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The photovoltaic solar energy conference Luxembourg, 27-30 September, 1977
Journal of Power Sources, 2 ( 1 9 7 7 / 7 8 ) 297 - 299 © Elsevier S e q u o i a S.A., L a u s a n n e - - P r i n t e d in t h e N e t h e r l a n d s
297
Conference Report
The Photovoltaic Solar Energy Conference Luxembourg, 2 7 - 3 0 September, 1977 With solar cells at their present price of a b o u t $2000 per sq metre, the day when roof-top arrays will provide clean, silent electricity from the sun may seem a long way off. Nevertheless, this Conference, with 468 participants from 31 countries, testified to the growing world-wide interest in photovoltaic conversion and the extensive efforts being made in research, development, test and demonstration to make the cheap, mass-produced solar generator a reality. Opening the Conference, the first of its kind to be organised by the EEC Commission, Dr G. Schuster, the Commission's Director General for Research, Science and Education, said that the energy problem created a dramatic situation, which called for the rapid and vigorous development of alternative sources. He was sure that solar energy would find increased use in the future b u t strenuous efforts would be necessary if it was to make a significant contribution b y the turn of the century. Professor R. Chabbal, the Director General of CNRS, Paris, and Chairman of the Commission's Advisory Committee on Programme Management, listed R&D tasks in the photovoltaic field as follows: • Reduce cell cost from $2000 to $300 and eventually to $50 per sq metre. • Increase conversion efficiency. • Construct, test and demonstrate system prototypes. • Reduce cost of electrical storage. Since lower costs depend to a great extent on market growth (and vice versa), artificial stimulation of the market was most important in the initial stages. While the Conference did not bring to light any outstanding advances, it showed evidence of steady progress and gave participants a good overall picture of the present state of the art. The well-established single-crystal silicon cells are n o w available with conversion efficiencies of up to 13% in terrestrial sunlight. Hopes of a substantial cost reduction are chiefly centred on cheaper starting material. One approach is cast polysilicon, with which Fischer of AEG Telefunken and Lindmayer of Solarex claimed to have achieved 10% efficiency. Other ideas discussed were the reduction of waste in larger ingots (Lauvray of RTC), recrystallisation of CVD-grown polysilicon (Bezemer of the University of Utrecht), growing single crystal rods from the vapour phase (Franzosi of
298
Montedison) and pulling continuous polysilicon layers on carbon substrates (Belouet of LEP). All are in the early stages of development. Progress in optimising the thin-film cadmium sulphide cell, which is potentially cheaper than silicon and perhaps more adaptable to mass production, was reported b y Barnett of the University of Delaware. He claimed to have achieved 8.6% efficiency and confidently expected to reach 14% in a modified design based on cadmium-zinc sulphide. Another approach to the cheap solar cell which is attracting considerable attention is the Schottky barrier (metal/semiconductor) type. Lillington of RMCS Shrivenham said that he had achieved 9% efficiency with 1 cm ~ aluminium/single crystal silicon cells and 8.6% with similar cells made from Wacker polysilicon. Green of the University of New South Wales expected to reach 12% b y the end of the year with a variant called the 'MISIM' cell. Interesting new possibilities have been opened up b y work at the University of Dundee on amorphous silicon films prepared by R F glow discharge decomposition from doped silane. This material has optical absorption characteristics similar to direct band-gap semiconductors and so can be effective in very thin (1 to 2 gin) layers. Wilson of Heriot-Watt University, Edinburgh reported on the early stages of their programme to develop Schottky barrier devices with this material in collaboration with Dundee. Thompson of the University of Sheffield claimed that similar films could be produced by RF sputtering. The Conference showed particular interest in the possibilities of concentrated sunlight as a means of reducing the cost of photovoltaic generation. Here the prime candidate is the gallium arsenide cell which, because of its higher energy gap, performs better than silicon at high intensities and temperatures. Fabre of LEP reported an efficiency of 17.5% in cells grown by vapour phase epitaxy, a process potentially cheaper than the liquid phase epitaxy used in the original IBM cells. For medium concentrations, up to 50 suns, optimised silicon cells m a y prove more economical. Gibbons of Stanford University, one of a number of investigators in this area, claimed silicon efficiencies at 20 suns of 16.5% at 30 °(3 and over 10% at 100 °C. The most intriguing of a group of papers on concentrating devices was presented b y Mash of Standard Telecommunication Laboratories Harlow on his 'solar eyeball'. This is an hermetically-sealed plastic sphere containing a Fresnel lens and a gallium arsenide solar cell, which floats on water or other liquid and is kept pointed at the sun b y an ingenious magnetic/pneumatic control system. An important session was devoted to presentations of the photovoltaic R&D programmes of USA, Europe, Japan, Mexico and India. Magid of the US Energy Research and Development Agency disclosed that ERDA's forward plan, which has to be ratified by the new Department of Energy, envisaged the supply of 50 GW of electricity from solar cells by the year 2000. Intermediate targets are to cut the price of solar arrays to $1 - 2/W {peak) by 1980, 50 c/W b y 1986 and 10 - 30 c/W by 1990, with a concurrent increase in manufacturing capacity from 20 MW pa in 1980 to 10,000 MW pa in 1990. (A 'peak' watt is 1 watt in bright sunlight at an intensity of 1 kW/m 2. At 10%
