Encyclopedia of Global Resources part 101 pptx

Petroleum fuels. See Gasoline and
other petroleum fuels
Petroleum refining and processing
Category: Obtaining and using resources
Petroleum is separated into a variety of fuels—gaso-
line, kerosene, and diesel fuel—and into feedstocks for
the chemical industry. Petroleum is first distilled, then
each of the “cuts” is further treated or blended to pro-
vide the various marketed products. A significant ef-
fort is devoted to gasoline production, in order to ob-
tain the quantities needed and the desired engine
performance.
Background
Petroleum, or crude oil, is found in many parts of the
world. It is not a chemically pure substance of uni-
form properties. Rather, petroleum is a complex mix-
ture of hundreds of individual chemical compounds
that occur in various proportions, depending on the
source and geological history of the particular sam-
ple. As a result, various kinds of petroleum range in
properties and appearance from lightly colored, free-
flowing liquids to black, tarry, odiferous materials. It
would beimpractical todesign furnacesor enginesca-
pable of efficient, reliable operation on a fuel whose
characteristics varied so widely. Therefore, to provide
products of predictable quality to the users, petro-
leum is separated into specific products that, through
treating, blending, and purification, goonthe market
as the familiar gasoline, kerosene, and diesel and
heating oils. Some petroleum supplies also contain
impurities, most notablysulfur compounds, that must

be removed for environmental reasons. The sequence
of separation, blending, treating, and purification
operations all make up the processes of petroleum
refining.
Distillation
The first major step in refining petroleum is distilla-
tion, the separation of components based on boiling
point. In principle, it would be possible toseparate pe-
troleum into each of its component compounds, one
by one, producing many hundreds of individual pure
compounds. Doing so would be so laborious that the
products would be too expensive for widespread use
as fuels or synthetic chemicals. Instead, petroleum is
separated into boiling ranges, or “cuts,” such that
even though a particular distillation cut will still be
composed of a large number of compounds, its physi-
cal properties and combustion behavior will be rea-
sonably constant and predictable.
Many crude oils contain dissolved gases, such as
propane and butane. These are driven off during dis-
tillation and can be captured for sale as liquefied pe-
troleum gas (LPG). The first distillation cut (that is,
the one with the lowest boiling temperature) that is a
liquid is gasoline.Products obtained in higherboiling
ranges include, in order of increasing boiling range,
naphtha, kerosene, diesel oil, and some heating oils
or furnace oils. Some fraction of the crude oil will not
distill; this is the residuum, usually informally called
the resid. The resid can be treated to separate lubri-
cating oils and waxes. If the amount of resid is large, it

can be distilled further at reduced pressure (vacuum
distillation) to increase the yield of the products with
higher boiling ranges and a so-called vacuum resid.
Catalytic Cracking
The product that usually dominates refinery produc-
tion is gasoline. Gasoline produced directly by distilla-
tion, called straight-run gasoline, is not sufficient in
quantity or in engine performance to meet modern
market demand. Substantial effort is devoted to en-
hancing the yield and quality of gasoline. The yield of
straight-run gasoline from very good quality petro-
leum is not more than 20 percent; from poorer quality
crudes, it may be less than 10 percent. About 50 per-
cent of a barrel ofpetroleum needs to be converted to
gasoline to satisfy current needs. Gasolineengine per-
formance is measured by octane number, which indi-
cates the tendency of the gasoline to “knock” (to deto-
nate prematurely in the engine cylinder). Knocking
causes poor engine efficiency and can lead to me-
chanical problems. Most regular grade gasolines have
octane numbers of 87; straight-run gasolines may
have octane numbers below 50.
Increasing the yield of gasolinerequiresproducing
more molecules that boil in the gasoline range. Gen-
erally the boiling range of molecules relates to their
size; reducing the boiling range is effected by reduc-
ing their size, or “cracking” the molecules. Octane
number is determined by molecular shape. The com
-
mon components of most crude oils are the paraffins,

