- Email: [email protected]
Crystal gazing in photovoltaics
Solar Cells, 12 ( 1 9 8 4 ) 167 - 169
167
CRYSTAL GAZING IN PHOTOVOLTAICS
M O R T O N B. P R I N C E
Research and Development Branch, Photovoltaic Energy Technology Division, U.S. Department of Energy, 1000 Independence Avenue, Washington, DC (U.S.A.)
1. Background In response to our editor's request to speculate on what might be the future for photovoltaics, I thought it would be interesting to review where we have been in the past, where we are now, and then to project (extrapolate) where we may be in 10, 20 and 30 years from now. 30 years ago (late 1953) the first paper [1] on the modern !arge-area photovoltaic cell had n o t been published. The only semiconductor materials with reasonable transport properties were germanium and silicon. III-V materials [2] were just beginning to be studied. CdS [3] was also being studied for its optical properties. The diffusion process for forming largearea p - n junctions in silicon had just been developed [4]. 20 years ago (late 1963) silicon solar cells were available (and expensive) commercially from at least two significant suppliers with space (air mass 0) efficiencies of up to 14%. Most of the production was for space satellite p o w e r b u t solar-powered radios were available and a limited number of terrestrial applications were using photovoltaic cells. Work on III-V materials had progressed well and solid state lasers and special detectors were announced based on these materials. Thin film photovoltaic devices (CdS/Cu2S) were being studied, but the theoretical understanding of these was unknown. The process of ion implantation of impurities into silicon for junction formation had just been announced. Just 10 years ago (late 1973) the National Science Foundation held its historic Workshop on Photovoltaic Conversion o f Solar Energy for Terrestrial Applications (Cherry Hill, NJ) [5]. The o u t c o m e of this workshop initiated the present Federal Photovoltaic Program. By that time two commercial entities had been organized to pursue terrestrial application opportunities and approximately 20 kW was produced by photovoltaics that year for terrestrial applications. Single~rystal silicon was the only material being exploited commercially for photovoltaics although experimental work was being carried o u t on CdS/Cu2S, polycrystalline silicon and III-V materials. R i b b o n silicon was in its infancy, systems were just being analyzed and amorphous silicon was a physical curiosity. Concentrators were n o t even being considered. 0379-6787/84/$3.00
© Elsevier S e q u o i a / P r i n t e d in The N e t h e r l a n d s
168 Today a viable industry exists based on single-crystal and semicrystalline silicon that produces cells, modules and systems (including concentrators). Several companies (in Japan and in the U.S.A.) have commercial products based on amorphous silicon. This industry will probably produce a b o u t 15 MW of products this year (1983). Other thin film photovoltaic devices are nearing commercialization; concentrator systems are operating effectively; inverters suitable for connecting photovoltaic systems to utility grids are now available; significant funds are available (both private and federal) for research and development to reduce the cost of photovoltaics further and to make systems more reliable and more efficient. Warranties have increased from 1 year in 1975 to 5 (and even 10) years today.
2. The Future As pointed o u t above, developments in photovoltaics have been advancing extremely rapidly when looked at over 10 year periods. There is no reason to believe that this rate will slow down significantly in the future now that many laboratories and a large number of eminent investigators are pursuing exciting research and development relating to photovoltaics. Thus extrapolating the past, we might expect to see the following accomplishments in the next 10, 20 and 30 years. By 1993 we should have large automated factories producing wide silicon ribbon devices at approximately 10% of present costs (in 1983 U.S. dollars). The modules made from these cells will have conversion efficiencies of about 15% and the manufacturers will be giving 20 year warranties. Competing with these flat-plate modules will be concentrator modules with 20% efficiency using single-crystal silicon devices and with 25% efficiency using GaAs single-junction single-crystal cells. Amorphous silicon (both single-junction and multijunction) cells will be produced in automated factories with 12% efficient modules warranted for 10 years. Multijunction III-V devices will still be in the laboratory b u t techniques will have evolved that will permit two-junction cells to be produced with 30% efficiency almost routinely. Inverters for all sizes of applications will be available commercially and large structures for holding both fixed flat-plate and tracking flat-plate and concentrator modules will be produced at a quarter of the cost of present lowest cost subsystems. Federal support will no longer be needed since the industry will have matured and will be able to support the necessary research and development for improved future devices and systems. Sales will have passed the 2 GW year -1 level with the first utility-sized system (greater than 500 MW) installed and operating. By 2003, at least three thin film materials will be available commercially with greater than 15% efficient modules for the flat-plate systems. Concentrators will incorporate multijunction devices with overall efficiencies of greater than 32%. Systems costs will have dropped by a factor of 2 in 1983 U.S. dollars over the past 10 years and systems will be warranted for 30
169
years. Up to 5% of the electricity generating capacity of the U.S.A. will be based on photovoltaics. Photovoltaics systems will be produced in at least 20 individual countries and world-wide production will reach 20 GW year -~" By 2013 the crystal ball becomes fuzzy. Multilayer thin film modules will reach 22% efficiency and will cost no more on a square meter basis than the modules produced in 2003. Concentrators will be produced with 35% efficiency. Systems cost will be low enough to encourage p u m p e d water storage and compressed gas storage to be used by utilities. Thus, photovoltaics will start to be used for base load operation of utilities worldwide. Production will be up to over 100 GW year -1, and there will be no need for any additional nuclear fission generators or even coal-fired generators. (It is assumed that oil and gas generating systems will have been superseded long before this time.) Thus if we can extrapolate the past into the future (and there is no reason to believe that the technology will not continue to improve at the same rate), photovoltaics will become a significant part of the electricity generating capacity of the world in the next 30 - 50 years.
