outdoor data acquisition system with advanced database ... - SolarLAB

3rd World Conferenceon Photovoltaic Energy Conversion, May 11-18, 2003, Osaka, Japan

OUTDOOR DATA ACQUISITION SYSTEM WITH ADVANCED DATABASE FOR PV MODULES CHARACTERIZATION Tadeusz Zdanowicz, Mariusz Prorok, Wlodzimierz Kolodenny and H.Roguszczak Wroclaw University of Technology, Faculty of Microsystem Electronics and Photonics, SolarLab ul. Janiszewskiego 11/17, 50-372 Wroclaw, Poland phone/fax +48 71 3554822 e-mail: [email protected]

ABSTRACT This paper presents operational facilities of the outdoor Data Acquisition System (DAS) developed in Solar Lab for simultaneous longterm performance tests of up to 15 PV modules of any size and type. Data measured and collected by DAS are stored in database, independent-ly for each of the installed modules, and can be accessed on the Solar-Lab’s website. Meteo data are stored in separate database which is public and free accessible while data related to tested modules may be accessed only by authorized persons. If necessary, authorization may be extended on the specified of modules only. Both databases are linked through the special reference records enabling to identify POA insolation and all weather conditions related to each I-V curve measurement. The unique feature of the database is that also full I-V curves of the modules are stored in a

special binary file and can be easily accessed through special reference field in the data record.

1. INTRODUCTION Currently used and well established since many years standards for characterization electrical performance of PV modules are based on power related parameters determined in so called Standard Test Conditions. However, such parameters do not reflect module’s behaviour in realistic conditions and especiallly they do not take into account changeable solar spectrum and module’s true temperature which may change in a range well exceeding even 100 oC. That is why there is a growing concern both in US as well as in Europe about establishing of reliable energy rating procedures [1,2] which would allow to characterize module’s performance in such way thereby to enable evaluating of PV energy

Fig.1 General view of the Data Acquisition System and its facilities developed in SolarLab for longterm outdoor testing of PV modules with actually 13 modules installed for tests. (see text for details)

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3rd World Conferenceon Photovoltaic Energy Conversion, May 11-18, 2003, Osaka, Japan

gain during long time of exploitation. This is especially important now with a variety of new thin-film modules appearing on the market. However, the energy rating approaches to PV module qualification in a wide variety of operating environments require high quality reference data sets which must be gathered during longterm outdoor tests. To extract from these large amounts of data informations necessary for accurate characterization of energy rated performance of the module effective database with flexible tool for data filtering is necessary.

current-ly only modules made of Si cells are tested in the system the developed DAS may be used for characterization of other modules, like a-Si, CdTe or CIS thin-film devices.

