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1

List of Content

Message from MBIPV Project Team 2

About Us 4

The Way Forward 5

History of Photovoltaics 6

Introduction to PV Technology and Functionality 9

Value Chain and Manufacturing Process (c-Si) 19

Value Chain and Manufacturing Process (Thin Film) 27

Malaysia; a Profit Center for Global Manufacturing 33

PV Industry and Market Development 35

PV Policy in Malaysia (August 2009) 45

Global and Local PV Manufacturing 50

Update on SURIA1000 55

MBIPV NewsBite 58

PV Industry Outlook 60

The Last Word - Realigning The Photovoltaic Industry 64

Malaysia PV Industry Directory 69

Facts and Figures 78

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2 P V I nd us tr y H an db oo k 2 00 9

In 2008, our years theme was SURIA1000 in Bloom.

The SURIA1000 program is certainly blooming and creating

new business opportunities for the local PV industry. Today,

our local players understand how to further explore the local

and global businesses alongthe photovoltaic (PV) value chain.

At the same time, our team will continue with our efforts in

2009 and2010 to support your interest andvision to be part

of the booming PV businesses.

Solar energy (photovoltaic, concentrating PV, and

concentratingsolar power) is projected to supply 30% of the

worlds energy demand by 2050, and create an industry far

bigger than the global automotive industry. As with all energy

technologies, early introduction requires a supportive policy

mechanism for the technologies to grow and bring benefits

to human kind. Driven by oil prices volatility and globalwarming

concerns, many Governments are forced to revise their

energy policy to incorporate green energy technology.It is a proven fact that thebest policy to promote PV (and

renewable energies) growth is the Feed-in Tariff (FiT)

mechanism, paying a guaranteed premium rate over a long

term, e.g. 21 years for the generated renewable electricity. It

is high noon for Malaysia to also introduce such a policy,

which would create a new industry and thousands of

sustainable new jobs.

For the PV industry, the race is to first achieve grid parity

with the most cost-effective products, and to then dominate

the markets. With significant production cost reductions and

escalating fossilfuel cost, it will nottake long beforegrid parity

is achievedin several countriesin Europe (Italy, Spain, France),

Japan and a few states in the USA (California, Hawaii).

Once thegrid-parity is achieved,PV marketwillsky rocket and

create an exploding industry, e.g. utility PV power plants and

residential PV power applications, and niche markets, such

as consumer products, non-building structures and many

more. In the meantime, the PV market will continue to record

fantastic growth thanks to Feed-in Tariff (FiT) programs in

Germany, France, Italy, Greece, etc. and other supportive PV

programs in the USA, China and Japan.

The futureof solar energy certainly looks bright. Different

reports from globalleading banks (e.g. CreditSuisse, Morgan& Stanley and others) and leading consulting companies and

publishers (e.g. Navigant Consulting, Frost & Sullivan and

Photon International) paint a very bright perspective, and

forecast a yearly growth of 40% to 50% until 2010, and

subsequently 20% to 25% annually until 2020.

Recognising the opportunity, the YAB Prime Minister of

Malaysia launched the Third Industrial Master Plan (2006-

2020) on 18th August 2006, where solar PV is identified as

one of the focused technologies. Through the Malaysia

Building Integrated Photovoltaics (MBIPV) Project, Malaysia

is building the right infrastructure to create a sustainable PV

market, and a strong local PV industry. The emphasis towards

local industry is to enhance the service quality and establish

successfulPV manufacturers.To achieve these goals, MBIPV

Project is continuously working with the local stakeholders to

develop new business opportunities and enhance local

manufacturing capabilities.

To date, four leading global PV enterprises (First Solar,

Sunpower, Q-Cells and Tokuyama) are now in Malaysia fortheir production facilities. Their collectiv e foreign direct

investments(FDIs) areequivalent to RM 14 billion andcreate

Message from

The MBIPV Project Team

Salam Sejahtera - Greetings

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3P V I n d u st r y H a n d b o ok 2 0 0 9

10,000 high skilled jobs. These multi-national companies

(MNCs) are offering an attractive next-door business

environment and the local industries can benefit from these

needs, such as the construction, logistic, materials supply,

recycling and many more.

We are working closely with the Malaysian Industrial

Development Authority (MIDA) to encourage international PV

manufacturers to select Malaysia as the preferred location

for their manufacturing facilities. Malaysia, with its well

educateduniversity graduates and skilled employees fromthe

semi-conductor and electronic industry, offers a conducive

environment for PV manufacturing. The PV industry has the

potential to grow in Malaysiaand ultimatelybecome one of the

new sources of economic growth for the nation. With a

focused national PV industry development program, Malaysia

canbecome oneof thetop five PV manufacturing countries in

the world and the established local PV industry can contributeup to 4% to the national GDP by 2020, with revenues

exceeding RM 500 billion.

In trying to be part of the PV industry, it is crucial to

understand the market and technology development, as well

as own capabilities and the financial requirements.

Competency in quality manufacturing, good international

networking and excellent understanding of the worldwide PV

market are a must before entering and growing your PV

business as a profitable venture.

We look forward to seeing you at one of our PV events,

and support and help you to explore new business

opportunities or to diversify your existing business into PV

industry. This handbook on PV technology and market will

hopefully provide you with valuable information as well as

answers to your manyquestions. In any case, please feelfree

to contact us should you require further information or

guidance.

Sincerely,

The MBIPV Project Team

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The Malaysia Building Integrated Photovoltaics (MBIPV)

Project is a national initiative by the Government of Malaysia

with co-financing from the Global Environment Facility (GEF)

whose fund is disbursed through the United Nations

Development Programme (UNDP). MBIPV Project is

implemented under the 9th Malaysia Plan (9MP) to promote

widespread and sustainable use of PV in buildings. The Project

was officially launched on 25 July 2005 and will last for five

years, until end of 2010.

TheMBIPV Projects objective is to reduce the long term

cost of BIPV technology in Malaysia. This is achieved through

the widespread implementation of BIPV applications and

creation of environmental andindustrialpolicyin Malaysia. The

project will establish the desired environment fora long-term

market development and set a target for a follow-up BIPV

programme in the 10th Malaysia Plan.

The project aims to achieve its objectives by:

- Developing and implementing strong financing mechanisms,

solid institutional and policy frameworks.

- Extensive education and capacity building campaigns to

generate awareness and improve local competency.

- Introduction of standards and guidelines, developing and

enhancing the market.

- Upgrading the local industry towards local manufacturing.

The MBIPV Project will induce an increase of BIPV

applications by about 330% with a cost reduction of 20% by

the year 2010. Subsequently, its success can be replicated

in neighbouring countries and thus have a significant input on

the overall reduction of GHG emissions.

For information on the MBIPV Project, please visit

www.mbipv.net.my.

The MBIPV Project is implemented by Pusat Tenaga

Malaysia (PTM), a non-profit company administered by the

Ministry of Energy, Green Technology and Water. PTM

functions as a one-stop centre and implementing agency on

national energy related matters.

Contact

Pusat Tenaga Malaysia (462237-T)

No. 2, Jalan 9/10Persiaran Usahawan, Seksyen 9

43650 Bandar Baru Bangi

Selangor Darul Ehsan, Malaysia

Tel: +603 8921 0800

Fax: +603 8921 0911

Website: www.mbipv.net.my

Date of print

September 2009

Editor : Daniel RuossAuthors : Daniel Ruoss, Gladys Mak, Wei Nee Chen, Nor Radhiha Mohd Ali, MIDA, Jennifer LeClaire, Power Advocate

Designer : Kawan Kreatif (M) Sdn BhdUnit 816, Block B, Kelana Square, No. 17, Jalan ss7/26, 47301 Kelana Jaya, Petaling Jaya, Selangor

Printer : Percetakan Skyline Sdn BhdNo. 35 & 37, Jalan 12/32B, TSI Business Industrial Park,Batu 61/2 Off Jalan Kepong, 52100 Kuala Lumpur


MBIPV

(2005 - 2010)Objective: To reduce GHG emissions

by reducing long term costof BIPV technology

Project cost US$25 Million(Co-nanciers: GoM, GEF,

Industry, Public)

Component 1:

Information services,

awarenessand capacity

building program

Component 2:

Market enhancement

and infrastructure

development

program

Component 3:

Policiesandnancing

mechanismprogram

Component 4:

Industry development

and technology

localisationprogram

PostMBIPV:Sustainable & widespread

BIPV applications,

National BIPV program

with 30% annual

BIPV growth

About Us

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The Way Forward

One of the key initiatives under the MBIPV project is the

Photovoltaic Business Development Program, which has as

an objective to improve the local capabilities to venture into

the PV business and compete in the global marketplace. The

program features different activities, such as newsletters,

business plan development, consulting along the PV value

chain and guided industry mission to selected PV conferences

and exhibitions.It has been organized successfully since 2006

through the PV industry missions to Bangkok, Singapore,

Shenzhen, Shanghai and Valencia, as well as arranging

business meetings and factory visits during the missions.