References 1 D. M. C h a p i n , C. S. F u l l e r a n d G. L. P e a r s o n , J. Appl. Phys., 25 ( 1 9 5 4 ) 676 - 677. 2 H. Welker, Physica, 20 ( 1 9 5 4 ) 8 9 3 - 909. 3 D. C. R e y n o l d s , G. Leies, L. L. A n t e s a n d R. E. M a r b u r g e r , Phys. Rev., 96 ( 1 9 5 4 ) 533 - 534. 4 C. S. Fuller a n d J. A. D i t z e n b e r g e r , J. Appl. Phys., 25 ( 1 9 5 4 ) 1 4 3 9 - 1 4 4 0 .
5 Proc. Workshop on Photovoltaic Conversion of Solar Energy for Terrestrial Applications, October 23- 25, 1973, in Rep. NSF-RANN-74-013, 1 9 7 4 ( N a t i o n a l Science Foundation-
R e s e a r c h A p p l i e d t o N a t i o n a l Needs).
167
CRYSTAL GAZING IN PHOTOVOLTAICS
M O R T O N B. P R I N C E
Research and Development Branch, Photovoltaic Energy Technology Division, U.S. Department of Energy, 1000 Independence Avenue, Washington, DC (U.S.A.)
1. Background In response to our editor's request to speculate on what might be the future for photovoltaics, I thought it would be interesting to review where we have been in the past, where we are now, and then to project (extrapolate) where we may be in 10, 20 and 30 years from now. 30 years ago (late 1953) the first paper [1] on the modern !arge-area photovoltaic cell had n o t been published. The only semiconductor materials with reasonable transport properties were germanium and silicon. III-V materials [2] were just beginning to be studied. CdS [3] was also being studied for its optical properties. The diffusion process for forming largearea p - n junctions in silicon had just been developed [4]. 20 years ago (late 1963) silicon solar cells were available (and expensive) commercially from at least two significant suppliers with space (air mass 0) efficiencies of up to 14%. Most of the production was for space satellite p o w e r b u t solar-powered radios were available and a limited number of terrestrial applications were using photovoltaic cells. Work on III-V materials had progressed well and solid state lasers and special detectors were announced based on these materials. Thin film photovoltaic devices (CdS/Cu2S) were being studied, but the theoretical understanding of these was unknown. The process of ion implantation of impurities into silicon for junction formation had just been announced. Just 10 years ago (late 1973) the National Science Foundation held its historic Workshop on Photovoltaic Conversion o f Solar Energy for Terrestrial Applications (Cherry Hill, NJ) [5]. The o u t c o m e of this workshop initiated the present Federal Photovoltaic Program. By that time two commercial entities had been organized to pursue terrestrial application opportunities and approximately 20 kW was produced by photovoltaics that year for terrestrial applications. Single~rystal silicon was the only material being exploited commercially for photovoltaics although experimental work was being carried o u t on CdS/Cu2S, polycrystalline silicon and III-V materials. R i b b o n silicon was in its infancy, systems were just being analyzed and amorphous silicon was a physical curiosity. Concentrators were n o t even being considered. 0379-6787/84/$3.00
© Elsevier S e q u o i a / P r i n t e d in The N e t h e r l a n d s
168 Today a viable industry exists based on single-crystal and semicrystalline silicon that produces cells, modules and systems (including concentrators). Several companies (in Japan and in the U.S.A.) have commercial products based on amorphous silicon. This industry will probably produce a b o u t 15 MW of products this year (1983). Other thin film photovoltaic devices are nearing commercialization; concentrator systems are operating effectively; inverters suitable for connecting photovoltaic systems to utility grids are now available; significant funds are available (both private and federal) for research and development to reduce the cost of photovoltaics further and to make systems more reliable and more efficient. Warranties have increased from 1 year in 1975 to 5 (and even 10) years today.
