Sunshine project in Japan - solar photovoltaic program

Solar Cells, 26 (1989) 87 - 96

87

SUNSHINE PROJECT IN JAPAN -- SOLAR PHOTOVOLTAIC PROGRAM KIYOSHI TAKAHASHI Tokyo Institute of Technology, Ohokayama, Meguro-ku, Tokyo (Japan)

1. Outline of the Sunshine Project in Japan In Japan, the so-called "Sunshine Project", which was organized by the Agency of Industrial Science and Technology in the Ministry of International Trade and Industry, was initiated in 1974. The research and development activities for the Sunshine Project are organized in five main areas as follows: solar energy; geothermal energy; coal energy; hydrogen energy; comprehensive research. Figure 1 shows the Sunshine Project long-term development schedule for major technology development projects. In its first five years of progress, the Sunshine Project has been pursued uniformly in the five main areas, generally by the research institutions affiliated to the Agency of Industrial Science and Technology as well as by academic sectors. The total annual budget, therefore, was only about 2400 million yen in 1974. In view of the experience gained from the second oil shock, the Ministry of International Trade and Industry implemented, in the fiscal year (FY) 1980, the "New Strategy to Accelerate the Promotion of the Sunshine Project", and gave particular priorities to the projects which were not only expected to become significant contributors to the future energy supply structure but which were also promising from the technological advancement and commercial point of view. These projects are photovoltaic power generation, coal liquefaction and gasification and the development of large-scale deep geothermal resources. Since then, the budgets have been sharply increased, and the annual budget amounted to 44 000 million yen in the fiscal year 1985. A summary of budgetary progress is shown in Fig. 2. The above-mentioned priority programs have been implemented by the semi-governmental corporation, the New Energy Development Organization (NEDO) which was established in October 1980, in accordance with the "Law for Advancing the Development and Introduction of the Energy Source Alternative to Oil". NEDO functions as a nucleus for promoting technological development of new energies, and mobilizing the technical expertise of both government and private sectors. Promoting the Sunshine Project, without any reduction in activities, even in the temporary tranquility of the world energy situation, is a vitally important policy of Japan. 0379-6787/89/$3.50

© Elsevier Sequoia/Printed in The Netherlands

88

E

~

E

~

w

li: i1~_v

~D

89

BI

tt

ii ii

N

II

.

II

II

II

ii

'* i1

~

t

II il II

iI

',;

~" !I

[i

N

E--------'I

II

t 3 ,,

~

"~ rl~

~

~•

tt

~

ZE

Ii

,it

1~

-

.C ii II

,,,,

o

Ii

'.-~ i o o~

~

i~

~

~ -:~

~:

-

~

~

=

90

50 Requesting

4O

"~ 30 T:=, -

20

I0

I

II/

0

1974 1975 1976 1977

1978

1979

1980 1981 1982

77J

1983 1984

//

il i 'li~,

I~/ I,,

1985

1986

I

L,;,;;', p?,;, ~,',d 1987 1988 1989

FY Fig. 2. Budgetary allowances for the Sunshine Project (shaded parts represent amount spent on solar energy). 2. Solar energy program

Activities associated with solar energy research and development in the Sunshine Project focus on the following three sub-programs as shown in Fig. 1 : solar photovoltaic power generation; solar heating and cooling system; solar thermal power generation system. Figure 2 (shaded parts) also illustrates the budgetary progress for solar energy technology.

3. Solar cell production system This part of the program has as a principal goal the reduction of the cost of solar cells and an increase in their conversion efficiency. This program consists of the following three sub-programs as shown in Fig. 3: manufacturing technology of crystalline solar cells; manufacturing technology of high efficiency new t y p e solar cells; manufacturing technology of amorphous solar cells. The program concerning the high efficiency new t y p e solar cells, will be initiated in the fiscal year 1989. 3.1. Crystalline solar cells A pilot plant for the low-cost production of crystalline silicon solar cells was completed in the fiscal year 1983. It is capable of producing 500 kW year -I of crystalline silicon solar modules by a continuous operation

91

o /

o=

Ii.

