Alternative Energy Sources
Alternative Energy Sources
Nonrenewable Energy Sources:
Oil Sands/Heavy Oil
Ocean thermal energy conversion
Not Primary Energy Sources
Hydrogen and Fuel Cells
Living Off Our Capital And The Limits Of Technology
Oil fuels the modern world. No other substance can equal the enormous impact
which the use of oil has had on so many people, so rapidly, in so many ways, and
in so many places around the world.
Oil in its various refined derivative forms, such as gasoline, kerosene, and
diesel fuel, has a unique combination of many desirable and useful
characteristics. These include a current availability in abundance, a currently
high net energy recovery, a high energy density, ease of transportation and
storage, relative safety, and great versatility in end use. Oil is also useful
as more than an energy source. It is the basis for the manufacture of
petrochemical products including plastics, medicines, paints, and myriad other
useful materials. Finally, the asphalt "bottoms" from refineries have
converted millions of miles of muddy trails around the world into paved highways
on which transport vehicles fueled by oil run.
Alternative energy sources must be compared with oil in all these various
attributes when their substitution for oil is considered. None appears to
completely equal oil.
But oil, like other fossil fuels, is a finite resource. True, there will
always be oil in the Earth, but eventually the cost to recover what remains will
be beyond the value of the oil. Also, a time will be reached when the amount of
energy needed to recover the oil equals or exceeds the energy in the recovered
oil, at which point oil production becomes no more than a break-even, or a net
energy loss situation.
Oil being the most important of our fuels today, the term "alternative
energy" is commonly taken to mean all other energy sources and is used here
in that context. Realizing that oil is finite in practical terms, there is
increasing attention given to what alternative energy sources are available to
replace oil. The imperative to pursue alternative energy sources is clearly
established by two simple facts. The world now uses more than 26 billion barrels
of oil a year, but new discoveries (not existing field additions) in recent
years have been averaging less than seven billion barrels yearly. The peak of
world oil discoveries was in the mid-1960's. Inevitably, the time of the peak of
world oil production must follow, with most current estimates ranging from the
year 2003 (Campbell, 1997) to 2020 (Edwards, 1997). Significantly, all estimates
of production peak dates are within the lifetimes of most people living today.
The amount of energy an individual can directly or indirectly command largely
determines that individual's material standard of living. This, of course, also
applies to nations as a whole. To provide adequate energy for future generations
introduces the concept of sustainability. What significant energy sources can be
drawn on indefinitely?
"Sustainable" is a popular and pleasant word, but when it is used
it needs to be clearly defined and placed within certain parameters. The term
"sustainable growth" is popular with Chambers of Commerce as well as
with corporations, but if this means increase in use of any resource, including
land for more people, more water for more people, and more and more food, or
more "things", then the term "sustainable growth" is an
oxymoron (Bartlett, 1994). Growth in terms of numbers of anything cannot be
sustained indefinitely. Sustainable growth in terms of better medical care,
improved sanitation, and other related qualities of life, and of intellectual
endeavors, among other things, is possible, and should be a continual goal.
Any consideration of "sustainable" must also be framed in the
concept of a fixed size of population. People use resources. And all energy
resources, even solar energy, are limited (Hardin, 1993). The problem of
population size is politically sensitive and therefore largely avoided in
discussions. But the energy problem cannot be sustainably solved if the demand
target is a continually growing population. It is important to keep this
overriding fact in mind. Eventually it will have to be faced. In defining a
sustainable society, it is also necessary to determine what reasonable standard
of living is to be achieved. This does not lend itself to an easy definition as
various cultures have differing views.
In considering what significant (in terms of quantity and quality)
sustainable alternative energy sources may exist, the factors of population and
living standards must be addressed. These matters are beyond this discussion,
which simply presents the basic facts of alternative energy sources. How these
sources, with their advantages and limitations may be applied to society at
large is here left for economists, sociologists, and politicians.
Energy InterchangeabilityThere is much casual popular thought that energy
sources are easily interchangeable. "When we run out of oil we will go to
alternative fuels." "We can run our cars on solar energy." Such
statements are legion. But the transition to alternative fuels will not be
simple nor as convenient as is the use of oil today, and it will involve much
time and financial investment. Energy carriers in terms of varied end uses and
ease of handling and storage, are not easily interchangeable.
