N01.1 Photovoltaic Technology.pptx

JNK – PV Technology 1
Photovoltaic Technology

About author
Name: Er. J N Karamchetti,
Qualifications: 1). B.E. (Elec): JNTU Kakinada,
2). M. Tech. (Elec): IIT, Kgp (1971-73)
3). Diploma Business & Finance - ICFA
Certifications:
Certified Energy Auditor - BEE/MoP
Master trainer: Rooftop Solar Grid Engineer - NISE/ MNRE
Experience:
Industrial experience: from Development Engineer to Chief Executive
Officer in Public limited companies, for 37 years.
Training of Engineers for 10 years with Engineering Staff College of
India, Hyderabad.

Solar Photovoltaic Technology Basics
Solar cells, also called photovoltaic (PV) cells, convert sunlight
directly into electricity.
PV gets its name from the process of converting light (photons)
to electricity (voltage), which is called the photovoltaic effect.
This phenomenon was first exploited in 1954 by scientists at
Bell Laboratories who created a working solar cell made from
silicon that generated an electric current when exposed to
sunlight.
Solar cells were soon being used to power space satellites and
smaller device such as calculators and watches.
Today, electricity from solar cells has become cost competitive
in many regions and photovoltaic systems are being deployed
at large scales to help power the electric grid.

Silicon Solar cells
• The vast majority of today's solar cells are made from
silicon and offer both reasonable prices and good efficiency.
• These cells are usually assembled into larger modules that
can be installed on the roofs of residential or commercial
buildings or deployed on ground-mounted racks to create
huge, utility-scale Power systems – called Solar parks.

Thin-Film Solar Cells
• Another commonly used photovoltaic technology is known
as thin-film solar cells because they are made from very thin
layers of semiconductor material, such as cadmium telluride or
copper indium gallium diselenide.
• The thickness of these cell layers is only a few
micrometers—that is, several millionths of a meter.

Thin-Film Solar Cells
• Thin-film solar cells can be flexible and lightweight, making
them ideal for portable applications—such as in a soldier’s
backpack—or for use in other products like windows that
generate electricity from the sun.
• Some types of thin-film solar cells also benefit from
manufacturing techniques that require less energy and are
easier to scale-up than the manufacturing techniques
required by silicon solar cells.

III-V Solar Cells
• A third type of photovoltaic technology is named after the
elements that compose them. III-V solar cells are mainly
constructed from elements in Group III—e.g., gallium and
indium—and Group V—e.g., arsenic and antimony—of the
periodic table. These solar cells are generally much more
expensive to manufacture than other technologies.
• But they convert sunlight into electricity at much higher
efficiencies. Because of this, these solar cells are often used
on satellites, unmanned aerial vehicles, and other
applications that require a high ratio of power-to-weight.

Next-Generation Solar Cells
• Solar cell researchers at NREL and elsewhere are also
pursuing many new photovoltaic technologies—such as
solar cells made from organic materials, quantum dots,
and hybrid organic-inorganic materials (also known as
perovskites).
• These next-generation technologies may offer lower costs,
greater ease of manufacture, or other benefits.
• Further research will see, if these promises can be realized.

Photovoltaic basics
• What is photovoltaic (PV) technology and how does it
work? PV materials and devices convert sunlight into
electrical energy.
• A single PV device is known as a cell. An individual PV
cell is usually small, typically producing about 3 or 4 watts
of power.
• These cells are made of different semiconductor
materials and are often less than the thickness of four
human hairs.
• In order to withstand the outdoors for many years, cells are
sandwiched between protective materials in a combination
of glass and/or plastics.

Photovoltaic basics
• To boost the power output of PV cells, they are connected
together in chains to form larger units known as modules or
panels.
• Modules can be used individually, or several can be
connected to form an array. One or more arrays is then
connected to the electrical grid as part of a complete PV
system.
• Because of this modular structure, PV systems can be built
to meet almost any electric power need, small or large.

Photovoltaic basics
• PV modules and arrays are just one part of a PV system.
Systems also include mounting structures that point panels
toward the sun, along with the components that take the
direct-current (DC) electricity produced by modules and
convert it to the alternating-current (AC) electricity used to
power some appliances at home.
• The Solar Star PV power station produces 579 megawatts
of electricity, while the Topaz Solar Farm and Desert
Sunlight Solar Farm each produce 550 megawatts.

