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Tilt angle dependence of output power in an 80 kWp hybrid PV system installed at Shiga in Japan
Solar Energy Materials & Solar Cells 75 (2003) 781–786
Tilt angle dependence of output power in an 80 kWp hybrid PV system installed at Shiga in Japan Satoshi Hiraoka, Takeshi Fujii, Hideyuki Takakura*, Yoshihiro Hamakawa Department of Photonics, Faculty of Science and Engineering, Ritsumeikan University, 1-1-1 Noji Higashi, Kusatsu, Shiga 525-8577, Japan
Abstract One-year field experience of an 80 kW PV system on a rooftop of the ROHM Memorial VLSI Research Center at the Ritsumeikan University is reported. All kinds of live technology available materials, c-Si, poly Si and a-Si solar cells are installed on the three tilt angles of 26.51 south, horizontal and north 26.51. Systematic PV performances have been measured from the beginning of June 2000 to the end of May 2001. Measurements were made mainly on DC output power from four kinds of PV arrays; c-Si south side, a-Si of horizontal and poly Si, a-Si north side. It has been shown from analyses of monthly data on each material that almost 70% of with that in the south side in the annual average. In summer a-Si module yields the maximum output power normalized to 1 kWp. On the contrary c-Si module shows larger output in winter. Some other unique results are demonstrated and discussed. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Hybrid PV system; Monthly output energy; Poly Si and c-Si-based PV array performance; The path of the sun; Scattered sun light; Temperature dependence of cell efficiency
1. Introduction Although most solar cells are installed on the south side, it is expected that solar cells will be installed in the horizontal and the north side of the roof of the building for the reason of the landscape and so on. However, when solar cells are installed in *Corresponding author. Tel./fax: +81-77-561-3938. E-mail address: [email protected] (H. Takakura). 0927-0248/03/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 7 - 0 2 4 8 ( 0 2 ) 0 0 1 3 1 - 9
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the horizontal and the north side, it is not understood in detail the amount of generation of electricity in comparison with the south side. In this work, we have investigated the output performance of monocrystalline silicon (c-Si) solar cells at 26.51 south, polycrystalline silicon (poly Si) solar cells at 26.51 north, a-Si solar cells at horizontal and north 26.51. We focused our attention to evaluate generated electric energy from each of the PV arrays. This experiment was started in February 2000 and will be operated for several consecutive years to establish a design concept on the basis of a long-term experimental result. In this paper, the results of evaluation of four different PV arrays, i.e., c-Si solar cells at 26.51 south, poly Si solar cells at 26.51 north and a-Si (single) (single-junction amorphous silicon) solar cells at horizontal and north 26.51 are reported. The monthly accumulated output power is measured precisely during the first year. The seasonal variation affects severely the performance of each PV array. That between winter and summer is mostly discussed.
2. System specifications and measurement An outlook of the rooftop PV system on the roof of the ROHM Memorial VLSI Research Center in the Ritsumeikan University is shown in Fig. 1.
Fig. 1. Rooftop view of the 80 kW PV system.
S. Hiraoka et al. / Solar Energy Materials & Solar Cells 75 (2003) 781–786
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The PV array installation is located in Shiga Prefecture, Japan (latitude: north 341580 , longitude: east 1351570 ). Total capacity of 80 kW modules were installed in February 2000 with 40 kW c-Si modules at the south side, 5.1 kW a-Si modules at the horizontal roof (51 facing due west) and 30 kW poly Si modules as well as 5.0 kW a-Si at the north side. Three tilt angles are south 26.51, horizontal and north 26.51. Fig. 2 illustrates the circuit diagram of the grid-connected PV system. Power conditioning system is constructed with four 10 kW inverter units for c-Si array, one for a-Si and three for poly Si array, respectively. AC output is connected to the utility grid and supplied to lightings and air conditioners in the research center. The instantaneous output power from 8 subarray systems is measured every 6 s with irradiance on three tilt angles. These data were accumulated for 1 min and recorded by the computerized systems.
