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Photovoltaic System in Progress: A Survey of Recent Development

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This paper provides a comprehensive update on photovoltaic (PV) technologies and the materials. In recent years, targeted research advancement has been made in the photovoltaic cell technologies to reduce cost and increase efficiency. Presently, several types of PV solar panels are commercially utilized and playing an important role in the market. Three generations of photovoltaic technologies are investigated and discussed; Crystalline Silicon Technology categorized as first generation of PV technology, Thin Film Technologies are second generation of PV technologies and Multi-junction Cells falls in the third generation PV technologies. However, Multi-junction Cells are still considered new and have not yet achieved commercialization status. The fundamental change observed among all generations has been how the semiconductor material is employed and the development associated with crystal structure. Silicon remains the prominent semiconductor within photovoltaic.
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Photovoltaic System in Progress: A Survey
of Recent Development
Ghulam Mustafa Shoro(B
), Dil Muhammad Akbar Hussain(B
),
and Dezso Sera(B
)
Aalborg University Denmark, Aalborg, Denmark
{gms,akh,des}@et.aau.dk
Abstract. This paper provides a comprehensive update on photovoltaic
(PV) technologies and the materials. In recent years, targeted research
advancement has been made in the photovoltaic cell technologies to
reduce cost and increase efficiency. Presently, several types of PV solar
panels are commercially utilized and playing an important role in the
market. Three generations of photovoltaic technologies are investigated
and discussed; Crystalline Silicon Technology categorized as first gener-
ation of PV technology, Thin Film Technologies are second generation of
PV technologies and Multi-junction Cells falls in the third generation PV
technologies. However, Multi-junction Cells are still considered new and
have not yet achieved commercialization status. The fundamental change
observed among all generations has been how the semiconductor mate-
rial is employed and the development associated with crystal structure.
Silicon remains the prominent semiconductor within photovoltaic.
Keywords: Solar cell technologies ·Photovoltaic technologies ·PV
technologies
1 Introduction
Energy is such an important component without which our modern world will
not be operational. Increasing global energy demand is one of the greatest chal-
lenges experienced by modern society. Today, main share of the energy gener-
ated worldwide is obtained from fossil fuels. Due to the reported decline in world
reserve of such fossil energy sources, as well as the environmental impacts asso-
ciated with their use, alternatively energy sources are the only solution. Solar
energy is an affordable, abundant and clean technology and one of the renewable
energy sources which could eliminate impending energy crises associated with
rising oil prices, global warming, environment and others energy issues. Solar
energy technologies consist of photovoltaic, solar thermal electricity, solar archi-
tecture and solar heating. Due to the climbing efficiencies in Table 1coupled with
lower PV module prices in Fig. 1, the production of photovoltaic cells and arrays
have advanced greatly and penetration in photovoltaic system has observed to
be growing. Table 1and Fig. 1is taken from reference [3], it can be seen that
c
Springer International Publishing Switzerland 2014
F.K. Shaikh et al. (Eds.): IMTIC 2013, CCIS 414, pp. 239–250, 2014.
DOI: 10.1007/978-3-319-10987-9 22
240 G.M. Shoro et al.
Table 1. Module Efficiency [3]
Technologies Module efficiency Surface area needed for 1 kwp
Mono-crystalline Silicon 13 %–19 % 5–8 m2
Poly-crystalline Silicon 11 %–15 % 7–9 m2
Copper Indium Gallium Selenide CIGS 10 %–12 % 8–10 m2
Cadmium Telluride (CdTe) 9 %–12 % 9–11 m2
Amorphous Silicon (a-Si) 5%8% 13–20 m2
Fig. 1. Module price trend [3]
how efficiency for these different technologies varies with the surface area (to get
1 kwp) and it can also be seen that the price variations in all the technologies as
modules have approximately similar downhill slope.