Based onthe feedback from thedelegates from the2008

industry missions, the activitiesprovidedexposure of the local

industry to international PV business and acted as an

excellent door-opener to networks, contracts as well as

capacity building. The missions providedfinancial incentive andsupport to the participants by providing information,

arranging networking as well as site visits to the BIPV

installations. As such for 2009, several industry missions

have been planned and the first mission was the industry

mission to Solarcon Singapore2009 from 20th to 22nd May

2009.

The MBIPV team under the Industry Mission Program

brought ten delegates from nine companies to the Solarcon

2009 to expose them to the latest information in the PV

industry and products. Besides visiting the 120 booths, the

delegates participated in theSolarPV Conference andvisited

the Solar Energy Research Institute of Singapore (SERIS). The

highlight of the mission was a site visit to several BIPV

installations in Singapore arranged by the local system

integrator, Grenzone PteLtd. One of the site visits was to the

Temple of Thanksgiving or also known as Poh Ern Shih which

is located on a small hilltop on Singapores southern coast.

This mission provided new exposure on PV industry

development in the ASEAN region, as well as creating newPV

businesses for some delegates.

The local PV industry needs to understand the global PV

business to be able to move forward in the PV industry. Thus,

a critical success factor is to follow the learning curve which

reflectsthe local industries capabilitiesand theglobal market

development. Today,the local market itself is not sufficient to

enhance the local expertise. Therefore, it is crucial to learn

from international examples andone thebest ways to learn is

by participating in industry missions and attending exhibitions

and conferences. The missionsoffer excellent opportunities to

network, match-make andget thelatestproduct andindustry

information.

As such, the local industry needs to look beyond the local

market by exposing themselvesto the globalPV business and

gain knowledge, experience and the latest market

developments in order to develop or adjust their business

strategies. To manage the development and growth

successfully,a comprehensive nationalstrategy and roadmap

is essential, encompassing human resources development,

supply chain security build-up, product and technologyroadmap, R&D enhancement, know-how transfer and

partnerships establishment.

This is The Way Forward for Malaysia and if local

stakeholders act in a coordinated approach, collaborate and

learn from thepast andinternational examples,Malaysiacan

create a world-class industry serving the global PV business

and create a better future for Malaysia. Malaysia will benefit

from the industry development and develops into a high-tech

industry benefiting hugely the local industry and creating

thousands of new jobs.

The Malaysian Delegates in front of The Temple of Thanksgiving with a 18.9 kWp BIPV system

Malaysian Delegates during a PV factory visitto Renesola in China

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The term "photovoltaic" comes from the Greek word

(phos) meaning "light", and "voltaic",meaning electrical,

from the name of the Italian physicist Volta,after whom a unit

of electrical potential, the volt, is named. The term "photo-

voltaic" has been in use since 1849.

The photovoltaic effect was first recognised in 1839 by

nineteen-year old French physicist Alexander Edmond

Becquerel. However, it was not until 1883 that the first solar

cellwas built, by Charles Fritts, who coated the semiconductor

selenium with an extremely thin layer of gold to form the

junctions. The device only managed to achieve an efficiency

of around 1%. Edward Weston received the first US patent

for solar cell in 1888and NikolaTesla received a US patent

for the utilisation of radiant energy in 1901. Albert Einstein

also made his mark in photovoltaics when he won the Nobel

Prize for the mathematical explanation of the photovoltaiceffect in 1922.

The modern age of solar power technology arrived in

1954 when Bell Laboratories, experimenting with

semiconductors, accidentally found that silicon doped with

certain impurities was very sensitive to light. This resulted in

the production of the first practical solar cells with a sunlight

energy conversion efficiency of around 4% (see figure 1).

The first spacecraft to use solar panels was the US

satellite Vanguard 1 (see figure 2), launched in March 1958

with solar cells made by Hoffman Electronics. This milestone

created interest in producing and launching a geostationary

communicationssatellite, in which solar energy would provide

a viable power supply. This was a crucial development which

stimulated funding from several governments into research

for improved solar cells and reducing cost. Research drove

PV costs down as much as 80%, allowing for applicationssuch as offshore navigation warning lights, lighthouses,

railroad crossings, and remote use where utility-grid

connections were not physically possible or too costly.

Followingthe oilcrisis in 1973 theinterest fordevelopment

of PV for terrestrial applicationsincreased and the firstpower

applications emerged in the deserts in the United States of

America. New companies (e.g. Solarex Corp, merged later

into BP Solar) were founded and started production of PV

modules.

In 1974, Japan formulated the Project Sunshine to fuel

the local PV research and development to become a global

leader in PV technology. Continued improvements in efficiency

and cost reductions enabled PV to become a popular power

source forconsumer electronic devices, such as calculators,

watches, radios, lanterns and other small battery chargingapplications. Consumer applications, off-grid power systems

and a few large-scale PV power stations dominated the early

markets until 1990, when decentralised PV power systems

on buildings started to emerge. The first grid-connected PV

residential systems were installed in the USA and Switzerland

in 1980-1982, marking the start of a new era for PV to

become an independent power source as an alternative to

fossil fuels.

History of Photovoltaics

Figure 1: Bell Lab Solar Battery (Courtesy: NREL)

Figure 3: 1st Tour de Sol 1987(1st Solar Challenge in Switzerland)

Figure 2: Satellite Vanguard 1 (Courtesy: NREL)

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In 1987, the first solar PV car challenge started in

Switzerland and attracted a huge and excited crowd. Twenty-

two years later, 60 teams from around the globe competed

in the Panasonic World Solar Challenge in a race over 3,000

kilometers across the desert in Australia.

Germany and Japan initiated substantial subsidy

programs to encouragethe adoption of distributed PV power

generation at the user end. In 1990, Germany launched the

100,000 Solar Roof Top program and in 1994 Japan

began the 70,000 Solar Roof Top program. These

schemes achieved some success in exceeding the stated

targets but not as much as was desired.

The turning point in the commercial development of PV

technology was in 1999/2000, when Germany implemented

the EEG (Renewable Energy Act), introducing the Feed-in Tariff

(FiT) scheme, which today has been successfully adopted by

more than 50 countries (or states/regions) worldwide. The

FiTmechanism kick-startedthe widespread adoption of PV as

a local power generating source and created an explosive

demand growth in the globalmarketwith Germanyemerging

as a market leader in terms of applications and also

production. Japan continued with its capital subsidy program

that resulted in steady growth in installed PV capacity. Spain

and South Korea followed the German example and

implemented the FiT scheme in 2004 and created new

blooming (or more precise booming) markets. Italy, Greece,

France and other countries have followed recently and

contribute to a growing market demand, exceeding 30% per

annum over the last 8 years and driving the cost for the

products down.

To date, theindustryhas achieved cost reductionof about97% since the first PV system by Bell Lab in 1954, and the

commercial solar cell efficiency for crystalline PV technology

has been improved from 4% to 22%. Note that these are

commercially available cell efficiencies while in laboratory

conditions the results achieved are much higher. See figure

77 for the development of solar cells for the different

technologies reported from global research institutes.

The currentworld record in solar cell efficiency is 41.1%,

set by scientistsat the German Fraunhofer Institute for Solar

Energy Systems ISE (figure 5). The metamorphic triple-

junction solar cell was designed, fabricated and independently

measuredat Fraunhofer ISE.The record 41.1% efficiency was

measured under concentrated light of 454 suns. One sun is

about the amount of light that typically hits earth on a sunny

day. The new cell is a natural candidate for the space satellite

market and for terrestrial concentrated photovoltaic arrays,

which use lenses or mirrors to focus sunlight onto the solar

cells.

Figure 4: Typical residential PV application from the 100,000 Solar Roof Top program in Germany

Figure 5: World record solar cell atFraunhofer ISE in Germany

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Higher efficiencies and innovative manufacturing

processes (e.g. ink-jet printing, large area PECVD, organic

and nanotechnology structures) will drive costs down further

and bring PV generated electricity cost closer to grid-parity

year-by -year. Grid-parity will be achiev ed in the various

markets at different times. When grid-parity is achieved; the

market demand will sky-rocket and PV will reach a crucial

milestone in being competitive with conventional energy

production. This will open the door to a new era, in which PV

will become one of the key components for future energy

planning and large-scale deployment of PV (such as in

figure 6).