1 i I l

~

NOI~VnlvA'~

o

w m

J

"

I I

NOX,T.VnlVA3

3

NOIZ¥flIVA3

NOIIVfilVA~

8

" m o

-

LI

m

~ ~

,LWlV^3

~OIIVnlVA~

l:l

!= 0

3 o

1¥I~J, VN

IV

l.l: 0

1130 HVIOS 3NIllVlS~IIO

N IXz

]lflaON

1123 ~13A¥'1 1']33 ~1

UOIONII;)3,I 113:) lOS SnOHd~ONV

92 using the following processes: production of solar grade silicon (SOG) from metallurgical silicon; fabrication of silicon sheet by the casting and/or slicing method and ribbon growth process; cell fabrication b y automatic p - n junction formation; automated panel assembling. Operational research has been under way to establish highly efficient and low-cost manufacturing technologies. This project is expected to make a significant contribution to the reduction of the production cost of polycrystalline silicon solar cells. As for the p - n junction formation process, two technologies are under research: the dry process and the wet process. The dry process uses ion implantation and electroless plating. To lower the production cost on a larger scale, a new high-current ion implanter was developed with a coaxial microwave ion source, an ion-beam scanning magnet and a specially designed process chamber. Solar cells were fabricated b y means of this implanter and a conversion efficiency of over 13% was obtained using semiconductor grade Czochralski wafers. The wet process uses painting and printing techniques. A c o m p o u n d painting solution containing diffusion dopant is prepared so that the p - n junction and antireflection coating are formed at the same time during the heat treatment of the silicon substrate paint. A screen printing technique is applied to replace the conventional electrode forming method. This process enables a fast, straight-forward automatic cell fabrication process to be used. A conversion efficiency of 15.3% was obtained using semiconductor grade Czochralski wafers.

3.2. Amorphous solar cells The research and development of amorphous solar cells has been undertaken in close cooperation with national research institutes, universities and private sector research organizations since the fiscal year 1980. The research and development for amorphous solar cells is shown in Fig. 4. This research and development program was slightly changed in 1985, and since 1986 the research and development of amorphous solar cells has concentrated on the following: the improvement of conversion efficiency and stability b y employing technologies such as impurity control, superlattice, multilayer structures {tandem structure) with amorphous silicon alloys, and alternative material deposition methods including photo- and laser chemical vapour deposition; continued experimental fabrication of amorphous solar cells by employing technologies such as high deposition rate and large-area deposition techniques; low cost transparent conductive film manufacturing technology. At present, a conversion efficiency of 11.7% for small-area (1 cm × 1 cm) and 8.6% for large-area (30 cm X 40 cm) cells has been achieved. The development of production techniques for power generating amorphous solar cells was started from the fiscal year 1984 as part of the research and development goal to establish practical application techniques

93 (hsl¢ (PhySiCal Property

Study)

Study) {tpp[ l c l t l o n

I

study o . P r a c t i c a l ^pplt~tL~l o f LOW-Colt ~o~lilene P r u d u c t I o n

s t u d y on l o ¢ 1 1 l t f l c t U r l of l - s t

~elearc~ a M OeveLOpltnt on P z o e ~ c ¢ i o a T e c h n i q u e I t H i g h ~ t e D e p o s i t i o n . by ~ w HeCI~IaXI

T~IxI/qU| study o! Etect~nLc Opttcsl

e n d O~co-

iL~mnLc

Pm~£+ls

Hethod o f S o l a r

Cells • -$L by c o l ~ . t e z ~ e ~ ~Lmu~i~Lon

s t u d y on 0 e { e c t sc~tn

2. B i l i c S t u d y on #aorphoue ? b i n - F i l m Sol*r c~.

F

|meeurch and Devudops~t

StUdy of P = a c t l c e t

~ e l c ~tudy o f a-sL Solar Cells

1. Study on H e a e u r e lent ~d ~il~ttOl,

T App~.Lcatlon S t u d y )

tPractL~l

Study}

©

Appl£catlon of H l ¢.~t~lLty p r o d u c t i o n Ys¢l~tlque

g

h

[

on ~ t g h A e I L * b L i L t y o2 a-S/. Solar Cell

n e s e l z c h and n e v e t o p i M c

R u l a E c h and D t V l l O p n ~ t of Ulgh [ f l L c t e n c y s o l e r C e l l s t~/ng Hey /morphous

on

High l e l i l b L l l t y T~h~que by N a t e r l * l Development ~nd /Other| /

Materials

Study on P r a c t i c a l A p p l i c a t i o n o f p a r t i c u l m r s~nltrate [Clrgmlc So,it.lie} Ceil

