1 Proc. of the International Conference on Advances in Mechanical Engineering, Augu;:,t3-5, 2009 SV National Institute of Technology, Surat , Gujarat, India Exploring regions of application of Single and Double axis Solar Tracking Systems M. A. Kadam and S. B. L Garg B. V University College of Engineering Dhankawadi, Pune Corresponding authors (em ail: Fixed solar collector installations of ai/ types, P V panels, Flat piates, parabolic and paraboloid, have poor collector efficiency. The collector efficiency can be increased by solar tracking. Because of bidirectional sun trajectory, bidirectional collector tracking is required. The studies have shown that both axes tracking does not give equal increase in the collector performance. Single axis tracking (East West) is generally quite effective and may increase the collector efficiency by 30 to 45%. The tracking in other direction (North South) may increase the performance further but by only 15 to 20%. Different types of solar collectors have different application range. One example is a solar water heater (which is essentially fixed in space). Many applications such as PV panels and parabolic collectors, used for generating electricity either by direct conversion or through hot water and steam, require high operational efficiency. For small power devices, the advantage gained by using a double axis tracking system may be considerably neutralized by extra expenditure on double axis tracking system and its maintenance. For many applications, an alternative is to provide a low cost single axis tracking system with some compromise on collector pettortnence. 1. Introduction The developments of last two centuries in physical sciences and their applications have caused unprecedented growth in all directions and have changed the living conditions on planet earth giving its inhabitants a comfortable living. These developments could not have been possible without availability of abundant energy in useable forms. During last two centuries, nature helped mankind by providing abundance of exhaustible fossil fuels in the form of coal and oil which have been used by man at frighteningly high rates, causing their fast depletion. The fast depletion of energy resources has made man conscious for developing alternative energy resources. Of these alternative resources, nuclear form is high intensity energy but has problem of waste disposal. Solar energy is freely available inexhaustible and environmentally clean energy. It is low intensity energy and therefore poses the problem of high collection area. The concentrated energy in heat form is achieved by solar concentrators like parabolic or paraboloid collectors. Devices using heat or thenmal energy can use the solar energy directly for low temperature applications (say about 100 C) or by concentrating it to obtain medium and high temperatures (100 to 600 ) for power production. Vigorous efforts are under way for using solar energy for electric power production and it is estimated that by 2030, about 7% world's energy will come from sun. For converting solar energy into electrical energy, photo voltaic cells are gaining popularity. A large number of solar cells connected in series and parallel are used as solar panels for generating electricity from sun energy directly. The panels directly convert the solar radiation falling on them into DC electricity. To get highest conversion efficiency, the sun rays must fall at right angles to the receiver surface. As the sun orientation is changing continuously, a sun tracking system must be used which should periodically modify the collector orientation for remaining normal to the sun rays. Development of an inexpensive and efficient solar tracking system is an important development problem for use with solar PV panels and concentrating col!ectors (parabolic and paraboloid). 342