3. Results and their analyses The daily and monthly accumulated electric energies data are also calculated with computerized system. Fig. 3 shows the monthly accumulated output from c-Si array facing south and poly Si facing north. It has been shown from the analyses of these data with normalized to 1 kW system. Accumulated irradiances on the horizontal plane
Fig. 2. Circuit diagram of the 80 kW PV system.
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Fig. 3. Monthly accumulated electric energy normalized to 1 kWp from c-Si and poly-Si arrays and monthly accumulated solar radiation.
Fig. 4. The path of the sun by the difference in the season.
(h-insolation) are also shown in this figure. Numbers on the top of the bars are the ratios of the output from poly Si array against that from c-Si. Fig. 4 shows the path of the sun by the difference in season. In June and July, almost the same output electric energies are generated from both arrays. It can be explained from Fig. 4. The sun is located on the north side in the morning and evening in summer. In December,
S. Hiraoka et al. / Solar Energy Materials & Solar Cells 75 (2003) 781–786
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about 1/4 of the electric energy from c-Si array is obtained from poly Si array although the sun does not irradiate to the north side array directly in this month. It scatters the solar light by the cloud. The light that the cloud scattered reaches the north side [1]. The accumulated output power from June to May from poly Si north side is 67% of that by c-Si south side. Another important information obtained from this result is that output power in summer from crystalline Si module is far less than the irradiance. Several authors have calculated the temperature coefficient for c-Si solar cells. Commonly, the module output varies by roughly 0.5%/1C for c-Si-based cells [2]. Therefore, this discrepancy is qualitatively explained by the temperature coefficient of the conversion efficiency of the c-Si solar cell and real operation temperature of the solar cell module. The output energy from each PV array from June 2000 to May 2001 is shown in Fig. 5. It has been shown from the analyses of these data normalized to the 1 kW system that there are some unique new informations in the PV system engineering. That is, larger output power with the a-Si module than that of c-Si module has been seen in summer. The sun is located on the north side in the morning and evening in summer. The efficiency of the c-Si array tends to decrease with temperature, but on the contrary, the a-Si array improves its efficiency. Several authors have calculated temperature coefficients for both c-Si- and a-Si-based solar cells. Commonly, the module output varies by roughly 0.5%/1C for c-Si-based cells, but in the case of most thin-film cells, the temperature coefficient is less than that of c-Si [2]. According to some of the reported cases, the temperature coefficient of a-Si, is considered to be 0.2%/1C [2]. However, apparently in our case, due to the thermal recovering effects, a-Si has a positive temperature coefficient. So, this temperature coefficient may depend on the competition between Staebler–Wronski degradation at intense illumination with thermal recovering process. It is also reported that in the case of a-Si, higher operation temperature results in a better
Fig. 5. Monthly accumulated electric energy normalised with 1 kWp from four arrays.
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operation performance [2]. For more precise determination of the thermal process effects, it will have to correlate directly with the cell temperature.
4. Conclusions Electrical output performances of ‘‘Tilt Angle Dependence of Output Power in an 80 kWp Hybrid PV System’’ consisting of crystalline-silicon-based solar cells at south side, amorphous-silicon based solar cells at the horizontal roof and the north side, polycrystalline-silicon-based solar cells at the north side have been evaluated. The processed data for monthly accumulated output power of polycrystalline- and crystalline-silicon-based arrays reveal significant differences, mainly with respect to the path of the sun due to seasonal variations and scattered light by a cloud’s scattering of direct sunlight. In summer, the output power accumulated in 1 month obtained from the north side a-Si is larger than that from the horizontal a-Si arrays. The accumulated output power from June 2000 to May 2001 from poly Si north side is 67% of that from the south side.
Acknowledgements This work is supported by NEDO, as a PV system field test project under the New Sunshine Project of MITI, Japan.
References [1] K. Shibata, Y. Utijima, The distribution of the solar energy and measurement, Japan Scientific Societies Press, pp. 41–49. [2] M. Itoh, H. Takahashi, T. Fujii, H. Takakura, Y. Hamakawa, Y. Matsumoto, Evaluation of electric performance by democratic module PV system field test, Sol. Energy Mater. Sol. Cells 67 (2001) 435–440.