Solar Photovoltaic cell Basics
• When light shines on a photovoltaic (PV) cell – also called a
solar cell – that light may be reflected, absorbed, or pass
right through the cell. The PV cell is composed of
semiconductor material; the “semi” means that it can
conduct electricity better than an insulator but not as good
as a metal conductor. There are several different
semiconductor materials used in PV cells.

• When the semiconductor is exposed to light, it absorbs the
light’s energy and transfers it to negatively charged particles
in the material called electrons. This extra energy allows the
electrons to flow through the material as an electrical
current. This current is extracted through conductive metal
contacts – the thin finger-lines on a solar cells – and can
then be used to power at homes and the rest of the electric
flows to grid.

• The efficiency of a PV cell is simply the amount of electrical
power coming out of the cell compared to the energy from
the light shining on it, which indicates how effective the cell
is at converting energy from one form to the other.
• The amount of electricity produced from PV cells depends
on the characteristics (such as intensity and wavelengths) of
the light available and multiple performance attributes of the
cell.

• An important property of PV semiconductors is the bandgap,
which indicates what wavelengths of light the material can
absorb and convert to electrical energy. If the
semiconductor’s bandgap matches the wavelengths of light
shining on the PV cell, then that cell can efficiently make
use of all the available energy.

Silicon Solar material basics

Different solar cell sizes.

Background
• Over the past few decades, mainly due to advances in technology
and reduction in cost, the size of silicon wafers used in solar
modules has evolved from an early stage 125mm to the current
standard M6 (166mm), M10 (182mm) and G12 (210mm).
• What impact do these larger modules have on related equipment?
• What should be considered when designing a system with these
modules?
• What are the impacts between high-current components and
inverters?
• In this Solis seminar, we will look at these so called “high-power”
modules in more detail and compare them using actual operating
conditions.

Wafer and improvements -1
• The “wafer”, which is only around 200 µm thick, is the basic
raw material for the fabrication of crystalline solar cells.
Wafer size counts in photovoltaic (PV), just as it does in the
semiconductor sector.
The wafer is the PV module’s power-generating component,
accounting for roughly 40% of overall module costs.
Generally, the power output of each wafer grows as the
wafer area gets bigger. However, the cost of production may
remain unchanged or increase by a modest amount.

• On the PV array side, the larger, more powerful wafer offers
cost savings. Balance-of-system costs can be reduced per
watt-peak installed by using a larger wafer, which includes
base pilings, support racks, or trackers, as well as all
electrical components such as inverters, junction boxes, and
cables. As a result, PV plants have a lower levelized cost of
power and a higher return on investment.

•
When looking back over the last 40 years in the PV sector,
the increase in wafer sizes has been a consistent trend.
Mainstream wafers were only approximately 100 mm long
forty years ago, but by the 2000s, they had grown to 125
mm. The M0, with a 156 mm edge was promoted in 2012.
Over the last few years, wafer sizes expanded in modest
steps, from M1 (156.75 mm length/205 mm diagonal length)
to M2 (156.75/210 mm) to M4 (161.7/211 mm).

• By 2018, 156.75 mm wafers accounted for over 80% of the
market. The revolution reached 158.75 mm wafer sizes in
2020. The module outputs here range from 370 to 390 watts,
and depending on the design, the dimensions are around 10
to 30 millimetres larger than a traditional 72-cell module -
making them still quite easy to carry and process. The
158.75 mm cell, which was introduced only a few years ago,
is, however, only accessible in restricted quantities.

CELL and its parts

Copper Contacts - TetraSUN

History of wafer M0 to G12
• the M0 type, with an edge length of 156 mm, was
promoted and eventually became the dominant size.
Wafer sizes have increased in small incremental ways
over the last seven years — from
• M1 (156.75/205 mm diagonal length) to
• M2 (156.75/210 mm), to M4 (161.7/211 mm),
• M6 (166 mm), wafer will increase the operational
current to around 13 amps, M10 182x182 mm, the new
M12 (210 /295 mm on the diagonal.)
M0 – 156, M2 – 156.75, M4 – 161.7, M6- 166, M10-182,
M12 – 210, G12 – 210 mm bifacial. All of them are square
with one side dimension in mm as indicated above.