History of Photovoltaics

Figure 6: Large-scale PV power utility plant (Courtesy: Sunpower)

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PHOTOVOLTAIC EFFECT

Photovoltaic (PV) modules generate electricity when they

are exposed to sunlight. The photovoltaic effect is the basic

physical process through which a PV cell converts sunlight

into electricity. Sunlight is composed of photons, or packets

of solar energy. These photons contain different amounts of

energy corresponding to the different wavelengths of the

solar spectrum.

PV cells are made from solar grade silicon that is treated

with negatively and positively charged semi-conductors,

Phosphorous and Boron through a process called doping.

When photons strike a PV cell, they may be reflected or

absorbed, or they may pass right through. When a photon is

absorbedit excites theelectrons withinthe cell andthe energy

of the photon is transferred to an electron in an atom of the

cell. With itsnewfound energy, the electron is able to escape

from itsnormal positionassociatedwith that atom to become

part of thecurrentin anelectrical circuit.Thisflowof electrons

(current)from the negative semi-conductor (Phosphorous)to

the positive semi-conductor (Boron) is what we call the

photovoltaic effect. By leaving this position, the electron

causes a hole to form and is able to recuperate again, thus

forming a continuous process to generate electricity.

The generated current, together with the cell's voltage

(which is a result of its built-in electric field thanks to the P-N

junction), defines the power (or wattage) that the solar cell

can produce and drive the current through an external

electrical load.

GENERATION OF SOLAR CELLS

Solar cells are classified into three generations which indicate the order in which each became prominent. At present

there is concurrent research into all three generations. However the first generation technology is most highly represented

in commercial production and the most developed technology for more than 30 years.

Introduction to PV Technology and Functionality

1stGen

2ndGen

3rdGen

Silicon Wafer

III - V Wafer

Glass Sheet orPolymer Sheet

Monocrystalline

Polycrystalline

Amorphous ( a - Si )

Tandem a - Si / SiCrystalline

Thin Film Si Crystalline

Thin Films

Silicon Wafer Based

CIS / CIGS

CdTeI I -VI

Glass Sheet orPolymer Sheet

LiquidElectrolyte

Jelly Electrolyte

Solid Electrolyte

DyeSensitized

Polymer - PolymerFullOrganic

Polymer - Fullerene

Polymer - InorganicHybrid

GaInP2 / GaAs

InGaP / InGaAs/ GeI I I -V

Figure 8: Overview of PV generations

Figure 7: Electricity from the sunlight

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1 0 P V I nd us tr y H an db oo k 2 00 9

FIRST GENERATION

First generation solar cells are crystalline based

photovoltaic cells that have, and still do, dominate the solar

module market. These solar cells, using silicon wafers of

between 4 to8 inchessize, account for 87.5%of theglobalPV

market share in 2008. They are dominant due to their high

efficiency and proven technology. This is despite their higher

manufacturing costs;a problem that secondgeneration cells

hope to remedy. First generation solar cell manufacturing

involves high energy intensive production effort and labor

inputs, whichprevented significant costreductionin production.

1st generation solar cells have the highest efficiency of all

three generations, between 13% to 20% and approaching

the theoretical limiting efficiency of around 30%. Today the

energy payback period for 1st generation PV is between 11/2

to 31/2years.

SECOND GENERATION

Second generation cells, also called thin-film solar cells,

are significantly cheaper to produce than first generation cells

but have lower efficiencies of between 6% to 12%. The great

advantage of second generation, thin-film solar cells, along

with lower cost in manufacturing, is their flexibility. Thin-film

technology has spurred lightweight, aesthetically pleasing

solar innovations such as solar shingles andsolarpanels that

can be rolled out onto a roof or other surface. It has been

predicted that second generation cells will dominate the

residential solar market and power utility application,especially as new, higher-efficiency cells are researched and

produced.

Second generation materials have been developed to

address energy requirements and production costs of solar

cells. Alternative manufacturing techniques such as vapour

deposition and electroplating are advantageous as they

reduce high temperature processing significantly. It is

commonlyacceptedthat as manufacturingtechniques evolve

production costs will be dominated by constituent material

requirements, whether this be a silicon substrate, or glass

cover. Second generation technologies are expected to gain

significant market share in the next decade.

The most successful second generation materials have

been cadmium telluride (CdTe), copper indium gallium

selenide (CIGS), amorphous silicon (a-Si)and micromorphous

silicon (m-Si). These materials are applied in continuous roll-

to-roll or batch process to supporting substrates such as

glass, stainless steel or polymer foil thus reducing materialmass and therefore costs. Several technologies, particularly

CIGS-CIS and CdTe, hold the promise of higher conversion

efficiencies and achieving significantly cheaper production

costs through economics of scale.

Among major manufacturers there is certainly a trend

tow ards secon d generat ion techn olo gie s. How eve r

commercialisation of these technologies has proven difficult.

In 2008 2nd generation represented ~15% of total market

share and have now an energy pay-back time in the range of

1 t o 11/2years.

THIRD GENERATION

Third generation solar cells are the cutting edge of solar

technology. Still in the research phase, third generation cells

have moved well beyond silicon-based cells. Generally, thirdgeneration cells include solar cells that do not need the p-n

junction necessary in traditionalsemiconductor,silicon-based

cells. Third generation technology contains a wide range of


Figure 9: 1st generation PV module (multicrystalline PV)

(Courtesy: Yingli)

Figure 10: 2nd generation PV module (a-Si PV)

(Courtesy: Kaneka)

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1 1P V I n d u st r y H a n d b o ok 2 0 0 9

potential solar innovations including polymer solar cells,

nanocrystallinecells,and dye-sensitized solar cells. If and when

these technologies are developed and produced, the third

generation technology seems likely to be divided intoseparate

categories. Third generation technologies aim to enhance

poor electrical performance of second generation (thin-film

technologies) while maintaining very low production costs.

Current research is targeting conversion efficiencies of 30-

60% while retaining low cost materials and manufacturing

techniques. There are a few approaches to achieving these

high efficiencies:

- Multijunction photovoltaic cell;

- Modifying incident spectrum (concentration); and

- Use of excess thermal generation to enhance voltages or

carrier collection.

FOURTH GENERATION

Several research institutes studies globally are lookingat

new innovative next generation, 4th generation, PV cells, e.g.

quantum well devices (quantum dots, quantum ropes, etc.)

and devices incorporating carbon nanotubes with a potential

of upto 45% cell efficiency. This generation ofsolar cells may

consist of composite photovoltaic technology, in which

polymers with nano-particles can be mixed together to make

single multi-spectrum layers. The multi-spectrum layers can

be stacked to make multi-spectrum solar cells more efficient

andcheaper. The layer that converts different types of light is

first,thenanother layer for thelightthatpasses and last is an

infra-red spectrum layer forthe cell - thus converting some of

the heat for an overall solar cell composite.Another promising approach is a material with exciting

possibilities: a form of iron oxide called hematite. With the

right kind of nanoscale architecture, scientists believe that

hematite might be made to deliver a similar 16%efficiency as

titanium oxide, but in the much larger energy range of visible

light. Iron oxide makes up a big portion of the earth's crust,

and that makesit about as cheap a material for solar cells as

you can get.

However, it is still a long way to go. Out of the four

generations listed above, only the first two have been

commercialised. Today, the bulk of the photovoltaic modules

deployed so far consist of crystalline silicon, 1st generation

PV. But it is crucial to find new ways to produce cheap and

abundant carbon-free energy, and this should be a global

priority.If we areever goingto solve the30-terawattquestion,

that is the estimate to power the world in 2050, it is going to

have to be something cheap,efficient, andstable. As of today,

we are not there yet and continuous research is required

globally.

Figure 11: 3rd generation PV module (dye-sensitized PV)

(Courtesy: Dyesol)

Nanowires

Photons

Figure 12: Concept of light trapping with silicon nanowires

(Courtesy: Wikipedia)

Figure 13: Silicon nanowires(Courtesy: Lawrence Berkeley National Laboratory)

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Figure 17: CIS


Figure 14: sc-Si

Figure 15: mc-Si cell

Figure 16: a-Si cell

TYPE OF SOLAR CELLS

Solar cells, according to their structure can be separated into four categories. The following is a short description of the two

generations of commercially available PV cells and some features of the four main types.