We here briefly examine alternative energy sources as to their advantages,
limitations, and their prospects for replacing oil in the ways and great volumes
in which we use oil today. Alternative energies closest to conventional oil
(from wells) are first considered, and then our energy horizons are expanded.
Energy sources can be divided into renewable and nonrenewable.
Alternative Energy Sources
Oil sands, heavy oil
Ocean thermal energy conversion
1Renewable for space heating,
2Not renewable with reservoirs
Nonrenewable Energy Sources
Oil Sands/Heavy OilThis oil exists in huge quantities (trillions of
barrels) particularly in Alberta, Canada and Venezuela. It is true oil but in
deposits which take special methods to recover the oil. Oil sands must either be
mined, or recovered by the SAGD (SAG-D) process (steam assisted gravity
drainage) in which steam is injected in the upper of two parallel pipes and the
oil is collected in the lower pipe. The oil must have lighter hydrocarbons added
to it to allow it to flow and be processed into conventional petroleum products.
Heavy oil deposits can be injected with hot water or steam. Because of the
energy expended in these processes, the net energy recovery is considerably less
than oil from conventional drilled wells.
At present about 500,000 barrels a day are recovered from the Athabasca oil
sands of Alberta. To increase this 10 fold to 5 million barrels a day would be a
very large task, with severe environmental limitations. This must be put in the
perspective of the 76 million barrels of oil the world now consumes daily. Other
similar oil deposits have the same problems of scale and net energy recovery. In
total, oil sands and heavy oil can replace conventional oil only to a small
degree. Canada's domestic needs for oil, with its growing population and
increasing industrialization, will likely soon absorb all the additional oil
which can be produced from oil sands and heavy oil with no surplus to export.
Natural GasNatural gas is methane (CH4) which commonly
has minor quantities of noncombustible gases such as carbon dioxide and nitrogen
associated with it. Natural gas is termed "associated gas" when it
occurs with oil, or "nonassociated gas" when it is not found with oil.
Natural gas is derived from organic material and can be formed at essentially
normal atmospheric temperature (such is the origin of "swamp gas" and
the gas associated with garbage dumps, now in places used for fuel to generate
Oil also is derived from organic materials, but to derive oil from organic
material, the material must pass through an "oil window". This is a
temperature-time relationship ranging from 70°C to about 150°C (158-302°F).
Below about 16,000 feet (4880 meters), the Earth is so hot that oil cannot exist
and only gas is found below that depth.
In terms of energy, one cubic foot of gas at one atmosphere has 1000 Btus.
Fifty-six hundred cubic feet (157 cubic meters) of gas has the same energy
equivalent as one barrel of oil. Natural gas is the cleanest burning of the
fossil fuels, and for that reason is the fuel of choice over coal for
electricity production as boiler fuel and in gas turbines. Natural gas can be
used as a substitute for gasoline or diesel fuel in internal combustion engines,
and is so used in a few places.
Natural gas is commonly moved by pipeline. It can be shipped in cryogenic
tankers but this is expensive and does not lend itself economically to large
scale transport, whereas oil is shipped economically worldwide. Natural gas can
be converted to a liquid (GTL —gas to liquid), and such conversion plants are
being built in areas not served by pipelines (e.g., the North Dome Field of
Qatar). The end product is a high grade substitute for gasoline. However, the
volumes of GTL which can be produced are modest and somewhat more expensive than
Natural gas is more widely distributed than. oil. But estimates are that in
total its energy in reserves is equal to or slightly less than that in world oil
reserves. Natural gas (and in GTL) is an alternative energy to petroleum, but
natural gas is also a finite fossil fuel.
CoalCoal is a very large energy source, but it must be
mined, it is not nearly so easy to handle and transport as is oil, and it has
much less energy density. For use in producing electricity in power plants
(burned under boilers), coal can replace oil. But converting it to a liquid fuel
which might be used in motor vehicles is expensive, and doing this on a scale
which could significantly replace oil in vehicle use would require impossibly
large mining projects. Coal can replace oil in some uses. Although considerable
progress has been made, coal production and burning still have environmental
problems which are of major concern. Adding to the greenhouse effect is one. The
energy in coal reserves worldwide is greater than oil, but it, too, is a finite
Shale OilProduction of oil from oil shale has been attempted at
various times for nearly 100 years. So far, no venture has proved successful on
a significantly large scale (Youngquist, 1998b). One problem is that there is no
oil in oil shale. It is a material called kerogen. The shale has to be mined,
transported, heated to about 450°C (850°F), and have hydrogen added to the
product to make it flow. The shale pops like popcorn when heated so the
resulting volume of shale after the kerogen is taken out is larger than when it
was first mined. The waste disposal problem is large. Net energy recovery is low
at best. It also takes several barrels of water to produce one barrel of oil.