2. The Future As pointed o u t above, developments in photovoltaics have been advancing extremely rapidly when looked at over 10 year periods. There is no reason to believe that this rate will slow down significantly in the future now that many laboratories and a large number of eminent investigators are pursuing exciting research and development relating to photovoltaics. Thus extrapolating the past, we might expect to see the following accomplishments in the next 10, 20 and 30 years. By 1993 we should have large automated factories producing wide silicon ribbon devices at approximately 10% of present costs (in 1983 U.S. dollars). The modules made from these cells will have conversion efficiencies of about 15% and the manufacturers will be giving 20 year warranties. Competing with these flat-plate modules will be concentrator modules with 20% efficiency using single-crystal silicon devices and with 25% efficiency using GaAs single-junction single-crystal cells. Amorphous silicon (both single-junction and multijunction) cells will be produced in automated factories with 12% efficient modules warranted for 10 years. Multijunction III-V devices will still be in the laboratory b u t techniques will have evolved that will permit two-junction cells to be produced with 30% efficiency almost routinely. Inverters for all sizes of applications will be available commercially and large structures for holding both fixed flat-plate and tracking flat-plate and concentrator modules will be produced at a quarter of the cost of present lowest cost subsystems. Federal support will no longer be needed since the industry will have matured and will be able to support the necessary research and development for improved future devices and systems. Sales will have passed the 2 GW year -1 level with the first utility-sized system (greater than 500 MW) installed and operating. By 2003, at least three thin film materials will be available commercially with greater than 15% efficient modules for the flat-plate systems. Concentrators will incorporate multijunction devices with overall efficiencies of greater than 32%. Systems costs will have dropped by a factor of 2 in 1983 U.S. dollars over the past 10 years and systems will be warranted for 30
169
years. Up to 5% of the electricity generating capacity of the U.S.A. will be based on photovoltaics. Photovoltaics systems will be produced in at least 20 individual countries and world-wide production will reach 20 GW year -~" By 2013 the crystal ball becomes fuzzy. Multilayer thin film modules will reach 22% efficiency and will cost no more on a square meter basis than the modules produced in 2003. Concentrators will be produced with 35% efficiency. Systems cost will be low enough to encourage p u m p e d water storage and compressed gas storage to be used by utilities. Thus, photovoltaics will start to be used for base load operation of utilities worldwide. Production will be up to over 100 GW year -1, and there will be no need for any additional nuclear fission generators or even coal-fired generators. (It is assumed that oil and gas generating systems will have been superseded long before this time.) Thus if we can extrapolate the past into the future (and there is no reason to believe that the technology will not continue to improve at the same rate), photovoltaics will become a significant part of the electricity generating capacity of the world in the next 30 - 50 years.
References 1 D. M. C h a p i n , C. S. F u l l e r a n d G. L. P e a r s o n , J. Appl. Phys., 25 ( 1 9 5 4 ) 676 - 677. 2 H. Welker, Physica, 20 ( 1 9 5 4 ) 8 9 3 - 909. 3 D. C. R e y n o l d s , G. Leies, L. L. A n t e s a n d R. E. M a r b u r g e r , Phys. Rev., 96 ( 1 9 5 4 ) 533 - 534. 4 C. S. Fuller a n d J. A. D i t z e n b e r g e r , J. Appl. Phys., 25 ( 1 9 5 4 ) 1 4 3 9 - 1 4 4 0 .
5 Proc. Workshop on Photovoltaic Conversion of Solar Energy for Terrestrial Applications, October 23- 25, 1973, in Rep. NSF-RANN-74-013, 1 9 7 4 ( N a t i o n a l Science Foundation-
R e s e a r c h A p p l i e d t o N a t i o n a l Needs).