or normal alkanes, characterized by straight chains of
928 • Petroleum refining and processing Global Resources
carbon atoms. These paraffins have very low octane
numbers; heptane, for example, has an octane num-
ber of 0. A related family of compounds, isoparaffins,
have chains of carbon atoms with one or more side
branches; these have very high octane numbers. The
compound familiarly referred to as iso-octane (2,2,4-
trimethylpentane) has an octane number of 100. In-
creasing the yield and engine performance of gas-
oline requires both cracking and rearranging the
molecular structures.
Both of these processes can be performed in a sin-
gle step, using catalysts such as zeolites. For this rea-
son, the overall process is known as catalytic cracking.
The feedstock to a catalytic cracking unit is a high-
boiling cut material of low value. Different refineries
may choose to use different feeds, but a typical choice
would be a vacuum gas oil, which is produced in the
vacuum distillation step. Much effort has gone into
the development of catalysts and into evaluating ap-
propriate choices of temperature, pressure, and reac-
tion time. Catalytic cracking is second only to distilla-
tion in importance in most refineries. It can produce
gasolines with octane numbers above 90 and in-
creases the yield of gasoline in a refinery to about 45
percent.
Catalytic Reforming
Straight-run gasoline and naphthas have acceptable
boiling ranges but suffer in octane number. Treating

these streams does not require cracking, only altering
Global Resources Petroleum refining and processing • 929
Separation and Uses of Petroleum
CRUDE OIL IN
PETROLEUM REFINERY
SEPARATING PURIFICATION
CONVERSION
ASPHALT
INDUSTRIAL
FUEL OIL
DE-WAXING
LUBRICANTS
AND
GREASES
DIESEL
OILS
FUEL
OIL
GASOLINE
BOTTLED
GAS
CRACKING
ROOFING
PAINTS
PLASTICS
PHOTOGRAPHIC
FILM
SYNTHETIC
RUBBER
WEED-KILLERS

AND
FERTILIZERS
MEDICINES
DETERGENTS
ENAMEL
SYNTHETIC
FIBERS
CANDLES
WAXED PAPER
POLISH
OINTMENTS
AND
CREAMS
JET FUEL
SOLVENTS
INSECTICIDES
the shapes of molecules—re-forming them—to en
-
hance octane number.This processalsorelies on cata-
lysts, though ofdifferent types thanthose used in cata-
lytic cracking. Reforming catalysts usually include a
metal, such as nickel or platinum. Catalytic reforming
can produce gasolines with octane numbers close to
100.
Hydrotreating
Other distillation cuts, such as kerosene and diesel
fuel, require less refining. Two processes of impor-
tance for environmental reasons are the removal of
sulfur and removal of aromatic compounds. Since
both involve the use of hydrogen, they are referred to

as hydrotreating.
Sulfur removal—hydrodesulfurization—is done to
reduce the amount of sulfur oxide emissions that
would have been produced when the fuel is burned.
Additionally, sulfur compounds are corrosive and can
have noxious odors. Hydrodesulfurization is per-
formed by treating the feedstock, such as kerosene,
with hydrogen using catalysts containing cobalt or
nickel and molybdenum. As environmental regula-
tions become more stringent, hydrodesulfurization
will become increasingly important.
Aromatic compounds also have several undesir-
able characteristics. Some compounds, such as ben-
zene, are carcinogens. Larger aromatic molecules,
which might be found in kerosene or diesel oil, con-
tribute to the formation of smoke and soot when
these fuels are burned. Soot formation is unpleasant
in its own right, but in addition, some soot compo-
nents are also carcinogens. Aromatic compounds are
reacted with hydrogen to form new compounds—
naphthenes or cycloalkanes—of more desirable prop-
erties.
Resid Treating
Resids can be treated with solvents to extract lubricat-
ing oils (these oils can also be made during the vac-
uum distillation of resid), waxes, and asphalts. Al-
though lubricating oils are produced only in low yield
(about 2 percent of a barrel of crude may wind up as
lubricating oil), they are commercially valuable prod-
ucts. Asphalts are of great importance for road pav-

