It has been 50 years since Gerald Pearson invented the solar cell. The solar cell is a non-polluting primary

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1 PROGRESS IN PHOTOVOLTAICS: RESEARCH AND APPLICATIONS Prog Photovolt: Res Appl 2005; 13: Published online in Wiley InterScience (wwwintersciencewileycom) DOI: /pip648 Special Issue The Present Status and Future Direction of Technology Development for Photovoltaic Power Generation in Japan Fukuo Aratani*,y New Energy Technology Development Department, New Energy and Industrial Technology Development Organization, Muza-Kawasaki Building, 18F, 1310 Omiya-cho, Saiwai-ku, Kawasaki-city, , Japan In 2004 NEDO established the PV Roadmap Toward 2030 PV2030 as a long-term strategy for PV R&D In this Roadmap, PV is expected by 2030 to supply approximately 50% of residential electricity consumption (cumulative installed capacity in the range of 100 GW) In terms of economic efficiency, electricity costs are targeted to equal commercial use, approximately 14 Yen/kW h, by 2020 and industrial use, approximately 7 Yen/kW h, by 2030 For future PV systems, it is essential to improve the stand-alone capabilities of PV system with electricity storage and to develop community-based PV systems using multi-function inverters Advanced technological innovations beyond the existing levels are also essential Therefore, NEDO is undertaking 2-year projects for preliminary research to make clear the next R&D of solar cells and PV system technology Copyright # 2005 John Wiley & Sons, Ltd key words: photovoltaic; roadmap; solar cell; technology development; national project; Japan INTRODUCTION It has been 50 years since Gerald Pearson invented the solar cell The solar cell is a non-polluting primary energy supply technology utilizing an almost limitless energy source In the early 1970s, worldwide photovoltaic (PV) technology development was undertaken on a large scale A program of PV power generation systems in Japan was started as part of a national program called the Sunshine Project in 1974 and it continues today The main issues have been cost reductions in manufacturing, improvement in solar cell performance, and the development of a mass production process Full-scale government support for advancements in PV technology started around 1990 Currently the domestic target for installed capacity of PV power generation systems by 2010 is 482 GW Various measures for mass deployment have been implemented to reach this goal Through these research and development (R&D) and mass deployment efforts, solar cell manufacturing costs have been reduced to approximately 1/100 of the original cost In addition, by virtue of its formation of the initial market for PV power generation, Japan is now the global leader in both PV shipment and installed * Correspondence to: Fukuo Aratani, New Energy Technology Development Department, New Energy and Industrial Technology Development Organization, Muza-Kawasaki Building, 18F, 1310 Omiya-cho, Saiwai-ku, Kawasaki-city, , Japan y aratanifko@nedogojp Received 29 November 2004 Copyright # 2005 John Wiley & Sons, Ltd Revised 8 February 2005

2 464 F ARATANI capacity It is crucial for PV power generation to be cost competitive vis-á-vis existing conventional residential power generation in order for it to become a primary energy source However, at present the PV electricity generation cost is still twice of conventional residential power charge Since energy resource and global environmental issues have emerged domestically and abroad, the importance of PV systems is ever increasing Further efforts are required to create a full-scale market for PV systems as well as to elevate the status of PV power generation to an established energy supply technology Under this backdrop, the New Energy and Industrial Technology Development Organization (NEDO) has investigated various PV issues and developed long-term objectives to make PV energy a viable, long-term energy source The result of these efforts is established as the PV Roadmap Toward 2030 (PV2030) Following the objectives laid out in PV2030, a new R&D program was developed In this paper, the present status of PV systems and R&D as well as the future direction of R&D for PV system are outlined PRESENT STATUS OF SOLAR CELL PRODUCTION Figure 1 shows the growth in global PV module shipments 1 Changes in installed capacity of PV systems and prices 2 are shown in Figure 2 Global PV module shipments grew to about 744 MW in 2003, an increase of 325% compared with the preceding year Japan produced 364 MW, or almost one-half of global PV module shipments There are different types of solar cells, such as crystalline silicon and thin-film silicon, which vary depending on the type of semiconducting materials Over 90% of PV module shipments today are crystalline silicon solar cells Solar cells using thin-film silicon and CIS have also been developed for practical use However, the market share for these types is still limited to a few percent of the total market % 1% 0% 1% 4%2% 61% Multicrystalline Si Singlecrystalline Si Ribbon Si a-si/mono Si shipment [MW] % Thin-Film Si a-si CIS Others Year JAPAN EU USA Others Figure 1 Global PV module shipment (MW)

