Comparison of Translation Techniques by PV Module Diagnostics at Outdoor Conditions

Transcription

1 Comparison of Translation Techniques by PV Module Diagnostics at Outdoor Conditions Martin KUSKO, Vladimír ŠÁLY, Milan PERNÝ Abstract The paper deals with diagnostics of PV modules based on Si. This diagnostics is based on measurement of -V characteristics at natural outdoor conditions and consequently in prediction of output parameters of observed modules by translation techniques to Standard Test Condition. Translation by STN EN (EC and methods of Anderson, Marion, Bleasser were acquired from three different irradiation and temperature conditions. The comparison shows an approximation to output power parameters of investigated PV modules. Keywords: PV modules, -V characterisation, translation techniques. ntroduction For understanding how PV device behave at cycling outdoor conditions is necessary to know the basic information of the device. t usually means the output parameters which are provided by producers with specific PV device. These data are transferred from -V curve characterization at conditions termed as Standard Test Conditions (STC or Standard Reported Conditions (SRC. These conditions are generally known (000 W.m - of.5 AM G at 5 C and it is the most widely used technique for PV device sorting. On the other hand, at real outdoor conditions these output data are insufficient for deeper understanding. Consequently investigation of one or two diode model parameters like series or parallel resistance shows the local behaving of PV device. Moreover the PV modules are exposed to the cycling conditions with many variables like temperature, irradiance, the sun Martin KUSKO: M. Eng.; Solartec, s.r.o.; Televizní 68, 7566, Rožnov pod Radhoštěm, Czech Republic; martin.kusko@solartec.cz; Vladimír ŠÁLY: Associated Professor, M.Eng., Ph.D., SUT Bratislava, Faculty of electrotechnology and nformation Technology, nstitute of Power and Applied Electrical Engineering, lkovičova 3, 8 9, Bratislava, Slovakia, e- mail: vladimir.saly@stuba.sk; Milan PERNÝ: M. Eng., SUT Bratislava, Faculty of electrotechnology and nformation Technology, nstitute of Power and Applied Electrical Engineering, lkovičova 3, 8 9, Bratislava, Slovakia, milan.perny@stuba.sk orientation, spectrum change and so on. The period of the variables changes with the season and finally contributes to the aging of PV devices. During the normal outdoor operation of the PV array, the data are usually simultaneously logged. Evaluating of collected data helps to predict the PV power generation along a year. For evaluating the degradation rate of PV device or just to determine the changing of the model parameters, the -V characterization is sufficient method. Here, the evaluation is more complicated especially in cases, when data obtained at outdoor condition should by compared with only information of the PV device, which usually is the producer nameplate with data obtained at STC []. n the past, the -V translation techniques based on algebraic translation procedures for the purpose, mostly of irradiance and temperature correction of measured -V curves were developed. First known as Sandstrom equation is used to date as translation procedure for measuring and sorting the PV devices as a part of standard EC 89 (or STN EN [4]. Over time, there were gradually published methods by Blaesser (988, Anderson (996, Hermann et al. (996, Marion (00, Tsuno et al. (005. All of mentioned methods help to solve the translation issue. n this work, there were applied several translation methods for nameplate data

2 46 ELECTROTEHNCĂ, ELECTRONCĂ, AUTOMATCĂ, Vol. 6 (03, Nr. approximation of small PV array, which is simultaneously prepared for daily work at nstitute of Power and Applied Electric Engineering at FE SUT in Bratislava. Accidentally measured -V curves of each PV module at three different irradiance and temperature condition were assigned for chosen translation procedures. Translations should help to monitor the behaving and some degradation processes on PV model parameters like series and parallel resistance in future. ( E E + α ( T Sc = + T ( k ( T T β ( T V S = V R T This translation differs from others methods (explained below with using the series resistance R S and curve correction factor k. The R S contributes to reduction of total output current linearly with temperature arising and nonlinearly with increasing of irradiation. The constant k is used for curve shape correction (curve compensation factor [5, 8].. Translation Methods and Evaluation The method of Blaesser dwells on the The base of whole data evaluation is the temperature effect on open circuit voltage -V curve characterization of PV device. t which consists in a shift from reference value draws the PV structure (cell structure or the (the V OC from nameplate in this case [3]. module structure as well dependence on The translation equations for marginal three primary variables like spectral evaluation are described as follows [3, 7, 8]: irradiance (Air Mass.5 Global, light radiation (E and air temperature (T. SC = SC [ + α ( T T ] ( E E (3 The wind speed, orientation of light source with related reflection can be VOC = VOC [ + β( T T + δ ln( E E ] (4 considered as the secondary variables and also the other environmental variables like humidity or rain which influence the module temperature and at the same time the effects of dust, snow and icing which reduces the incident light influence the overall output []. For obtaining the current data the ratio of respective SC is applied to every current point of -V curve. Deviation of V OC is applied with acceptation of series resistance (R S influence to obtain the voltage curve data points as follows [7, 8]: The evaluation of output parameters of = ( PV devices at STC follows the standard SC SC (5 EC (987 or EN (993 which V = V + VOC VOC + R S ( for Slovak Technical Norm is this standard (6 called STN EN The Anderson s method describes Besides the STC conditions which are translation at first with starting points ( SC, well-known the evaluation procedure is V OC by equations of as follows [4]: strictly construed for preventing mainly the temperature negative contribution during SC = SC [ + α ( T T ] ( E E (7 testing. The translation equations for current and voltage translation are described as follows [,, 4]: V _ OC = V _ OC / + β T _ T _ + δ ln E _ E _ (8 and similar with Marion s method which is described as follows [6]: V ( E E [ + α ( T ] SC SC T = (9 [ + β ( T T ] [ + δ ( E E ] OC VOC ln = (0 The translation process for last two methods is little different for marginal evaluation ( SC, V OC but the same for curve evaluation point by point (U, using the constant ratios for each data pair [4, 6]: = ( SC SC ( V ([ ( ] [ ( ] = V ( V OC V OC 3. The outdoor measurements ( ( ( The data evaluation at outdoor condition was performed accidentally at three days within June to September to obtain different temperature dependence at higher temperature than 5 C and highest possible global irradiation (at mentioned location. Figure shows the hourly irradiation at the investigated days (June 4 th, August 5 th and September 6 th of 0.

