IOSR Journa of Engineering (IOSRJEN) ISSN (e): 2250-3021, ISSN (p): 2278-8719 Vo. 05, Issue 04 (Apri. 2015), V1 PP 09-15 www.iosrjen.org The infuence of temperature of photovotaic modues on performance of soar power pant Modestas Pikutis 1, Dominykas Vasarevičius 2, Romanas Martavičius 3 1( PhD student, Department Of Eectronic System, Vinius Gediminas Technica University, Vinius, Lithuania) 2 (PhD, Department Of Eectronic System, Vinius Gediminas Technica University, Vinius, Lithuania) 3 (Professor, Department Of Eectronic System, Vinius Gediminas Technica University, Vinius, Lithuania ) Abstract: - Studies and research of photovotaic power pants in rea word conditions with a goa to find more effective contro agorithms require significant investment in equipment and takes a ot of time. To acceerate the research, mathematica modes are designed, which aow to simuate processes in photovotaic power pant under conditions cose to the rea ones. To investigate the effects of temperature variations, the bock of temperature is designed, which aows imitating the processes asting for month or even severa years. This bock is used in a mode of photovotaic power pant, deveoped in earier studies. The mode described in this paper consists of four structura bocks: a bock, imitating the soar energy fux; the bock, for simuation of temperature variations; the bock, imitating photovotaic modue and the contro agorithm, in which the maximum power point tracking is performed using IncCond agorithm. The mode of photovotaic power pant is impemented in Matab/Simuink environment. The mode is used to investigate the effects of photovotaic modue temperature on performance of the power pant during a coudy day. It is proved, that due to overheated photovotaic modues the efficiency of power pant is decreased. It is proved, that it is possibe to increase the efficiency of photovotaic power pant from 11 % to 31 % appying forced cooing to a of the photovotaic modues. Keywords: temperature of photovotaic ce, maximum power point tracking, shadows. I. INTRODUCTION Many researches are conducted with a goa to improve physica properties of photovotaic (PV) ces. The efficiency of the most of PV ces is ess than 20 %. Since the efficiency of PV ces is sma, it is important, that they aways operate at maximum power point (MPP). To maintain such operationa conditions, specia controers, impementing different maximum power point tracking (MPPT) agorithms are used [1], [2]. The seected contro agorithm infuences how quicky MPP of the PV modue wi be found and how precisey it wi be tracked. MPP tracking in soar power pant is compicated because of unpredictaby varying environmenta conditions and different characteristics of different PV ces or modues. These differences can appear on some of the PV modes of a singe power pant if it affected be partia shadow, snow cover, hoarfrost, dust or tree eaves stuck on the surface of some PV modues. These effects are of random nature and it is impossibe to predict their infuence for different PV modues. Because of these effects it is not possibe to predict the correct oad of soar power pant at certain time intervas. It is very important to keep the correct oading of PV modues, because ony in this case the soar power pant wi operate at MPP and wi utiize the avaiabe soar power fux (SPF) with highest efficiency. The position of MPP in current-votage characteristics of PV modue can vary because of temperature [3]. Earier simuations were performed, assuming, that the temperature is 25 C and is constant. MPPT agorithms were investigated ony depending on variations of SPF. However, in order to accuratey assess and investigate the operation of soar power pant under conditions, cose to rea word, it is important assess the infuence of variations of PV modue temperature. Studies and research of soar power pants in rea word conditions require significant investment in equipment and takes a ot of time. This can be avoided by investigating the deveoped mathematica mode of soar power pant and simuating rea word conditions. This aows to compare the operation of soar power pant at certain time intervas, when ony preferred parameters are changed. 9 P a g e
In this work, the infuence of temperature performance of separate PV modues and whoe soar power pant is investigated. To achieve this, the Matab/Simuink mode, deveoped in previous works is used [4]. A bock, imitating temperature variations at defined time interva is added. II. INFLUENCE OF TEMPERATURE TO THE PERFORMANCE OF PHOTOVOLTAIC MODULE From previous studies it is known that the power pant controer is particuary sensitive to rapid changes of SPF. However, it is not known how the controer responds when to main factors, infuencing it`s operation are varying simutaneousy changing SPF and modue temperature [5]. The operation of the soar power pant is studied in the foowing order: firsty the impact of environmenta conditions on one PV mode is studied, then on soar power pant, consisting of four PV modues. Figure 1 MPP at different SPF and temperatures [6] Varying SPF, faing to the surface of PV modue is simuated, when modue temperature grows from 25 C to 50 C. Simuated current-votage characteristics are presented in Fig. 1. The first series show the ocation of MPP, when PV modue temperature is 25 C and it is iuminated by SPF equa to 1000 W/m 2. The second series show the ocation of MPP, when