1ST GENERATION PV

Mono (or single) crystalline silicon (sc-Si) cells are made from very pure mono

crystalline silicon and have a single and continuous crystal lattice structure with

almostno defectsor impurities. Theprincipleadvantage is their high efficiency,

typicallyaround 18%. Althoughthe manufacturing process required to produce

mono crystalline silicon is complicated, resulting in higher costs than other

technologies. Differentmanufacturing methods are used, one dependinglargely

upon the Czochralski method of growing, or pulling, a perfect crystal, another

is based on the string ribbon technique; two hightemperature strings are pulled

vertically througha shallowsilicon melt and the molten silicon spans and freezes

between the strings. Anothertechnique is the so called EFG (Edge defined Film

fed Growth), where the cells are cut from an octagon.

Multi crystalline silicon (mc-Si) cells are produced using numerous grains of

mono crystalline silicon. In the manufacturing process, molten polycrystalline

silicon is cast into ingots, which are square or rectangular in shape. These

ingots are then cut into very thin wafers and assembled into complete cells.

Multi crystalline silicon cells are cheaper to produce thanmono crystalline ones,

due to the simpler manufacturing process. However, they tend to be slightlyless efficient, with average efficiencies of around 15%.

2ND GENERATION PV

Amorphous silicon (a-Si) cells are composed of silicon atoms in a thin

homogenous layerrather than a crystal structure. Amorphous silicon absorbs

light more effectively than crystalline silicon, so thecells canbe thinner. Forthis

reason, amorphous silicon is also known as a "thin film" PV technology.

Amorphous silicon can be deposited on a wide range of substrates, both rigid

and flexible. Amorphous cells have typical efficiencies of around 7%, are

cheaper to produce and have lower temperature behaviour under hot

conditions than the c-Si cells. High temperatures will reduce operating voltage

and therefore photovoltaic performance. A-Si modules and also other thin film

types are most suited for application in hot climates and di ffused irradiance

conditions.

A number of other promising materials such as copper indiumdiselenide (CIS)

and cadmium telluride (CdTe) are now being used for PV modules. The

attraction of these technologies is that they can be manufactured by relatively

inexpensive industrial processes, certainly in comparison to crystalline silicontechnologies, yet they typically offer higher module efficiencies than amorphous

silicon.

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Figure 18 presents an overview of the different solar cells and table 1 compares the typical efficiencies on the market today

and looks at what can be achieved in thelaboratory in the future.

PV ARRAY

The solar cell is the basic unit in a PV system. For

crystalline PV technology, an individual solar cell can vary insize from about 4 inchesto about 8 inchesacross and typically

produces between 1 and 4 watts, hardly enough power for

the great majority of applications. But we can increase the

power by connecting cells together to form largerunits called

modules. The individual crystalline cells are soldered to form

strings in order to combine the cells into an effective unit that

will reliably supply power for decades. These strings form the

electrical basis of the solar module. To fully protect the cells

from the environmentalimpacts (rain,sun, hail, etc.),they are

often encapsulated in ethylene vinyl acetate (EVA) films, Teflon

as backing foil, and usually a low-reflective and tempered glass

as cover. An aluminum frame is applied around the sandwich

combination to protect the unfinished module from any

damage during transport, installation and operation.

Galliumarsenide,

varioustypes**

*Research,experimentalstage

**Aerospace,concentrators

Polycrystalline

cells

Mono-

crystalline

cells

Organic cells*Dye-sensitized

cells*HybridHIT cells

Microcrystalline

and

micromorphous

cells

Cadmium

telluridecells

(CdTe)

Copperindium

selenidecells

(CIS/GIS)

Amorphous

Sicells

Crystalline silicon cell Thin lm cell

12

34

5

6

1 - Aluminium frame

2 - Seal3 - Glass

4 - Encapsulating

5 - Crystalline cell6 - Tedlar sheet

Figure 18: Overview of solar cell technologies

Table 1: Comparison of solar cell efficiencies

Figure 19: Structure of crystalline PV module

Standard product Commercial maximum Maximum recordedlaboratory efficiency

Mono crystalline (sc-Si) 15-20% 23.4% 25.0%

Multi crystalline (mc-Si) 13-16% 17.3% 20.3%

Amorphous silicon (a-Si) 6-8% 8.3% 15.4% (triple junction)

Cadmium telluride (CdTe) 8-10% 10.9% 16.5%

Copper indium (gallium) 10-12% 12.2% 19.0%

diselenide (CIS/CIGS)

Micromorph silicon (m-Si) 9-11% 12% 15%

Dye sensitized solar cell 4-8% 8% 11.1%

Organic solar cell 2-5% 5% 6.5%

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can automatically start the generator and initiate a recharge

cycle when the batterybank is depleted, or a load is too large

for the batteries to support independently.

The photovoltaic array is exposed to the elements.

Depending on design, the interconnecting wires may also be

exposed. All exposed wiring must therefore meet electrical

codes for outdoor application, notably exposure to UV

radiation. The electrical power produced by the photovoltaic

array has someunique characteristics which require special

attention. It is direct currentandthesource is limitedby current.

Some installers may not be familiar with direct current and

the system will require special components for switching and

isolation. In some jurisdictions, electrical codes require the

photovoltaic array be capable of being isolated from the

inverter through a DC isolationswitch. The decision on whereto locate this switch should therefore be a balance between

proximity to the array and accessibility for the operator.

BALANCE OF SYSTEM COMPONENTS

Modules or arrays, by themselves, do not constitute a

complete PV system. We must also have mechanical

structures on which to putthem and orientate them towards

the sun, and components that take the direct-current (DC)

electricity produced by array andcondition the electricity so it

can be used in the specific application. These structures and

components are referredto as the balance of system (BOS).

Those elements account for approx. 30% of the total

investment cost for a PV installation.

INVERTER

The heart of grid-connectedPV systems, a power converter

that inverts the DC power from the modules into AC power.The characteristics of the output signal should match the

voltage, frequency and power quality limits in the supply

network. It is the link to the outside world and basically

performs three functions. First the inverter controls the

operation of the photovoltaic array. As the sun rises in the

morning, it connects the photovoltaic array to the utility

system. As light and temperature change throughout the day,

the inverter adjusts the array current and voltage levels to

maximize the energy yield of the photovoltaic array. Finally as

the sun sets in the evening it disconnects the array from the

utility system. This may be described as the power tracking

function of the inverter.

Thesecond function of theinverteris to changethe direct

current from the photovoltaic array to alternating current

with a frequency and voltage matching the supply from the

local utility. Thirdly, the inverter functions as a safety

component. An invertermustnot feed powerbackto anyutility

distribution system experiencing a power outage, and during

periodsof normal operation,power fed to the utilitymust meet

standards for voltage, frequency and harmonic content.

Safety and power quality issues are the main concern of

utilities.

The inverter will require periodic inspection andmaintenance. Often the inverter incorporates a display panel

indicating power production or fault conditions. It should

therefo re be installed in an accessible location and, unless

designed for outdoor exposure, it should be located in a dry

and temperate environment. Some inverters are known to

generate somebackground noise. The sound can be irritating

when the high frequency switching coincides with certain

psychologically annoying frequencies. Noise may therefore be

a factor in selecting the location of the inverter.

For a grid-connected PV system, inverterssend the power

from PV modules direct to the grid. They do not use a battery

bank and therefore they do not give you any power back up in

the event of a grid power failure. The advancedgrid-interactive

inverters perform the same function as grid-feed inverters;

however they allow power to flow 'both ways'. They also

incorporate a battery bank and have an automatic built in

charger. This type of system gives you back up power in the

event thatthe gridfails orgoesoutof tolerance interms ofits

voltage and frequency.

The overall efficiency of the system depends on the

efficiency of the sunlight-into-DC and the DC-into-AC

conversion efficiency of the inverter. The first onevariesup to

3% over a year. The second one, instead, shows a muchgreater variability. The efficiencyof the inverter varies with the

load level. Although this relation is different for each inverter,

DC

DC/ACinverter

AC

Light

Light

Computer

Television

Television

Radio

Telephone

Video

Controller

Storagebattery

Figure 23: Off-grid PV system

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a conventional model has a load/efficiency curve similar to

figure 24. Therefore, a key consideration in the design and

operation of inverters is how to achieve high efficiency with

varying power output.

It is necessary to maintain the inverter at or near full load

in order to operate in the high-efficiencyregion. However, this

is not possible, as some installations would never reach their

rated power due to deficient tilt, orientation or irradiation in

the region. Nowadays, there are several concepts on the

market availableand it is very dynamic, which is the preferred

and optimised concept. Following is a short description of the

two main concepts applied and some of their advantages:

One of the main concepts for an inverter is the central

conversion covering approx. 50% of all applications. The PVmodules are connected in strings andin parallel on a junction

box, which collects the DC power and feeds to the central

inverter. The inverter is connected to the grid in either single

or three phase configuration, depending on the PV capacity.