Larger size Solar CELL

Power Characteristics of selected Bifacial
Modules based on G12 Wafer size

144 cells HC 72 cells

SILICON
• Silicon is, by far, the most common semiconductor material
used in solar cells, representing approximately 95% of the
modules sold today. It is also the second most abundant
material on Earth (after oxygen) and the most common
semiconductor used in computer chips.
• Crystalline silicon cells are made of silicon atoms connected
to one another to form a crystal lattice.
• This lattice provides an organized structure that makes
conversion of light into electricity more efficient.

SILICON
• Solar cells made out of silicon currently provide a
combination of high efficiency, low cost, and long lifetime.
Modules are expected to last for 25 years or more, still
producing more than 80% of their original power after this
time.

THIN-FILM PHOTOVOLTAICS
• A thin-film solar cell is made by depositing one or more thin
layers of PV material on a supporting material such as
glass, plastic, or metal. There are two main types of thin-film
PV semiconductors on the market today: cadmium
telluride (CdTe) and copper indium gallium
diselenide (CIGS). Both materials can be deposited directly
onto either the front or back of the module surface.

PEROVSKITE PHOTOVOLTAICS
• Perovskite solar cells are a type of thin-film cell and are
named after their characteristic crystal structure. Perovskite
cells are built with layers of materials that are printed,
coated, or vacuum-deposited onto an underlying support
layer, known as the substrate. They are typically easy to
assemble and can reach efficiencies similar to crystalline
silicon. In the lab, perovskite solar cell efficiencies have
improved faster than any other PV material, from 3% in
2009 to over 25% in 2020. To be commercially viable,
perovskite PV cells have to become stable enough to
survive 20 years outdoors, so researchers are working on
making them more durable and developing large-scale, low-
cost manufacturing techniques.

ORGANIC PHOTOVOLTAICS
• Organic PV, or OPV, cells are composed of carbon-rich
(organic) compounds and can be tailored to enhance a
specific function of the PV cell, such as bandgap,
transparency, or color. OPV cells are currently only about
half as efficient as crystalline silicon cells and have shorter
operating lifetimes, but could be less expensive to
manufacture in high volumes. They can also be applied to a
variety of supporting materials, such as flexible plastic,
making OPV able to serve a wide variety of uses.

Quantum
• Quantum dot solar cells conduct electricity through tiny particles of
different semiconductor materials just a few nanometers wide, called
quantum dots. Quantum dots provide a new way to process
semiconductor materials, but it is difficult to create an electrical
connection between them, so they’re currently not very efficient.
However, they are easy to make into solar cells. They can be deposited
onto a substrate using a spin-coat method, a spray, or roll-to-roll
printers like the ones used to print newspapers.
• Quantum dots come in various sizes and their bandgap is customizable,
enabling them to collect light that’s difficult to capture and to be paired
with other semiconductors, like perovskites, to optimize the performance
of a multijunction solar cell (more on those below).

Quantum Dot

MULTIJUNCTION PHOTOVOLTAICS
• Another strategy to improve PV cell efficiency is layering
multiple semiconductors to make multijunction solar cells.
These cells are essentially stacks of different semiconductor
materials, as opposed to single-junction cells, which have
only one semiconductor.
• Each layer has a different bandgap, so they each absorb a
different part of the solar spectrum, making greater use of
sunlight than single-junction cells. Multijunction solar cells
can reach record efficiency levels because the light that
doesn’t get absorbed by the first semiconductor layer is
captured by a layer beneath it.

MULTIJUNCTION PHOTOVOLTAICS
• While all solar cells with more than one bandgap are
multijunction solar cells, a solar cell with exactly two
bandgaps is called a tandem solar cell. Multijunction solar
cells that combine semiconductors from columns III and V in
the periodic table are called multijunction III-V solar cells.
• Multijunction solar cells have demonstrated efficiencies
higher than 45%, but they’re costly and difficult to
manufacture, so they’re reserved for space exploration. The
military is using III-V solar cells in drones, and researchers
are exploring other uses for them where high efficiency is
key.

