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Chapter 1 An Overview of Photovoltaics
1
Chapter 1
An Overview of Photovoltaics
Contents:
1.1 The Development of Photovoltaics . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Current and Emerging Opportunities . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Advantages of Photovoltaic Technology . . . . . . . . . . . . . . . . . . . . . 3
1.4 Disadvantages of Photovoltaic Technology . . . . . . . . . . . . . . . . . . . 3
1.5 Environmental, Health, and Safety Issues . . . . . . . . . . . . . . . . . . . 3
1.6 Photovoltaic System Components . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.7 Photovoltaic System Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
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The Development of
Photovoltaics
Photovoltaic systems are solar energy systems that
produce electricity directly from sunlight.
Photovoltaic (PV) systems produce clean, reliable
energy without consuming fossil fuels and can be
used in a wide variety of applications. A common
application of PV technology is providing power for
watches and radios. On a larger scale, many utilities
have recently installed large photovoltaic arrays to
provide consumers with solar-generated electricity, or
as backup systems for critical equipment.
Research into photovoltaic technology began
over one hundred years ago. In 1873, British scientist
Willoughby Smith noticed that selenium was
sensitive to light. Smith concluded that seleniums
ability to conduct electricity increased in direct
proportion to the degree of its exposure to light. This
observation of the photovoltaic effect led many
scientists to experiment with this relatively
uncommon element with the hope of using the
material to create electricity. In 1880, Charles Fritts
developed the first selenium-based solar electric cell.
The cell produced electricity without consuming any
material substance, and without generating heat.
Broader acceptance of photovoltaics as a power
source didnt occur until 1905, when Albert Einstein
offered his explanation of the photoelectric effect.
Einsteins theories led to a greater understanding of
the physical process of generating electricity from
sunlight. Scientists continued limited research on the
selenium solar cell through the 1930s, despite its low
efficiency and high production costs.
In the early 1950s, Bell Laboratories began a
search for a dependable way to power remote
communication systems. Bell scientists discovered
that silicon, the second most abundant element on
earth, was sensitive to light and, when treated with
certain impurities, generated a substantial voltage. By
1954, Bell developed a silicon-based cell that
achieved six percent efficiency.
The first non-laboratory use of photovoltaic
technology was to power a telephone repeater station
in rural Georgia in the late 1950s. National
Aeronautics and Space Administration (NASA)
scientists, seeking a lightweight, rugged and reliable
energy source suitable for outer space, installed a PV
system consisting of 108 cells on the United States
first satellite, Vanguard I. By the early 1960s, PV
systems were being installed on most satellites and
spacecraft.
Today, over 200,000 homes in the United States
use some type of photovoltaic technology. Solar
modules contribute power to 175,000 villages in over
140 countries worldwide, producing thousands of jobs
and creating sustainable economic opportunities. In
2001, worldwide sales of photovoltaic products totaled
over 350 megawatts and over $2 billion in the global
market. The applications include communications,
refrigeration for health care, crop irrigation, water
purification, lighting, cathodic protection,
environmental monitoring, marine and air navigation,
utility power, and other residential and commercial
applications. The intense interest generated by current
photovoltaic applications provides promise for this
rapidly developing technology.
1.2
Current and Emerging
Opportunities
Conventional fuel sources have created myriad
environmental problems, such as global warming, acid
rain, smog, water pollution, rapidly filling waste
disposal sites, destruction of habitat from fuel spills,
and the loss of natural resources. Photovoltaic systems
do not pose these environmental consequences. Today,
the majority of PV modules use silicon as their major
component. The silicon cells manufactured from one
ton of sand can produce as much electricity as burning
500,000 tons of coal.
Photovoltaic technology also creates jobs. Solar
industries directly employ nearly 20,000 people and
support over 200,000 jobs in areas such as glass and
steel manufacturing, electrical and plumbing
contracting, architecture and system design, and
battery and electrical equipment manufacturing. By
some estimates, 3,800 jobs are created for every $100
million in PV sales.
The photovoltaic market grows each year.
Economists have predicted that photovoltaics will be
the most rapidly growing form of commercial energy
after 2030, with sales exceeding $100 billion. In fact,
the use of solar and renewable energy is expected to
double by the year 2010, which would create more
than 350,000 new jobs. It is no surprise that this
clean, reliable source of electric power is regarded as
the future of energy production.
PHOTOVOLTAICS: DESIGN AND INSTALLATION MANUAL
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Section 1.1 1.2
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Advantages of
Photovoltaic Technology
Photovoltaic systems offer substantial advantages
over conventional power sources:
Reliability. Even in harsh conditions,
photovoltaic systems have proven their
reliability. PV arrays prevent costly power
failures in situations where continuous
operation is critical.
Durability. Most PV modules available today
show no degradation after ten years of use. It
is likely that future modules will produce
power for 25 years or more.
Low Maintenance Cost. Transporting
materials and personnel to remote areas for
equipment maintenance or service work is
expensive. Since PV systems require only
periodic inspection and occasional
maintenance, these costs are usually less than
with conventionally fueled systems.
No Fuel Cost. Since no fuel source is
required, there are no costs associated with
purchasing, storing, or transporting fuel.
Reduced Sound Pollution. Photovoltaic
systems operate silently and with minimal
movement.
Photovoltaic Modularity. PV systems are
more cost effective than bulky conventional
systems. Modules may be added
incrementally to a photovoltaic system to
increase available power.
Safety. PV systems do not require the use of
combustible fuels and are very safe when
properly designed and installed.
Independence. Many residential PV users cite
energy independence from utilities as their
primary motivation for adopting the new
technology.
Electrical Grid Decentralization. Small-scale
decentralized power stations reduce the
possibility of outages on the electric grid.
High Altitude Performance. Increased
insolation at high altitudes makes using
photovoltaics advantageous, since power
output is optimized. In contrast, a diesel
generator at higher altitudes must be de-rated
because of losses in efficiency and power
output.
1.4
Disadvantages of
Photovoltaic Technology
Photovoltaics have some disadvantages when
compared to conventional power systems:
Initial Cost. Each PV installation must be
evaluated from an economic perspective and
compared to existing alternatives. As the
initial cost of PV systems decreases and the
cost of conventional fuel sources increases,
these systems will become more economically
competitive.
Variability of Available Solar Radiation.
Weather can greatly affect the power output
of any solar-based energy system. Variations
in climate or site conditions require
modifications in system design.
Energy Storage. Some PV systems use
batteries for storing energy, increasing the
size, cost, and complexity of a system.
Efficiency Improvements. A cost-effective use
of photovoltaics requires a high-efficiency
approach to energy consumption. This often
dictates replacing inefficient appliances.
Education. PV systems present a new and
unfamiliar technology: Few people
understand their value and feasibility. This
lack of information slows market and
technological growth.
1.5
Environmental, Health,
and Safety Issues
Electricity produced from photovoltaics is much
safer and more environmentally benign than
conventional sources of energy production. However,
there are environmental, safety, and health issues
associated with manufacturing, using, and disposing
of photovoltaic equipment.
The manufacturing of electronic equipment is
energy intensive. On the other hand, photovoltaic
modules produce more electricity in their lifetimes
than it takes to produce them. An energy break-even
point is usually achieved after three to six years.
As with any manufacturing process, producing
PHOTOVOLTAIC ELECTRIC PRINCIPLES
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Section 1.3 1.5
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