IlLgh Pezfomence T z l n l *

pirlnt C o n d u c t i v e OxZde

pzlxiuctJ.on Technlq.4

C~iCLnQ Oa GIllS $ ~ 0 l t r l t e l Studies o~

ZntlrtlCl *-Sl

S t u d y on P r & c t i { l l A p p l i c a t i o n o! Pa~lcular Substrate

Study on A p p l i c a t i o n o f La[ge A~ea SOIIr C e l l product Ion Technique study

(FleXible | o ~ e t z a t t ) C e l l Technlq.e

P~UCtI~

an ~ev SL-kl~

~lor~houl H l t l { i l l l r Survey a M s t u d y on p z l c c t c a t

fortllgh/morpho~Pr°ductivitYSolarT~hn°l°gYCelll I application analysis Study ~

PhOtO-CYD rLlm

HICMnA~ ~d

Pl13pl~ttll

................... tII

--

(EvaZuation System Study)

o~ High ~ t e Film OeposLt£on ~ Othlzl ~[

"Research i ~ D e l l O ~ l N t 0~ fl ~ l t ~ ~oz ~voLtiL~ C e i l s i n d Module_e"

Fig. 4. Research and development program for amorphous solarcells.

,,

+

for photovoltaic power generation systems. The four points in the development are high quality, large area, high efficiency, and low-cost monosilane production techniques. Since the progress of techniques in the field of amorphous solar cellsis very rapid, domestic and overseas technical tendencies are reflected in the aims and directions of the development of power generating amorphous solar cells in the above four key fields. For this purpose, domestic and overseas technical developments of amorphous solar cellswill be surveyed and the costs and energy requirements of fabricating amorphous solar cells will be analyzed in parallel with the development of cellproduction techniques. 3. 3. High efficiency new type solar cells The research and development of high efficiency new type solar cells will be initiated in the fiscal year 1989. This program includes high efficiency thin layer crystalline solar cells, amorphous/polycrystalline tandem structure solar cells, and a m o r p h o u s / c o m p o u n d tandem structure solar cells. 4. Achievements and milestones for solar cells Table I shows the achievements at present (July, 1988), and the milestones aimed for in the fiscal year 1992 for conversion efficiencies of solar cells.

94 TABLE 1 Present conversion efficiencies and those aimed for in 1992 Ite m

Efficiency achieved (July, 1988)

Target efficiency (1992)

Single-crystal Polycrystalline

20.5 (2 x 2 cm 2) 15.3

23 (2 X2 cm 2) 18 (10 × 10 cm 2 ) 17 ( 1 5 X 1 5 c m 2)

Amorphous

11.7 (1 X l em 2) 9.5 (10 X 10 cm 2) 8.6 (30 X40 cm 2)

13 (lXl cm2) 12 (10X10cm2) 10 (30 X40 cm2)

(%)

Amorphous/polycrystalline Amorphous/compound

(%)

14 (10 X 10 cm 2) 13 (30 × 40 cm 2)

5. Photovoltaic power generating systems As part of Japan's Sunshine Project, the research and development of photovoltaic power generating systems is continuing in parallel with the development of low-cost high-efficiency solar cells, so that power generated by photovoltaic systems, that is photovoltaic output, will reach the same level as that of the existing system in every respect. The contents of these activities are shown in Table 2, and the objectives of these activities are shown below.

