PERFORMANCE MONITORING OF DIFFERENT PV TECHNOLOGIES AT A PV FIELD IN NORTHERN ITALY A.Colli1, W.Sparber1, M. Armani2, B. Kofler1, L.Maturi1,3 EURAC Research, Institute for Renewable Energy, Viale Druso 1, 39100 Bolzano, Italy Phone: +39 (0)471 055600; Fax: +39 (0)471 055699 E-mail:
[email protected],
[email protected],
[email protected],
[email protected] 2 SolarTotal s.r.l., Via Galvani 40/C, 39100 Bolzano, Italy. E-mail:
[email protected] 3 Università degli studi di Trento, via Belenzani 12, 38100 Trento (TN), Italy. 1
ABSTRACT: This paper describes the details of the new multi-technology ground-mounted photovoltaic (PV) field installed at the Airport of Bolzano Dolomiti (ABD) in the Italian Alps. The plant, owned by ABD and developed with a co-financing of the European Regional Development Fund (ERDF), is divided into two main parts: a 662 kW commercial installation, mounting 8538 CdTe modules First Solar 277, and a 62 kW experimental installation, mounting 24 different types of modules, divided into 39 groups ranging between 1 and 2 kW each. In this experimental installation the modules are mounted on fixed racks, as well as on mono-axial and bi-axial active trackers. EURAC Research is the scientific responsible of this test facility and follows the monitoring and test activities to evaluate the performance and the lifetime degradation of the modules. The aim of the monitoring activity is to allow a better understanding of module loss mechanisms for each technology and evaluating the performance in the alpine climatic conditions. The PV modules are evaluated in relationship to meteo data from an on-site station, counting a sensor for ambient temperature, an anemometer, a pyrheliometer, three pyranometers, an albedometer and also a sun photometer which allows evaluating the influence given by aerosols, ozone and vapors in the atmosphere to the irradiance. PV reference cells are also used, mounted horizontally, on the module plane, and on the two trackers. The PV plant has been connected to the MV network on August 10, 2010, and it is presently in course of approval by GSE (Gestore Servizi Energetici) for the incentive scheme in force. Monitoring results can be presently shown only for a couple of days for a limited number of groups. Keywords: Monitoring, performance, grid-connected, multi-technology field installation. 1
INTRODUCTION
With the recent booming of photovoltaic (PV) installations in Italy [1], a realistic outdoor performance analysis of various types of modules is needed. This action supports both the scientific community and the different actors in the PV environment, such as developers, producers, installers, financing institutions, as well as decision-makers and customers. The possibility to assess the performance of different types of modules in a specific geographical context, under various irradiance levels and wavelengths is very important to evaluate the energetic behavior of future installations and direct them toward the most suitable technology to be used. This is the background that has brought to the installation of a multi-technology PV field at the Airport of Bolzano Dolomiti (ABD), in the North-East of Italy. The project has been developed with a co-financing of the European Regional Development Fund (ERDF) 2007-2013 of the European Union. The plant is owned by ABD and has been installed by Leitner Solar (Brunico, Bolzano) under the direction of Thaler Engineering Studio (Bolzano), with the technical and scientific supervision of EURAC Research, based in Bolzano. Conceptually started in 2008, the PV plant has been recently completed and has been connected to the medium voltage (MV) network on August 10, 2010. At the moment, it is under evaluation by the GSE (Gestore Servizi Energetici [1]) for access to the Italian incentive scheme. Performance comparisons among various technologies have been already going on in various other locations (see, for example, [2], [3] and [4]). Anyhow, the installation presented along this paper is to be noted for the large number of PV modules under consideration, for its characteristics, and for being, to the Authors
knowledge, the first one of this type in Italy, as well as in Europe. The paper in hand highlights the characteristics of the ABD PV plant, offering an overview on the monitoring activities that will take place, and presents performance results for two prevalently sunny summer days. 2
PLANT CHARACTERISTICS
ABD PV plant has an overall power of 724 kWp and is divided into two main parts: • A 62 kWp experimental installation. • A 662 kWp commercial installation.