Oneof the main advantages is a higherefficiencyfor a central

large inverter compared to smaller units. Common sizes are

from 20kW upto 1,000 kW.

If applying string inverters, normally no junction box is

needed, thus resulting in cost reduction due to material

savings and fasterinstallation. The individual strings are oftendirectly connected to the inverter. String inverters are

available in size from 0.7 kW to 8 kW. The converted AC

power is collected and oftenfed to the grid on a single phase.

String inverters need a better and detailed monitoring

concept than central inverters, as a larger number of

inverters have to be properly monitored.

100

90

80

70

60

50

40

30

20

10

00 10 20 30 40 50 60 70 80 90 100

Output Power Relative to R ated Power [%]

Eciency[%]

Consumer

GridCentral

Inverter

PVModules

kWh

Grid

kWh

String Inverter

Consumer

PVModules

Figure 24: Typical inverter efficiency curve

Figure 26: Central inverter (Courtesy: Sputnik)

Figure 27: String inverter concept

Figure 25: Central inverter concept


Figure 28: String inverter (Courtesy: Fronius)

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Table 2: Inverter concepts overview

Table 2 presents the important features for the two

inverter concepts. Generalising, a central inverter costs

slightly less then the same capacity of string inverters, but

shows higher cost in the installation, due to the involved

components like wiring and junction box. However string

inverters need a better monitoring concept compared to a

central inverter. Both concepts have their pros andcons,and

needto be applied considering the site-conditions, e.g. shading

or obstaclesand theresulting total cost of theinstallation. For

smaller PV systems up to 100 kWp string inverters are a

preferable choice, and for PV system larger 100 kWp

installers tend to apply central inverters.

ELECTRICAL COMPONENTS

Fuses, breakers and switches normally function as

required and are likely to function according to specifications

for the life of the photovoltaic systems. Their reliability may

reflect their passive role as well as the maturity of the

electrical industry. Array string blocking diodes have failed in

some systems due to lack of heat dissipation. AC breakers,

along with the PV DC array switches, serve to isolate the

inverterfor servicing. Photovoltaicmodulesproduce electricity

whenever the sun shines and if they perform well for the first

year, they are likely to continue to perform for a very long time.

While perhaps not a reliability issue, one reason for

reported poor system performance has been the overrating

of module power by the manufacturers. It is strongly advised

to check the received modules on their power capacity by I/V

checker or request for detailed test protocols from the

module manufacturer.

Any future problems occur most likely in the inverter

(approximately 60% of the cases), the wiring, connectors or

DC combiner box (around 30% of the cases) or the module

junction box (around 10% of the cases). The junction box is

very exposed to the elements and mounted on the back of themodule, it experiences temperature higher than ambient

values. Evidence of corrosion in the module or in the junction

box terminal may show after ten to fifteen years of operation.

The wiring on the DC side is required to be double

insulated, UV stable cables, either 2.5 or 4 mm2. If a longer

distance forthe wiringis neededor high currentmodules are

applied one should apply 4 mm2 cables, and less wiring loss

is expected.The cablesmust further resisttemperatureup to

60C and should come in two different colours for () and (+)

connection.

For PV applications exceeding the string inverters

configuration, allstrings shall be connected in a DC combiner

box, which is preferablylocated very close to thePV array and

not in direct contact with the outdoor conditions. A DC

combiner box must have identical features like a cable, UV

resistant, suitable for high temperature and has to be

watertight, e.g. IP 65.

As each string is controlled by a DC rated fuse, the DC

combiner box shall be easily accessible, if needed. Overvoltage

protection elements (SPDs) and the DC isolating devices are

included too. ThePV-DCisolating deviceis neededto separate

the PV array at any time from the inverter. It is very important

to note that this device operates under DC conditions and the

operatingcurrent will vary at anytime.Some devices arefilled

with sand, while others will eliminate electronically the

resulting arcing when disconnecting. The device must besuitably rated for the PV array short current and the open

circuit DC voltage.


Comparison matrix of the two inverter concepts and the individual features:

Inverter Cost Dimension Weight Efficiency Installationconcept (USD/WpAC)

Central 0.5 to 0.85 A0 size > 200 kg 93% to 96% Junction box, more wiring,higher effort

String 0.6 to 0.90 A3 size Between 93% to 98% Easy wiring5 to 20 kg and fast installation

Figure 29: Module junction box (Courtesy: Huber & Suhner)

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MONITORING

Regularmonitoringof the PV installation is recommended,

as the inverter is an electronic component and can have

failures. If a central or string inverteris not properlymonitored

and breaks down, the produced solar energy is not being

converted and the PV owner loses money.

Nowadaysmost inverters offer the possibility to download

the data via modem and even access it over internet to control

the system performance. With a suitable PC program the

user can check the performance of the invertersor receives

automatically an error message in case of a failure. If this is

not available the inverter may be checked visually and

indicators at the inverter can show the operating status. As

the design approach shifts towards several inverter per

installation, e.g. string inverters, the monitoring should be

done automatically on a daily basis and in case of a failure, an

automatically generated error message should be sent. This

will safeguard the PV owners interest and helps to improve

the performance of a PV installat ion. The recorded data

should be analyzed daily and will give the opportunity to react

if strings are disconnected or other failures occur.

AlarmDatalogger

Archiving

Operation

Energy Meter

Local Alarm

Inverter

45678


Figure 30: AC/DC combiner box

Figure 31: Concept for monitoring

Courtesy: Solamas

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SILICON

Silicon is the second most plentiful element in the earths

crust, found in both quartz and sand. Silicon (Si) exists usually

as an oxide, being an element among about 100 different

elements. Silicon is found near the earth's surface, in

abundance second only to oxygen, and is considered to be

limitless in supply. Silica occurs in minerals consisting of

(practically) pure silicon dioxide in different crystalline forms.

Sand, amethyst, agate, quartz,rock crystal,chalcedony, flint,

jasper, and opal are some of the forms in which silicon

dioxide appears. Silicon also occurs as silicates (various

minerals containing silicon, oxygen and one or another

metal), for example feldspar. These minerals occur in clay,

sand and various types of rock such as granite and

sandstone. Despite its abundance, silicon is complex and

therefo re expensive to process.

Figure 33 shows a process, based on the Siemens

purification process, from mining to the final product either

forthe PV or theIC industry. Thedetailed manufacturingsteps


Value Chain and Manufacturing Process (c-Si)

Silicon PhotovoltaicSystem

Silicon Ingots

Monocrystalline

Multicrystalline

Wafers

Cells

PV Modules

Monocrystalline

Multicrystalline

Monocrystalline

Multicrystalline

Monocrystalline

Multicrystalline

Figure 32: Crystalline PV value chain

Figure 33: From silica to IC chips or PV modules (Courtesy: MBIPV)

CRYSTALLINE PV VALUE CHAIN

The crystalline PV value chain has six essential components which constitute the value chain, each dependent on each

other (see figure32). Some companiesconcentrateon specific segments of thevalue chain while othersaddress allsegments

as integrated solar PV companies. These components are:

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will be described in this chapter. It is importantto understand

that feedstock for PV modules or the IC industry can be

produced from polycrystalline silicon (or semicrystalline

silicon,polysilicon, poly-Si,or simply polyin context).Depending

on the follow-up process (ingot pulling or melting) either

monocrystalline or multicrystalline silicon can be produced.

The solar industry has historically relied on top-and-tails

and other off-cuts from the semiconductor industry. A

combinationof the semiconductor industrys recoveryand the

solar industrys growth has put pressure on the availability of

supply. As a result, silicon manufacturers are still in a strong

position in the overall PV value chain. The solar PV industry

and semiconductor manufacturers are the two main

consumers of polysilicon.

In 2000 the solar industry consumed only 10% of the

world's silicon supply. In 2008 the PV industry consumedmore than 70% of the world's available supply of polysilicon

forthe first time ever. This historic shift illustrates thegrowing

size and importance of the solar PV industry. The recent

bottleneck in 2004-2006 in polysilicon feedstock led to an

influx of new manufacturing and the production may exceed

the demand in 2010, depending on global PV policy programs

driving the market demand. The expected production in 2010

is estimated between 130,000and 190,000 tons, compared

to 70,000 tons in 2008.

In a first manufacturing step, silicon is prepared by the

reaction of high-purity silica with wood, charcoal, and coal, in

an electric arc furnace using carbon electrodes. At

temperatures over 1,900 C, the carbon reduces the silica

to silicon. Liquid silicon collects in the bottom of the furnace,

and is then drained and cooled. The silicon produced via this

process (see figure 34) is called metallurgical grade silicon

(MG-Si) andis at least 98%pure. In 2008, metallurgicalgrade

silicon cost between USD 1.50/kg to USD 2.00/kg.