PV modue is iuminated by SPF equa to 600 W/m 2 whie the temperature is the same 25 C. The third series show MPP when SPF is ony 400 W/m 2 and the temperature is sti the same 25 C. These series characterize the ocation of MPP at the same temperature and different SPF. The fourth and fifth curves show the infuence of temperature rise from 25 C to 50 C on the ocation of MPP. Comparing first, second and third series reveas, that at constant temperature, the decrement of SPF causes significant decrement of PV modues output current. The decrement of SPF from 1000 W/m 2 to 600 W/m 2 causes the decrement of current by 1.9 A and votage by 1.1 V. Thus power decreases by 32.7 W (series 1 and 2). When the temperature of the PV modue is 50 C and SPF fas from 800 W/m 2 to 600 W/m 2 the current decreases by 0.97 A and votage by 0.6 V (series 4 and 5). This causes the decrement of power by 14.2 W. When SPF is at constant eve of 600 W/m 2 and temperature rises from 25 C to 50 C, the output current of PV modue remains amost unchanged, but the votage decreases by 2.3 V, so the power decreases by 9 W (series 2 and 4). According to series 2 and 4 it is seen, that when the SPF is 600 W/m 2, the output power of PV modue is higher at ower temperature. Anaysis of the mode proves that the increment of PV modues temperature decreases its efficiency, so ess power is avaiabe at the output of the mode at the same SPF. It can be stated that the characteristics of operation of PV modue depend not ony on SPF, but aso on modue temperature and it is necessary to keep it as ow as possibe. III. STRUCTURAL DIAGRAM OF A MODEL In Fig. 2 the structura diagram of soar power pant, for evauation of temperature effects on performance is presented. In this mode, the power pant can consist of the required number of PV modues. Each PV modue consists of 28 PV ces. The overa power of the PV modue at standard test conditions is 78 W. For this experiment four modues are being used so the tota power of the soar power pant is 300 W. Simiar signa ST, imitating SPF is sent to each PV modue. It is generated by SPF bock. The parameters of this bock are seected in such a way, that it imitates SPF signa, cose to the rea one on a partiay coudy day. 10 P a g e
To simuate the effects of temperature to the performance of the soar power pant, the temperature simuation bock is used. In the mode it is assumed, that a the modues are of the same type, and they are affected with the same soar radiation, so the same temperature signa is used for a the modues. Thus, these bocks simuate SPF and instantaneous temperature of the modues [4],[7]. Figure 2 Structura diagram of a mathematica mode PV modues affected by SPF and temperature output votage UFVM and the current IFVM, which fows through the oad. In the anayzed soar power pant MPPT is performed according to IncCond agorithm [2]. According to the agorithm, PV modues output power derivative with respect to votage dp/du is cacuated. The resut describes the position of systems operation point in the power characteristic in reation with MPP. According to the resuts, the oad resistance is increased or decreased by step ΔR 1. IV. MATHEMATICAL MODEL OF SOLAR POWER PLANT To investigate the infuence of temperature variations on performance of soar power pant, according to described structura diagram (Fig. 2) the mathematica mode is deveoped in Matab/Simuink environment (Fig. 3). The core of the mode is bock, imitating SPF signa. This bock has the foowing inputs: incination ange, abedo, day of the year, ongitude and time zone. These parameters can be adapted to simuate SPF faing to the incined surface in any ocation on Earth at any time. The mode aso incudes the bock to simuate coud cover. This bock attenuates the SPF signa and imitates additiona diffused and refected components of soar radiation. After appying Gaussian fiter, the SPF signa, imitating rea word conditions is formed [8]. The generated SPF signa imitates sunrise at 6:00 o cock and sunset 21:00 o cock. Thus tem maximum power point tracking in soar power pant continues for 15 hours the whoe dayight time. The simiar SPF signa fas to a four PV modues of the soar power pant. The temperature of PV modues is defined in temperature simuation bock, which sends generated signa to a PV modues. This bock sets the temperature of PV modues depending on intensity of soar radiation and wind speed [9]. The goa of research is to determine the infuence of temperature variation of PV modues on performance of soar power pant, when temperature changes rather fast (high wind speed) and sow (ow wind speed). 11 P a g e
Figure 3 Matab/Simuink mode with temperature bock V. PLANT INCCOND ALGORITHM In this work, IncCond agorithm is seected to perform maximum power point tracking [10]. This agorithm has simpe contro structure and is abe to keep the system in MPP, when it is found. Simpe mathematica impementation of agorithm aows achieving fast operation on the equipment with imited hardware resources such as embedded systems. The fowchart of IncCond agorithm is presented in Fig. 4. The MPPT agorithm impemented in the mode aows fast and precise finding of MPP and has the abiity to keep the system in MPP, unti the environmenta conditions wi change. Most of other agorithms are not abe to precisey track MPP, and the system osciates around it. Figure 4 The fowchart of IncCond agorithm, impemented in the mode of soar power pant MPPT is performed by cacuating the power derivative with respect to votage. dp d( IV ) di I V dv dv dv (1) 12 P a g e