3 PV POWER GENERATION IN JAPAN 465 Cumulative installed PV capacity Others Germany USA Japan Estimated electricity cost (Yen/KWh) Year Figure 2 Changes in cumulative installed PV capacity and estimated PV electricity costs The global installed capacity of PV systems in 2003 grew to 1809 MW and recently Germany s capacity has grown significantly Approximately 48% of the total, or 860 MW, was installed in Japan More than 80% of this capacity was installed in residential PV systems In 1993, the installation price of a 3 kw residential PV system was about 11 million Yen The price decreased to about 2 million Yen by 2003 This price corresponds to a cost of about 45 Yen/kW h, or nearly twice that of conventional residential power PV R&D PAST AND PRESENT This development of PV systems was the result of PV R&D support by the Sunshine Project Figure 3 shows the outline of PV R&D in Japan from the Sunshine Project in 1974 through today Multi-crystalline silicon solar cells and thin-film silicon solar cells were essential PV R&D for the creation of practical applications and for the development of technologies to attain cost reductions, high efficiency, and mass production The change in the conversion efficiency of multi-crystalline silicon solar cells, module production costs, and module prices are shown in Figure 4 as one example of the development results achieved by 2000 During this period, technology for crystalline silicon solar cells became established as the primary technology for residential PV systems Thin-film solar cell technology, on the other hand, has yet to break a manufacturing cost of 140 Yen/W (electricity cost, approximately 30 Yen/kW h) In 2001, NEDO became the main organization behind the technology development of PV power generation and established a 5-year master plan for PV R&D To achieve the necessary module manufacturing cost reductions in order to attain the Japanese government s cumulative PV installation target of 428 GW, the following four research projects were developed: Advanced Solar Cell Technology, Advanced Manufacturing Technology, Infrastructure, and Innovative PV Technology Advanced Solar Cell Technology is the core component of PV R&D for achieving the target of 428 GW The targets are to initially develop elemental technologies by 2005 and subsequently to achieve practical use An efficiency of 184% has been attained with multi-crystalline silicon solar cells 3 For the super-highefficiency InGaP/InGaAs/Ge solar cells, a conversion efficiency of 281% has been realized in a 500 light concentrating system 4 The development of thin-film silicon solar cells and thin-film CIS solar cells with a target manufacturing cost of 100 Yen/W is currently underway

4 466 F ARATANI Figure 3 PV R&D projects sponsored by NEDO With regard to thin-film silicon solar cells, microcrystalline silicon/amorphous silicon-hybrid solar cells have been developed with improved light-trapping and rapid CVD technologies using VHF plasma An initial efficiency of 147% (measured at Kaneka) for small-area cells and 131% for prototype modules of 3825 cm 2 has been obtained 5 In addition, for thin-film CIS solar cells, 132% efficiency for the 3456 cm 2 prototype module produced through a selenization method, has been attained 6 Figure 4 Changes in cell efficiency and module production cost

5 PV POWER GENERATION IN JAPAN 467 Advanced Manufacturing Technology is an industrial technology development project that transfers these R&D results to commercial mass production Technologies for the production of silicon raw materials for solar cells and the manufacturing process for thin-film silicon solar cells have been developed for practical use In the Infrastructure project, technologies for evaluating the performance of solar cells, modules, and systems have been developed For PV systems to be mass deployed in the future, it is critical that these systems will be as recyclable as possible Elemental technologies for recycling/reusing recovered modules have been developed under this project Finally, Innovative PV Technology has furthered improvement of the performance and economic efficiency of PV system Seeds Search after 2010, has investigated novel materials for thin-film high-efficiency solar cells and the development of dye-sensitized cells for high performance This program has been modified in light of Roadmap (PV 2030), the preliminary research vehicle for the next generation of PV systems in October 2004 OVERVIEW OF PV ROADMAP TOWARD 2030 (PV2030) In June 2004, following the establishment of the overview PV Roadmap 2030 (PV2030), technical issues were compiled for a long-term strategy 7 This framework was based on the anticipated position of PV power generation by 2030, by which time PV power generation could supply approximately 50% of residential electricity consumption (cumulative installed capacity in the range of 100 GW) A scenario was developed for realization of mass deployment of PV systems, as shown in Figure 5 Two pillars for PV R&D in the Roadmap are the improvement of economic efficiency and the enlargement of PV application areas for practical use With regard to the improvement of economic efficiency, targeted electricity costs to be realized by 2030 will be equivalent to that for industrial use (approximately 7 Yen/kW h) The intermediate targets, by 2010, will be equivalent to the electricity charge for residential use (approximately 23 Yen/kW h) and by 2020 will be equivalent to that for commercial use (approximately 14 Yen/kW h) Concrete items and targets for the improvement of economic efficiency were also laid out, as shown in Table I Among others, module production technology is critical The technological targets by 2030, namely PV module manufacturing cost reduction to 50 Yen/W and extending PV module durability to more than 30 years and cell Figure 5 Scenario for realization of mass deployment of PV systems