Tilt angle dependence of output power in an 80 kWp hybrid PV system installed at Shiga in Japan Satoshi Hiraoka, Takeshi Fujii, Hideyuki Takakura*, Yoshihiro Hamakawa Department of Photonics, Faculty of Science and Engineering, Ritsumeikan University, 1-1-1 Noji Higashi, Kusatsu, Shiga 525-8577, Japan
Abstract One-year field experience of an 80 kW PV system on a rooftop of the ROHM Memorial VLSI Research Center at the Ritsumeikan University is reported. All kinds of live technology available materials, c-Si, poly Si and a-Si solar cells are installed on the three tilt angles of 26.51 south, horizontal and north 26.51. Systematic PV performances have been measured from the beginning of June 2000 to the end of May 2001. Measurements were made mainly on DC output power from four kinds of PV arrays; c-Si south side, a-Si of horizontal and poly Si, a-Si north side. It has been shown from analyses of monthly data on each material that almost 70% of with that in the south side in the annual average. In summer a-Si module yields the maximum output power normalized to 1 kWp. On the contrary c-Si module shows larger output in winter. Some other unique results are demonstrated and discussed. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Hybrid PV system; Monthly output energy; Poly Si and c-Si-based PV array performance; The path of the sun; Scattered sun light; Temperature dependence of cell efficiency
1. Introduction Although most solar cells are installed on the south side, it is expected that solar cells will be installed in the horizontal and the north side of the roof of the building for the reason of the landscape and so on. However, when solar cells are installed in *Corresponding author. Tel./fax: +81-77-561-3938. E-mail address: [email protected] (H. Takakura). 0927-0248/03/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 7 - 0 2 4 8 ( 0 2 ) 0 0 1 3 1 - 9
782
S. Hiraoka et al. / Solar Energy Materials & Solar Cells 75 (2003) 781–786
the horizontal and the north side, it is not understood in detail the amount of generation of electricity in comparison with the south side. In this work, we have investigated the output performance of monocrystalline silicon (c-Si) solar cells at 26.51 south, polycrystalline silicon (poly Si) solar cells at 26.51 north, a-Si solar cells at horizontal and north 26.51. We focused our attention to evaluate generated electric energy from each of the PV arrays. This experiment was started in February 2000 and will be operated for several consecutive years to establish a design concept on the basis of a long-term experimental result. In this paper, the results of evaluation of four different PV arrays, i.e., c-Si solar cells at 26.51 south, poly Si solar cells at 26.51 north and a-Si (single) (single-junction amorphous silicon) solar cells at horizontal and north 26.51 are reported. The monthly accumulated output power is measured precisely during the first year. The seasonal variation affects severely the performance of each PV array. That between winter and summer is mostly discussed.
2. System specifications and measurement An outlook of the rooftop PV system on the roof of the ROHM Memorial VLSI Research Center in the Ritsumeikan University is shown in Fig. 1.
Fig. 1. Rooftop view of the 80 kW PV system.
S. Hiraoka et al. / Solar Energy Materials & Solar Cells 75 (2003) 781–786
783
The PV array installation is located in Shiga Prefecture, Japan (latitude: north 341580 , longitude: east 1351570 ). Total capacity of 80 kW modules were installed in February 2000 with 40 kW c-Si modules at the south side, 5.1 kW a-Si modules at the horizontal roof (51 facing due west) and 30 kW poly Si modules as well as 5.0 kW a-Si at the north side. Three tilt angles are south 26.51, horizontal and north 26.51. Fig. 2 illustrates the circuit diagram of the grid-connected PV system. Power conditioning system is constructed with four 10 kW inverter units for c-Si array, one for a-Si and three for poly Si array, respectively. AC output is connected to the utility grid and supplied to lightings and air conditioners in the research center. The instantaneous output power from 8 subarray systems is measured every 6 s with irradiance on three tilt angles. These data were accumulated for 1 min and recorded by the computerized systems.