2 Proc. of t~e International Conference on Advances in Mechanical Engineering, August 3-5, 2009 S.\}. Nationallnstilute of Technoloqy. Surat , Gujarat, India 2. Solar Tracking Sun tracking systems ensure that the solar collector receives maximum solar irradiation all times u'j n 1 3 L jng the sun rays fall normal to the collecting surtace. During the day. the sun's movement is East - West and ~Jorth-South. The collector surface can be kept normal to the sun rays (called sun tracking) by providing motions to the collector in both the directions. A good tracking mechanism must be reliable and should be able to track the sun at the right angles even in the periods of cloud cover. For making the tracker to orient the collecting surface for absorbing maximum insolation on its surface. the transducers for determining the intensity of insolation must be set for Maximum Power Point Tracking (MPPT) [1). This would enable the collector to collect maxiruurn energy. For working at Maximum Power Point. photo voltaic cell operated solar panels are used. The effectiveness of a solar panel connected to a fixed constant load voltage using MPPT has been investigated in references [1, 2). In 24 hours (one full day) the earth completes one rotation; rotating by 15 in one hour in E-W direction. The polar axis of the earth is inclined and the angle of declination changes in a cyclic manner. The position of sun on its path provides input data for tracking. Because of periodic motion of earth in f'js and EW directions, for ideal tracking, the collector orientation must be continuously adjusted in botb directions (see Figure 1). C 0> E c Q> co.":.-,h-:" : ~ ~ 0..: ' ~ -lob ~-,: e>1 ~ '----=~ I _ Sol;s~ce Fiqure 1 Sun movement in c-vj and N-S directions - source-[ ~1J Figure L Daily alignment of collector for Single axis tracking [4J Solar tracking systems Solar tracking in two directions requires design and fabrication of two directional movements making tracking an expensive proposition. The preference of Fixed, Single axis or Bidirectional tracking depends upon the application and desired collection efficiency. Since, continuous tracking requires powerful tracking motors (depcndlnq up on the size of the collector); tracking at discrete intervals may be sufficient in large number of cases (particularly in cases not used for power generation). Reference (3) has examined the issue of contirrous vis discrete two positional tracking. Figure shows perfonmance of a collector with tracking :,- e-w direction 3~ two hour interval. It is seen that collector performance is not severely affected. Single axis tracking systems Sing:e axis tracking system is cheaper and can be used for collectors with low to medium concentration ratios but misalignment should be taken care of at regular intervals. The axis of the coilector should be regularly adjusted in N-S plane at the angle of the latitude of the concentrator's site i.e. along the polar axis equal to sun's declination for the day. The alignment of the collector in the N-S direction is needed to be adjusted [4) for the number of days from equinox. Figure 2 gives alignment angles to be adjusted for number of days after equinox The frequency of adjustment per week decides the efficiency of the collector. For E-vV direction, the sun is tracked by the collector continuously by following it at the rate of earth's rotation. For single axis tracking systems, continuous tracking is done only for E-W direction, for N-S direction, if the misalignment between the sun and the concentrator normal is within accepted angle limits, perfect tracking can be assumed. 343
3 Proc. of the International Conference on Advances in Mechanical Engineering, August 3-5, 2009 S.\I. Iatronat lnstitute of Technology, Surat Gujarat, In,ja Two axis tracking systems Both the directional movements (E-W and N-S) are the most commonly used sur. tracking metnoo and have their own sun tracking formulae, vhich not inter-related. This makes it nece sary to provide independent control for movement for both directions. Reference [5. 2J presents a general formula combininq both movements. The movement of the two axes of the tracker is microprocessor controlled . Following types of systems have been developed for solar tracking. (i) Microprocessor controlled (ii) Electro- optical type For finding the sun direction, the microprocessor controlled types are based en mathematical formulation for both movements and the tracking is carried out by utilizing the astronomical coordinates of the sun. The electro-optical types use sensors for finding solar intensities by two or more separate sensors mounted at two different positions such that the difference of intensities found by both is used to orient the collector such that this difference is reduced to a minimum. 3. Application of Sun Trackers to different Sular Collectors Five decades of intensive research for developing alternative resources of energy has resulted in use of following application dependent solar devices. (a) Fixed Flat plate type solar collectors These devicesare fixed in space type and are generally bulky. They are not generally subjected t~ sctar ~:2ck!;!g 25!