Schott G5 aa 127W initial

Progress in a-Si/a-Si Tandem Junction Thin Film Solar Modules P. Lechner, W. Frammelsberger, W. Psyk, J. Reuner, R. Geyer, S. Dandl., A. Haslauer, M. Berginski, H. Maurus SCHOTT Solar Thin Film GmbH, Hermann-Oberth-Str. 11, 85640 Putzbrunn, Germany D. Lundszien, H. Wagner, M. Renno, H. Popp, C. Erbe, H. Koster, R. Weidl, E. Diegel, P. Bartholome, B. Eichhorn SCHOTT Solar Thin Film GmbH, Otto-Schott-Str. 13, 07745 Jena, Germany ABSTRACT: SCHOTT Solar Thin Film has successfully brought her a-Si/a-Si tandem cell technology for ASITM modules to full production. The production site in Jena with a capacity of 35 MW/a started end of 2007 and ramp up was completed in 2008. Due to continuous process improvements the initial power of the best module could be improved to 127 W which corresponds to 9.4 % initial aperture efficiency. Indoor and outdoor light induced degradation of the 1.4 m² modules is demonstrated to be reproducible around 18 %. Recently a new power class with stabilized 103 W could be introduced. Best small area development cells stabilize at 8.5 % which give the near term perspective of 110 W stable module power or 8 % module aperture area efficiency. A round robin comparison together with various institutes shows a high degree of reproducibility and accuracy for the power measurement of stabilized ASITM modules within +/- 1 %. Long term monitoring of some of our early PV installations demonstrates an excellent stability over more than one decade. Schott ASITM modules with thermally isolated rear side reveal a significant annealing effect and show an improved PR of up to 4 %. Keywords: Silicon, Thin Film Solar Cell, Module, Long Term Stability 1 INTRODUCTION Amorphous Silicon (a-Si) PV technology still attracts a lot of attention due to several attractive features like low energy consumption, use of abundant and heavy-metal- free raw materials, excellent manufacturability with very high production yield and most important for our customers high energy yields for a-Si based PV installations. Recently in Jena, Germany, a fully automated series production line was successfully ramped up to full production. The production fab which has an annual capacity of 35 MW/a of 1.4 m² ASITM modules, was completely designed by Schott Solar procuring equipment from various suppliers. Our cell design is based on an amorphous a-Si/a-Si tandem junction, which currently seems to be the best compromise between efficiency and production economy, if a-Si single junction, a-Si tandem junction and micromorph devices are compared [1]. Module efficiency of our ASITM modules is about 15 % higher compared to state of the art a-Si single junction based modules. On the other hand efficiency is only 5 to 15 % lower as compared to micromorph modules where the cell is four to five times thicker. The installation-friendly module design was chosen to help reducing BOS costs. The module combines high maximum system voltage with very low module voltage and therefore allows more than 30 modules with over 3 kW per serial string. The framed and low weight module is ideally suited not only for roof-top installations but also for multi-MW power plants. SCHOTT Solar´s thin film R ca. 1000 hours indoor light soaking at 45 to 50 °C module ID initial stabilized LID (W) (W) (%) 8-08 102.2 85.0 -16.9 8-22 117.0 98.0 -16.3 8-30 116.4 97.6 -16.2 8-39 120.8 99.0 -18.1 9-10 120.9 98.9 -18.2 Table 2: Initial and stabilized module power; outdoor test from Oct. 2008 to June 2009 in Jena module ID initial stabilized LID (W) (W) (%) 8-23 112.9 93.0 -17.6 8-27 113.9 94.2 -17.3 8-27 115.9 95.0 -18.0 8-27 116.6 95.6 -18.0 5 MODULE DESIGN The installation-friendly module design was chosen to help reducing BOS costs. The module combines high maximum system voltage up to 1000 V with very low module voltage and therefore allows more than 30 modules with over 3kW per serial string. The module frame protects the glass edge during transport, installation and operation most effectively. As a result glass breakage can practically be avoided. Back foil encapsulation results in a low weight module which is ideally suited not only for roof-top installations but also for multi-MW power plants. 6 LONG-TERM STABILITY BEHAVIOUR In order to investigate the long-term stability of our a- Si/a-Si tandem junction modules, produced in the Putzbrunn pilot line in 1996, a number of modules have 0 20 40 96 98 00 02 04 06 08 10 STC Module Power (W) 2 years Stabilisation period 11 years stable operation Figure 7: STC-power monitoring of 32 W a-Si/a-Si tandem junction modules for almost 13 years. been deployed on the roof top of our production site in solar simulator at standard test conditions (STC). This procedure provides a long-term performance monitoring Munich. The power output of these a-Si/a-Si tandem modules was periodically measured with a calibrated without the influence of variation of temperature, solar irradiance and spectrum on the measurement. Figure 7 shows, after the initial stabilization period, a convincing stable behavior during the following 11 years of outdoor exposure. A 2.4 kW roof-top PV-installation in Gaggenau, Southern Germany, also based on our a-Si/a-Si tandem modules, which started operation as early as 1994, has been partially monitored by Fraunhofer ISE since then. 0 20 40 60 80 100 1993 1995 1997 1999 2001 2003 2004 2006 2008 2010 Performance Ratio (%) 2 years stabilisation period 13 years stable behavior Figure 8: Monthly PR