ing. Resid is also converted by heating into petroleum
coke, a solid material high in carbon content. High-
quality petroleum cokes are used to manufacture syn
-
thetic graphite, which has a range of uses, the most
important of which is for electrodes for the metallur
-
gical industry. Poorer quality petroleum cokes can be
used as solid fuels.
Petrochemicals
Petroleum is the source not only of liquid fuels but
also of most synthetic chemicals and polymers. Some
products having low value as fuels, such as naphtha or
even waxes, can be decomposed to produce ethylene,
the most important feedstock for the chemical indus-
try. Ethylene is converted to polyethylene, polyvinyl
chloride, polyvinyl acetate, and polystyrene, which to-
gether make up a large share of the total market for
plastics. Another petroleum product of great use in
the chemical industry is propylene, the starting mate-
rial for making polypropylene and polyacrylonitrile.
Harold H. Schobert
Further Reading
Berger, Bill D., and Kenneth E. Anderson. Modern Pe-
troleum: A Basic Primer of the Industry. 3d ed. Tulsa,
Okla.: PennWell Books, 1992.
Gary, James H., Glenn E. Handwerk, and Mark J. Kai-
ser. Petroleum Refining: Technology and Economics. 5th
ed. Boca Raton, Fla.: CRC Press, 2007.
Jones, D. S. J. Elements of Petroleum Processing. Chich-

ester, England: John Wiley & Sons, 1995.
Leffler, William L. Petroleum Refining in Nontechnical
Language. 4th ed. Tulsa, Okla.: PennWell, 2008.
Meyers, Robert A., ed. Handbook of Petroleum Refining
Processes. 3d ed. New York: McGraw-Hill, 2004.
Royal Dutch/Shell Group of Companies, comp. The
Petroleum Handbook. 6th ed. New York: Elsevier,
1983.
Speight, James G. The Chemistry and Technology of Petro-
leum. 4th ed. Boca Raton, Fla.: CRC Press/Taylor &
Francis, 2007.
Szmant, H. Harry. Organic Building Blocks of the Chemi-
cal Industry. New York: Wiley, 1989.
Web Site
U.S. Department of Energy, Energy
Information Administration
Refining
/>analysis_publications/oil_market_basics/
refining_text.htm
See also: Gasoline and other petroleum fuels; Oil
and natural gas chemistry; Oil industry; Petrochemi
-
cal products; Propane.
930 • Petroleum refining and processing Global Resources
Phosphate
Category: Mineral and other nonliving resources
Where Found
Phosphate rock ore is mined in Florida and North
Carolina (more than 85 percent of U.S. output), as
well as Idaho and Utah. Major world producers in

-
clude China, followed by the United States, Morocco
and the western Sahara, Russia, Tunisia, and Brazil.
Primary Uses
Phosphate rock is used primarily in the production of
fertilizers. In the United States, more than 95 percent
is used in the manufacture of phosphoric acids, which
Global Resources Phosphate • 931
Data from the U.S. Geological Survey, . U.S. Government Printing Office, 2009.Source: Mineral Commodity Summaries, 2009
28,000,000
11,000,000
600,000
2,400,000
3,700,000
800,000
7,800,000
30,900,000
10,800,000
Metric Tons
60,000,00050,000,00040,000,00030,000,00020,000,00010,000,000
United States
Syria
South Africa
Senegal
Russia
Morocco and
western Sahara
Togo
Tunisia
Other countries

2,300,000
6,000,000
800,000
50,000,000
3,000,000
3,100,000
5,500,000
Egypt
China
Canada
Brazil
Australia
Israel
Jordan
Phosphate Rock: World Mine Production, 2008
in turn are usedto make ammoniumphosphate fertil
-
izers and feed supplements for animals.
Technical Definition
Phosphate rock is a general term for any earth mate-
rial from which phosphorus can be extracted at a
profit. The principal phosphorus-bearing mineral in
these deposits is a hydrated calcium phosphate called
apatite, Ca
5
(PO
4
)
3
(OH). Apatite can also accommo-

date variable amounts of fluorine (F) and carbonate
ion (CO
3
) and contains from 18.0 to 18.7 percent
phosphorus.
Description, Distribution, and Forms
In its organic form, apatite occurs as the main compo-
nent of bones and teeth, and it makes up the shells of
some marine invertebrates. Some phosphate depos-
its, particularly those in Florida, also contain certain
aluminum phosphate minerals. Commercial phos-
phate deposits occur in two major forms: (1) marine
sedimentary deposits, in which phosphate-rich beds
are associated with carbonate rocks (limestones,
dolostones) and mudstones or shales deposited on
the floor of an ocean or shallow sea, and (2) igneous
deposits, in which apatite has crystallized from for-
merly molten plutons (molten magma that solidifies
below ground).
The sedimentary deposits are by far the most im-
portant phosphate producers. In the United States
these areas are located in the eastern states of Florida,
Tennessee, and North Carolina, and the western
states (the “western field”) of Wyoming, Montana,
Idaho, Utah, and Nevada. The most widespread, con-
tinuous deposits of phosphate rock in the United
States occur in the Phosphoria formation of Utah, Wy-
oming, Idaho, Montana, and Nevada.
By far the most important phosphate localities
worldwide are in North Africa and Russia. Elsewhere

