single axis solar cell, it occurred at about10:00 to 11:00 and for the dual axis solar tracker, this peak occurred atbetween 9:00 and 10:00.

A plot of the average Solar Energy power output and the time of the day

(Fig. 11) shows that even though all the cells show a peak power output atbetween 12:00 and 13:00, the solar cell tracked by the dual axis heliostatproduced the highest power of about 50 W. The Stationary module was onlyable to deliver 30 W within this same peak time. At all times considered, theDual axis heliostat outperformed both the Single axis Heliostat and the fixedsolar panel module.

8:00 10:00 12:00 14:00 16:00 18:00 20:00

0

5

10

15

20

25

30

35

40

45

50

55

SolarEnergyPowerOutput(Watt)

Time of the Day (Hour)

Stationary Module

Single Axis Tracker

Dual Axis Tracker

Fig. 11 Average Solar Energy Output versus the Time of the day

We compared the relative performance of the Stationary module with theDual axis Heliostat, the Stationary module with the SingleAxis Tracking

System and the SingleAxis Tracking System with the Dual axis Heliostat.


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Table 2 presents the result of the percentage difference/relative performanceof these systems. We observe that a gain of 56.31% is obtained when thedual axis heliostat is used instead of the fixed module. A gain of 45.46% isobtained when a single-axis heliostat is used instead of the fixed module. Therelative advantage of the Dual axis heliostat over the single axis heliostat ishowever approximately 19.39 %.

Table 2: Percentage difference/relative performance of the three Solar Cellsystems

7 Days Average Power(Watt) Percentage Difference Between

TimeStationaryModule

SingleAxis

Heliostat

DualAxis

Heliostat

StationaryModule& Single

AxisHeliostat

Single AxisHeliostat &Dual AxisHeliostat

StationaryModule& Dual

AxisHeliostat

8:00 0.16 0.46 0.57 64.23 19.38 71.17

9:00 6.95 22.33 28.98 68.90 22.92 76.03

10:00 25.63 35.60 45.83 27.99 22.32 44.07

11:00 30.57 35.12 43.60 12.97 19.45 29.90

12:00 28.00 44.46 52.60 37.03 15.46 46.76

13:00 32.44 43.75 51.32 25.85 14.75 36.79

14:00 23.26 34.54 44.22 32.65 21.89 47.40

15:00 27.30 31.97 41.50 14.62 22.95 34.21

16:00 15.94 30.58 38.92 47.87 21.43 59.04

17:00 5.17 32.16 36.74 83.92 12.47 85.93

18:00 3.05 12.04 14.19 74.65 15.19 78.5019:00 0.05 0.12 0.16 54.80 24.51 65.88

45.46 % 19.39 % 56.31 %

Figure 12 presents the plot of the relative performance of the Stationarymodule with the Dual axis Heliostat, the Stationary module with theSingleAxis Tracking System and the SingleAxis Tracking System with theDual axis Heliostat. We observe that the relative performance of the Dualaxis heliostat over the single axis heliostat was relatively constant andindependent of the time of the day.


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The relative performance of the single-axis heliostat system over thefixed solar module was equal at between 12:00 and 13:00.i.e. equalperformance. However, at other times, the relative performance diverges.This shows that tracking the suns ray become advantageous only when theangle of incidence of the sun is large. The large drop in the relativeperformance of both the single axis- and the dual axisheliostat at 18:00 is

due to the disappearance of the sun below the horizon.

8:00 10:00 12:00 14:00 16:00 18:00 20:00

10

20

30

40

50

60

70

80

90

RelativePerformanceORPercen

tageDifference(%)

Time of the Day (Hour)

Stationary Module & Dual Axis Heliostat

Stationary Module & Single Axis Heliostat

Single Axis Heliostat & Dual Axis Heliostat

Figure 12: Percentage difference/relative performance of the threeSolar Cell systems

Conclusion

In order to collect the greatest amount of energy from the sun, solarpanels must be aligned orthogonally to the sun. For this purpose, a new solar


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tracking technique based on an intelligent positioning design was achievedwithout the use of microcontrollers was implemented and tested in this study.The tracking system presented has the following advantages: The trackingsystem is not constrained by the geographical location of installation of thesolar panel since it is designed for searching the maximum solar irradiance inthe whole azimuth and tilt angle (except hardware limitations ) during day

times; namely, the angle of elevation does not need to be adjustedperiodically. The operator interference is minimal because of not needing tobe adjusted. A drawback of the tracker is being effected by temporalvariations in the atmospheric refractions caused by rain, cloud, fog, etc.Thus, the system may sometimes on a cloudy day give an erroneousdetection in the direction of the sun, and lead to wrong positioning of thesolar panel.

References

Ahmed Abu Hanieh(2009). Automatic Orientation of Solar Photovoltaic Panels.

GCREEDER, AmmanJordan, March 31st April 2nd 2009Davies, P.A.(1993). Sun-Tracking Mechanism Using Equatorial and Ecliptic Axes.

Solar Energy, v.50, 6:487-489.Harakawa, T., Tujimoto, T.(2001). A proposal of efficiency improvement with solar

power generation system. Industrial Electronics Society, 2001. IECON '01.The27th Annual Conference of the IEEE, 1:523-8.

Konar, A., Mandal,. A. K.(1991). Microprocessor Based Automatic Sun Tracker.IEE Proc.-A. Vol. 138, 4:237-1.

Koyuncu, B., Balasubramanian, K.(1991). A microprocessor controlled automaticsun tracker. IEEE Trans. on Consumer Elects., Vol. 37, 4 : 913-7.

Kreider, J. F., Kreith, F.(1981). Solar Energy Handbook, McGraw-Hill BookCompany, pp : 1-9.

Philipp Schramek, David R. Mills,(2004). Heliostats for maximum ground coverage.

Elsevier, Energy 29 701713Saxena, A. K., Dutta, V.(1990). A Versatile Microprocessor Based Controller forSolar Tracking. Photovoltaic Specialists Conference, Conference Record of theTwenty First IEEE, 2 : 1105-9.

Schramek P, Mills DR.,(2000). Potential of the heliostat field of a Multi Tower SolarArray. Proceedings of the 10th SolarPACES International Symposium on SolarThermal Concentrating Technologies, Sydney 810 Marz.,p. 15763.

Low Cost Dual Axis Automated Sunlight Tracker

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