Photovoltaic system is comprised of PV cells assembled into modules, which
are connected into arrays, and the so called balance of system (BOS) components
[2]. A PV system can produce outputs from microwatt to megawatt. Global focus
has increasingly shifted from using conventional methods of generating electricity
to photovoltaic system and large investments have been made with the testing
and installation of large PV power plants [3]. Currently, the use of photovoltaic
system placed after the use of wind and hydro power, as the biggest renewable
power source with regards to globally installed capacity. Considering the cost and
the fact that PV systems is limited in generating any power during night periods
demands that the highest possible efficiency during day light hours should be
achieved which is very critical for solar power viability. So, the trend is going
in a right direction, so that the reduction in the cost of PV systems will be
accomplished through improved materials usage and higher efficiencies. In this
context the paper reviews the current status of three generations of photovoltaic
technologies and investigates their reliability, efficiency and cost. Furthermore,
developments and future potentials with these systems will also be summarized.
Photovoltaic System in Progress: A Survey of Recent Development 241
2 Solar Resource and Worlds Energy Consumption
2.1 The Solar Potential
The Sun is the main source (directly or indirectly) of almost all power, used on
earth. The Sun is center of our solar system and 150 million kilometers away from
the earth [4]. Solar energy is the radiant heat and light from the sun. This energy
supports life and can be converted to other forms of energy that are useful to
humans. The radiation emitted by the sun is estimated to be about 63 MW/m2
of this huge solar potential, the energy that reaches the earths surface without
any significant absorption is measured to be 1353–1366 W/m2; this is referred as
the solar constant [5]. A normal quantity of solar radiation reaching the surface
of Earth is 1.05 ×105terawatts (TW) in a year, even though global electricity
need averages 1.99 (TW) in a year [6].
2.2 History of Solar Cells
Solar energy has been used to produce electrical power for a couple of centuries
using a range of constantly evolving technologies. The Table2shows a summary
on the progress of the PV cells with time [7]. Solar cells were developed during the
1950s, primarily at the Bell Telephone laboratories. These cells proved to be the
best power sources for extra-terrestrial missions, and more than 1000 satellites
using solar cells were launched between 1960 and 1970. In mid-seventies, efforts
were initiated to make solar cells for terrestrial applications. Last three decades
saw newer device technologies enabling reduction in cost and hence opening new
horizons for commercial applications of solar cells.
Table 2. Dates of relevance to photovoltaic solar energy conversion [7]
Scientists and innovations Year
Edmond Becquerel discovered the photovoltaic effect 1839
W.G. Adams and R.E. Day observed photovoltaic in selenium 1876
Max Planck claimed the quantum nature of light 1900
Alan Wilson proposed quantum theory of solids 1930
Mott and Schottky develop the theory of solid-state rectifier diode 1940
Schottky, Bardeen and Brattain invented the transistor 1949
Pearson, Charpin and Fuller announced 6 % efficient silicon solar cell 1954
Reynolds et al. highlight solar cell based on cadmium sulphide 1954
First use of solar cells on an orbiting satellite Vanguard 1 1958
242 G.M. Shoro et al.
3 Basics of Photovoltaic
3.1 Photovoltaic Effects
Photovoltaic effect can be observed when certain semiconductor materials exposed
to sunlight. Using this technique, semiconductors which have the photovoltaic
effect can then be used to convert solar rays into direct current electricity.
3.2 Principle of Solar Cell Operation
A solar cell is a semiconductor electrical junction device which is usually made up
of element silicon. Sunlight is composed of energy packets called photons. These
photons consist of energy packets corresponding to the different wavelengths
associated with light [8]. When a solar cell is struck by photons with appropriate
energy, the photons are consumed through the space charge region of the p-n
junction of cell, this leads to transfer of the photons energy to an electron. The
electron thus becomes excited to knock free from its atoms and electron hole
pairs formed in the junction. In order to generate electricity, the electrons and
holes need to be separated. When a load is connected at the terminals that
causes an electron current flow and electrical power is available at the load. The
free electron movement from one layer to the next generates electricity. Due to
well-designed structure of photovoltaic cell, the electrons are permitted to go in
one way. An array of solar cells converts solar power into direct current (DC)
electrical power.
4 Photovoltaic Technologies
Photovoltaic power generation uses solar panels and these panels are composed
of an array of packaged solar cells, constructed from semiconductor material.