~e g2!!'1 if! pe:!0.!'":f!'::r1ce t.!s!!:g!rac~!ng coes not just!fy the!f'!\/est~~0.~ ;~ instaltinq a tracking device. Flat Plate Collectors are used for water heating and solar cooking ana are simple in design haviaq no moving parts requirinq little maintenance. As in any collection device, the principle ~o:lowed is to expose a dark (blackened) surface to solar radiation. The surface absorbs radiation awl the absoi bed radiation is transferred to a fluid like air or water. Temperatures ranging from 40 0 C to about C are achieved. Some common solar devrces are son«drier, solar water tioeter and solar stius. The results of some studies made for sora. driers. solar stills and solar water heater are g;ven below. (i) Solar duet Mwithiga and Kigo  studied,he performance of a soiar drier w;tr. lirr.ited number of discrete sun trackinq, The drier performance was rr.easurec by measurinq the moisture ratio of coffee beans at two hour interval starting from a AM. The study was conducted for fixed drier, and for three, five ar,ci nine tracking positions. o~f~' :g s I '" J ' 06 ;;.~ 0 os, c ~ 120. o ~ - - \ 0' t.' r I./ I I ~ OJ I, I : ao,.- '" t: i :--- I --!- '5 il2 on. I,ul-,-.IS n _. L,--/~ I 01 < " u j- o L;:;/ E! I -r----;-- I I t ::J - j;r,<\;--- I 4~ ','--... <lj <lj ~ ~ -... j 0 C c I U 6 3 '0 12 Time, hours ~Oj ~c...~_ '6 '8 <., Locat nme "(h) Figure 3 Moisture content removed as a function of time -source[7j) Figure 4 Condensate collected in ml in a Solar.31'"- source[8j Figure 3 gives a clear effect of the tracking condition. With more tracking, (9 positions). ana auer eigrlt hours the moisture content is reduced from 100'10 to 25~o whereas 'without tracki',g. Il I.) reduced from 100% to 50% only showing that solar tracking drastically reduces the drying in.e and should be employed if possible. (ii) Solar still 344
4 Proc. of the International Conference on Advances in Mechanical Engineenng, August 3-5, 2009 S.V. Nauonallnstitute of Technology. Sur at Gujarat. india Abdallah and Badran [8J have studied the productivity enhancement of solar stills for producing clean water using sun tracking system. The sun rays rail on the inclined glass and enter the still for heating water in the basin. The heated water evaporates and condenses on the glass plate to flow along the glass plate and is collected as a condensate. Figure ~ shc.vs the rate of water production in the form of collected condensate. For the case of tracking. it IS considerably more and increases from 20 ml to 85 ml between 11 AM and 2 PM. It is important to consider this point before a decision for investment is made for employing tracking system as an increase in yield of about 20% is obtained by using two axis trackers. (iii) Solar water heater Prakash, Garg and Harikishan [9J studied the effect of tracking on the performance of built in storage type of solar water heaters for fixed surface, single axis tracking and double axis tracking. The results of hourly variation of water temperature with respect to day time are given in Figure 5. It is seen that there is hardly any difference in the performance of single and double axis tracking systems. However with fixed systems the difference is noticeable and there is difference of 6-7 in the peak temperatures reached. It is found )hat without trackinq a lower performance is obtained. The double axis and single _.:_ ' 1.: :.. I....,.I.... ;...J.. r _ oai:> licl... t\nl~ YI\'C:;:ICOIIY :;)clilic :C~Ufl. Il t:;viuc;lil IIUIII this study, that a single axis tracking system is gond enough for most purposes. In this case a single axis tracker is sufficiently good. o g 40 I! 20 r-.~ I IL '~_" E~::-:,eO:~)'~~'~::.JU Fig 5 Eiiect 0; Sun Tracking on water temperature in a solar water heater [9 J (b) Persbotic collectors srvd Pl/ panels Parabolic couectors are used for heating fluids at relatively high temperatures (say between ioo" anc 300\ Single axis and double axis tracking systems are useful for paracone and paraboloid solar collectors and PV panels workinq on Phoio Voltaic principie [10, 11]. Table 1 gives the efficiencies for fixed. single and two axes trackino systems for both summer arid winter seasons for a particular place. The values are only of relative importance and will vary irorr. piace to piace. Table 1. Typical efficiency values for Fixed, Single, and Double axis