299 conversion efficiency, 1 m 2 of solar cells is equivalent to 100 peak watts.) Spending in the current fiscal year, up to 1 October 1977, amounted to $51.9M, over half of which was on silicon development. In the past three years, silicon array costs had fallen by a factor of 5 and industry was beginning to invest risk capital in photovoltaics. In Magid's opinion, explosive growth of the market would begin when the price reached $1 - 2/W. Van Overstracten, speaking for the EEC Commission, said that photovoltaic conversion absorbed 32% of the total budget of 16.62 M units of account allocated for the 4-year solar energy programme. (1 unit of account = about $0.71 or £0.42 at current rates of exchange.) The EEC contributes only a maximum of 50% of the total cost of a project. The first phase of 18 months, due to end this year, had been devoted to a broad exploration of possible approaches, the funds being fairly evenly divided between single crystal silicon, poly and amorphous silicon and other materials. In the second phase more emphasis would be placed on module design, materials and manufacture, storage and p r o t o t y p e system demonstrations, while the most promising Phase 1 projects would receive continued support. In a panel discussion on the short-term market, Durand of LEP outlined various possible scenarios for future growth, including ERDA's. He t h o u g h t that, if one spoke in terms of true commercial price, ERDA's target date of 1980 to reach $1 - 2/W might prove to be too optimistic and he warned that new technology would be needed to go beyond this cost barrier. Polgar of Telediffusion de France listed the current market outlets as navigational aids, remote radio and microwave stations, TV repeaters, educational TV, warning and signalling systems, small scale water pumping in arid climates and a range of battery charging applications. From the practical experience of operating a number of solar-powered school TV sets in Niger over the past four years, he showed that the running cost of solar cells a m o u n t e d to less than half that of the alternative alkaline batteries. Among many other examples of solar cells in service, he mentioned water pumping installations and a 100 W array for a copper refining plant in the Chilean desert, which had been operating satisfactorily for the past 17 years. In the short term, he saw future markets for solar cells in remote village electrification, medium-scale irrigation schemes, mobile homes and drug conservation. Green of the University of NSW reported that Telecom Australia planned to start operating n e x t year a solar-powered telephone and TV microwave network spanning a large area of Australia. Each of the 13 repeater stations would be equipped with a 1 kW {peak) array. It was generally agreed that some market stimulation by Governments and international agencies was essential for the timely development of this socially
297
Conference Report
The Photovoltaic Solar Energy Conference Luxembourg, 2 7 - 3 0 September, 1977 With solar cells at their present price of a b o u t $2000 per sq metre, the day when roof-top arrays will provide clean, silent electricity from the sun may seem a long way off. Nevertheless, this Conference, with 468 participants from 31 countries, testified to the growing world-wide interest in photovoltaic conversion and the extensive efforts being made in research, development, test and demonstration to make the cheap, mass-produced solar generator a reality. Opening the Conference, the first of its kind to be organised by the EEC Commission, Dr G. Schuster, the Commission's Director General for Research, Science and Education, said that the energy problem created a dramatic situation, which called for the rapid and vigorous development of alternative sources. He was sure that solar energy would find increased use in the future b u t strenuous efforts would be necessary if it was to make a significant contribution b y the turn of the century. Professor R. Chabbal, the Director General of CNRS, Paris, and Chairman of the Commission's Advisory Committee on Programme Management, listed R&D tasks in the photovoltaic field as follows: • Reduce cell cost from $2000 to $300 and eventually to $50 per sq metre. • Increase conversion efficiency. • Construct, test and demonstrate system prototypes. • Reduce cost of electrical storage. Since lower costs depend to a great extent on market growth (and vice versa), artificial stimulation of the market was most important in the initial stages. While the Conference did not bring to light any outstanding advances, it showed evidence of steady progress and gave participants a good overall picture of the present state of the art. The well-established single-crystal silicon cells are n o w available with conversion efficiencies of up to 13% in terrestrial sunlight. Hopes of a substantial cost reduction are chiefly centred on cheaper starting material. One approach is cast polysilicon, with which Fischer of AEG Telefunken and Lindmayer of Solarex claimed to have achieved 10% efficiency. Other ideas discussed were the reduction of waste in larger ingots (Lauvray of RTC), recrystallisation of CVD-grown polysilicon (Bezemer of the University of Utrecht), growing single crystal rods from the vapour phase (Franzosi of
298