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MEASURING UNIT

The measuring system shows major improvements when compared to earlier DAS developed in SolarLab nearly ten years ago [7,8] in a frames of another EC project. The new DAS consists Users Acces Rights Sessions of 15 independent circuits allowing to User Reference Session Reference Access Reference measure current with 16 bit resolution on User Reference Password User Reference either of 10, 5, 2.5 or 1.25 A range and User Reference Login Date&Time Password UserReference Reference User Name Module Login Date&Time Logout Date&Time UserLevel Name Module Flags Reference Access Access voltage with 12 bit resolution on 100, 50, Logout Date&Time Last Request Access Level Access Flags Last Request Session ID 25, 12.5 or 6.25 V range, respectively [9]. Session ID Both ranges are set automatically to give Modules General Module Info Current Measurements maximum resolution of the measurement General Module Info for any insolation level. Full I-V curves are Module Reference cmChannel Reference measured with preset time interval and scan Module Area Channel No. Moduletype Reference Module Urate Area Channel No. Module Reference ModuletypeReference Reference Manufacturer rate has been optimized to avoid distortion General ModuleUrate Info Reference Module Reference Measurement Status Manufacturer Reference General Module Info Comments 1 Reference Measurement Status of the curve shape due module’s capacity Comments Comments 2 1 Comments 2 loading effects [10]. The example view of a PV Values computer screen during measurements is Module Manufacturer I-V Curves Manufacturer shown in a picture located in a left upper I-V Curve Reference Module Reference Reference Filename corner of Fig.1. Global irradiation in the Value Reference Manufacturer Name Filename Status Flag Manufacturer Name plane of modules (POA) is measured with Status Flag Module Reference POA Global Irradiation Module Reference Date&Time from POA Global Irradiation Module Temperature K&Z CM21 pyranometer and values of Date&Timetofrom Date&Time ModuleIsc Temperature ModuleType Date&Time to VocIsc actual temperature of the modules are ImVoc Moduletype Reference VmIm measured using miniature Pt100 sensors Vm Irate Moduletype Name I-V CurveIrate Pointer attached to the back side of the modules. I-V Curve Pointer I-V Curve Reference I-VCurve CurveLength Reference I-V Each Pt100 thermoresistor is connected to I-V Curve Length Date&Time separate precise R-I converter equipped Backups Date&Time kU Module Default Directories kI kU with RS485 serial communication port. Meteo Record kI Reference Module Reference Meteo Record Reference All meteo data are gathered by a I-V Curve Reference Directory I-V Filename Curve Reference Directory separate system using set of sensors and Filename Version Meteo Data Record Version Combilog 1020 data logger from Theodor Meteo Record Reference Friedriche & Co. (see left lower corner in Archive Items Dataloggers Wind speed Wind speed Wind direction Fig.1). Stored data are uploaded to PC with Datalogger Reference Wind direction Atmospheric pressure RS485 port. In the meteo system values of Atmospheric pressure Air humidity Datalogger Name I-V Curve Reference humidity AmbientAir Temperature Datalogger Name IP I-V Curve Reference Archive Reference both global solar irradiation as well as its Temperature Global Ambient Irradiation (Hor. Plane) PortIP Archive Reference GlobalIrradiation Irradiation(Hor. (Hor. Plane) Diffused Plane) Port Device diffused component are measured on the DiffusedData&Time Irradiation (Hor. Plane) Device Last uploaded Data&Time Data Archive Last uploaded horizontal plane using K&Z CM21 Archive Reference pyranometers and shadow ring (seen over Mediatype the modules on the photo in lower right side Mediatype Path Path Date&Time of Fig.1) . With other meteo data they are Date&Time ID ID then used to calculate actual solar spectrum according to formulas described in [2]. Fig.2 Scheme of Database storing data of PV modules measurements by Software used to control and visualiSolarLab’s Data Acquisition System; field referenced as ’I-V Curve ze current measurements has been written Reference’ enables to identify record describing beginning of I-V curve using mainly Borland Delphi v. 4.0 data in the appriopriate file while field ’Meteo Record Reference’ shows compiler. where to find complete meteo data record corresponding to I-V curve of the specified module. The purpose of the work was to provide a reliable tool for outdoor characterization of PV modules developed by partners from AFRODITE project. It was assumed that developed system should meet all requirements of the 904-1 [3], IEC 904-3 [4], IEC 1829 [5] and IEC 60891 [6] standards both as to used technique as well as accuracy of the measurements. Though

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DATABASE

Database software is the most sophisticated part of the SolarLab’s DAS. It has been written using MS SQL and MS Visual C++ programming languages. Its operating scheme is shown in Fig.2. Besides standard data calculated from the curves, like ISC, VOC, PM, FF, Eff, etc., also charge and energy related parameters

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3rd World Conferenceon Photovoltaic Energy Conversion, May 11-18, 2003, Osaka, Japan

calculated by integrating in time values of ISC, IRAT (current at module’s rated voltage point) and PM are stored in the database. Via the special fields, named ‘I-V Curve Reference’ and ‘Meteo Record Reference’ in Fig.2, each record in the database corresponding to any of tested modules may be linked to corresponding records in meteo database and in a special file storing complete I-V curves. Together with I-V values also actual values of global POA irradiation and temperature value of a module are stored. Other meteo data are sampled every one minute independently of I-V measurements and, if required, system makes link to meteo data record which is nearest to a chosen I-V curve (in time domain). Each month stored data are converted to MS Excel file and can be easily downloaded by the authorized user from the SolarLab website. Authorization refers only to specified modules. In order to enable on-line browsing through database, special, so called ”client type” software, must be installed on user’s PC. Example result of such browsing is shown in Fig.3 where filtering options were set in such way thereby to show practically all measured curves in a specified time period. Selected range of measurements may be converted to MS Excel file for further downloading by other users.

Fig.4 Example of using database for selecting I-V curves of a chosen PV module corresponding to conditions close to STC (see text for details).