3 ELECTROTEHNCĂ, ELECTRONCĂ, AUTOMATCĂ, Vol. 6 (03, Nr. 47 Figure.. The hourly irradiation of specific days (dashed line with irradiations obtained during measurements (full line The dashed lines illustrate the daily irradiance dependence at the dates when investigation was performed. These data were provided by Slovak Hydrometeorology nstitute (SH and curves introduce the average between two distant locations in Bratislava. Full lines are the values of irradiances obtained at each -V characterization of whole modules. Difference between data obtained by SH and date obtained at place of PV module investigation can be caused by the way of irradiance collecting, time scale data logging and place difference of collection. The data were obtained at three different irradiance and temperature conditions by the -V curve meter PROVA SMA 0 (Solar Module Analyzer. As the tested devices measured on-site were three mono-si modules from Suntech and three thin-film multi-si modules from Solara as showen in Figure (the nameplate data are in Table. Figure : The small PV array at PAEE (at FE-SUT in Bratislava using the thin-film multi-si (on right left and mono-si (on right side PV modules Table. The nameplate data of investigated PV modules P max [W] V OC [V] SC [A] V max [V] max [A] Suntech Solara Measurements of the levels of irradiation were detected in a parallel way with PV modules by Radiometer Oriel model 800 and temperature detection of PV modules were performed by CE Thermometer model 307 with TPK-0 thermal probe. 4. Coefficient selection After data collection the definition of current and temperature coefficients is necessary to obtain. The current temperature coefficient α is applied to evaluate SC, only for STN EN case is used for evaluation each curve data. This coefficient is usually defined either as / C or A/ C. For V OC evaluation it is used the temperature coefficient β with the same meaning (/ C or V/ C. The third coefficient often used is δ (/ C, the voltage irradiance correction as function of PV module temperature. These coefficients can be obtained by techniques described in [, 3, 4]. They are generally different for each PV module technology and vary in defined ranges []. The values used for translation procedures by each applied method in this investigation (STN, Blaesser, Anderson and Marion are shown in Table and application follows the coefficient evaluation described for particular PV module technology (in particular crystalline Si by corresponding method. Table. Translation coefficients evaluated by relevant method and applied for conversion to STC α β R δ S k [A/ C] [V/ C] [Ω] [Ω/ C] STN α [/ C] β [/ C] δ [/ C] R S [Ω] Anders. mono-si Anders. multi-si Anders. TF-Si Marion * mono-si T Marion *T multi-si Blaesser One can see that the method of Anderson and Marion enables a more possibilities for different Si technology shown in Table which were used for translation and comparison too. 5. Approximation and comparison Translations from environmental conditions to STC are shown in Figure 3 for monocrystalline Si panels and figure 4 for TF k

4 48 ELECTROTEHNCĂ, ELECTRONCĂ, AUTOMATCĂ, Vol. 6 (03, Nr. multicrystalline Si panels. corresponding translation coefficients. Figure 3. The -V curve translation comparison for one of investigated PV modules based on mono-si. Each -V curve is translated from corresponding condition (E, T. n both figures is a similar effect attended. The translation by STN method causes the shift of the curve from voltage axes (figure 3. For evaluation the V OC is necessary to add the ΔU value. Similar effect happened in translations by Blaesser method but from the current axis (Δ. For elimination of shifts is necessary to known the parasite components (described by the model of PV cell/module like series (R S and parallel resistance (R SH. Because of the presence of unwanted shifts the comparison was made with P max points of investigated PV modules. The following Figure 4 shows comparison in way that each module were traced at different environmental condition (see Figure, only in cases with irradiances higher than 000 W/m where the fluctuation was lower than %. Figure 4. The -V curve translation comparison for one of investigated PV modules based on TF multi-si n general, the translation is more accurate with less dispersion of data from STC. Figure 5 and 6 are a bit complex and introduces each module technology with Figure 5. The comparison of P max evaluated from chosen translation methods of mono-si modules (different color = different module Figure 6. The comparison of P max evaluated from chosen translation methods of TF multi-si modules (different color = different module The evaluated points (at given E and T are separated by temperature at adequate irradiation. The colored values of temperature means that the data are evaluated from one of three investigated PV module. Figure 6 includes two translations by Anderson because of option coefficients which are available for multi-si as well as for thin film-si (no further specification. For other translation (in the TF multi module case were available coefficients for multi-si or just the crystalline Si. The uncertainties may have occurred during measurements caused by nonuniformity of module temperature, angle of incidence and also by accuracy of each translation method. 6. Conclusions n the near term the claim to make fast, cheap and on-site diagnostic of PV array or modules will be necessary. For this purpose was the translation technique proposed in the special case of measuring and sorting at indoor condition. Other techniques which should help to evaluate output data at