in the world, significant deposits are found in North
Africa, specifically Algeria, Tunisia, Morocco, and
Egypt. The principal igneous deposits occur in Russia
(the Kola Peninsula) and in Ontario, Canada.
History
Production started in the United States in 1867, with
mining of the extensive Florida deposits beginning
in 1888. Over time, the price of phosphate rock
jumped—with a notable spike in 2007—as agricul
-
tural demand increased worldwide. The mining of
phosphate rock has also spiked in China, as that na
-
tion’s development escalates. Interest in the produc
-
tion of phosphate has prompted exploration of new
resources, particularly sources off the coasts of Mex-
ico and Namibia.
Obtaining Phosphate
Phosphate rock is the ore of the element phosphorus
(P). It occurs mostly as marine (saltwater) sedimen-
tary deposits in which the predominant phosphorus-
bearing mineral is apatite, a hydrated calcium phos-
phate. Phosphate rock is mined from sedimentary
marine phosphorites both on land and on continen-
tal shelves and seamountsand is available via aprocess
in which sea organisms die and settle to the bottom of
a given water body. Through mining, inorganic phos-
phates are obtained and can be separated from other
chemicals.

Uses of Phosphate
Most of the mined phosphate rock is turned into wet-
process phosphoric acid, which is used for fertilizers
and supplements in animal feed. It is also used in
many industrial processes, including the manufac-
ture of phosphoric acids and other chemicals used in
the fields of metallurgy, photography, and medicine
and in sugar refining, soft drinks, preserved foods, ce-
ramics, textiles, matches, and both military and com-
mercial pyrotechnics (munitions and fireworks).
John L. Berkley
Web Site
Florida Institute of Phosphate Research
/>See also: Eutrophication; Fertilizers; Mohs hardness
scale; Phosphorus cycle; Sedimentary processes, rocks,
and mineral deposits.
Phosphorus cycle
Category: Geological processes and formations
Phosphorus stimulates rapid growth of algae in water
and is the maincause of eutrophication. Fertilizers, de
-
tergents, and animal waste are major sources of phos
-
phorus.
932 • Phosphorus cycle Global Resources
Definition
The phosphorus cycle describes the continuous move-
ment of organic and inorganic phosphorus from the
Earth’s crust and living organisms to water bodies and
the atmosphere.

Overview
The element phosphorus (abbreviated P) exists pri-
marily in its highest oxidized state—that is, the phos-
phate ion (PO
4
). Phosphorus can be found ina variety
of inorganic and organic compounds. Geochemical
phosphorus occurs mainly as calcium phosphate (apa
-
tite),Ca
3
(PO
4
)
2
, and as hydroxyapatite, Ca
5
(PO
4
)
3
(OH),
and is relatively insoluble. Even when phosphorus is
leached into solution through weathering, it readily
reacts with other elements to form calcium, alumi-
num, manganese, and iron phosphates or binds to
clay minerals, resulting in other insoluble phases.
Phosphorus has no stable gaseous compounds. There-
fore, phosphorus is transported mainly in particulate
form by means of overland and riverine runoff and to

a lesser extent by atmospheric precipitation.
Phosphorus is essential to all life processes. Along
with carbon and nitrogen, phosphorus is a highly im
-
Global Resources Phosphorus cycle • 933
Assimilation
by plant cells
Weathering of rock
Incorporation into sedimentary
rock; geologic uplift moves this
rock into terrestrial environments
Phosphates
in solution
Loss in
drainage
Phosphates
in soil
Decomposition by
fungi and bacteria
Urine
Animal tissues
and feces
Plant
tissues
The Phosphorus Cycle
The biogeochemical phosphorus cycle is the movement of the essential element phosphorus through the earth’s ecosystems. Released largely from
eroding rocks, as well as from dead plant and animal tissues by decomposers such as bacteria and fungi, phosphorus migrates into the soil,
where it is picked up by plant cells and is assimilated into plant tissues. The plant tissues are then eaten by animals and released back into the
soil via urination, defecation, and decomposition of dead animals. In marine and freshwater aquatic environments, phosphorus is a large
component of shells, from which it sediments back into rock and can return to the land environment as a result of seismic uplift.