Montedison) and pulling continuous polysilicon layers on carbon substrates (Belouet of LEP). All are in the early stages of development. Progress in optimising the thin-film cadmium sulphide cell, which is potentially cheaper than silicon and perhaps more adaptable to mass production, was reported b y Barnett of the University of Delaware. He claimed to have achieved 8.6% efficiency and confidently expected to reach 14% in a modified design based on cadmium-zinc sulphide. Another approach to the cheap solar cell which is attracting considerable attention is the Schottky barrier (metal/semiconductor) type. Lillington of RMCS Shrivenham said that he had achieved 9% efficiency with 1 cm ~ aluminium/single crystal silicon cells and 8.6% with similar cells made from Wacker polysilicon. Green of the University of New South Wales expected to reach 12% b y the end of the year with a variant called the 'MISIM' cell. Interesting new possibilities have been opened up b y work at the University of Dundee on amorphous silicon films prepared by R F glow discharge decomposition from doped silane. This material has optical absorption characteristics similar to direct band-gap semiconductors and so can be effective in very thin (1 to 2 gin) layers. Wilson of Heriot-Watt University, Edinburgh reported on the early stages of their programme to develop Schottky barrier devices with this material in collaboration with Dundee. Thompson of the University of Sheffield claimed that similar films could be produced by RF sputtering. The Conference showed particular interest in the possibilities of concentrated sunlight as a means of reducing the cost of photovoltaic generation. Here the prime candidate is the gallium arsenide cell which, because of its higher energy gap, performs better than silicon at high intensities and temperatures. Fabre of LEP reported an efficiency of 17.5% in cells grown by vapour phase epitaxy, a process potentially cheaper than the liquid phase epitaxy used in the original IBM cells. For medium concentrations, up to 50 suns, optimised silicon cells m a y prove more economical. Gibbons of Stanford University, one of a number of investigators in this area, claimed silicon efficiencies at 20 suns of 16.5% at 30 °(3 and over 10% at 100 °C. The most intriguing of a group of papers on concentrating devices was presented b y Mash of Standard Telecommunication Laboratories Harlow on his 'solar eyeball'. This is an hermetically-sealed plastic sphere containing a Fresnel lens and a gallium arsenide solar cell, which floats on water or other liquid and is kept pointed at the sun b y an ingenious magnetic/pneumatic control system. An important session was devoted to presentations of the photovoltaic R&D programmes of USA, Europe, Japan, Mexico and India. Magid of the US Energy Research and Development Agency disclosed that ERDA's forward plan, which has to be ratified by the new Department of Energy, envisaged the supply of 50 GW of electricity from solar cells by the year 2000. Intermediate targets are to cut the price of solar arrays to $1 - 2/W {peak) by 1980, 50 c/W b y 1986 and 10 - 30 c/W by 1990, with a concurrent increase in manufacturing capacity from 20 MW pa in 1980 to 10,000 MW pa in 1990. (A 'peak' watt is 1 watt in bright sunlight at an intensity of 1 kW/m 2. At 10%
299 conversion efficiency, 1 m 2 of solar cells is equivalent to 100 peak watts.) Spending in the current fiscal year, up to 1 October 1977, amounted to $51.9M, over half of which was on silicon development. In the past three years, silicon array costs had fallen by a factor of 5 and industry was beginning to invest risk capital in photovoltaics. In Magid's opinion, explosive growth of the market would begin when the price reached $1 - 2/W. Van Overstracten, speaking for the EEC Commission, said that photovoltaic conversion absorbed 32% of the total budget of 16.62 M units of account allocated for the 4-year solar energy programme. (1 unit of account = about $0.71 or £0.42 at current rates of exchange.) The EEC contributes only a maximum of 50% of the total cost of a project. The first phase of 18 months, due to end this year, had been devoted to a broad exploration of possible approaches, the funds being fairly evenly divided between single crystal silicon, poly and amorphous silicon and other materials. In the second phase more emphasis would be placed on module design, materials and manufacture, storage and p r o t o t y p e system demonstrations, while the most promising Phase 1 projects would receive continued support. In a panel discussion on the short-term market, Durand of LEP outlined various possible scenarios for future growth, including ERDA's. He t h o u g h t that, if one spoke in terms of true commercial price, ERDA's target date of 1980 to reach $1 - 2/W might prove to be too optimistic and he warned that new technology would be needed to go beyond this cost barrier. Polgar of Telediffusion de France listed the current market outlets as navigational aids, remote radio and microwave stations, TV repeaters, educational TV, warning and signalling systems, small scale water pumping in arid climates and a range of battery charging applications. From the practical experience of operating a number of solar-powered school TV sets in Niger over the past four years, he showed that the running cost of solar cells a m o u n t e d to less than half that of the alternative alkaline batteries. Among many other examples of solar cells in service, he mentioned water pumping installations and a 100 W array for a copper refining plant in the Chilean desert, which had been operating satisfactorily for the past 17 years. In the short term, he saw future markets for solar cells in remote village electrification, medium-scale irrigation schemes, mobile homes and drug conservation. Green of the University of NSW reported that Telecom Australia planned to start operating n e x t year a solar-powered telephone and TV microwave network spanning a large area of Australia. Each of the 13 repeater stations would be equipped with a 1 kW {peak) array. It was generally agreed that some market stimulation by Governments and international agencies was essential for the timely development of this socially