CONCENTRATION PHOTOVOLTAICS
• Concentration PV, also known as CPV, focuses sunlight
onto a solar cell by using a mirror or lens. By focusing
sunlight onto a small area, less PV material is required. PV
materials become more efficient as the light becomes more
concentrated, so the highest overall efficiencies are
obtained with CPV cells and modules. However, more
expensive materials, manufacturing techniques, and ability
to track the movement of the sun are required, so
demonstrating the necessary cost advantage over today's
high-volume silicon modules has become challenging.

PHOTOVOLTAIC CELLS
Photovoltaic cells make use of a semiconducting material
that, when struck by sunlight, generates a small current as
a result of the photovoltaic effect,
Unlike some power plants that require steam, solar power
using photovoltaic cells is created directly by transforming
energy from the Sun into electricity,
The vast majority of photovoltaic cells are composed of
silicon semiconductors and interact with incoming photons
in order to generate an electric current.

Types of Photovoltaic
• Photovoltaic cells or PV cells can be manufactured in
many different ways and from a variety of different materials.
• Despite this difference, they all perform the same task of
harvesting solar energy and converting it to useful electricity.
• The most common material for solar panel construction
is silicon which has semiconducting properties.
• Several of these solar cells are required to construct a solar
panel and many panels make up a photovoltaic array.

Types of Photovoltaic
• There are three types of PV cell technologies that dominate
the world market: monocrystalline silicon, polycrystalline
silicon, and thin film.
• Higher efficiency PV technologies, including gallium
arsenide and multi-junction cells, are less common due to
their high cost, but are ideal for use in concentrated
photovoltaic systems and space applications.
• There is also an assortment of emerging PV cell
technologies which include Perovskite cells, organic solar
cells, dye-sensitized solar cells and quantum dots.

Monocrystalline
• The first commercially available solar cells were made from
monocrystalline silicon, which is an extremely pure form of
silicon. To produce these, a seed crystal is pulled out of a
mass of molten silicon creating a cylindrical ingot with a
single, continuous, crystal lattice structure. This crystal is
then mechanically sawn into thin wafers, polished
and doped to create the required p-n junction. After an anti-
reflective coating and the front and rear metal contacts are
added, the cell is finally wired and packaged alongside
many other cells into a full solar panel. Monocrystalline
silicon cells are highly efficient, but their manufacturing
process is slow and labour intensive, making them more
expensive than their polycrystalline or thin film counterparts.

Polycrystalline cells
• Instead of a single uniform crystal structure, polycrystalline
(or multicrystalline) cells contain many small grains of
crystals (see figure),
• They can be made by simply casting a cube-shaped ingot
from molten silicon, then sawn and packaged similar to
monocrystalline cells,
• Another method known as edge-defined film-fed growth
(EFG) involves drawing a thin ribbon of polycrystalline
silicon from a mass of molten silicon,
• A cheaper but less efficient alternative, polycrystalline silicon
PV cells dominate the world market, representing about
70% of global PV production in 2015,

Solar Cells

Thin Film PV cell
• One type of thin film PV cell is amorphous silicon (a-Si)
which is produced by depositing thin layers of silicon on to a
glass substrate,
• The result is a very thin and flexible cell which uses less
than 1% of the silicon needed for a crystalline cell,
• Due to this reduction in raw material and a less energy
intensive manufacturing process, amorphous silicon cells
are much cheaper to produce,
• These cells also suffer from a 20% drop in efficiency within
the first few months of operation before stabilizing, and are
therefore sold with power ratings based on their degraded
output,

Other type thin film cells
• Other types of thin film cells include copper
indium gallium diselenide (CIGS)
and cadmium telluride (CdTe).
• These cell technologies offer higher
efficiencies than amorphous silicon, but
contain rare and toxic elements
including cadmium which requires extra
precautions during manufacture and eventual
recycling.

Copper, indium, gallium and selenide (CIGS)
thin film solar PV
• The benefits of CIGS solar cells include:
• High absorption: This direct-bandgap material can absorb a
significant portion of the solar spectrum, enabling it to
achieve the highest efficiency of any thin-film technology.
• Tandem design: A tunable bandgap allows the possibility of
tandem CIGS devices.
• Protective buffer layer: The grain boundaries form an
inherent buffer layer, preventing surface recombination and
allowing for films with grain sizes of less than 1 micrometer
to be used in device fabrication.

thin film solar PV
Copper, indium, gallium and selenide (CIGS)
https://www.youtube.com/watch?v=mO80ycDj9fU