6 468 F ARATANI Table I Targets of PV R&D toward 2030 Item Present status Target by Production cost of PV module Production: 100 Yen/W (2010) 250 Yen/W (2003) 75 Yen/W (2020) Conversion efficiency of PV module Expected development: 140 Yen/W (2007) <50 Yen/W (2030) Durability of PV module 20 years Service life 30 years (2020) Silicon feedstock consumption 1013 g/w 1 g/w (2030) Inverter (power conditioner unit) Yen/kW Yen/kW (2020) Accumulator battery 10 Yen/W h (for automobile) 10 Yen/W h (2020) Durability 10 years Table II PV module conversion efficiency targets (cell efficiency targets) Solar cell type Present status Conversion efficiency target (%) Crystalline silicon solar cell mc-si: (201) 16 (20) 19 (25) 22 (25) Thin-film silicon solar cell 10 (147) 12 (15) 14 (18) 18 (20) CuInSe solar cell (195) 13 (19) 18 (25) 22 (25) III V solar cell Concentrator (389) 28 (40) 35 (45) 40 (50) Dye-sensitized solar cell (105) 6 (10) 10 (15) 15 (18) module performance are shown in Table II In addition, regarding the enlargement of PV application areas, PV system applications will be shifted from conventional grid-connected systems to new system structures that do not overload the grid To enlarge PV application areas, it is crucial to develop PV systems for various uses, and then, to increase the utilization of PV systems in terms of both installation sites and environments In shifting to a new PV system that exerts fewer loads on the grid, it is essential to improve the stand-alone capabilities of PV system with electricity storage capacity and to develop community-based PV systems using multi-function inverters With such R&D, it is also important to establish new types of energy systems such as community-scale/wide-area energy networks combining different types of new and renewable energy systems or a large-scale energy system based on hydrogen generation In addition, it is necessary to develop PV modules applicable to various locations, patterns of use and purposes In considering the goals for 2030, it is essential to advance technological innovations beyond the existing levels including drastic improvements in solar cell performance, manufacturing process innovations and qualitative changes in the concept of PV systems In this Roadmap, immediate establishment of new projects for next-generation technology of PV systems are proposed PV R&D IN THE FUTURE R&D geared toward 2010 objectives is focusing on ongoing R&D and its practical applications R&D on elemental technologies, such as thin-film silicon solar cells and CIS thin-film solar cells, will be completed by 2005 in order to achieve earlier commercialization at a 100 Yen/W module manufacturing cost R&D for technological infrastructure such as technologies for the evaluation of PV system performance and power generation output will be promoted R&D for practical uses will also be enhanced for mass production and mass deployment Objectives subsequent to 2010 include R&D for next-generation technologies to achieve the targeted cost reductions by 2020 (14 Yen/kW h electricity cost) NEDO has recently undertaken 2-year projects for preliminary research These projects have been promoted to develop next-generation technologies based on the results of Seed Search technologies from the Innovative Technology program as well as basic research, which have already been progressed in universities and