At present, materials used for photovoltaic cells are consists of monocrystalline
silicon, polycrystalline silicon, amorphous silicon cadmium telluride and copper
indium gallium selenide. Figure 2provides how different types of solar cells are
constructed; this figure has been taken from reference [1]. The following subsec-
tions will provide the brief description of these materials.
4.1 Crystalline Silicon Cell Technologies
Solar cells constructed with crystalline silicon (Si) semiconductor are most effi-
cient [1]. Silicon is currently predominating solar cell material and is expected
to remain dominant until a more inexpensive material and higher efficiency PV
technologies are developed [7]. As outlined by NREL, throughout 2011, 90%
of market sales were from Silicon based photovoltaic (PV) products and the
annual production of Si-based PV was reported to reach 15 GW [9]. However,
crystalline silicon solar cells achieved the highest efficiency on the expense of
high manufacturing cost.
Photovoltaic System in Progress: A Survey of Recent Development 243
Fig. 2. Types of solar cell [1]
4.1.1 Monocrystalline and Multicrystalline
A crystalline silicon solar cell could be designed with distinct techniques such as
the industry dominating single-crystalline/monocrystalline and polycrystalline/
multi-crystalline techniques. Commercial manufacture of standard monocrys-
talline silicon cells has obtained a good efficiency of 17–18 % [1], although
multicrystalline silicon cells currently have achieved 16–17 % efficiencies. Tech-
nological developments are currently in progress to develop cells with higher
efficiencies [1]. Crystalline cells are made from silicon wafers simply by cleaning
as well as doping the particular wafer and in a separate manufacturing process;
several cells are then wired up to form a module.
4.1.2 Hetrojunction with Intrinsic Thin Layer (HIT)
HIT (Hetrojunction with Intrinsic Thin-layer) solar cells are attracting a growing
number of interests after appearing in 1992. When compared to a-Si solar cells,
the efficiency of HIT solar cells is much higher [10]. On the other hand, the low
temperature technology of HIT solar cells makes it possible to reduce cost by
the application of low quality Si materials and high temperature performance
is improved a lot compared to the c-Si solar cells. HIT Cell design processes
involve an ultra-thin layer of amorphous silicon that is deposited on both faces
of textured or thin single-crystal wafer [1]. Efficiency of HIT cells can be improved
using both crystalline and amorphous silicon layers to efficiencies over 22 %.
4.2 Thin Film Cells Technologies
Silicon as a solar cell material has many advantages; however, it also conveys
disadvantages. Table 3from reference [13] describes that silicon is an indirect
semiconductor and its absorption coefficient near to band edge is low. Thus, a
fairly thick substrate is required for crystalline silicon cell manufacturing. This
leads to substantial material and mechanical processing costs.
244 G.M. Shoro et al.
Table 3. Properties of common solar cell material [13]
Material Ge CuInSe2 Si Ga CdTe
Type Indirect Direct Indirect Direct Direct
Band gap (eV) 0.67 1.04 1.11 1.43 1.49
Absorption edge (µm) 1.85 1.19 1.12 0.87 0.83
Absorption coef. (cm1) 5.0×1041.0×1051.0×1031.5×1043.0×104
Thin-film technology is an attempt to reduce the cost and maintain the effi-
ciency of crystalline solar cells. Thin-film technology uses direct semiconductor
materials which has absorption coefficient higher than silicon. This means that
fewer micrometers of thickness of semiconductor material are sufficient for the
development of solar cells. Thin film solar cells could therefore be manufac-
tured with small amount of semiconductor material leading to decreases in price
ranges. The cost of raw material is much lower than the capital equipment and
processing since thin film production unit requires more space. Thin film cells
are prepared by depositing layers of semiconductor material barely 0.3–2µm
thick onto glass or stainless steel substrates [11]. This provides roll-to-roll layer
that gives positive aspects with reference to manufacturing and current carrying
capability. Efficiencies of 11–14 % have been achieved with this construction [12].