portant nutrient of freshwater bodies. Carbon and ni
-
trogen are more readily available than phosphorus,
and the short supply of phosphorus can control the
growth of aquatic vegetation and other microorgan-
isms. Thus, phosphorus can act as a limiting factor.
An abundance of phosphorus can lead to excessive
growth of filamentous algae, a condition called eutro-
phication, which can create odor and taste problems
and can cause biofouling of the filters, pipes, and in-
strumentation that are crucial parts of water supply
systems.
Much phosphorus input is anthropogenic—in
other words, human activities contribute to phospho-
rus input at a much greater rate than natural pro-
cesses do. Human waste and detergents in domestic
and industrial sewage, along with leaching and runoff
of fertilizers andanimal waste from agricultural lands,
are the major sources of phosphorus.
Inorganic phosphorus is taken up by living cells
and becomes a major constituent of nucleic acids,
phospholipids, and different phosphorylated com-
pounds. In nature, organic phosphorus is derived
from dead and living cells through excretion and de-
composition respectively.
Generally, both inorganic and organic phosphates
are transformed into dissolved inorganic orthophos-
phate. The orthophosphate either precipitates or is
consumed or released by phytoplankton or bacteria.
Through these lower forms of life, phosphorus is

first assimilated by zooplankton and subsequently by
higher order organisms. Precipitated phosphorus is
utilized by aquatic plants and is diffused into the am-
bient water or is buried in deep sediments. In eutro-
phic (nutrient-rich, particularly phosphorus-rich)
lakes the amount of phosphorus precipitated from
the atmosphere is relatively insignificant in compari-
son to the amount present in water and sediments.
On the other hand, atmospheric phosphorus may be
a significant source of phosphorus for oligotrophic
(oxygen-rich) lakes.
In stratified lakes during the spring season under
well-mixed oxidized conditions phosphorus may bond
to the bottom sediments. However, in winter, under
anoxic (oxygen-deficient) conditions, phosphorus is
released from the sediments into the water column.
Therefore, phosphorus-laden sediments can serve
as internal sources of phosphorus and can continue
to promote eutrophication long after the external
sources have ceased to exist.
Panagiotis D. Scarlatos
See also: Agriculture industry;Clean WaterAct; Envi
-
ronmental engineering; Eutrophication; Fertilizers;
Food chain; Lakes; Phosphate; Soil; Water pollution
and water pollution control.
Photovoltaic cells
Categories: Energy resources; obtaining and using
resources
Photovoltaic cells convert the abundant, free, and

clean energy of the Sun directly into electricity. Already
widely used in satellites, many consumer products,
and residential or commercial electrical systems
throughout the world, photovoltaic technology is one of
the most promising alternative, renewable energy re-
sources.
Background
Since ancient times, people have used energy from
the Sun. In the seventh century b.c.e., mirrors and
glass were used to concentrate heat tolight fires. Solar
energy can also be converted into electricity. Photo-
voltaic (PV) cells, also called solar cells, convert sun-
light directly intoelectricity at the atomic level through
the process called photovoltaics.
A PV cell is made of a special semiconductor mate-
rial, so that when photons, or small light particles,
strike the cell, some of them are absorbed within the
photoelectric material. The energy of the absorbed
light loosens electrons (negatively charged compo-
nents of an atom) and causes them to flow freely, pro-
ducing an electric current.
French physicist Alexandre-Edmond Becquerel
discovered the photovoltaic effect in 1839. He no-
ticed that when exposedto light,certain metals or ma-
terials produced small quantities of electric current.
In 1883, Charles Fritts built the first working solar cell
by coating the semiconductor material selenium with
a thin, almost transparent layer of gold. The early so-
lar cells had low energy conversion efficiencies, trans-
forming less than 1 percent of the absorbed solar en-