monitoring for the Gaggenau roof-integrated PV system from 1993 to 2009. Doted line interpolates missing data from 1998 to 2006. Monitoring done by Fraunhofer ISE 0 20 40 60 80 100 Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Performance Ratio (%) PR 1997 PR 2007 Figure 9: Monthly PR monitoring for the Gaggenau roof-top system for the years 1997 and 2007 For the monthly performance ratio (PR) we observe similar long term behaviour as for the modules shown in Fig. 8. After the initial stabilization period with an LID of about 19 % (decay of PR from approximately 90 to 73 %), beside of small annual fluctuations, we can not observe any indication for a performance degradation. Figure 9 allows an even closer look at the monthly PR for the years 1997 and 2007. Again, except of seasonal fluctuations, no decay of PR within 10 years seems to be detectable. 7 ENERGY YIELD ASITM VERSUS c-Si In order to monitor PR behavior and energy output of our a-/Si/a-Si technology, two small (0.8 kW) ASITM PV systems (ASI 1 and ASI 2), and a 0.6 kW c-Si based reference system were installed in Putzbrunn end of 2007. The energy output and thus the PR will not be not related to the name plate rating (as is usually done), but 24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany 2392 to the individual STC-power measurement of the individual modules used here. This measure will increase accuracy regarding characteristic differences between ASITM and c-Si. Figure 10 shows the PR of system ASI 1 and the c-Si from Jan 2008 to Aug 2009. Clearly the for amorphous Si typical “summer high” and “winter low” PR can be observed, while c-Si shows quite the opposite trend. Also a lower PR for ASI in 2009 compared to 2008 can be seen due to the stabilization effect. Feb and Mar 2009 were two snowy months where ASITM unexpectedly outperforms c-Si. It is probable, that the c-Si PV-system suffers more from partial shadow and low illumination conditions coming from the snow coverage. 60 70 80 90 100 Jan. 08 Mrz. 08 Mai. 08 Jul. 08 Sep. 08 Nov. 08 Jan. 09 Mrz. 09 Mai. 09 Jul. 09 Sep. 09 AC-Performance Ratio (%) ASI 1 c-Si Figure 10: PR of two test PV systems based on ASITM and c-Si modules Table 3: Energy yield for the PV systems ASI 1 c-Si Delta (kWh/kW) (kWh/kW) ASI/c-Si 2008 1199 1091 +9.9 % 2009-09 883 824 +7.1 % In the first year of operation (2008) the ASI system yields with excellent 1199 kWh/kW almost a surplus of 10 % as compared to the crystalline reference (Table 3). Due to the stabilization effect the advantage in the second year (Jan to Sep) is lower, but a 7 % higher energy yield can still be obtained. As mentioned above, a second system ASI 2 is in operation as well since Jan 2008. During the course of the first 1.5 years it could be confirmed, that both ASI systems behave very similar. End of May 2009 the modules of ASI 2 were thermally isolated on their back side. By this measure the typical cell temperature under operation (NOCT) went up by about 10 K, thus from typically 50 °C to roughly 60 °C. This procedure should simulate the thermal situation of a roof-integrated system with no ventilation on the back side and a much warmer location like Southern Europe respectively. While according to the small, but negative temperature coefficient the power output at elevated temperatures should lead to lower energy yields, the annealing effect, which is only valid for a-Si, but not for other thin film technologies sustainably increases the module efficiency. Figure 11 shows the preliminary effect of the thermal isolation of system ASI 2 on the energy yield. With a certain delay of about one month the PR of the thermally isolated ASI 2 system improves to over 90 % as compared to about 86 % of the “normal” ASI 1 system. This demonstrates clearly, that the annealing effect over compensates the negative temperature coefficient. From this observation it can be concluded that ASITM modules are ideally for PV installations in hot areas. 75 80 85 90 95 Apr 09 Mai 09 Jun 09 Jul 09 Aug 09 Sep 09 AC-Performance Ratio (%) ASI 1 ASI 2 Figure 11: PR of the two ASI systems. ASI 2 was thermally isolated end of May 09 7 SUMMARY SCHOTT Solar Thin Film has successfully ramped up its production in Jena. The best module shows 127 W initial power or 9.4 % initial aperture efficiency. LID is demonstrated to be reproducible around 18 %. Power measurement is in very good agreement with recognized calibration institutes. Various long-term monitored outdoor installations proof stable behavior without performance loss. Thermally isolated ASITM modules reveal a significant annealing effect leading to an improved PR of up to 4 %. REFERENCES [1] P. Lechner, W. Frammelsberger, W. Psyk, R. Geyer, H. Maurus, D. Lundszien, H. Wagner, B. Eichhorn, Proc. of the 23rd European Photovoltaic Solar Energy Conference, (2008) [2] H. Schade, P. Lechner, R. Geyer, H. Stiebig, B. Rech, O. Kluth, Proc.of the 31st IEEE Photvoltaic Specialists Conference and Exhibition (2005) [3] P. Lechner, W. Frammelsberger, W. Psyk, R. Geyer, D. Lundszien, E Heckel, H. Maurus, Proc. of the 21st European Photovoltaic Solar Energy Conference, (2006) [4] W. Frammelsberger et al., this Conference [5] D. L. Staebler, C. R. Wronski, Appl. Phys. Lett. 31, 1977, p. 292 [6] W. Herrmann, S. Zamini, F. Faero, T. Betts, N. van der Borg, K. Kiefer, G. Friesen, W. Zaaiman, Proc. of the 23rd European Photovoltaic Solar Energy Conference, (2008) 24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany 2393