3. Results and their analyses The daily and monthly accumulated electric energies data are also calculated with computerized system. Fig. 3 shows the monthly accumulated output from c-Si array facing south and poly Si facing north. It has been shown from the analyses of these data with normalized to 1 kW system. Accumulated irradiances on the horizontal plane
Fig. 2. Circuit diagram of the 80 kW PV system.
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Fig. 3. Monthly accumulated electric energy normalized to 1 kWp from c-Si and poly-Si arrays and monthly accumulated solar radiation.
Fig. 4. The path of the sun by the difference in the season.
(h-insolation) are also shown in this figure. Numbers on the top of the bars are the ratios of the output from poly Si array against that from c-Si. Fig. 4 shows the path of the sun by the difference in season. In June and July, almost the same output electric energies are generated from both arrays. It can be explained from Fig. 4. The sun is located on the north side in the morning and evening in summer. In December,
S. Hiraoka et al. / Solar Energy Materials & Solar Cells 75 (2003) 781–786
785
about 1/4 of the electric energy from c-Si array is obtained from poly Si array although the sun does not irradiate to the north side array directly in this month. It scatters the solar light by the cloud. The light that the cloud scattered reaches the north side [1]. The accumulated output power from June to May from poly Si north side is 67% of that by c-Si south side. Another important information obtained from this result is that output power in summer from crystalline Si module is far less than the irradiance. Several authors have calculated the temperature coefficient for c-Si solar cells. Commonly, the module output varies by roughly 0.5%/1C for c-Si-based cells [2]. Therefore, this discrepancy is qualitatively explained by the temperature coefficient of the conversion efficiency of the c-Si solar cell and real operation temperature of the solar cell module. The output energy from each PV array from June 2000 to May 2001 is shown in Fig. 5. It has been shown from the analyses of these data normalized to the 1 kW system that there are some unique new informations in the PV system engineering. That is, larger output power with the a-Si module than that of c-Si module has been seen in summer. The sun is located on the north side in the morning and evening in summer. The efficiency of the c-Si array tends to decrease with temperature, but on the contrary, the a-Si array improves its efficiency. Several authors have calculated temperature coefficients for both c-Si- and a-Si-based solar cells. Commonly, the module output varies by roughly 0.5%/1C for c-Si-based cells, but in the case of most thin-film cells, the temperature coefficient is less than that of c-Si [2]. According to some of the reported cases, the temperature coefficient of a-Si, is considered to be 0.2%/1C [2]. However, apparently in our case, due to the thermal recovering effects, a-Si has a positive temperature coefficient. So, this temperature coefficient may depend on the competition between Staebler–Wronski degradation at intense illumination with thermal recovering process. It is also reported that in the case of a-Si, higher operation temperature results in a better
Fig. 5. Monthly accumulated electric energy normalised with 1 kWp from four arrays.
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operation performance [2]. For more precise determination of the thermal process effects, it will have to correlate directly with the cell temperature.
4. Conclusions Electrical output performances of ‘‘Tilt Angle Dependence of Output Power in an 80 kWp Hybrid PV System’’ consisting of crystalline-silicon-based solar cells at south side, amorphous-silicon based solar cells at the horizontal roof and the north side, polycrystalline-silicon-based solar cells at the north side have been evaluated. The processed data for monthly accumulated output power of polycrystalline- and crystalline-silicon-based arrays reveal significant differences, mainly with respect to the path of the sun due to seasonal variations and scattered light by a cloud’s scattering of direct sunlight. In summer, the output power accumulated in 1 month obtained from the north side a-Si is larger than that from the horizontal a-Si arrays. The accumulated output power from June 2000 to May 2001 from poly Si north side is 67% of that from the south side.
Acknowledgements This work is supported by NEDO, as a PV system field test project under the New Sunshine Project of MITI, Japan.
References [1] K. Shibata, Y. Utijima, The distribution of the solar energy and measurement, Japan Scientific Societies Press, pp. 41–49. [2] M. Itoh, H. Takahashi, T. Fujii, H. Takakura, Y. Hamakawa, Y. Matsumoto, Evaluation of electric performance by democratic module PV system field test, Sol. Energy Mater. Sol. Cells 67 (2001) 435–440.