Cadmium Telluride Photovoltaics
As of 2013, on a lifecycle basis, CdTe PV has the smallest carbon footprint,
lowest water use and shortest energy payback time of any current photo
voltaic technology. CdTe's energy payback time of less than a year allows
for faster carbon reductions without short-term energy deficits.
Cadmium telluride (CdTe)
photovoltaics isa photovoltaic (PV)
technology based on the use
of cadmium telluride in thin
semiconductor layer designed to
absorb and convert sunlight into
electricity.[1] Cadmium telluride PV is
the only thin film technology with lower
costs thanconventional solarcell made
of crystalline silicon in multi-kilowatt
systems.

CIGS solar cells technology
• CIGS solar cells stand for copper indium gallium selenide solar
cell (sometimes referred to as CIS cell or CI(G)S) is a thin film
solar cell which is used to convert solar energy into electrical
energy.
• It is manufactured by depositing a thin layers of copper, indium,
gallium and selenium on plastic or glass backing, besides the
electrodes on the front and back sides to collect current.
• Since the material has a high absorption coefficient and absorbs
sunlight strongly, a much thinner film is required in comparison to
other semiconductor materials.
• There are three mainstream technologies for thin film PV, CIGS
being one and the other two being cadmium telluride and
amorphous silicon.

CIGS solar cells technology
• CIGS and the two other materials have similar properties and are
all thin enough to be flexible, allowing their simple deposition on
flexible substrates.
• Yet, since all of these technologies typically use techniques that
utilize high temperature deposition, the optimum performance
normally comes from cells deposited on glass material, despite the
advancement in low temperature deposition of CIGS cells erasing
nearly all of this performance difference.
• The performance is much better than polysilicon at the cell level,
but the module efficiency is still lower, because of less developed
upscaling. They are mostly used in the polycrystalline form. The
best efficiency achieved was 21.7% which was recorded in 2014.

CIGS solar cells market share
• The market share of thin film PV is around 15 percent, with
conventional solar cells made of crystalline silicon still
leading the most of the PV market.
• The market share of CIGS presents nearly about 20 percent
of all thin film technologies combined market share.
• CIGS solar cells technology continues to being rapidly
developed, and they allow for huge capacity as it has shown
it can reach nearly the same efficiency levels of silicon cells,
while still maintaining the same benefits of typical thin film
technology, which are low cost, light weight and compact
design which allows for flexibility in installation.

Gallium Arsenide
• Other cell technologies have been developed which operate
at much higher efficiencies than those mentioned above, but
their higher material and manufacturing costs currently
prohibit wide spread commercial use.
• Silicon is not the only material suitable for crystalline PV
cells. Gallium arsenide (GaAs) is an alternative
semiconductor which is highly suitable for PV applications.
Gallium arsenide has a similar crystal structure to that of
monocrystalline silicon, but with alternative gallium and
arsenic atoms.

Gallium Arsenide
• Due to its higher light absorption coefficient and wider band
gap, GaAs cells are much more efficient than those made of
silicon. Additionally, GaAs cells can operate at much higher
temperatures without considerable performance degradation,
making them suitable for concentrated photovoltaics.
• GaAs cells are produced by depositing layers of gallium and
arsenic onto a base of single crystal GaAs, which defines the
orientation of the new crystal growth.

Gallium Arsenide
• This process makes
GaAs cells much more
expensive than silicon
cells, making them
useful only when high
efficiency is needed,
such as space
applications.
• Fig: NASA's Juno Spacecraft with
gallium arsenide multi-junction
solar cells

Multi-Junction
• The majority of PV cells, including those discussed above,
contain only one p-n junction of semiconductor material which
converts energy from one discreet portion of the solar
spectrum into useful electricity.
• Multi-junction cells have 2 or more junctions layered on top of
each other, allowing energy to be collected from multiple
portions of the spectrum. Light that is not absorbed by the first
layer will travel through and interact with subsequent layers.
• Multi-junction cells are produced in the same way as gallium
arsenide cells—slowly depositing layers of material onto a
single crystal base, making them very expensive to produce,
and only commercially viable in concentrated PV systems and
space applications.

