TOWARD GIGA-WATT PRODUCTION OF SILICON PHOTOVOLTAIC CELLS, MUDULES AND SYSTEMS

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1 TOWARD GGA-WATT PRODUCTON OF SLCON PHOTOVOLTAC CELLS, MUDULES AND SYSTEMS Takashi Tomita Corporate Director and Group General Manager of Solar Systems Group SHARP CORPORATON, 282-1, Hajikami, Katsuragi-shi. Nara JAPAN NTRODUCTON Energy depends largety on fossil fuels or nuclear power. Recent energy-related news, however, report varieties of subjects to be resolved such as unexpected hikes of crude oil, blackouts attacked on larger scales in world major cities, prevailing fears on power shortages and increasing volume of CQ emissions. Moreover, fossil fuel resources are said to be exhausted in about 40 years to come'']. and so increases the demand for photovoltaic electricity supply as the next generation power source. Photovoltaic systems were first applied 40 years ago to the power generations in non-electrified areas like lighthouses, radio transmission stations on remote mountains or space satellites. n Japan, the national Sunshine Project propelled their development about 30 years ago. Thus they were applied to consumer products tike calculators and wristwatches about 20 years ago. Residential incentives and generated power buyback started in Japan 10 years ago that were powerful and supportive to the quick growth of photovoltaic systems, which have contributed to the well-balanced growth of the photovoltaic market and industries. The photovoltaic generation systems market is expanding with 30% growth ratio annually for these several years as shown in Fig. ". SHARP Corporation estimates the world production of photovoltaic cells will reach 867MW in 2004 and will exceed 1.1GW in Hence, the market expansion and technology developments have pushed down the costs of photovoltaic systems: Fig.1 The market of photovoltaic geneation systems Fig. 2"' shows the matrix of market size vs retail prices of Japanese residential markets. The system retail price in 1994 was 2 million yen (or US$19,000) per kw with only 500 installations, while yen with 50,000. installations this year. This means the price was down to one third for these ten years. The electricity price generated by photovoltaic system is now about 48 yen (or US$0.46) per kwh. which is nearly double of averaged utility electricity bills. Fig2 Markel $12. vs. rstail prices of Japanese residential market ASSESSMENT OF PHOTOVOLTAC GENERATON SYSTEMS The author has approached the assessment of values possessed by photovoltaic generation systems, and classified them in countables and uncountables in Table. The generation of electric power by conversion of sunfight irradiation is the typical countable value. The peak power mitigation, the cut down in transmission cost, the reduction of COZ emissions and the energy consumption control are also classified in this value. On the other hand, those regarded as uncountable values are the economy push-up efficiency, the improvement of energy security, the contribution to the international society and the environment conservation, etc. Thus, the photovoltaic generation systems resew lots of values. The fair and appropriate assessment on these vafues intrinsic to them will lead to their much greater expansions in the world. Also required are various policy supports, constant efforts for new technology development, improvement in product reliability. offers of wider product applications and further cost reductions /05/$ EEE. 7

2 able 1 Assessment of photovoltaic generation system VPUEdPl-DOKXTbKS ctwithsi Fig.3 Development of new manufacturing technology :sheet -we wafer 1 STATUS OF POLY-SLCON FEEDSTOCK The today's thriving market of semi-conductors business and.the rapid growth of photovoltaic industries extremely tighten the supply of poly-silioon feedstock. The current world poly-silicon productions are 27,000 tons per year, of which about 10,000 tons are appropriated to photovoltaic usages together with scrap materials coming from semiconductors market. These volumes account for nearly 1,000MW of photovoltaic celldmodules. The supply and demand gap, however, looks getting wider. And this gap will put the rapidly growing siticon-based photovoltaic business ' into serious confusion and difficulties unless the dynamic increase.of poly-silicon feedstock is seen. Against these situations, R8D is pushed ahead for the development of innovative production method of new solar-grade silicon, or the expansion of production capacity is planned by polysilicon 'manufacturers. STATUS OF SlLlCON WAFERS SHARP Corporation is under development of a new wafer manufacturing technology with financial assistance by NED0 (The New Energy and ndustrial Technology Development Organization); the silicon sheet production technology to make sheet wafer through soaking of the substrate into silicon molten (Fig. 3). t cuts the process of. wire saw slicing of silicon ingot which is needed in conventional wafer manufacturing process,.and consequently is expected to reduce the production cost. STATUS OF CRYSTALLNE SLCON SOLAR CELL The more efficient usage of poly-silicon feedstock under their serious shortage circumstances, the development of thinner ylk is under way. t was over 400pm at time of small productions long before, and was still 350pm even in mid nineties when productions were drastically increased. RBD-level theoretical simulation showed the possibility of thinner cells, but it was not achieved in the actual production base due to dificldties in automated line process., The PV manufacturers are demanded for the more PV volumes with limited quantity of materials; i.e. much thinner cells. The current cell thinness of SHARP Corporation is already 180pm. far down from 300pm in We aim for 150pm to be achieved in the near future, and will look for the possibility of less than 100pm. Fraunhofer SE of Germany made two different. thickness single crystalline cells (240pm and 40pm) at the lgrh EU-PVSEC held in, June 2004, and made the evaluation of those cells. ts result has shown nearly equal efficiencies, indicating that the current technology can make efficient cells, from less than 100pm thin wafers. The Fig. 4 shows the PV demand forecast made by SHARP Corporation until 2010 and the volumes required of poly-silicon feedstock. This shows that 41,000 tons of feedstock is required in 2010 if the cell thickness is 200pm while however 22,000 tons is enough if it is loopm thin. The thinner cells thus not only reduce silicon materials but also cut down the risk of additional capital investment for materials. Moreover, RbO to make possible the reuse and recycle of photovoltaic modules is also under way. 8