Figure 1: A row of the experimental section of the ABD PV field, and, in the back, the mono-axial (left) and bi-axial (right) trackers, mounting respectively 3 and 4 groups of modules. The experimental section (see Figure 1) of the field allows monitoring 24 different types of modules, divided into 39 groups ranging between 1 and 2 kW each. The modules taken into consideration are listed in Table I.
Figure 2: The dual-axis active tracker DEGER 7000NT. While the most of the modules on the entire PV field have a 30° tilted position and are mounted on FS Schletter system supports (entering about 2 m. into the ground), some are installed also on the two tracker systems. Table I: Type of modules installed at ABD PV field along with their corresponding peak power. Module technology Module m-Si Solarwatt M230-96 GET AK m-Si Solarwatt 32 GEG opaque LK m-Si Solarwatt 36 GEG LK BC m-Si SunPower WHT 300 p-Si AlfaSolar PYR60 p-Si Solarworld SW225-POLY p-Si Trina TSM-230-PC05 p-Si REC 225-PE p-Si Kyocera KD210GH-2PU p-Si Canadian Solar CS6P p-Si Day4Energy 48MC-S HIT Sanyo HIP-215NKHE5 Ribbon Evergreen ES-A-205-fa3 Thin-film a-Si SchottSolar Asi Thru 30SG Thin-film a-Si Parabel UNIFLAT Thin-film a-Si EPV Solar 50 a-Si Inventux X115 a-Si semi SchottSolar Asi TM 100+ a-Si & μ-cryst. Sharp NA-F135 G5 μ-crystalline Bosch Solar Module μm-Si plus CIGS Solyndra SL-001-182 CIGS Würth WSG0036E80 CIS Sulfurcell SCG55-HV-F CdTe First Solar FS 277
Wp 220 124 140 300 222 225 230 225 210 230 175 215 205 27 272 50 115 100 135 110 182 80 55 77.5
The DEGER Top tracker 40NT, a single axis active tracker, has an inclination of 30° and the possibility to rotate in the East-West direction with a maximum angle of ±45° (considering the South as home position). The modules installed on this single axis tracker are: 1. SunPower WHT 300. 2. Sanyo HIP-215NKHE5. 3. Kyocera KD210GH-2PU. The DEGER tracker 7000NT (see Figure 2), a dualaxis active tracker, has the possibility to move according to two axis to adjust elevation and rotation according to the best light-receiving position. The elevation angle is between 15° and 90°, while the East-West rotation can be active for a 360° angle with adjustable limit switches. This tracker is also equipped with a wind sensor, which is going
to direct it to the horizontal safety position in case of strong wind. The modules on the dual-axis tracker are: 1. SunPower WHT 300. 2. Sanyo HIP-215NKHE5. 3. Kyocera KD210GH-2PU. 4. First Solar FS 277. The field configuration allows the comparison among fixed and moveable supports, as well as among the two trackers. The purpose is to evaluate and quantify differences in terms of performance among the different solutions. Mono-crystalline Si, multi-crystalline Si and HIT technologies are comparable between the fixed orientation and mono- and bi-axial trackers, while CdTe is only comparable between the fixed orientation of the commercial installation and the biaxial tracker. This experimental multi-technology part of the PV field counts a total of 30 inverters SMA. The types are: • SB 1100 (15 inverters). • SB 1200 (2 inverters). • SB 1700 (4 inverters). • SB 4000-TL 20 (9 inverters).