Photovoltaic Technologies
Crystalline
Silicon cells
CdTe
CIS/CIGS
Poly crystalline
Mono crystalline
Thin Film Cells
Microcrystalline
Amorphous
Silicon

Emerging Cell Technologies
• Electricity can be produced through the interaction
of light on many other materials as well. Perovskite solar
cells, named after their specific crystal structure, can be
produced from organic compounds of lead and elements
such as chlorine, bromine or iodine.
• They are relatively cheap to produce and can boast
efficiencies close to those of commercially
available silicon cells but they are currently limited by a
short lifespan.
• Organic solar cells consist of layers of polymers and can
be produced cheaply at high volumes. These cells can be
produced as a semi-transparent film but suffer from
relatively low efficiencies.

Perovskite solar panel

Emerging Cell Technologies
• Dye-sensitized solar cells can be produced using
semiconducting titanium dioxide and a layer of 'sensitizer'
dye only one molecule thick. These cells boast modest
efficiencies but cannot withstand bright sunlight without
degrading. Quantum dots utilize nanotechnology to
manipulate semiconducting materials at extremely small
scales. 'Nanoparticles' consisting of a mere 10,000
atoms can be tuned to different parts of the solar
spectrum according to their size and combined to absorb a
wide range of energy.
• Although theoretical efficiencies are extremely high,
laboratory test efficiencies are still very low.

What do we mean by photovoltaics?
The word itself helps to explain how
photovoltaic (PV) or solar electric
technologies work. First used in about
1890, the word has two parts: photo, a
stem derived from the Greek phos, which
means light, and volt, a measurement unit
named for Alessandro Volta (1745-1827),
a pioneer in the study of electricity.
So, photovoltaics could literally be translated as light-
electricity. And that's just what photovoltaic materials and
devices do; they convert light energy to electricity, as
Edmond Becquerel (photo) and others discovered in the
18th Century.

III. PHOTOVOLTAIC (PV) TECHNOLOGIES
• Photovoltaic cells are semiconductor devices which convert
energy of light into electricity.
• A semiconductor is a substance, usually a simple element or a
compound, that can conduct electricity under some conditions
but not always, making it a good medium for the control of
electric current.
• Silicon, a group IV element, is the most commonly used
semiconductor for PV cells.
• Other materials from a combination of group III and group V
(called III-V semi-conductors), or from group II and group VI
(called II-VI semiconductors) are also used.

• Examples of compound semiconductors: GaAs (Gallium
Arsenide), GaP (Gallium Phosphide), AlAs (Aluminum
Arsenide), AlP (Aluminum Phosphide) and InP (Indium
Phosphide).
• The conduction property of pure semiconductor is altered
by a process called doping to produce p-type and n-type
material.
• A PV cell is made up of combining p-type and n-type
semiconductors.

Photo Voltaic cell
Electrode
P-Type Semiconductor
N-Type Semiconductor
Reflect-Proof Film
Electrode
Solar Energy
Load
Electric
Current
Fig-2: Schematic of PV CELL
• Schematic of a PV cell is shown in Fig. 2 and its working is as
follows:

• When photons hit the p-n junction
(Fig. 3), electrons are knocked
loose from the valence band and
raised to the conduction band
overcoming the band-gap energy,
Eg. (The valence band is the
highest range of electron energies
in which electrons are not free to
move and the conduction band is
the lowest range of electron
energy in which they are free to
move).
Fig3 : energy Bands

Efficiency over a Range of Relatively Photovoltaic Generator Powers
• In case of silicon, the energy gap is 1.12 eV. That means
photons with energy level 1.12 eV and above will result in cell
current, while energy level below 1.12 eV will pass through
without absorption.
• The lifting of electron from valence band to conduction band
results in a hole in the valence band.
• The free electrons in the conduction band and holes in the
valence band are responsible for the current flow, when the
PV cell is connected across a load.

How to use the energy of electrons to
generate electricity?
• To be able to use this
energy, the photovoltaic
solar cell is closed with
the aid of contacts to a
load: electrons flow via the
load to the rear-side
contact of the photovoltaic
solar cell and electricity is
generated.

Tandem cells
One method to increase the efficiency of a solar cell is to split the
spectrum and use a solar cell that is optimised to each section of
the spectrum.
Tandem solar cells can either be
individual cells or connected in
series. Series connected cells are
simpler to fabricate but the current is
the same though each cell so this
contrains the band gaps that can be
used. The most common
arrangement for tandem cells is to
grow them monolithically so that all
the cells are grown as layers on the
on substrate and tunnel junctions
connect the individual cells.