5 ELECTROTEHNCĂ, ELECTRONCĂ, AUTOMATCĂ, Vol. 6 (03, Nr. 49 outdoor condition are different from each other and use a different evaluation of coefficients. The headstone of each method is the correct determination of coefficients. n this work were used chosen translation methods with given coefficients to find which are proper for diagnostics of mentioned small PV array or modules at FE-SUT (or in general. The good choice seems to be an Anderson s method and the Marion s which shows the smallest diversion of maximum power points compared to the STC nameplate data. But the cionfirmation of such statement needs more investigation in longer period. 6. Acknowledgment This contribution is the result of the project VEGA /0443/00 supported by MŠ SR. Authors would like to thank Mrs. ng. Eva Čepčeková from Slovak Hydrometeorology nstitute for rendered data. 7. Nomenclature current point at outdoor condition translated current point to STC SC measured short circuit current SC translated short circuit current to STC E irradiation at outdoor condition E irradiation at STC (000 W/m P max maximum power point R S series resistance T temperature of PV module during measurement T temperature at STC (5 C V voltage point at outdoor condition V translated voltage point to STC V OC open circuit voltage at outdoor condition V OC translated voltage point to STC 8. References [] LUQUE A, HEGEDUS S, Handbook of Photovoltaic Science and Engineering, London: John Wiley & Sons Ltd, 003. [] EU Standard: Photovoltaic devices, Slovak nstitute of Technical Normalization, STN EN [3] BLEASSER G, PV System Measurement and Monitoring - The European experience, in Solar energy materials and solar systems, Vol.47, 997, p [4] Andreson AJ, Photovoltaic Translation Equation, in NREL/TP-4-079, 996, Jan. [5] W.Herwmann, Current-Voltage Translation Procedure for PV Generators in the German 000 Roofs -Programme, retreived: /content/personen/wiesner_wolfgang/veroeffe ntlichungen/6_proceed.pdf [6] US General Accounting Office (997 February. Telemedicine: Federal strategy is needed to guide investments. (Publication No. GAO/NSAD/HEHS retrieved: September 5, 000, from General Accounting Office Reports Online: aces/aces60.shtml?/gao/index.html [7] MARON B, A Method for modeling the Current-Voltage curve of a PV Module for Outdoor Conditions, Prog. Photovolt: Res. Appl. 403, pp. 05-4, 00. [8] ORTZ-RVERA E, PENG FZ, Analytical Model for a Photovoltaic Module using the Electric Characteristics provided by the Manufacturer Data Sheet, in EEE, p , /05, 005. [9] AGROU K et al., ndoor and outdoor photovoltaic modules Performance based on thin films solar cells, in Revue des Energies Renouvelables Vol. 4 N 3, pp: , Biography Martin KUSKO was born in Košice (Slovakia in 985. He graduated the TU in Košice, Faculty of Electric Engineering and nformation Technology (Slovakia in 009 as Diploma Engineer. He starts the PhD degree in 009 in electrotechnology and materials from the University of Technology of Bratislava (SUT FE. Since 0 he is external PhD student and works in R&D deppartment for Solartec comp. as the participant in international research and educational EU project MATCON (Czech Republic. His research interests concern: photovoltaics, materials for energy conversion and electric diagnostics. Vladimír ŠÁLY was born in Slovakia in 956. Faculty of Electric Engineering and nformation Technology, Slovak University of Technology in Bratislava (SUT FE finished as Diploma Engineer (MSc. in Electrotechnology and in 985 he received the scientific degree PhD. from the same university. Since 003 he is employed as Associated Professor at SUT FE. He works in material science, especialy dielectric and semiconductor structures and photovoltaic renewable energy sources research.

6 50 ELECTROTEHNCĂ, ELECTRONCĂ, AUTOMATCĂ, Vol. 6 (03, Nr. Milan PERNÝ was born in Slovakia in 985. He graduated the Faculty of Electric Engineering and nformation Technology, Slovak University of Technology in Bratislava (SUT FE in 009 as Diploma Engineer in Materials and technology. Nowadays he is finishing the PhD. He is working in material science, photovoltaic and renewable energy sources research.