Figure 3: Rows of the commercial section of the ABD PV field, mounting First Solar FS 277 modules. In parallel to the experimental part, the installation is composed by a commercial section mounting 8538 CdTe modules First Solar 277, with a nominal peak power of 77.5 Wp each (Figure 3). The whole PV field is installed on an area covered with 20 cm of white gravel, a material with a reflectivity around 25-30%. The field orientation is 8.5° West from South direction. 2.1 The Solyndra group As a particular example from the experimental multitechnological PV field, the group mounting Solyndra modules (see Figure 4) is described with more details, including also the results from a performance simulation. Solyndra modules have quite an innovative shape in the PV world. For this reason they attract a large interest and they can be considered particular elements in the scientific part of the plant. The installed modules have a peak power of 182 W each and use CIGS tubular cells, with the capability to absorb the solar radiation directly from the sun and also reflected from below the module. To achieve the best performance, Solyndra modules require a horizontal installation on a white reflecting surface, with cells prevalently oriented along the NorthSouth axis. In the presented case, the field orientation of 8.5° West has been maintained to better allow comparison
among the various technologies at a later stage. Anyhow, a Solyndra cell orientation along the EastWest axis would lead to a loss of only 3% in energy production.
Figure 4: The Solyndra group in the experimental section of the ABD PV field. The group is composed by 6 modules 182 Wp, for a total power of 1092 Wp. With the support of Solyndra Italy, it has been possible to have a specific simulation of the energetic performance for the group installed. The results of the simulation will be validated with the long-term monitoring activity which will be performed on the group part of the ABD PV field. Results for the energy production expected for the first year are shown in Figure 5. The simulation is carried on along the 30 years of estimated lifetime of the installation. Comparing year 1 to year 30, the AC energy production is expected to decrease 6.6%.
Figure 5: Simulation results for the monthly energy output of the first year of production for the Solyndra group. Given the shape of the Solyndra modules and according to the sun position, the portion of energy production connected to the reflectivity from below the module could vary in the range between 0% and 39.3%. Thus, the importance of the membrane reflectivity index is clear in the evaluation of Solyndra modules performance. It must be stated that this simulation uses values as per [5]. At ABD the modules are installed on a horizontal surface, covered with a white waterproof roofing membrane Alkorbright pvc-p from Renolit. 3
MONITORING ACTIVITY EURAC Research is the scientific responsible of the
experimental installation of ABD PV field and follows the monitoring and test activities to evaluate the performance and the lifetime degradation of the modules. Both activities will involve outdoor and indoor tests. The monitoring work aims at better understanding the module loss mechanisms for each technology and evaluating the performance in the alpine climatic conditions. In performing the monitoring activity, EURAC is following best practice experiences [6] [7], guidelines [8], as well as international standards [9]. The monitoring activity consists in checking the modules electric performance in terms of voltage, current, power and energy production. In parallel, meteorological information on the irradiation level, wind intensity and direction, ambient temperature, as well as the temperature of the modules, are considered. The evaluations will be done at a yearly, monthly and daily base. The measurement of the solar radiation in all its components is very important to check and evaluate the behavior of PV modules [10]. For this reason, the following components are measured: • Global horizontal radiation: measured by a pyranometer and by reference cells (normal and KG5-filtered). • In-plane global radiation: measured by a pyranometer and by reference cells (normal and KG5-filtered). • Diffuse horizontal radiation: measured by a pyranometer. • Direct radiation: measured by a pyrheliometer. • Direct radiation with evaluation of aerosols, ozone and vapors in the atmosphere: measured by a sun photometer. PV reference cells (normal and KG5-filtered) are also used, positioned horizontally, on the module plane, and on the two trackers. To allow measuring the different solar radiation components, the on-field meteo station counts a pyrheliometer (CHP1, Kipp & Zonen), three pyranometers (CMP11, Kipp & Zonen), an albedometer (CMA11, Kipp & Zonen), a CIMEL sun photometer (which will be connected to the NASA AERONET network), along with a sensor for ambient temperature (Thies Clima) and a 2-axis ultrasonic anemometer (Gill Instruments). Two pyranometers and the pyrheliometer are installed on the Solsys2 (Kipp & Zonen) sun tracking system. The meteo station is positioned at 46° 27’ 27.9” N and 11° 19’ 43.1” E. The site elevation is 247 m.s.l. Table II: Classification of the meteo instruments according to international standards. Instrument Pyrheliometer Pyranometers Albedometer Amb. T sensor