Thin film technologies including amorphous silicon/microcrystalline silicon
(a-Si/c-Si), Copper Indium Selenide (CIS), Cadmium telluride (CdTe) absorb the
solar spectrum and are much more efficiently than c-Si or mc-Si [14]. Presently,
the thin film technologies a-Si/c-Si, CIS, CdTe have included integrated adjust-
ments to help size fabrication and enjoy good commercial results. Overall, thin
film solar panels are less efficient but widely used in PV industry due to its afford-
ability. Figures 3and 4shows the relative efficiency of these technologies and the
market share by them respectively [15].
4.2.1 Amorphous Silicon/Microcrystalline (a-Si/c-Si)
Amorphous silicon was developed in the early days of thin film technologies. It
is a non-crystalline form of silicon. It requires small quantity of active material
and has considerably better light absorption capability i.e. 1 µm thick film will
absorb light significantly better when compared with crystalline silicon. Thin film
a-Si solar cell provides an advantage since cells can be manufactured onto rigid
(glass) or flexible substrates and could potentially offer lower costs. However,
the disordered nature of the amorphous silicon results in dangling bonds and
lattice defects. Consequently this produces less charge carriers as a result of
the lower efficiency i.e. 4–8%. In spite of low reported efficiencies, amorphous
silicon is mass produced for applications where efficiency is not crucial and can
be tolerated.
Photovoltaic System in Progress: A Survey of Recent Development 245
Fig. 3. Efficiency comparison of technologies [15]
Fig. 4. Market share of thin-film technologies related to total worldwide PV produc-
tion [15]
4.2.2 Copper Indium Selenium (CIS) or Copper Indium Gallium
Diselenide (CIGS)
Copper Indium Selenium (CIS) is designed to obtain higher optical absorp-
tion coefficients along with electrical characteristics enabling device tuning [7].
Among all thin-film modules, CIGS and CIS technologies have the maximum
efficiencies. 20 % efficiency has been recorded under laboratory conditions. Com-
mercially available modules possess 7–12% efficiency [1]. A long-term issue with
CIS technology is however the available resources. All known reserves of indium
would only produce enough solar cells to provide a capacity equal to all present
wind generators [16]. The main problem associated with CIGS modules has been
the limited capability to scale up the procedure regarding large throughput, large
yield along with low-cost. Several deposition methods are used: sputtering, ink
246 G.M. Shoro et al.
printing and electroplating [7,17,18] with each having different throughput and
efficiencies. Currently, research about deposition processes is at a development
stage with specific concentration on making this technology cheaper from a busi-
ness perspective to compete with Silicon modules [19].
4.2.3 Cadmium Telluride (CdTe)
Cadmium Telluride is the most cost-effective and efficient thin film technology.
CdTe modules usually are low-priced compared to c-Si, with a higher efficiency
with regard to a-Si thin film technology. The efficiency of CdTe modules is in
the range of 7–11% (lower than c-Si), but greater in comparison with single
junction a-Si [20]. CdTe solar panels are manufactured on glass. CdTe panels
perform significantly better in high temperatures and in low irradiation levels
[21]. CdTe are toxic and have low natural abundance [22] but various research
reports showed that module recycling is necessary for CdTe to solve toxicity and
the future availability problem of Tellurium.
4.2.4 Dye-Sensitized Cells (DSC)
Dye-Sensitized Cell (DSC) is a successful thin-film photovoltaic cell with demon-
strated good results. Inspired by the principle of natural photosynthesis, Dye-
Sensitized Solar cells have become a credible alternative to solid-state pn junction
devices [22]. Conventional roll-printing techniques are widely-used to manufac-
ture DSCs and most of the materials utilized are usually low-cost. DSCs offer
the possibilities to design solar cells with a large flexibility in shape, color, and
transparency [23]. They absorb more sunlight per surface area than standard
silicon-based solar panels. Its efficiency is comparable to amorphous silicon solar
cells but with a much lower cost [24]. Dye-sensitized solar cells can be potential
replacements for silicon-based solar cells. Uncomplicated processing, low-cost
material resources along with broad range of applications are reasons support-
ing DSCs. A limitation issue of the dye-sensitized cells is its stability over the
time and the temperature range which occurs under outdoor conditions [25].