Fig.3 Example of browsing database with data filter set to show all measurements performed in specified time period. In the lower right side corner of the screen data taken from meteo record closest to marked I-V curve are visible. Optionally solar spectrum may be calculated and presented as is seen in Fig.1

When setting data filter in a proper way user may also easily estimate each module’s parameters correspond-ing to Standard Test Conditions. An example result of such operation is shown in Fig.4 for data collected in April 2002. To provide conditions very close to those specified for STC only narrow ranges of POA irradiation values (940 - 1020 W/m2), module’s temperature (20 – 30 oC) and time (11.30 a.m. – 12.30 p.m.) were set in data filter. The last condition, i.e. time very close to noon, has been set due to requirement of nearly perpendicular angle of solar incidence onto module’s plane which for the case is oriented exactly to the south. Using PV-Translator, which is user-friendly software developed in SolarLab for I-V curve translation and series resistance determination, selected curves may now be translated to STC with satisfactory accuracy using either of three optional formulas, i.e. IEC 60891 [6], Blaesser’s [12] or Anderson’s [11], respectively. Setting other data filtering options user may easily determine such parameters of a module as its series resistance according to procedure described also in IEC 60891 [6] or NOCT (Nominal Operating Cell Temperature) [7]. The example of using database for finding NOCT value is shown in Fig.5. The other attractive possibilities of using database is determination of such parametrs of PV modules as thermal coefficients in a wide range of irradiation levels, numerical constants necessary for calculation of the so

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3rd World Conferenceon Photovoltaic Energy Conversion, May 11-18, 2003, Osaka, Japan

called Equivalent Cell Temperature [14] and investigation of the effect Air Mass factor on the module’s performance [15]. Built-in procedures allow to investigate different energy rating approaches across a wide variety of operating environments.

[3]

[4]

[5]

[6]

[7] [8]

[9]

[10]

[11]

Fig.5 Example of using database for NOCT value determination for a PV module; determined NOCT value is 45.3 oC in the case.

[12] [13]

ACKNOWLEDGEMENTS This work was supported by the European Communities under 5th EC FP AFRODITE project, contract No ENK5CT-2000-00345 and Polish State Committee for Scientific Research under Grant No PBZ 05/T11/98. REFERENCES [1]

[2]

IEC 61853 - draft 82/254/NP, ”Performance Testing and Energy Rating of Terrestrial Photovoltaic (PV) Modules”; C.M.Whitaker and J.D.Newmiller, ”Photovoltaic Module Energy Rating Procedure”, NREL Final Subcontract Report,

[14]

[15]

Subcontract No. AAI-4-14192-01, Jan.1998; IEC 60904-1 ”Photovoltaic devices – Part 1: Measurement of PV current-voltage characteristics”; IEC 60904-3 “Photovoltaic devices – Part 3: ”Measurement principles for terrestrial photovoltaic (PV) solar devices with reference spectral irradiance data”; IEC 1829 ”Crystalline silicon photovoltaic (PV) array – On-site measurement of I-V characteristics”; IEC 60891 ”Procedures for temperature and irradiance corrections to measured I-V characteristics of crystalline silicon photovoltaic devices” 1st Progress Report of PECO-Project no PL932049, Sept. 1994, p.71-90.; T. Zdanowicz, H.Roguszczak, ”Automated Outdoor Data Acquisition System for Prolonged Testing of PV Modules”, Proceedings of 13th EC PV Solar Energy Conference, 23-27 Oct. 1995, Nice, p.2322; T. Zdanowicz, H.Roguszczak, M.Prorok, ”Facilities for PV Modules and Cells Characterization in SolarLab”, Proceedings of International Conf. PV in Europe – From PV Technology to Energy Solutions, Rome 7-11 Oct. 2002, p.722; T.Zdanowicz, ”PV Modules Characterization”, Proceedings of the PVNET Workshop on “Cross-Fertilization between the Photovoltaic Industry & other Technologies” held at JRC Ispra, 28-29 May 2002; A.J.Anderson, ”Photovoltaic Translation Equations. A New Approach”, prepared under Subcontract No. TAD-4-14166-01, Final Subcontract Report No. NREL/TP-411-20279, NREL, Jan. 1996; G.Blaesser, Proc. 9th Intern. PV Science and Engineering Conf., Miyazaki, 13-15 Nov. 1996; IEC 61215 (Ed. 2.0) ”Crystalline silicon terrestrial photovoltaic (PV) modules – Design qualification and type approval” ; T.Zdanowicz, T.Rodziewicz, M.ZabkowskaWacla-wek, ” Effect of Air Mass Factor on the Performance of Different type of PV Modules”, this conference; IEC 60904-5 ”Photovoltaic devices – Part 5: Determination of the equivalent cell temperature (ECT) of photovoltaic PV devices by the open-circuit method”.

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