Environmental Friendly PV Power Plant

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Energy Procedia

Energy Procedia (2011) 000–000 Energy00Procedia 16 (2012) 32 – 37 www.elsevier.com/locate/procedia

2012 International Conference on Future Energy, Environment, and Materials

Environmental Friendly PV Power Plant Nuofu Chena, Xiulan Zhangb, Yiming Baia, Han Zhangb b

a School of Renewable Energy Engineering, North China Electric Power University, Beijing 102206, China Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083, China

Abstract Energy is the biggest crisis to humanity in the future. Nowadays, most of the energy used on earth comes from oil, gas and coal. According to the recent exploring and consuming rates, the energy will be exhausted in 50-100 years. Whether we can solve the crisis is closely related to the survival of humanity on the earth. The irradiation from the sun is the biggest energy source. Building PV power plant to utilize the energy from sun will be an only way to sustain the life cycle on the earth. However, the development of PV power plants require the huge supply of PV cell and the fabrication process may bring a quantity of pollution and waste, which is harmful to the environment. On the other hand, super large PV power plant will occupy huge land. If the land cannot be explored and used reasonably, this will not benefit the human life either. In this article, we address the discussions about the above problems and propose the initial suggestions about development trend of PV industry and the safety operation mode of super PV power plant. © 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of International Materials Science Society. © 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of [name organizer] Keywords: Environmental Friendly, PV Power plant, Solar Cell

1. The significance of PV power plant As an important material for the development of national economics and daily lives of human beings, the amount of conventional fossil energies is decreasing year by year. The serious environmental pollution originating from fossil energie consumption is also destroying the earth. Moreover, there is still more than two billion habitant suffering from the energy shortage. To solve these challenging problems, the renewable energies like biomass, wind, and solar energy have been regarded as potential routine to cope with serious energy dilemma. Among those green energy strategies, solar energy has attracted vast attention due to its huge amount, being the base for other green energy, and easily-accessed characteristic. Concretely, it is reported that the

1876-6102 © 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of International Materials Science Society . doi:10.1016/j.egypro.2012.01.007

Nuofu Chen et al. / Energy Procedia0016(2011) (2012)000–000 32 – 37 Author name / Energy Procedia

amount of solar irradiation received by earth can be as high as 0.8 million kilowatts. If 0.1% of the solar energy received by earth were changed into electricity with 5% of converting efficiecy, 5.6 T kwh electricity would be obtained, which be more than 40-times of the total energy consumed by the current world [1-4]. On the basis of this viewpoint, it is very promising to expect solar energy dominating future energy market. According to the forecast of Joint centre of European research (JCR), as can be seen from Fig.1, the renewable energy in the whole energy structure can be up to 30% in 2030, and the PV (PV) power would be 10%. Approaching 2050, the corresponding value can be, respectively, improved to 50% and 20%. At the end of 21st century, the specific number for two ratios would be 80% and 60%, respectively, indicating the importance of PV power [4].

Fig. 1. World energy consumption distribution[4]

2. Environmental Friendly PV Power plant Depending on whether power plant is on-grid or not, the PV power plant can be divided into on-grid and off-grid or individual PV power plants. The latter power plant is generally applied in power supply in the remote village, pastoral area, and island. Off-grid PV power is also used for some special occasion such as communication relay station, navigation mark, meteorological station, and border post. As the popular strategy in PV power generation, the on-grid connected plant employs on-grid inverter and switch to transport the generated electric power into the conventional electric grid. Accompanying with the rapid development of PV technology, the on-grid power generation are gradually dominated the whole PV market, indicating its immeasurable application in the future energy revolution. With the help of on-grid power generation, the development of PV power generation has been switched from off-grid and special applications to the concentrate grid power aspect, from supplemental energy into alternate energy source and establishing the renewable energy applications. In is reported that the more than 16 GW PV power plant has been built in the world, in 2010. Benefiting from the pull of European PV market, the PV industry in China has experienced rapid development from 2004. The annual growth in the past five years is over 100%. Since 2007, the product of PV modules in China has positioned the first site among the world. In the new capacity of 16GW in

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Nuofu Chen et al. / Procedia Energy Procedia 16 000–000 (2012) 32 – 37 Author name / Energy 00 (2011)

2010, more than half of amount comes from China. As indicated in the Table 1, 4 mainland PV enterprises and 3 Taiwan enterprises occupied the world’s ten largest PV producers and dozens of PV corporations in China succeeds in overseas market. In August 2011, Chinese national development and reform committee (NDRC) issued the “feed-intariff” policy of China. It was reported that the NDRC will implement the unified power price for the nonbidding solar power project. Beginning from 2012, the feed-in-tariff was established as 1 Yuan per kwh, making the photovoltaic power price having the unified reference, and also providing the flexibility for the local government to carry out the specific allowance policy. This might be a milestone to advance the