4.2.5 Organic Solar Cell
High efficiency Photovoltaic technologies are usually produced from inorganic
materials, which often require higher material price together with manufacturing
price. In recent years, organic solar cells have attracted scientific and economic
interest. This was mainly triggered by growing demand for cost-effective pro-
duction of photovoltaic modules. Organic semiconductors represent promising
approaches as they use plastic which have low production costs in high vol-
umes and can be processed into large-areas. The optical absorption coefficient
of organic molecules is higher; consequently a substantial amount light might be
consumed with a small amount of materials. The drawback related with organic
photovoltaic cells is reduced efficiency, low stability and low strength when com-
pared with inorganic photovoltaic cells [26]. Significant challenges related to
Photovoltaic System in Progress: A Survey of Recent Development 247
organic cells are low efficiency, low stability, and low strength to protection
against environmental influences compared to inorganic photovoltaic cells.
4.3 Multi-junctions Cells Technologies
The efficiency of solar cells can be significantly enhanced by stacking several p-n
junctions in a cell [25]. Alloys of semiconductors with various band gap energies
are layered on top of one another. The band gap energy indicates the wave length
until which a semiconductor may process light and convert it into electricity [1].
This makes best possible use of the energy contained in the solar spectrum.
Although solar cells designed with one semiconductor material have achieved
theoretical efficiencies of 33 % and solar cells using two semiconductors with dif-
ferent band gaps have shown 42 % efficiencies [1]. Multijunction cells constructed
from alloys merging the elements of group III and group V semiconductor mate-
rials in the periodic table, showed higher efficiencies matched by simply no other
existing photovoltaic technology. Multijunction cells are composed off 3 layers of
material which have different band gap while the bottom layer has the smallest
band gap. This design allows less energetic photons to pass through the upper
layers and be absorbed by lower layers which boost the overall efficiency of solar
cells [27].
5 Current Status of PV System
5.1 PV Modules and Balance of System (BOS)
Photovoltaic systems have two key subsystems, PV modules and Balance of Sys-
tem (BOS). A PV module is a grid of PV cells. It has 72 cells wired in several
parallel circuit packaged in metal frame for strength. Modules are protected from
weather with lamination on front and back surfaces. Under standard conditions,
commercial solar modules produce power capacity of 175–300 W. A PV array
is a group of modules attached serially and strongly affixed to a firm struc-
ture. BOS are secondary components which are required to install PV modules
and arrays. It contain wires for connecting modules in series, junction boxes
for merging the circuits, power electronics for managing the PV arrays output
and mounting hardware. BOS requirements differ caused by reliability, environ-
mental conditions, power storage and site-specific power needs. The expansion
of photovoltaic market has produced higher system integration and experienced
system designers and installers. As a result, BOS cost reduced and this reduction
are comparable to or even higher than module cost reductions.
5.2 PV Installation, Manufacturing, and Cost
Solar system is the fastest growing energy source in the world, powering homes,
businesses and utility grids across nations. The solar photovoltaic (PV) indus-
try has experienced 2012 to be an historic year. According to figures from the
248 G.M. Shoro et al.
Fig. 5. Annual installations and cumulative PV capacity [28]
Table 4. Outlook for the solar sector (2011–2016) [29]
2011 2012 2013 2014 2015 2016
Global installations (GW/yr) 28 34 34 43 52 54
Average Chinese module price ($/W) $1.31 $0.74 $0.66 $0.73 $0.74 $0.66
Global revenue pool ($bn) $103 $99 $96 $122 $138 $132
Manufacturing operating profit pool ($bn) $0 $9 $7 $3 $1 $1
BOS and trading operating profit pool ($bn) $14 $10 $11 $15 $16 $15
Global system operating profit pool ($bn) $15 $0 $4 $11 $17 $14
Manufacturing operating profit margin (%) 1% 32 % 31 % 10% 2% 2%
Global operating profit margin (%) 14 % 0% 4% 9% 12 % 11 %
EPIA [28], the cumulative global installed PV capacity passed the 100-gigawatt
(GW) mark, achieving just over 101 GW in 2012. The solar PV industry has
installed 30 GW capacity around the world and made it operational within 2012.