The largest shale oil deposits in the world are in the Colorado Plateau, a
markedly water poor region. So far shale oil is, as the saying goes: "The
fuel of the future and always will be." Fleay (1995) states: "Shale
oil is like a mirage that retreats as it is approached." Shale oil will not
replace conventional oil.
Gas HydratesThese are very large deposits of methane which are in
a solid substance composed of water molecules forming a rigid lattice of cages.
These are discussed separately in this treatise.
Nuclear FissionThere are two isotopes of uranium, uranium-235 and
uranium-238. Only uranium-235 is fissionable, and it is only .7 percent of all
uranium. The 99.3 percent which is uranium-238 is not fissionable, but
uranium-235 can be used to produce a new element from uranium-238, plutonium239,
which is fissionable. Although uranium in both forms is a finite resource,
converting uranium-238 to plutonium-239 (a process called "breeding")
could possibly extend our use of uranium for power by perhaps 100 times (Meyers,
1983). However, plutonium is an exceedingly toxic substance, and also the basis
for a deadly bomb. Because of this there is much opposition to the breeder
reactor, and to uranium for power in general due to safety and environmental
considerations. However, coal and uranium are the only two alternative sources
of energy which can be developed in large amounts, and provide a dependable base
load in the reasonably near future. Nuclear power development has been stopped
in the United States. Elsewhere, some countries are abandoning nuclear power
(e.g., Sweden, Germany), whereas others are pursuing it (e.g., Japan, Russia).
Ultimately, however, nuclear power in any form is nonrenewable because uranium
reserves are limited.
The end product of nuclear fission is electricity. How to use electricity to
efficiently replace oil (gasoline, diesel, kerosene) in the more than 700
million vehicles worldwide has not yet been satisfactorily solved. There are
severe limitations of the storage batteries involved. For example, a gallon of
gasoline weighing about 8 pounds has the same energy as one ton of conventional
leadacid storage batteries.. Fifteen gallons of gasoline in a car's tank are the
energy equal of 15 tons of storage batteries. Even if much improved storage
batteries were devised, they cannot compete with gasoline or diesel fuel in
energy density. Also, storage batteries become almost useless in very cold
weather, storage capacity is limited, and batteries need to be replaced after a
few years use at large cost. There is no battery pack which can effectively move
heavy farm machinery over miles of farm fields, and no electric battery system
seems even remotely able to propel a Boeing 747 -14 hours nonstop at 600 miles
an hour from New York to Cape Town (now the longest scheduled plane flight).
Also, the considerable additional weight to any vehicle using batteries is a
severe handicap in itself. In transport machines, electricity is not a good
replacement for oil (Jensen and Sorensen, 1984). This is a limitation in the use
of alternative sources have where electricity is the end product.
Where oil is used for electric power production, nuclear fission can replace
oil as a fuel. However, in the U.S. now only about 2 percent of electric power
is generated from oil. Elsewhere, such as island economies, oil is now the chief
source for electric power generation and nuclear fission has the prospect of
significantly replacing that oil.
Geothermal EnergyThis is heat from the Earth. In a few places in the
world there is steam or very hot water close enough to the surface so that the
resource can be reached economically with a drill. The steam, or hot water
flashed to steam, can turn a turbine, turning a generator producing electricity.
At best, because of the scarcity of such sites, geothermal energy can be only a
minor contributor to world energy supplies, and the product is electricity,
which is subject to limited end uses. It should be noted that all electric power
geothermal generating site reservoirs are now declining, because the geothermal
requirements to produce electric power draw down the reservoirs faster than
their recharge ability. Some projects are now reinjecting water from the
condensed steam back into the reservoir to see if this problem can be mitigated,
but results so far are inconclusive. However, when lower temperature reservoirs
are used for space heating, with a more modest demand on the reservoir using
down-well heat exchangers or ground to air heat pumps using the natural heat
flow of the Earth, geothermal energy appears to be a renewable energy source.