ergy into electricity.
In 1905, Albert Einstein published his theories
about the nature of light and the PV effect, which laid
the foundation for photovoltaic technology. The first
silicon photovoltaic cell was developed by Daryl M.
Chapin, Calvin Fuller, andGerald Pearsonat Bell Lab
-
934 • Photovoltaic cells Global Resources
oratories in 1954. With an efficiency of 6 percent, it
was the first solar cell that could convert enough en-
ergy to power ordinary electrical equipment. After sil-
icon was adopted for many kinds of electronic cir-
cuitry in the 1960’s, silicon production increased
exponentially, resulting in lower prices. Silicon be-
came the standard semiconductor material for PV
cells. At first, the crystalline form of silicon was more
common, but the amorphous form eventually be-
came widespread.
Applications
The first practical application of photovoltaics oc-
curred in 1958, when the U.S. satellite Vanguard 1
used a radio transmitter powered by solar cells. Un-
like the battery-powered transmitter on board, which
broadcast for less than one month, the solar battery
sent signals for years. This breakthrough demon-
strated the reliability of PV for electric power genera-
tion in space, and solar cells became indispensable in
subsequent satellites. In 2000, solar panels were intro-
duced at the International Space Station, which held
the largest solar power array in space.

During the energy crisis in the 1970’s, interest in
PV technology for applications other than those for
space and commerce grew. By 1978, the first commer-
cial solar-powered calculators and wristwatches were
introduced.
Stand-alone PV systems have become a major
source of energy for remote areas far from conven-
tional power lines. PV technology provides the neces-
sary amount of reliable energy most economically.
Applications of PV cells include ocean navigational
buoys and lighthouses, remote scientific research and
weather stations, telecommunications systems such as
mountain-top radio transceivers, and emergency call
boxes or road signs.
In industrialized nations, PV technology is used in
grid-connected electrical systems to supplement con-
ventional energy generation. Centralized PV power
stations and PV systems in buildings are the two kinds
of grid-connected installations. PV power stations,
Global Resources Photovoltaic cells • 935
This jail in Germany is fueled by the photovoltaic cells installed on the roof. (AP/Wide World Photos)
which send power instantaneously into the grid or dis
-
tribution network through transformers and invert-
ers, are especially cost-effective during hours of peak
demand. A PV system in a building is a decentralized
system with distributed generation in grid-connected
PV arrays or in solar panels on the roofs of residential,
commercial, or industrial buildings.
More than 70 percent of thepeople in the world do

not have electricity. In developing countries andrural
areas that do not have access to conventional electri-
cal supplies, PV technology is playing an increasingly
significant role. Domestic PV systems supply the
power for lighting, refrigeration, and basic appliances
in many villages and island communities. PV water
pumps are also used worldwide for village water sup-
plies and irrigation.
Advantages and Disadvantages
Photovoltaic technology has significant advantages
over conventional and other alternative energy tech-
nologies. First, because PV systems make electricity di-
rectly from sunlight without gaseous or liquid fuel
combustion, there is minimal impact on the environ-
ment. PV production is clean andquiet, producing no
greenhouse gases or hazardous waste by-products.
Ranging from microwatts to megawatts, PV energy is
also flexible and can be used for a wide range of appli-
cations.
PV technology is also cost-effective over the life of
the system. Sunlight is free and ubiquitous,so PVhasa
free, abundant fuel supply. PV systems are also inex-
pensive to construct and easy to operate and maintain
for long periods of time, because there are no huge
generators, complicated wiring, transmission lines,
transformers, or moving parts that require frequent
servicing or replacement. Because of this high reli-
ability and ability to operate unattended, PV technol-
ogy has been the choice for space satellites and re-
mote areas, where power disruptions and repairs