Expression (1) aows to cacuate the derivative in votage-current characteristics and to determine the direction of change in oad resistance. According to Fig 3 the oad resistance changes can be described by these conditions: di dv di dv di dv I, V R = R + R, I, V R = R R, I, V R R m, (2) where, ΔR step of oad resistance change, R oad resistance for PV modues, Rm characteristic oad resistance, at which the PV modue is operating with maximum power output. The soar power pant operates at MPP when the third condition of expression (2) is satisfied. VI. INFLUENCE OF TEMPERATURE ON PERFORMANCE OF SOLAR POWER PLANTS A concusion section must be incuded and shoud indicate ceary the advantages, imitations, and possibe appications of the paper. Athough a concusion may review the main points of the paper, do not repicate the abstract as the concusion. A concusion might eaborate on the importance of the work or suggest appications and extensions. Figure 5 Soar power fux (a), temperature of PV modues during a sighty windy day without forced cooing (b-1), temperature of PV modues during a sighty windy day with forced cooing to 18 C (b-2), instantaneous power of soar power pant without forced cooing (c-3), instantaneous power of soar power pant with forced cooing to 18 C (c-4), instantaneous difference of output power (d). In this work different environmenta conditions were simuated in separate tests. First test assumed sow rate of change of temperature of PV modues, which sometimes rise to 75 C. This scenario is common for a cear day with sma wind speed. Increasing the SPF causes the rise of PV modues temperature. The SPF chart, shown in fig. 6 a) imitates dayight time, when SPF varies from 0 to 1000 W/m 2. In fig 6 b) the first series show the variation of PV modues temperature during day. The second series show the temperature of PV modues when the forced cooing is engaged. Forced cooing is enabed when temperature reaches 18 C. In fig 6 c) series 3 show the instantaneous power at the output of soar power pant, when the forced cooing is not used and series 4 when the temperature of PV modues is cooed to 18 C or ower. Fig 6 d) shows the instantaneous difference in power when the PV modues are not cooed and with forced cooing. 13 P a g e
When the temperature of PV modues is dependent on environmenta conditions, the soar power pant during a dayight time produces 1558 Wh of energy. During the same period of time and under the same environmenta conditions, the soar power pant with forciby cooed modues produces 2051 Wh of eectrica energy. The second test assumes the faster rate of change of PV modues temperature and it sometimes rises to 50 C. This pattern is typica for a day with a gusty wind. Strong wind causes faster cooing of PV modues, so their temperature cannot rise significanty. Fig. 7 a) shows SPF signa, which is simiar to the previous test. In fig. 7 series 1 shows the dependence of PV modues temperature in dependence on SPF and series 2 shows the temperature of PV modues, when the forced cooing is used. In fig. 7 c) series 3 show instantaneous output power when PV modues are not cooed and series 4 when forced cooing is used. Same as in previous test the comparison of output power between cooed and not cooed system is provided (Fig. 7 d)). Figure 6 Soar power fux (a), temperature of PV modues during windy day without forced cooing (b-1), temperature of PV modues during windy day with forced cooing to 18 C (b-2), instantaneous power of soar power pant without forced cooing (c-3), instantaneous power of soar power pant with forced cooing to 18 C (c-4), instantaneous difference of output power (d). When wind is gusty, the temperature of PV modues changes rapidy, and it does not rise significanty. During the 15 hours of daytime the power pant produces 1822 Wh of eectrica energy. In case of forced cooing, when the temperature of PV modues is kept not higher than 18 C, the soar power pant produces 2029 Wh of eectrica energy during the same period of time. This study show that during the 15 hours of dayight, the amount of energy, produced in the soar power pant was by 264 Wh smaer when the temperature of PV modues changed sowy and reached 75 C. When the forced cooing of PV modues is used during a day with sma wind speeds, the energy production of soar power pant increases by 492 Wh, and in case of a day with strong, gusty wing, the energy increment is 207 Wh. VII. CONCLUSION The efficiency of PV modue decreases when its temperature increases. Studies have shown: 1. The efficiency of soar power pant can be significanty increased by appying the forced cooing of PV modues, especiay, when soar power pant is instaed in the ocation with sma wind speeds. 2. Appying a forced cooing to PV modues and keeping their temperature not higher than 18 C, during a day with sma wind speed, the eectrica energy output of soar power pant increases by 31.5 %, compared to the case, when cooing is not used. 3. Appying a forced cooing to PV modues and keeping their temperature not higher than 18 C, during a day with strong, gusty wind, the eectrica energy output of soar power pant increases by 11.3 %, compared to the case, when cooing is not used. 14 P a g e
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