Tracking Systems SUNIMER EFFICIENCY WINTER EFFICIENCY' Fixed axis 52% Fixed axis 44% Sinqle Axis 68% Single Axis 47% Double axis 82% Double axis 55% The effect of using a fixed, single axis and double axis tracker are shown in figure 6 and 7. The research has resulted in considerable improvements in conversion efficiency of PI) ceus Presently direct conversion efficiency is about 14%. It is expected that in near future convers-o» efficiency will approach about 28% or more \'vhi:::il would be a remarkable attainment. DL..:~; summer for single and double axis systems the collection efficiency approaches 70% for si~;~~ and 80% for double axis trackers (see Figure 6). Figu~e 7 show that during winter (in Jar.'.C30/ 1 tne collection efficiencies are poor varying from 40% to 55%. This is perhaps for the reason tr a: whether is cloudy; for places havmq clear sky, better efficiencies can be expectea. 'fit ""I';;'" axis system is therefore net usetul in winter fer a!! places. i i
5 Proc. of the International Conference on Advances in Mechanical Engineering, August S.V. Nauonal lnsu l,.,l)of Technology, Surat , Gojarat, India lsov JOOO -:: / "i 200J I,' ; 1500 I, f. igvo f ;; OL- ~~--~ a 2. Time Figure 6 Typical power output curve far doubleaxis, single-axis and fixed array system respectively for one summer day-source[ 1OJ Figure" Typical power output curve for double-axis, single-axis and fixed array system respectively for one winter day - source[ioj 4. Conclusions 1. Solar trackers give substantial advantage fur increasing collection efficiency for solar concentrating devices like parabolic collectors arid PV panels. The advantage gained depends upon the whether. In summer with clear sky, the efficiency of energy collection may reach 80-90%, whereas in winter the efficiencies may be as low as 40-50%. 2. For heat to direct electric power conversion devices solar tracking gives substantial advantage by increasing solar collection efficiency. This is particularly true for direct energy conversion devices like PV pane!s, whil;' presently give about ~4% overall solar energy to electricity conversion efficiency. With fur-her development in technoroqy, this figure may reach a Substantially high value of about 28% in near future. 3. For solar driers, solar stills and solar water heaters, usinq direct solar heat er.ergy, a single axis tracking system is sufficient. Cne need not go to double axis sola. trackers as by using double axis systems, the efficiency of ene:-gy collection is only itiargin311y increased and does not justify the investment in a double axis tracker. The efficiency of collection of solar energy over a fixed collector can be increased by ~5-30"10 by using a single axis trackinq system. Referen:::es [11 Hwang, LH, SK Na, HS Kim, ~S Oh, YS Kim, Han Xiao, Yu MingZhi. MT Cho, SC Chang and GS Choi, 'A development of Solar position tracker on Program Method for Smail typed Star.d Alone Pv System, The r: International Conference on Power Eiectromcs. Octooer LL-ib, 2007/EXCO, Daegu, Korea.  Arrnsstronq S, and WG Hurley, ' Investigating the erfect of Maximum Power Point Tracking for a Solar system', /05 (c) 2005 IEEE.  Teolan Tomson, 'discrete two position tracking of solar collectors', Science Digest, Renewable Energy', 33 (2008) [41 Cope AWG, and N. Tully, 'Simple Tracking Strategies for Solar Concentrators'. Solar Enerqy VoI.27,No ,1981. [5J Chong KK, CW Wong, ' General formula for on-axis su., (;acking system anc,:.; c~~,,';.;l:,::,;-,.t. improving tracking accuracy of solar collector, Science Digest, Solar Energy 83 (2009)  Sawawu, RI and TA Oduyemi,' d microprocessor controlled solar tracking system'. j(;vmai of Micro computer Applications, (1987)  Gikuru Mwithiga and Stephen Njoroge Kigo, 'Performance of a solar drier with i;~;ieo sun tracking capability', Science diret, availabie online. [8J Abdallah S, 00 Badran,' Sun tracking system for productivity enhancement 0: scrar 5:.::. Science Direct, Desalination 220 (2008) [91 Prakash J. HP Garg and OS Hrishikeshan. ' Effect of tracking performance of a blj:i:-;r: ~;~-;:;~-= type solar water heater, Solar and Wind technology, Vol,S, No. 4,pp [~O] Chun-Sheng Wu, Wang Yi-80, Liu Si-Yang, Peng Yan-chang and Xu Honq-Hua.' ::L':;, ::r: Automatic sun tracking Technology in PV Generation' DRPT200a 6-9 April 2008 [11 J Alexandru Catalin,and Claudiu Penza, 'Virtual prototype of a Dual-axis Trackiilg Svs.err ;,.3~: for Photo Voltaic panels', / (c) IEEE.