Spectrolab’s Triple-Junction Solar Cell
 Spectrolab has reported a conversion efficiency of 40.7% with this
solar cell structure operating at ~ 250 suns.
 More recently Fraunhofer ISE has obtained an efficiency of 41.1% with
a triple-junction cell operating at ~ 454 suns.

Tandem Technology

Solar cells – number of elements
• Single elements – Si, Ge
• Binary compounds (two elements) – GaAs, InP,
CdTe
• Ternary compounds (three elements) – Aluminium
Gallium Arsenic (AlGaAs), HgCdTe
• Quaternary – Copper Indium Gallium Selenide
(CIGS), InGaAsP
• - ve Copper
• + ve Aluminum .
10/27/2022 JNK /Solar cell 74

First Solar to produce solar
modules with tandem technology
• Evolving from a single-product company, SunPower is now
moving to provide the “full energy product eco-system” by
providing storage, EV charging, smart home solutions. And
soon SunPower will offer choices in solar modules.
SunPower CEO, chairman and director, Peter Faricy,
announced its new partnership with First Solar, calling it
“Tandem Technology” that will combine First Solar’s thin-film
semiconductor design with crystalline silicon. The stacked
tandem solar module could be available to customers as
soon as 18 months.

• The design differs from traditional silicon or thin film modules,
using two different photovoltaic absorbers to harvest more
energy. SunPower says that it will be the most sophisticated
technology commercially available to residential customers
and that it will significantly raise the bar for solar module
efficiency and aesthetics.

• Meanwhile, SunPower has ambitious plans for the residential
market, having recently sold its Commercial & Industrial
Solutions (CIS) to TotalEnergies, majority owner of SunPower.
In November of last year SunPower hinted at its move away
from commercial and more deeply into residential. In February
of this year, the company signed the definitive agreement with
TotalEnergies, and confirmed that SunPower was putting its
eggs in the residential basket

• For improving the efficiency of a PV cell over the SQ
limit, several means are being tried.
These include:
I. use of more than one semiconductor material in a cell,
II. use of more than one junction in a cell, in which energy of
individual colour of lights is absorbed by using a different
material,
III. concentrator photovoltaics (CPV) in which lenses and mirrors are
used to focus sunlight onto multi-junction cells and (iv) PV-
thermal hybrid collector (PVT), which converts solar radiation
into heat and electric energy.
PHOTOVOLTAIC (PV) TECHNOLOGIES

The following are the different types of solar cells.
1. Crystalline silicon solar cell (c-Si)
2. Amorphous Silicon solar cell (a-Si)
3. Cadmium telluride solar cell (CdTe)
4. Copper indium gallium selenide solar cells
(CI(G)S)
5. Gallium Arsenide solar cell (GaAr)
6. Concentrated PV cell (CVP and HCVP)
7. Biohybrid solar cell.
8. Dye-sensitized solar cell (DSSC)
What are the types of solar cells?

Standard Solar Panel Dimensions
• Standard solar panels come in two common
configurations: 60-cell and 72-cell.
• An individual solar cell is a 6” x 6” square.
60-cell panels are laid out in a 6×10 grid. 72-
cell panels are laid out in a 6×12 grid, making
them about a foot taller.
• 60-cell panels: 39″ x 66″ (3.25 feet x 5.5 feet)
• 72-cell panels: 39″ x 77″ (3.25 feet x 6.42
feet)
Solar Panel Size chart
Configuration Width Height Depth
60-cell 39″ 66″ 1.3 – 1.6″
72-cell 36″ 77″ 1.3 – 1.6″
96-cell 41.5″ 62.6″ 1.38″
Solar Panel Size
Chart

Longi’s heterojunction solar cell hits 26.5%
Longi's solar cell achieved a fill
factor of 86.08%.