7 PV POWER GENERATION IN JAPAN 469 Glass Substrate with transparent electrode High quality wide-bandgap materials Top-cell preparation High Mid-cell preparation quality novel materials Bottom-cell preparation Narrow-bandgap materials Back-electrode preparation Development of novel multijunction materials (Top cell materials) Microcrystalline3C-SiC Nanostructure silicon thin film High quality a-si (Bottom cell materials) Microcrystalline S I Ge materials High quality silicon thin film SiGe thin film materials Multi-junction preparation technology (Light-trapping technology, Voc voltage increase) High quality Film manufacturing technology in large-area Cell structure Microcrystalline SiC hetero-junction solar cells 3 -junction thin film solar cells Cell manufacturing process Rapid and high quality CVD technology High productivity equipments Ultra-large-area CVD process Figure 6 Preliminary research on thin-film silicon solar cells industries The projects cover five different categories: thin-film silicon solar cells; crystalline silicon solar cells; compound types of solar cells; dye-sensitized solar cells; and PV power generation system technology The aims of this preliminary research are to make clear R&D direction and a process for achieving the targets by 2020 shown in Table II The outline of the research in each category is as follows: Thin-film silicon solar cells Figure 6 shows the outline of the preliminary research for thin-film silicon solar cells A novel materials with both wide and narrow bandgaps and multi-junction solar cells using these novel materials will be developed aiming for greater than 14% module conversion efficiency Additionally, technologies for ultra-large-area plasma CVD and microwave-plasma will be developed for low-cost manufacturing Crystalline silicon solar cells Figure 7 shows the outline of preliminary research for crystalline silicon solar cells The main objectives of this research are to reduce the consumption of silicon feedstock in addition to obtaining efficiency greater than 19% and reducing production costs Technologies for high-quality silicon ingot production by controlling crystal growth, slicing ingots to obtain ultra-thin wafers, and surface passivation of multi-crystalline silicon wafers will be investigated CIS solar cells Research is focusing on high efficiency, therefore novel wide-bandgap materials and multi-junction solar cells using these materials will be investigated to obtain high efficiency Dye-sensitized solar cells Basic R&D is being carried out for the improvement of cell efficiency Because of the simple structure and manufacturing process of dye-sensitized solar cells, a drastic reduction of module manufacturing costs can be expected for this type of solar cell However, further improvement of cell performance will be necessary if these are to be utilized in PV power generation systems For this reason, research is focusing on an improvement in cell performance to conversion efficiency of 15% (presently 105%) through the development of new dyes and advanced cell structure, as well as development of production technology for large area modules with integrated circuits with various substrates

8 470 F ARATANI High-purity silicon Improvement of durability Ingot producing Slicing Cell manufacturing Panel High-quality silicon ingot 50 m m thick ultra-thin slicing technology Light & Carrier-trapping Handling of ultra-thin wafer in cell process High quality crystallization technology Controls of crystal growth and grain boundary New slicing technology Wire sawing (verification of limitation) Plasma etching Laser slicing etc Light and carrier-trappings of cells with ultra-thin wafers and processing technology Novel hetero-junction solar cells All-dry cells process High efficiency cell manufacturing process Light-trapping, Back reflection Passivation Cell technology for ultra thin wafers Figure 7 Preliminary research on crystalline silicon solar cells PV system technology New system technology for the mass deployment of PV systems is being studied in this project In this study, the following PV system technology issues will be investigated: System components such as a new inverter system for stand-alone capability of PV systems and system simulation for the concept of community-based clustered systems SUMMARY PV R&D over the past 30 years in Japan has produced significant achievements, such as the establishment of the technological foundation to be the world s leader in solar cell production Seed Search for PV technology will also continue on a long-term basis However, since PV power generation needs to be one of the main primary energy supply technologies, further PV R&D is required in various areas, such as efficiency improvements, low-cost manufacturing process and system technologies Therefore, it is essential to make further technical breakthroughs in order to realize innovative technologies It is also important to collaborate with other renewable energy technology fields REFERENCES 1 PV News 2004; No 2 and No 3 2 IEA Report IEA-PVPS TI-12, Komatsu Y, et al Proceedings of the 12th Workshop on Crystalline Silicon Solar Cell Materials and Processes, 2002; 67 4 Araki K, et al Proceedings of the 19th European Photovoltaic Solar Energy Conference, 2004; Nakajima A, et al Proceedings of the 19th European Photovoltaic Solar Energy Conference, 2004; Kushiya K, et al Proceedings of the 19th European Photovoltaic Solar Energy Conference, 2004; Kurokawa K, et al Proceedings of the 19th European Photovoltaic Solar Energy Conference, 2004; 2731