In a next step, MG-Si is reacted with HCI to form a liquid

that is distilled and then vapourised. The resulting gas is then

deposited onto heated silicon rods (1100 C). The majority of

polysilicon used by the semiconductor and PV industry is

produced via a process of chemical deposition. The most

commonly used process, named after the company that

developed the process (Siemens), uses trichlorosilane gas

(TCS) as the deposition material. TCS has many advantages,

including a high deposition rate and high volatility (which

makes it easier to remove two compounds that are

problematic in solar cells (boron and phosphorous). One of the

disadvantagesof usingTCS is the highelectricity requirement

to maintain process temperatures.Another process further refines TCS to produce

monosilane (SiH4). This gaseous monosilane is then

depositedon heated silicon rods. Monosilane is a higher purity

starting material which leads to more pure polysilicon. This

higher purity also makes it more expensive to produce.

The final product of the above two processes is a rod of

polysilicon that is broken up into smaller pieces; at this point

the product is called chunk polysilicon (see figure 35 & 36).

A third processfor polysilicon production uses a fluidized bed

reactor (FBR) with a final product of granular silicon.

Raw MaterialConsumable

Electrodes

Electric EnergyFilter

Cleaned Gas

Silica

Recovered

Energy

Crater

Sizing

Silicon

Rening

Liquid Metal

Charge

Material

C SiO

Figure 3 4: Process t o manufacture M G-Si Figure 3 6: Polysilicon chunks

Figure 35: Polysilicon rods


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As figure37 shows,the Siemensprocess hasdominated

the market in the last years and will still have a market share

of around 75% in 2010. The two most promising

technologies are the FBR process and to upgrade MG-Si

(UMG-Si) acceptable for solar cells.

High purity silicon ("polysilicon") is the key feedstock for

most solar cells and modules, and IC chips produced today.

Crystalline silicon-based PV cells and modules accounted for

~88% of all PV production in 2008. From polysilicon one can

create either electronic grade (EG) - 99.999% (in nine 9s) -

or solargrade (SoG) silicon - 99.9999%(in six9s).The former

requires a greater level of purification than the latter.

The leaders in polysilicon manufacturing are Hemlock andREC from the USA, Wacker from Germany, Mitsubishi and

Tokuyama from Japan. Each of these companies has

indicated that they will expand their productions significantly.

Wacker and Tokuyama have launched initiatives to develop

granular si l icon. Wacker uses fluidized bed reactor

technology while Tokuyama uses a vapour to liquid reactor.

Commercialisation of these methods is expected in 2009/

2010.

Further significant expansion of polysilicon manufacturing

is taking place in China using mainly the Siemens process.

However, globally several other companies are developing

photovoltaic grade silicon from other sources, such as

upgrading metallurgical silicon via purification process. Today

the first solar cells made from UMG-Si are availableand result

in lower cost than with the conventional Siemens process.

New processes and significant upscaling will help to reduce

the production cost and bring crystallinePV technology closer

to grid-parity level.

Figure 38 presents the follow-up process flow of

polysilicon to the solar cell.

INGOT

Silicon consumers in the solar PV industry must convert

silicon feedstock into silicon ingots to enable further

processinginto wafers, cellsand modules. Silicon-based solar

modules fall into two categories: monocrystalline and

multicrystalline. In each category, the polysilicon must beconverted into a crystalline structure.


9%

91%

2005

13%

11% 1%

75%

2010

Siemens MG-SoGFBR Other

silicongranulate(polysilicon)

directed solidification

cutting intoblocks

phosphorousdiffusion

applyinganti-reflectivecoating

frontandbackcontacts

sawing intowafers

polycrystalline

monocrystalline

cutting

block

czochralski drawingprocess

Figure 38: Crystalline PV value chain

Figure 37: Percent of polysilicon produced by technology in

2005 and estimate for 2010 (Source: Greentech Media)

Figure 40: Multicrystalline ingot

Figure 39: Monocrystalline ingot

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A multicrystalline ingot contains numerous smaller silicon

crystals and often has a mottled or flecked appearance. A

monocrystalline ingot is comprised of one large crystal

structure, which yields a uniform colour and texture

throughout the ingot and produces solar cells with a higher

efficiency.

The most common technology used in the production of

ingots for monocrystalline solar cells is based on a technique

called the Czochralski process.

In the CZ process (seefigure 41), high-purity polysilicon is

putinto the quartzcrucible of a monocrystal growing system.

Next, the process room is evacuated and the silicon is then

melted down in an argon controlled atmosphere via resistive

heating. After temperature stabilisation of the melt

(approximately 1,420C), a rotating monocrystalline seed

crystal is dipped into the melt. As a result of a slight

temperature decrease, crystallisation of silicon material on

the seed crystal is now initiated. As the seed crystal is slowly

pulled upwards, a cylindrical silicon monocrystal hanging on

the seed crystal is then formed.

The production of monocrystalline ingot requires precise

specifications and careful monitoring to ensure uniform

crystal growth and contaminant-free ingots (99.9999%

purity). Completing a single cylindrical silicon crystal ingot

takes between 36 and 40 hours and yields an ingot of

approximately 2 meters long and 6 to 8 inches in diameter.

Once the ingot has been produced, the silicon is sawed

into blocks and then into wafers using specialised wire saws.

Such a process can waste up to half of the material in saw

slurry. Key to cutting costs is the development of thinner

wafers, while maintaining structural strength.

But it is unlikely that wafer manufacturers experience

the same rate of long-term growth as the overall solar

industry; wafers remain a high value added part of the solar

value chain.

For the simpler production of multicrystalline ingots, thesilicon is meltedin thecrucibleand then directionally solidified

in a carefully controlled thermal environment. The process is

known as vertical gradient freeze (VGF) or directional

solidification or, in a similar form, as Bridgman method. The

polysilicon is melted down in a silica crucible via resistive

heating. The slow cooling of the melt, where large areas of

crystal with regular structure are formed, takes place in the

melting crucible. The heated zone (temperature gradient) is

slowly moved upwards so that liquid silicon is present in the

top area at the end of the process, whilst solidification into

multicrystalline materialtakes place fromthe crucible bottom.

Crystallisationis controlled by the shifting of the temperature

gradient. In the Bridgman process, instead of the

temperature gradient, the crucible with the melt is moved

through the temperature field. The advantage of the VGF

method is that no mechanical motion occurs during the

crystallisation process. VGF methodhas becomeestablished

for multicrystalline solar cells.

Melting of

polysilicon,

doping

Introduction

of the seed

crystal

Beginning

of the crystal

growth

Crystal

pulling

Formed crystal

with a residue

of melted silicon


Figure 41: Czochralski (CZ) process

Figure 4 2: Czochralski i ngot p uller Figure 4 3: VGF i ngot c rystallizer

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Innovative approach without pulling ingots first and then

sawing into wafers are the so-called string ribbon growing

method, or in a similar form the edge-defined film-fed growth

(EFG) method. Both methods result in hardly any cutting

losses in wafer manufacture, and thus have a very high

material efficiency.

String ribbon is a concept originating from the natural

science of surface tension. In simple terms the making of a

string ribbon wafer is just like the making of a soap bubble

the surface tension between the soapy bubble solution and

the wand creates the bubble. The only difference is that

instead of the ring inside which a bubble forms, two parallel

wires are used between which a thin film of silicon is formed.

Two heat-resistant wiresare pulled verticallythrough a silicon

melt, with a continuous granular polysilicon feed, and the

molten silicon spans and solidifies between the strings. The

process is continuous, silent and clean: long wires unwind

from spools, run through the molten silicon and pull a long

ribbon of silicon out of the melt. The ribbon is harvested

periodicallyand a laser cuts the solar wafers from the ribbon.

WAFER

Wafer sawing is the process of cutting the mono- or

multicrystalline ingot intothin slices to enable the processing

of silicon into solar cells.

The key to cutting costs is the development of thinner

wafers, while maintaining structural strength. Producing

thinner wafers and reducing silicon waste is a major area of

focus in the solar industry's campaign to lower the cost ofmodule production and ensure more efficient use of silicon.

Todays standard waferthickness is between 180mto250

m, and the development goes towards 150 m to further

reduce the amount of silicon per watt, and thus drive down

the cost. Leading wafer manufacturers state that their

amount of silicon per watt is between 5.8 to 7.5 g/W.