Solar Technology classification

• PERC Solar Cells - What Exactly
Is PERC Solar Cell Technology? ...
• To start, PERC stands for Passivated
Emitter and Rear Cell technology and in
the simplest terms, it means that
manufacturers add an extra layer to the
rear side of a solar cell, as seen below.
10/27/2022 JNK /Solar cell 83
PERC

• A HIT solar cell is composed of a mono
thin crystalline silicon wafer surrounded by
ultra-thin amorphous silicon layers.
• The acronym HIT stands for
Heterojunction with Intrinsic Thin layer.
• HIT cells are produced by the Japanese
multinational electronics corporation
Panasonic
HIT Cell

Bifacial solar Cell
• Bifacial solar cells are
designed to allow light to
enter from both sides. ...
Rather than cover the
entire back surface with a
reflective aluminium
contact, a 'finger' grid is
used in its place in order to
allow sunlight through the
rear.

• A cell is the basic building
block of a PV system with
power output of around 4 W.
To get higher outputs, many
cells are connected in series
to form a module.
Fig 4 a typical CELL

• A module may have 48, 60, 72, or higher number of cells in series.
For higher power outputs, modules are connected in series and
parallel as arrays.
• Fig. 4 shows a typical PV cell and a module. Data sheet of a 72 cell
module is shown in Table 1.

Solar Modules

• The PV datasheet values are derived at STC (Standard Test
Conditions). STC represents; irradiance: 1000 W/m2, module temp.:
25 °C, wind speed: 0 m/s, AM 1.5, and light incidence angle: 90°.
• Air mass (AM) represents the optical path length of the Earth's
atmosphere.
• At sea level during mid-day, AM is 1.0. AM 1.5 means the light has
to travel atmospheric depth of 150% than that at mid-day.

• The single diode model (shown in Fig. 6) of a solar PV is used
by the manufacturers to represent the PV data.

Fig-7: Current-Voltage & Power-Voltage curves of a PV module

Table -2 Comparison of Common PV technologies

• A wide range of PV technologies are currently available.
Popular among them include silicon based mono and poly
crystalline, thin-film technologies of amorphous silicon (a-Si),
cadmium telluride (CdTe), copper-indium-gallium-diselenide
(CIGS), multi-junction & emerging technologies such as
Organic PV (OPV) and Concentrating PV (CPV) technologies.

• PV types differ according to the material, manufacturing
process, efficiency and cost. Crystalline silicon modules
represent about 85% of the global PV market.
• Space requirements for crystalline PV are around 7 - 8
m2/kW (4.5 - 5 acres/MW) and for thin-film PV, it is around
10 - 15 m2/kW (9 - 10 acres/MW).
• Table 2 shows a comparison of common PV technologies.

III. PHOTOVOLTAIC (PV)
TECHNOLOGIES
Fig. 8: Energy conversion efficiency and losses in a PV cell

PHOTOVOLTAIC Modules
These modules are oriented to
face the Sun.
For residential use, panels can
be placed on the rooftop to
generate electricity for the
home.
For utility scale electricity
generation on solar parks,
large numbers of these panels
are arranged in an array to
collect significant amounts of
electricity.

• Basic arrangement of a PV based power generation
system is shown in Fig. 5.
• Major components of the system are: PV array,
inverter(s), a step up transformer in case of high
voltage grid connection and optional trackers.
Fig. 5: Basic arrangement of a solar PV generation system

• A PV system generates DC power, which is converted into AC
power by using inverters, commonly called Central
inverter/String Inverters.
• In a 1000 V inverter, a string may have 18 to 20 modules
connected in series to get around 750 to 950 V DC.
• These inverters may be of transformer-based (TB) or
transformer-less (TL) type.
• TL inverters are more compact, lightweight and have higher
efficiency 97% (nearly 2% more than TB inverters).

• Latest PV inverters use a control philosophy called maximum
power point tracking (MPPT) to optimize the PV power output.
• Maximum power point represents a unique point on the
Current-Voltage (I-V) and the Power-Voltage (P-V) curves at
which a PV module produces its maximum power
corresponding to the available solar radiation.
• The location of MPP is searched using complex algorithms. TL
inverters usually have two MPPT trackers as against one
MPPT in TB inverters.

• For representing the electrical behaviour of a PV cell, it is
usually modelled as an equivalent circuit consisting of a photo-
current source (Iph) in parallel with a single diode D (or two
diodes for more detailed analysis), a shunt resistor (Rsh) and
a series resistor (Rs) in the load branch.
• The I-V and P-V characteristics of a PV module are shown in
Fig. 7.

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N01.1 Photovoltaic Technology.pptx

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