Table 1. 2010 Top 10 PV cell manufacturers 2010

PV cell manufacturers

1

Suntech Power

2

JA Solar

3

First solar

4

Q-cell

5

Motech

6

Gintech

7

Kyocera

8

Sharp

9

Trina solar

10

Sunpower

development of PV industry, and to stimulate the construction of PV power plant. On the basis of this background, it is very interesting to search the specific type of environmental-friendly power plant. Historically, there are three generation of PV cells being applied in PV power plant. The first generation of PV cells is the single p-n junction cells like single-crystalline silicon cell, poly-crystalline silicon cell, gallium arsenide cell, and others, sharing together around the 85% PV market. Owing to its abundance in earth, silicon-based PV power plant will still play the dominating role in future PV power plant. Unfortunately, the production of poly-crystalline silicon has been regarded as a high-pollution, energy-intensive industry, conflicting with the green PV concept, making its development suffering from the official suppression. In 2009, the poly-crystalline silicon industry was even treated as over-capacity in the Document No. 38 issued by the State Council. As far as gallium arsenide is concerned, the highly toxic of arsenic is also conflict with the green concept. Therefore, much effort should be paid on the environmental-protection and reducing the energy consumption during the construction of solar modules. Meanwhile, other green power plants have also been proposed and developed by PV community [5-7]. In order to reduce the material consumption and lower the device cost, the so-called second generation PV cells, thin-film PV cells, appears. By depositing cell active layer structure of several micrometers on the economical substrate, the material consumption as well as cell cost can be greatly reduced, showing the appealing feature for the scalable-production. At present, the thin-film solar cell materials mainly include the micro-crystalline silicon, amorphous silicon, and CdTe. Specifically, the additional attention must be paid on the production of CdTe cells due to the toxic cadmium [8-10]. Thin-film poly-crystalline cells, of less silicon consumption and small energy consumption, would be the future preferable power plant component. As compared in the Fig.2, thin-film silicon technology can

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reduce the 2/3 energy consumption, and reduce the 3/4 material consumption. In Table.2 [7], the best conversion efficiency of different silicon cells have been listed. It is easily concluded that the comparable cell performance might be attained once the technical breakthrough is achieved in thin-film silicon cells.

Siemens multicrystal silicon

Cast ingot

slice

trichlorosilane

Multicrystal silicon piece

Fig. 2. The comparison of fabrication process between thin-film poly-crystalline cell and crystalline cell Table 2. 2010 Top 10 PV cell manufacturers Type of silicon cell

Efficiency (%)

Voc(V)

Jsc(mA/cm2)

FF(%)

Single-crystalline silicon cell

24.7

0.706

42.2

82.8

Multi-crystalline silicon cell

20.3

0.664

37.7

80.9

Thin-film multi-crystalline silicon cell

16.6

0.645

32.8

78.2

Amorphous silicon cell

9.5

0.859

17.5

63

In order to further improve the conversion efficiency, the PV researchers start to deeply study the limited efficiency and the specific energy loss mechanisms, and establish the new generation PV technology, namely third-generation PV technology, including the concentrated PV module, quantum structure cell, and others. One of particular interest here is the concentrated PV technology consisting of cheap optical concentrator and high-efficiency multi-junction tandem cell. Concretely, the solar irradiance was firstly concentrated by economical Fresnel lens with 500~1000 concentration onto the small cell chip, the PV cell chip consists of three subcells fabricated from different semiconductors connected with highquality tunnel junctions. Experimentally, impressive demonstration with conversion efficiency beyond 40% has been reported very recently with assistance of an additional high-flux concentrator [11-13]. As estimation, a single concentrator PV cell with the area of 5mm×5mm under the 500× solar irradiation can generate electric power more than a poly-crystalline cell with the area of 156mm×156mm. In this way, high-flux concentrator PV power system can not only achieve the higher energy conversion efficiency, but also effectively reduce the device area and thus reduce the occupation of land obviously, as shown in Fig. 3 [14]. Let’s take a 10MW PV power plant for example. If the traditional crystalline silicon technology is adopted, 300, 000 square meters land will be totally occupied. Although the land area will be also the same as crystalline silicon by employing concentrated PV cell technology, the fixation base on land for each 10KW CPV power generator actually occupies less than 4 square meters, and the 10MW CPV power plant actually occupies only 4000 square meters. Therefore, the high efficiency CPV power plant is a real environment-friendly renewable energy source.