Thewafersawing process is thestandardtechnique used

to slice ingots into wafers and can waste up to half of the

originalmaterial excluding the EFG and string-ribbon growth

process. A large source of lost silicon is "kerf",the silicon dust

produced duringthe sawingprocess. "Kerf loss" refers to the

silicon removed from the ingot in the sawing processusedto

produce the wafers. Because the sawed grooves are

approximately the same width as the produced wafers, kerf

loss can approach 50% of the total silicon in the ingot.

The raw ingot is first cooled and then the top and tail of

the ingot are cut off and can later be reused in the ingot

production process as reclaimable silicon. Next, the ingots

are cut into 400-500 cm long sections and the cylindrical

shape is 'squared' into four equal sides, so as to be mounted

safely inthe wire saw machine.In the sawingprocessa single

strand of stainlesssteel wire hundreds of kilometers in length

and 160 to 200 microns thick is pulled over the ingot by

grooved rollers. To complete this process, usually a mixture

made up of oil and normally an abrasive material known asslurryis pumpedover the wires to provide thefriction needed

for the cutting action.


Silicon Feed

Rear Ribbon

Front Ribbon

Molten

Silicon

Crucible

StringSolid-Melt

Interface

Figure 45: Wafers (Courtesy: LDK Solar)

Figure 44: String ribbon growing method

(Source: Evergreen Solar)

Figure 46: Wire saw machine (Courtesy: Meyer & Burger)

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CELL

Solar cell manufacturing typically involves a number of

steps that are performed under great cleanliness and highly

controlled conditions. Similar to the needs of semiconductor

facilities in the 1980s, new, larger solar cell manufacturing

plants require solutions that manage the employee and

environmental risks of hazardous materials and process

byproducts.

Generally a crystalline silicon solar cell consists of a p-n

junction embedded in the wafer, sandwiched between front

andback contacts (seefigure 47), although solar cell designs

vary by company.

The solar cell includes a layer of material, typically silicon

nitride, on the front surface of the silicon that serves as an

antireflective coating (ARC) to increase the amount of light

absorbed by the cell,and a passivation layer, whichpassivates

the bulk defects present in the wafer. In general, c-Si solar cells

are manufactured using mono- or polycrystalline wafers, but

some manufacturers use ribbons of silicon to minimise the

amount of Si used and hence their costs.

The first step in this process is to texture the wafer

surface, which increases the active surface area. Next, is the

doping and diffusion process,which creates the p-n junctionby

forming an n-doped (electron rich) layer on top of the p-doped

wafer. A layer of phosphorous silicate glass (PSG) forms on

top of the n-doped layer, and this is removed by either wet- or

dry-etch processes. After the PSG has beenremoved, a layer

ofsilicon nitride is deposited onthe front surface ofthe cell to

reduce reflection (ARC) and passivate the surface. Typically

the layer is deposited using plasma-enhanced chemical

vapour deposition (PECVD) or physical vapour depositio n

(PVD). PECVD gases and byproducts-such as SiH4, NH3, NF3,

F2, H2, and HF-are pyrophoric, flammable, toxic, and a

considerable safety risk.

Screen printing is the primary technology for depositingback electrical contacts and reflective coatings. Electrical

contacts areessential to a photovoltaic (PV) cell because they

bridge the connection between the semiconductor material

and the external electrical load, such as a light bulb. The back

contact ofa cell on theside away from theincoming sunlight

is relatively simple. It usually consists of a layer of aluminum

or molybdenum metal. But the front contact on the side

facing the sun is more complicated. When sunlight shines

onthe PVcell, a currentof electronsflows all over its surface.

If we attach contacts only at the edges of the cell, it will not

work well because of thegreatelectrical resistanceof thetop

semiconductor layer. Only a small number of electrons would

make it to the contact.

To collect the most current, we must place contacts

across the entire surface of a PV cell. This is normally done

with a "grid" of metal strips or "fingers." However, placing a

large grid, which is opaque, on thetop of thecell shadesactive

parts of the cell from the sun. Thecell's conversion efficiency

is thus significantly reduced. To improve the conversionefficiency, we must minimise these shading effects.

Another challenge in cell design is to minimise the

electrical resistance losses when applying grid contacts to

the solar cell material. These losses are related to the solar

cell material's property of opposing the flow of an electric

current, which results in heating the material. Therefore, in

designing grid contacts, we must balance shading effects

against electricalresistance losses.The usual approach is to

design grids with many thin, conductive fingers spreading to

every part ofthe cell'ssurface.The fingers ofthe gridmustbe

thick enough to conduct well (with low resistance), but thin

enough not to block much of the incoming light. This kind of

grid keeps resistance losses lowwhile shading only about 3%

to 5% of the cell's surface.

After the back reflective coating and contact layer have

been deposited, the solar cell is complete and the wafer

moves to the module production line.



Figure 47: Structure of crystalline solar cell

Figure 48: Monocrystalline solar cell (Courtesy: Q-Cells)

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MODULE

A crystalline PV moduleis a finished product consisting of

the assembly of PV cells that have been electrically connectedand laminated in a highly durable, weatherproof unit. Solar

modules are the basic end-use product of the solar industry

and may be produced in various sizes and shapes depending

on intended usage.

Module assembly involves electrically connecting strings

of cells (tabbing and stringing) and laminating the cells in a

durable, clear polymer material with special properties to

protect the cells against the environment. The encapsulating

material, typically ethylene vinyl acetate (EVA), is applied at

high temperature under a vacuumtogetherwith a front glass

and normally with a backing material known as TPT, a

combination of Tedlar and Polyester.

This laminate, after curing, is framed with an Aluminium

frame to protect from physical stress. A junction box and a

set of connection cables on the back of a module allow the

easy connection of one module to another at the site of

installation.

The power output of a module depends on the size and

number of cells in the module as well as theefficiency ofeach

cell. Recent trends have favoured the production of higher

power modules through a combination of larger, more

efficient cells and the inclusion of more cells per module.

It is important to ensure that the modules comply withinternational standards, such as IEC 61215, IEC 6146, TUV

safety class II and CE certification.

SYSTEM

A PV array consistsof a numberof modules eitherframed

or unframed (laminates).Modules are installed on residentialand commercial roofs, ground-mounted in large-scale solar

parks, and almost anywhere else where solar power can be

used. System installationcovers a broad range of possible PV

applications, from utility-scale PV, to commercial and

residential rooftops, to buildingintegrated photovoltaic(BIPV),

to off-grid industrialand residentialsystems in rural areas and

consumer applications.

Figure 49: Multicrystalline PV module

Figure 50: PV laminators in Chinese PV company

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84% of todays PV generating capacity consists of grid-

connected PV systems and about 16% is off-grid capacity;

consumer application account for less than 1% (graph 1). In

2008, around 59% of all PV applications were installed in the

built environment and 36% as ground-based PV systems, e.g.PV power plants in Spain, USA, SouthKorea and Germany. Off-

grid PV systems were 5% market share only (figure 66).

For PV systems in the built environment support

structures hold the PV modules in place and the PV arrays

shouldbe installedto ensuremaximumsolar exposure forthe

active PV area while at the same time minimising wind

loadingson the array surface. Also, for retro-fit of photovoltaic

systems on existing buildings, the addition of the support

structure on the roof should not compromise the structural

integrityor weatherseal of the existing roof. In general, flat or

sloped roof applications are less affected by building codes

than over head or faade installations.

Each category (ground-based, PV in the builtenvironment

and off-grid) presents its own unique challenges for cost

effectively deploying PV solar modules.


Figure 51: BIPV system (Courtesy: Envision)

Grid-connected centralized

O-grid

Grid-connected distributed (in built environment)

16%25%

59%

Graph 1: Distribution of cumulative PV capacity by end of 2008

(Source: Envision) Figure 53: PV powering the rural life

Figure 52: Large scale ground-based PV system


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THIN FILM PV VALUE CHAIN

Thin film PV cells differfrom crystalline solar cells in many

ways, for example in their electrical behaviour, efficiency,

temperature and shading impact, atomic structure and also

their value chain. Whereas crystalline PV technology has six

essential components, thin film PV has (using the identical

approach as for c-Si) four essential components and is

significantly simpler in manufacturing, and thus offers the

highest potential for cost reduction.

THIN FILM INTRODUCTION

Thin film cells can be divided into technologies with and

without silicon. There are several types of solar cells

containing silicon, from fully amorphous forms via nano and

microcrystalline forms and combinations. Thin film cellswithout silicon arerepresentedby twokindsof light absorbing

semiconductors: II-VI connections (CdTe) and I-III-VI

connections,whereby chalcopyrite with Cu(In,Ga)(S,Se)2 (CIS,

CIGS) variants is the most important representative. Dye-

sensitised cells Graetzel cell and organic cells are just

beginningto emerge in themarketand will be explainedin this

chapter.