Class First class (ISO 9060) Secondary standard (ISO 9060) Secondary standard (ISO 9060) Class B, 1/3 DIN tolerance
To maintain the quality of the monitoring instruments and assure the reliability of the results, regular checks and maintenance, as well as calibrations, are going to be done. The field instruments will be calibrated on a yearly base by comparison (following ISO 9846 [11] and 9847 [12]) with reference instruments kept in the laboratory. Differently from the other instruments, PV reference
cells need more frequent verifications. As stated in the international standard IEC 60904-2 [13] “the calibration of reference cells in frequent use shall be cross-checked against a stable reference cell at intervals no more than one month by comparing their short-circuit currents under the same irradiance”. In addition to the monitoring instrumentation, the performance and the degradation of the modules under test at the ABD installation will be evaluated indoor using a solar flash simulator. This activity requires the maintenance of at least an internal reference module for each type installed on the field. In parallel to EURAC´s monitoring activities, a collaboration agreement with RSE-GSE (Milano, Italy) is under elaboration and additional data will be gathered on the DC and AC sides of about 4-5 groups. This will allow a verification & validation analysis to support the dissemination of performed results. 4
PERFORMANCE RESULTS FOR TWO GROUPS
Given the limited amount of operational days of the ABD PV plant due to the recent connection to the MV network (less than 1 month before the 25th EU PVSEC), in this paper it has been possible to elaborate monitoring results for only a couple of days. The days taken into consideration are August 16 and 17, 2010, two average sunny days in Bolzano. In addition, due to the fact that not all the monitoring devices are at the moment installed on the field (the complete monitoring system is going to be in place by the end of 2010), results are shown only for a limited number of groups and variables. At this stage, it must be stressed that the results are indicative and will be re-validated with the future monitoring activity, which will be performed by EURAC Research during the whole lifespan of the installation. 4.1 DC performance comparison between a-Si and CIS. In this section, performance results are shown for two groups of the experimental part of ABD PV field. The groups into consideration mounts thin-film amorphous silicon (a-Si) and CIS modules, with a total power respectively of 1 kWp and 1.1 kWp. Indications on climate data for the days of 16 and 17 August shows respectively an average daily temperature of 20.3°C and 22.4 °C, an average wind speed of 0.6 m/s and 0.7 m/s. The module temperature, registered only for the CIS group, reaches a maximum value of 58.1°C at 13:00 hours on August 16 and 58.3°C at 15:15 hours on August 17. The daily irradiance [W/m2] is shown in Figure 6. The curve indicates a better irradiation, especially in the afternoon, for August 17. Calculated values for the overall daily irradiance on the modules active surface also follow the same trend.
Figure 6: In-plane irradiance (30° tilted from horizontal) for the two monitored days of August 16 and August 17. The paths of the DC power production for both groups (see Figure 7 for thin-film a-Si and Figure 8 for CIS), in both days, follow the irradiance profile. The cumulative DC daily energy production is shown in Figure 9, and highlights a higher production for August 17, with a better energy performance given by the thinfilm a-Si group. This behavior could be attributed to the typical stabilization process that normally occurs during the first months of service of the thin-film a-Si modules into analysis, leading to an initial power output that could be 20% higher than the stabilized value. In addition, a thermal effect improving the a-Si performance should be considered, given the summer day and the registered module temperature (only for the CIS, mounted in the same way as a-Si, thus we can assume a similar temperature trend for the a-Si system) above 40°C from 11:00 till 15:45 [14]. Differently, the behavior of CIS module can be considered unique for each element (even coming from the same producer), depending on different chemical and physical factors inherent to the material that can influence the meta-stable state of each device [15]. CIS module could improve their performance in relation to exposition to the light for a certain period [14], thus we could expect an improvement of the CIS group energy production. Anyhow, these are general indications confirmed by literature. Future tests and monitoring activities on the groups will show possible variations in performance in time and will give the possibility to better verify and comment the present results.
Figure 7: PV power (DC) for the thin-film a-Si group during the two monitored days of 16 and 17 August 2010.