Research and development of on-site systems. The objectives are to develop system configurations suitable for various loads. Research and development of stand-alone systems. The objectives are to develop system configurations suitable for photovoltaic systems unconnected to an existing grid. TABLE 2 Present activities in solar energy research and development Items On-site systems Private houses

Collective houses

Contents To study the photovoltaic system suitable to private h o u s e s containing one household by operating the 3 kW system installed in 1982 To study a photovoltaic system suitable for collective houses containing many households by operating a 2 0 kW .system installed in the fiscal year 1 9 8 2 (continued)

95 TABLE 2 (continued)

Items

Contents

Factories

To study a photovoltaic system suitable for industrial use, /.e. in factories by operating a 100 kW system installed in the fiscal year 1983

Schools

To study a photovoltaic system suitable for public buildings such as schools by operating a 200 kW system installed in the fiscal year 1984

Stand-alone systems R e m o t e areas in mountains

Power supply for isolated islands

Desalination for isolated islands

Marine use

To study a photovoltaic system in mountains isolated from an existing grid by operating a 5 kW system with a small fuel cell as backup equipment installed in the fiscal year 1984 To study a photovoltaic system in islands isolated from an existing grid by supplying electric power to 14 households operating a 50 kW system with diesel generators as backup equipment installed in the fiscal year 1985 To study a desalination system by photovoltaic energy as one of the systems suitable for various characteristic loads, by operating a 25 kW system installed in the fiscal year 1985 To study a system using photovoltaic energy as one of the systems suitable for various characteristic loads, which supplies power to marine loads, by operating a 10 kW system installed in the firscal year 1985

Hybrid system with a woodburning power generator

To study a photovoltaic system combined with other conservative energy to supply electric power stably in remote areas isolated from an existing grid, by operating a 5 kW system with a wood-burning power generator installed in the fiscal year 1985

Hybrid system with a methane gas power generator

To study a photovoltaic system combined with other conservative energy to supply electric power stably in remote areas isolated from an existing grid, by operating a 5 kW system with a methane gas power generator installed in the fiscal year 1985

Centralized p o w e r systems Dispersed power supply system

To study the operation method as a power plant when photovoltaic systems are dispersed at a distance, which will be installed in urban areas, by operating a total 200 kW system in the fiscal year 1984

Centralized power supply system

To study the operation method as a power plant when photovoltaic arrays are set up at the same place, which will be installed in rural areas, by operating a 1000 kW system in the fiscal year 1986

Photovoltaic/solar thermal hybrid systems System with concentrated arrays System with fiat-plate arrays

To study high efficiency hybrid systems To study low cost hybrid systems

96 R e s e a r c h a n d d e v e l o p m e n t o f c e n t r a l i z e d p o w e r s y s t e m s . The objectives are to develop system configurations suitable for photovoltaic systems as power plants. Research and development of photovoltaic and solar thermal hybrid s y s t e m s . The objectives are to develop system configurations able to utilize

b o t h photovoltaic and solar thermal energy efficiently. 6. International cooperation for solar energy research and development In addition to the above, international programs including multilateral cooperation and bilateral cooperation are actively to be pursued. The following activities are to be continued from those of the preceding year. Japan-Australia cooperation in the evaluation and field testing of solar cells, as well as in the design of photovoltaic systems for remote areas in Australia. Japan-U.S.A. cooperation involving exchanges of professionals for technical study and information gathering. Multilateral cooperation in the solar energy research and development administered b y the International Energy Agency. Multilateral cooperation in the solar photovoltaic power activity through the Summit Working Group. 7. Conclusion The solar cell production in Japan stood at a b o u t 5000 kW in 1983, and amounted to 12 500 kW (amorphous solar cells, 9000 kW) in 1986. Most of the cells are used in consumer appliances such as calculators, watches, radios and toys. If the research and development of solar cells prove successful, solar cells will be used in large-scale power generation and the solar cell production is estimated to rise to at least a b o u t 100 MW by the end of this century. Acknowledgement The author would like to express appreciation to Mr. T. Kobayashi, Headquarters of Sunshine Project Promotion in the Ministry of International Trade and Industry, for his permission to release the information contained in this paper from the following references [1, 2] and for his helpful advice. References 1 T. Mukai, Tech. Dig. 1st Int. Photovoltaic Science and Engineering Conf., Kobe, 1984, p. 3. 2 Sunshine News, 14 - 15 (1986), 16 - 17 (1987), 18 (1987), Japan Industrial Technol-

ogy Association.