If you use a solar-powered calculator, you've seen a solar

cell based on thin film technology. The thinness of the cell is

the defining characteristic of the technology hence the

name thin film. Unlike silicon-wafer cells, which have light-

absorbing layers that are traditionally 350 microns thick,

thin f ilm solar cells have light-absorbing layers that are just

1 m thick.

Thin film solar cell manufacturers begin building their

solar cells by depositing several layers of a light-absorbing

material, a semiconductor onto a substrate, either coated

glass, metal or plastic material. The materials used as

semiconductors don't have to be thick because they absorb

energy from the sun very efficiently. As a result,thin film solar

cells can be lightweight, indestructible and easy to use.

Thin film solar cells are called second generation

technologies and have yet to prove their maturity. Secondgeneration materials have been developedto address energy

requirements and production costs of solar cells. Alternative

manufacturing techniques such as vapour deposition and

electroplating are advantageous as they reduce high

temperatureprocessing significantly. It is commonlyaccepted

that as manufacturingtechniques evolve productioncosts willbe dominated by constituent material requirements, whether

this be a silicon, substrate or glass cover. Second generation

technologies are expected to gain market share in the next

few years.

Thin film PV has a high potential for cost reduction as the

manufacturing processes can bring costs down to a little

under USD 1.00 per watt, but the defects inherent in the

lower quality processing methods, have much reduced

efficienciescompared to first generation technologies. Among

major manufacturers there is certainly a trend towards

second generation technologies though commercialisation of

these technologies has proven difficult.

THIN FILM TECHNOLOGIES

The most successful second generation materials have

beencadmium telluride (CdTe),copper indiumgallium selenide

(CIGS or CIS), amorphous silicon (a-Si) and micromorphous

silicon (c-Si). These technologies do hold promise of higher

conversion efficiencies, and cheaper production costs

particularly CIGS/CIS and CdTe. Presented are following the

main types of thin-film solar cells, depending on the type of

semiconductor used: amorphous silicon (a-Si), cadmiumtelluride (CdTe) and copper indium gallium deselenide (CIGS),

and explain what dye-sensitized and organic cells are.

Value Chain and Manufacturing Process (Thin Film)

Mining

Cu, Cd,

Te, Ga,

In

PhotovoltaicSystem

Processing

PV Modules

Process Cu,

Cd,Te, Ga,

In and

others intogas form

Figure 55: Flexible thin film solar cell(Courtesy: UniSolar, USA)

Figure 54: Thin Film PV value chain

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AMORPHOUS AND MICROCRYSTALLINE SILICON

(a-Si/c-Si)

Amorphoussilicon is basicallya trimmed-down version of

the traditional silicon-wafer cell and has a disordered

structure unlike crystalline silicon. A-Si is well understood

and is commonly used in solar-powered electronics and

consumer applications for decades. Solar cells, which are

based on amorphous silicon and its alloys, are still the

dominant types of thin film solar cells, although CdTe has

gained significant market share in 2007 and 2008.

The first a-Si cells were realised in 1976 (Carlson and

Wronski) andearlyproduction started at Chronar Corp in the

USA, followedby theSolarexand Unisolar, also in theUSA.The

manufacturing process improved largely in the last two

decades. The option of band-gap engineering by the

introductionof C and Ge resulted in the first break-through of

amorphous silicon desired characteristics. Next, the very

important issueof monolithicintegration by structuredsteps,

which in the meantime have been realised for all thin film

technologies, was developed by a-Si technology.

Plasma Enhanced Chemical Vapour Deposition (PECVD)

is used for the industrial production of a-Si:H in general.

Amorphous silicon from monosilane (SiH4) and hydrogen

(H2) gas can be depositedat very low temperatures, as low

as 75 degrees Celsius, which allowsfor deposition on notonly

glass, butplastic as well, making it a candidate for a roll-to-rollprocessing technique. The relatively lower electronic

performance of low-temperature a-Si devices could be

compensated by the cheaper production, for future, ultra-low-

cost, high-volume applications.

Depending on the deposition parameters and chosen

materials, this can yield:

- Amorphous silicon (a-Si or a-Si:H), figure 56

- Microcrystalline silicon (c-Si orc-Si:H), figure 57

Amorphous silicon has a higher bandgap (1.8 eV) than

crystalline silicon (c-Si) (1.1 eV), which means it absorbs the

visible part of the solar spectrum more strongly than theinfrared portion of the spectrum.As c-Si has about thesame

bandgap as c-Si, thec-Si(a mixture of nanometer-sized 5 to

500nm silicon crystals) and a-Si can advantageously be

combinedin thinlayers,creating a layered cellcalled a tandem

cell and achieve the highest efficiency, i.e. up to 14.8%. The

top cell in a-Si absorbs the visible light and leaves the infrared

part of the spectrum for the bottom cell in nanocrystalline Si,

also called microcrystalline silicon. Figure 57 presents the

structure of a microcrystalline solar cell.

CADMIUM TELLURIDE (CdTe)

The fastest growing generation of thin-film solar cells uses

thin layers of cadmium telluride. The CdTe solar cell has one

electrode made from a layer of carbon paste infused with

copper, the other from tinoxide(SnO2) or cadmium stannate

(Cd2SnO4). The semiconductor in this case is cadmium

telluride (CdTe), which, along with cadmium sulfide (CdS),

creates the n-type and p-type layers required for the PV cell

to function see figure 58 for details.

Cadmium telluride is an efficient light-absorbing material

for thin-film cells. Compared to otherthin-film materials, CdTe

is easier to depositandmoresuitable forlarge-scale production.

Titanium

Copper-doped Zinc Telluride

Glass

Cadmium Sulde

Cadmium Telluride

Stanous Oxide

Metal TCO a-Si

P1 P2 P3

Substrate

Light

3-5 mm

TCO

AmorphousSi

Microcrystalline Si

2 m

Glass

Value Chain and Manufacturing Process (Thin Film)

Figure 58: Cadmium telluride (CdTe)

Figure 57: Microcrystalline silicon (m-Si)

Figure 56: Amorphous silicon (a-Si)

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Despite much discussion of the toxicity of CdTe-based

solar cells, this is the only technology (apart from amorphous

silicon) that can be delivered on a large scale. The perception

of the toxicity of CdTe is based on the toxicity of elemental

cadmium, a heavymetalthat is a cumulative poison. However,

it has been shown that the release of cadmium to the

atmosphere is lower with CdTe-based solar cells than with

silicon photovoltaics and other thin-film solar celltechnologies.

COPPER INDIUM GALLIUM SELENIDE

(CIGS OR CIS)

CIGS films can be manufactured by several different

methods. The most common vacuum-based process co-

evaporates or co-sputters copper, gallium, and indium, then

anneals the resulting film with a selenide vapour to form thefinal CIGS structure. An alternative is to directly co-evaporate

copper,gallium, indium and seleniumonto a heated substrate.

A non-vacuum-basedalternativeprocessdepositsnanoparticles

of the precursor materials on the substrate and thensinters

them in situ.

The basic structure of a Cu(In,Ga)Se2 thin-film solar cell

is depicted in figure 59.

Themost commonsubstrate is soda-limeglassof around

3 mm thickness. This is coated on one side with molybdenum

(Mo) that serves as metal back contact. The heterojunction

is formed between the semiconductors CIGS and ZnO,

buffered bya thin layer ofCdS and a layer ofintrinsic ZnO. The

CIGS is doped p-type from intrinsic defects, while the ZnO is

doped n-type to a much larger extent through the

incorporation of aluminum (Al). This asymmetric doping

causes the space-charge region to extend much further into

the CIGS than into the ZnO.

For the production of modules, individual cells are divided

and monolithically interconnected by a series of scribing stepsbetween the layer depositions. Additionally, susceptibility to

dampness makes module encapsulation a requisite for long

lifetimes.

One company, Nanosolar, based in San Jose, Calif., has

developed a way to make the CIGS material as an ink

containing nanoparticles. A nanoparticle is a particle with at

least one dimension less than 100 nanometers(one-billionth

of a meter,or 1/1,000,000,000 m). Existing as nanoparticles,

the four elements self-assemble in a uniform distribution,

ensuring that the atomic ratio of the elements is always

correct.

Notice that there are two basic configurations of a CIGS

solarcell. The CIGS-on-glass cellrequiresa layerof molybdenum

to crea

pv ind 2009 final

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