Figure 8: PV power (DC) for the CIS group during the two monitored days of 16 and 17 August 2010.
Figure 9: Values of the DC daily energy production of the monitored thin-film a-Si and CIS groups on 16 and 17 August 2010. To better characterize the performance of a PV system, and following the indications of the international standard IEC 61724 [6], the performance ratio (PR) is calculated for both groups during the two days into consideration. Being: Yf = E/P0 Yr = H/G PR = Yf/Yr Where E is the energy produced by the PV system, P0 the installed peak power, H is the in-plane irradiance, and G is the irradiance at STC (1 kW/m2). The values of the calculated PR are shown in Table III, highlighting, again, a better performance of the fhinfilm a-Si group. Table III: PR values for the thin-film a-Si and the CIS groups on August 16 and 17. Group Thin-film a-Si CIS
August 16 0.94 0.84
August 17 0.94 0.85
4.2 AC energy production comparison among five different cell technologies. As previously stated in this paper, the monitoring results have been elaborated for only two days (August 16 and 17, 2010). Considering that August 17 shows a better irradiance path (see Figure 6), a comparison among five different module technologies is performed for that day. The comparison is based on the overall energy output (AC) per kWp of installed power for five
monitored groups. The results are shown in Figure 10. The daily energy diagrams in Figure 10 highlight that the major differences in performance among the considered cell technologies can be seen in the central hours of the day, and for the only CIS technology, in the late afternoon. Concerning thin-film a-Si and CIS, the same considerations expressed in the previous section can be repeated. Nevertheless, the highest level of performance is shown by HIT cells in comparison with other crystalline silicon cells, while back-contact monocrystalline cells and multi-crystalline technologies have a similar performance.
Figure 10: PV daily energy production (AC) per kWp of installed power for five different cell technologies evaluated for August 17, 2010. The values are given in kWh/kWp. Anyhow, it must be stressed that at this stage the results are indicative and they have to be verified and validated with further analysis and over a long time period. 5
CONCLUSIONS AND OUTLOOK
The multi-technology PV plant set up at the Airport of Bolzano Dolomiti (ABD) is an innovative installation, to the knowledge of the Authors unique in Europe for the number of technologies under evaluation. The PV plant mounts 24 different types of modules, installed on 30° tilted racks, as well as on a single-axis and on a double-axis tracker. This frame is going to allow large comparisons among PV modules and PV cells technologies on different mounting options, as well as a characterization of the modules behavior in the specific Alpine weather and environmental conditions. The monitoring activities performed at ABD PV field are supported by valid and reliable instruments, as well as by collaborations which will help in the data verification & validation process. Given the plant very recent connection to the MV network, monitoring results are shown only for a couple of days (August 16 and 17, 2010) and for a limited number of groups and variables. Even thou reliable considerations on the modules performance cannot be done at the moment and will need further monitoring and analysis, it can be stated that the performance behavior of the different considered cell technologies is at the moment comparable with the results available in the existing literature.
In addition to this monitoring activity, EURAC Research is developing a wide project called PV Initiative, which started in April 2010 and will last for a period of 3 years. PV Initiative aims at evaluating the criteria affecting modules performance and build surfaces which will put the analyzed factors in mutual relation. The purpose is to evaluate different PV technologies from the point of view of their deterioration, degradation, energy output, as well as to create a web-based tool to evaluate the potential of PV installations in specific areas, starting from the city of Bressanone. This activity will be carried on in parallel to the data gathering and analysis done at the ABD PV installation. 6
ACKNOLEDGEMENTS
The Authors would like to thank the European Regional Development Fund (ERDF) for co-financing this project. Acknoledgements are due to the management of the Airport of Bolzano Dolomiti (ABD), Thaler Engineering Studio, Leitner Solar, and the whole CoPES Consortium. Special thanks also to Willem Zaaiman (EC DGJRC-Ispra), Salvatore Guastella and Matteo Marzoli (RSE-GSE), and Francesco Maria Brani (Solyndra Italy). 7
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