3 r 10 f L Lo 4n Lo i - 00 m 2(108 "0 F d Yea Fig.4 The photovoltaic demand forecast THN FLM SLCON SOLAR CELL There are different types of structures in thin film silicon solar cells: amorphous silicon, microcrystalline silicon and a tandem structure type where those two are layered. The efficiency of thin film is lower than that of crystalline silicon cells while it saves the quantity of silicon materials to be used. t also has the advantage for a larger size cell as well as for less influence in power output by temperature increases with superior temperature characteristics. The tandem structure type thin film is becoming the mainstream among all thin films due to those features that reduce the degradation of the photovoltaic power output and.so increase the efficiency. On the other hand, microcrystalline silicon is widely under development for application into a lower layer of the tandem Celt due to the quality of silicon film generation getting much higher. The disadvantage of this microcrystalline silicon, however. is that its absorption ratio of sunlight irradiation in a visible area is not so high as that of amorphous silicon, and hence it needs more than ten times of thickness in the absorption layer. For an expected productivity of micro crystalline cells, therefore, required are the developments in technologies of tight captures by even surfacing of TCO (Transparent Conducting Oxide), of large size fitm processing and highly integrated manufacturing as well as of high speed thin film processing technology. As for cell efficiency, 13.0% was achieved in tandem type by recent technology developments. DEVELOPMENTS OF PHOTOVOLTAC PRODUCTS SHARP Corporation has introduced an 'lluminating Solar Panel" as new lighting systems combined with seethrough type thin film sotar cells and LEDs {Fig. 5). This is the a three function combined solar panel with features of photovoltaic generation, see-through and lighting. which is expected to appeal world users to create revolutionary photovoltaic systems. PRCES OF PHOTOVOLTAC GENERATON SYSTEMS Photovoltaic cell manufacturing is one of semiconductor industries, whose manufacturing costs hence largely depend on the production scale. Table 2 shows the forecast of photovoltaic cell production capacities by Japanese PV manufacturers. All of them, including SHARP Corporation, are planning very aggressive expansions in capacity to meet rapidly growing worfd demand. These expansions in world production will reduce systems costs and retail prices to users as per Fig. 6, a forecast estimation by SHARP Corporation. 9

4 i (Mw'year) 0 for residential use j Milestone - i A FUTURE VSON ON PHOTOVOLTAC GENERATON fndustrles Several associations in Japan. Europe and the USA have already introduced future visions of photovoltaic generation industries. n order to achieve these visions, much larger-scale productions are required. For getting to this goal, the diversification is necessary in terms of scale expansion. This is the new type photovoltaic system as shown in Fig. 7 in addition to current mainstream silicorr based photovoltaic systems. [O Gdng demand dsobr-1. maow mo aoed m... swariwsartima$ Fig.7 New type photovoltaic system Am0 Photovoltaic generation system contributes to the conservation of the global environment For example, 4kW residential system will cut down 275 gallons of crude oil per year, and this means the CO2 reductions by yearly 5,952 pounds. The more aggressive expansions to install photovoltaic systems will make an environmental contribution in a positive spiral effect. Fig. 8 shows the forecast of world power supply by photovoltaic generation estimated by SHARP Corporation, who sees 8.6% of the total world electricity supply by photovoltaic generations in m When photovoltaic generations are reviewed from the sight of an industry, they have a lot of variety of production processes and related, industries involved all over the world. The employment in, 2003 engaged in photovoltaic industries is said to be over 30,000. Since this industry will continue growing. its employment wilt increase further. And therefore. the photovoltaic industries will no doubt make a big ro!e in the world and contribute to the society. CONCLUSON have explained in the above the current situations of photovoltaic generation industries and its subjects toward the next Giga-watt production phase. Followings are the summaries of this contribution: * Photovoltaic generation systems expand installations to all comers of the world. * Prices of photovoltaic generation systems continue going down. * Photovoltaic generation systems will become a competitive power generation source within Photovoltaic generation systems will make a key role in social contributions as a vital energy supply source and as an important industry. Lastly, SHARP Corporation has the challenging slogan of "Cover All the World Roofs with Solar Generation Svstems!" And here today would like to propose that all of us engaged in photovoltaic generation industries share this slogan. ' 10

5 Challenge of SHARP ACKNOWLEDGEMENT The author would like to thank Dr. Masafumi Yamaguchi. Professor of Toyota Technological nstitute for the opportunity of this contribution, and also thank Ms. K. Ogawa, Mr, H. Tanigawa and Mr. Y. lnoue for the data and discussions. REFERENCES [] The nstitute of Applied Energy (AE), Website ( [Z] SHARP Corporation estimates [3] D. Kray et al., COMPREHENSVE EXPERMENTAL STUDY ON THE PERFORMANCE OF VERY THN LASER-FRED HGH-EFFCENCY SOLAR CELLS-, Proceeding of 19th EU-PVSEC, Pans (2004) pp