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Nuofu Chen et al. / Energy Procedia 16 (2012) 32 – 37 Author name / Energy Procedia 00 (2011) 000–000

Fig. 3. The application of CPV power plant

3. PV pumped storage According to the prospect, both the specific ratios for the renewable energy and the PV power in the whole energy structure would be 80% and 60%, respectively, at the end of 21st century. According to the current management technology of electric network operation, once PV generation exceed more than 20%, it is very hard to protect the stability of electric network and the utilization safety of terminal user. Therefore, it is urgent to solve the problems of transport stability and the safety of PV power. If we make use of the portion of PV power exceeding the safe capability of electric network to actualize the application of pumped storage, sustaining power would be obtained day and night through hydraulic power generation. This activity may loss part of the conversion efficiency but actually safeguard the stability of electric network and the utilization safety of terminal user. At the same time, the combination of pumped storage and farm field irrigation may also improve the environment of agriculture. Thus a real environmental friendly PV power plant would be realized, as shown in Fig.4.

Fig. 4. The plan for solar energy swamped land

Nuofu Chen et al. / Energy Procedia 16 (2012) 32 – 37 Author name / Energy Procedia 00 (2011) 000–000

4. Conclusions The issued feed-in-tariff policy for PV power price will play a vital role in the large-scale development of PV power plant. It is the tendency to build environment-friendly power plant, especially the development of thin film silicon PV power plant and the application of CPV power plant. Actually, the PV industry in china, which is a potentially huge market, has not been well explored. After the issue of the “feed-in-tariff” policy of China by NDRC, the target scale of construction for the PV power plant has been lifted up to 15GW. How to reasonably utilize green energy and keep sustainable development is the most important challenge for humanity in this century. As a huge green energy source generated from the sun, PV industry will gain the best opportunity to grow up. We should grasp the opportunity to build the most suitable environmental friendly PV power plant, and welcome a better tomorrow. References [1] Dinghuan Shi, Shengwu Xie. The Present Status and Development of Solar PV Generation in China. Shanghai: 15th International PV Science & Engineering Conference (PVSEC-15), 2005: 1-5 [2] Luque A, Hegedus S. Handbook of PV Science and Engineering . New York: John Wiley & Sons Ltd, 2003: 359 [3] http://en.wikipedia.org/wiki/Solar_cell [4] Junfeng Li, Sicheng Wang, Minji Zhang, etc,

2007 Chinese photovotaic development report. Beijing: 1st. China

Environmental Science Press, 2007 [5] M.A. Green, A.W. Blakers, S.R. Wenham, Improvement in silicon solar cell efficiency, in Proc. Record of the 18th IEEE PVSC, 1985: 39-42. [6] J.H. Zhao, A.H. Wang, and M.A. Green, 24.5% efficiency silicon PERT cells on MCZ substrates and 24.7% efficiency PERL cells on FZ substrates, Prog. Photovolt: Res. & Appl. 1999(7):471-474. [7] M.A. Green, K. Emery, Yoshihiro Hishikawa, W. Warta, Solar cell efficiency tables, Prog. Photovolt: Res. & Appl., 2010(18): 346-352. [8] M. A. Green, Consolidation of Thin-film PV technology: the coming decade of opportunity, Pro .Photovolt: Res. Appl., 14, 383-392, (2006). [9] W. J. Wang, Y. Xu, H. Shen, Polycrystalline silicon thin-film solar cells on various substrates, Phys. Stat. Sol. (a), 203, 721731, (2006). [10] M. A. Green, Solar cells: Operating Principles, Technology and System Applications, The University of New South Wales, Sydney, 1998. [11] Guter W, Schone J, Philipps S P, et al. Current-matched triple-junction solar cell reaching 41.1% conversioin efficiency under concentrated sunlight. Appl Phys Lett, 2009, 94(22): 223504 [12] King R R, Law D C, Edmondson K M, et al. 40% efficient metamorphic 2GaInP/GaInAs/Ge multijunction solar cells. Appl Phys Lett, 2007, 90(18): 183516 [13] Geisz J F, Friedman D J, Ward J S, et al. 40.8% efficient inverted triple-junction solar cell with two independently metamorphic junctions. Appl Phys Lett, 2008, 93(12): 123505 [14]http://www.solarnovus.com/index.php?option=com_content&view=article&id=538:tutorial-concentrated-PV-cpvsolar&catid=39:tutorials&Itemid=238

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