In 2011, cumulative global installed PV capacity was around 70 GW. The expo-
nential growth rate in installed capacity seen in recent years, global progression
in PV installations outside Europe with a least 13 GW allowed the global mar-
ket to reach the 30GW mark again in 2012. Figure 5shows the evolution of
PV capacity globally, which indicate an exponential growth [28]. According to
Photon consulting [29], installation volume is expanding rapidly across an exten-
sive set of markets segments far from European countries, with bright prospects
for growth in Brazil, Chile, China, India, Israel, Japan, South Africa, Thailand,
Ukraine, U.K. and U.S. In 2010 more than 450 companies was active in PV
manufacturing, within two years (by 2012) the figure is reduced to 154 which
is even less than half. The reason is not being closer to the markets, most did
not learn to adjust and adapt by listening to markets and getting closer to the
customers. In reality, companies need tighter supply chains and more timely
Photovoltaic System in Progress: A Survey of Recent Development 249
local market knowledge to adjust products, production, bundles, shipments and
prices. It is expected that global PV installations will be 54 GW/year, module
price reduction and increased revenue pool, manufacturing operating profit pool,
BOS and trading operating profit pool, in 2016 [29]. The following Table 4taken
from reference [29] shows a comprehensive/forecast data of the solar sector; from
installation, price revenue to BOS and profit etc., by the year 2016.
6 Conclusion
Today, Photovoltaic has more significant impact upon energy use, huge number
of individuals making use of PV technology to power their homes and busi-
nesses, electric utility companies are also using it for large power grid stations.
Photovoltaic costs have been gradually decreasing due to on-going advances
in technology and rapid growing demand for photovoltaics system. Crystalline
Silicon PV technology has highest efficiency but they are costly. Fabrication,
installation and operational cost reduction is possible. We observed during the
investigation of various technologies that we can expect small advances in the
production efficiencies. However, the on-going research on new concepts for PV
materials will certainly lead to greater efficiency and will make it less expensive
in the coming years. The chances of getting to this goal are good due to wide
variety of promising materials and the various concepts which have emerged
[25]. Thin-film PV technologies requires only small amounts of material. It is
advantageous for high-volume manufacturing and low material costs. Third gen-
eration PV technologies are new and not fully developed yet but expected to
reduce the cost and enhance the performance of solar cells. Third generation
technologies includes some multi-junction constructs and concepts based on the
emerging fields of quantum technology, nanotechnology, optical meta materials
and polymer semiconductor science.
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... The silicon-based photovoltaic (PV) technology is under continuous improvement [1,2] and nowadays plays an essential role in the decarbonisation of electrical systems mainly due to its feasibility, competitive costs and the achievement of high efficiencies [3][4][5]. ...
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Book
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Written in clear, concise language and designed for an introductory applied energy course, Applied Energy: An Introduction discusses energy applications in small-medium enterprises, solar energy, hydro and wind energy, nuclear energy, hybrid energy, and energy sustainability issues. Focusing on renewable energy technologies, energy conversion, and conservation and the energy industry, the author lists the key aspects of applied energy and related studies, taking a question-based approach to the material that is useful for both undergraduate students and postgraduates who want a broad overview of energy conversion. The author carefully designed the text to motivate students and give them the foundation they need to place the concepts presented into a real-world context. He begins with an introduction to the basics and the definitions used throughout the book. From there, he covers the energy industry and energy applications; energy sources, supply, and demand; and energy management, policy, plans, and analysis. Building on this, the author elucidates various energy saving technologies and energy storage methods, explores the pros and cons of fossil fuels and alternative energy sources, and examines the various types of applications of alternative energies. The book concludes with chapters on hybrid energy technology, hybrid energy schemes, other energy conversion methods, and applied energy issues. The book takes advantage of practical and application-based learning, presenting the information in various forms such as essential notes followed by practical projects, assignments, and objective and practical questions. In each chapter, a small section introduces some elements of applied energy design and innovation, linking knowledge with applied energy design and practice. The comprehensive coverage gives students the skills not only to master the concepts in the course, but also apply them to future work in this area.
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The following values have no corresponding Zotero field: Author Address: Solopower Inc.
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