would be costly. Another significant advantage of PV
systems is that they are modular, so the systems can be
configuredin a variety of sizes and moved as needed.
PV technology is more expensive than producing
electricity from a grid, but it can provide energy dur-
ing peak demand times, such as the hours when air
conditioners are turned on during the summer. Dur-
ing these times, a grid-connected PV array can be used
to meet the peak demand, rather than relying on ex
-
tremely expensive peaking power plants or other lim
-
ited energy resources. Thus, PV systems can prevent
power outages such as brownouts and blackouts. Solar
panels connected to a grid can also produce surplus
electricity when the Sun is shining, and this excess is
credited against electricity used, resulting in an aver-
age 70 to 100 percent savings on electric bills.
Other limitations include efficiency and perfor-
mance. Because PV technology depends on sunlight,
weather conditions affect output. However, even on
extremely cloudy days, a PV system can generate up to
80 percent of its maximum output.
The Future of Photovoltaics
Although sunlight is free, PV hardware manufactur-
ing has been too expensive to compete with utilities.
Hence, PV technology has been most cost-effective in
remote or rural areas without conventional sources of
electricity, rather than in urban areas with traditional
grid power. However, as more research is done on less

expensive materials, the technology improves, and
costs decline, PV has thepotentialto become the lead-
ing alternative energy resource. It is estimated that in-
stalling PV systems in only 4 percent of the area of the
world’s deserts would be enough to supply electricity
for the whole world.
During the 1990’s, research into other materialsin-
creased efficiency to more than 10 percent. In 1992,
the University of South Florida developed a 15.89 per-
cent thin-film cell. In 1994, the National Renewable
Energy Laboratory (NREL) fabricated a solar cell
made of gallium indium phosphide and gallium arse-
nide, which exceeded 30 percent efficiency. In 1999,
the NREL and Spectrolab combined three layers of PV
materials into a single 32.3 percent efficient solar cell.
In the twenty-first century, PV power generation
has expanded to meet global energy needs. In 2008,
the world PV market reached a record high of 5.95
gigawatts, up 110 percent from 2007. The global mar-
ket consisted of eighty-one countries. Spain, Ger-
many, the United States, Italy, and Japan were the top
five markets. Global revenues for the PV industry to-
taled $37.1 billion. Thin-film production grew 123
percent to 0.89 gigawatt. World solar cell production
was 6.85 gigawatts, up from 3.44gigawatts in the previ-
ous year. China and Taiwan increased their share of
solar-cell production from 35 percent in 2007 to 44
percent in 2008. In 2008, huge multimegawatt PV
plants were built in Germany and Portugal. In the
United States, the growing PV industry helps gener

-
ate jobs, reduce dependence on foreign oil, and pro
-
tect the environment.
936 • Photovoltaic cells Global Resources
By 2009, China had made a commitment to reach
-
ing 2-gigawatt solar capacity by 2011 and become a
leader in the PV industry, especially in the production
of source parts and components. China has estab-
lished installation incentives and built assembly the
plants in the United States. The Chinese company
Suntech Power Holdings increased sales in the United
States by reducing prices on its solar panels. In 2009,
the American company Evolution Solar Corporation
announced it was moving its physical location to China
to take advantage of opportunities there.
Alice Myers
Further Reading
Davidson, Joel, and Fran Orner. The New Solar Electric
Home: The Complete Guide to Photovoltaics for Your
Home. Ann Arbor, Mich.: Aatec, 2008.
Goetzberger, A., and Volker U. Hoffmann. Photovol-
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See also: Buildings and appliances, energy-efficient;
Department of Energy, U.S.; Energy storage; Fuel
cells; Solar chimneys; Solar energy.
Pinchot, Gifford
Category: People
Born: August 11, 1865; Simsbury, Connecticut
Died: October 4, 1946; New York, New York
A leading figure in the conservation movement of the
late nineteenth century, Pinchot advocated the scien
-
tific management of the nation’s forests to assure a con
-
tinuing supply of wood for future growth.
Biographical Background
In 1889, Gifford Pinchotgraduated from the Yale For-
est School (now the Yale School of Forestry and Envi-
ronmental Studies), which his father had helped to
found, and then studied forestry in Europe, the first
American to do so. When a federal Bureau of Forestry
was established, Pinchot was appointed as its head.
The bureau became the United States Forest Service
in 1905, and Pinchot continued as its leader until
1910, at which time he became president of the Na-

tional Conservation Committee. He also taught for-
estry at Yale University from 1903 to 1906.
Impact on Resource Use
Pinchot established the basic principles of American
forest policy. In contrast to later environmentalists,
Pinchot viewed wooded lands principally in terms of
their economic value and was concerned with opti
-
Global Resources Pinchot, Gifford • 937
From 1905 to 1910, Gifford Pinchot served as the first head of the
United States Forest Service. (Library of Congress)