Renewable Energy Sources
Wood and Other BiomassWood has long been used as a fuel, now to the extent
that large areas worldwide are being deforested resulting in massive erosion in
such places as the foothills of the Himalayas, and the mountains of Haiti. Wood
can be converted to a liquid fuel but the net energy recovery is low, and there
is not enough wood available to be able to convert it to a liquid fuel in any
Other biomass fuel sources have been tried. Crops such as corn are converted
to alcohol. In the case of corn to ethanol, it is an energy negative. It takes
more energy to produce ethanol than is obtained from it (Pimentel, 1998).. Also,
using grain such as corn for fuel, precludes it from being used as food for
humans or livestock. It is also hard on the land. In U.S. corn production, soil
erodes some 20-times faster than soil is formed. Ethanol has less energy per
volume than does gasoline, so when used as a 10 percent mix with gasoline
(called gasohol), more gasohol has to be purchased to make up the difference.
Also, ethanol is not so environmentally friendly as advocates would like to
believe. Pimentel (1998) states:
Ethanol produces less carbon monoxide than gasoline, but it
produces just as much nitrous oxides as gasoline. In addition, ethanol adds
aldehydes and alcohol to the atmosphere, all of which are carcinogenic. When
all air pollutants associated with the entire ethanol system are measured,
ethanol production is found to contribute to major air pollution problems.
With a lower energy density than gasoline, and adding the energy cost of the
fertilizer (made chiefly from natural gas), and the energy costs (gasoline
and/or diesel) to plow, plant, cultivate, and transport the corn for ethanol
production, ethanol in total does not save fossil fuel energy nor does it's use
reduce atmospheric pollution.
A comprehensive study of converting biomass to liquid fuels by Giampietro and
others (1997) concludes:
Large scale biofuel production is not an alternative to the
current use of oil, and is not even an advisable option to cover a significant
fraction of it.
Originally thought of as a clean, non-polluting,
environmentally friendly source of energy, experience is proving otherwise.
Valuable lowlands, which are usually the best farmland, are flooded. Wildlife is
displaced. Where anadromous fish runs are involved as in the Columbia River
system with its 30 dams, the effect on fish has been disastrous. Only to a small
extent is hydro-electric power truly renewable. This is when the "run of
the river" without dams is used, as, for example with a Pelton wheel. If
reservoirs are involved, in order to provide a dependable base load as is the
case of most hydro-electric facilities, hydro-electric power in the longer term
is not a truly renewable energy source. All reservoirs eventually fill with
sediment. Some reservoirs have already filled, and many others are filling
faster than expected. A dam site can be used only once.
We are enjoying the best part of the life of huge dams. In a few hundred
years Glen Canyon Dam and Hoover Dam will be concrete waterfalls. And, again,
the end product is electricity, not a replacement for the important use of oil
derivatives (gasoline, etc.) in transportation equipment.
This is a favorite possible source of future energy
for many people, comforted by the thought that it is unlimited. But, quite the
contrary is true. The Sun will exist for a long time, but at any given place on
the Earth's surface the amount of sunlight received is limited —only so much
is received. And at night; or with overcast skies, or in high latitudes where
winter days are short and for months there may be no daylight at all, or
available in small and low intensity quantities. Direct conversion of sunlight
to electricity by solar cells is a promising technology, and already locally
useful, but the amount of electricity which, can be generated by that method is
not great compared with demand. Because it is a low grade energy, with a low
conversion efficiency (about 15%) capturing solar energy in quantity requires
huge installations —many square miles. About 8 percent of the cells must be
replaced each year. But the big problem is how to store significant amounts of
electricity when the Sun is not available to produce it (Trainer, 1995), for
example, at night. The problem remains unsolved. Because of this, solar energy
cannot be used as a dependable base load. And, the immediate end product is
electricity, a very limited replacement for oil. Also, adding in all the energy
costs of the production and maintenance of PV (photovoltaic) installations, the
net energy recovery is low (Trainer, 1995).
This energy source is similar to solar in that it is
not dependable. It is noisy, and the visual effects are not usually regarded as
pleasing. The best inland wind farm sites tend to be where air funnels through
passes in the hills which are also commonly flyways for birds. The bird kills
have caused the Audubon Society to file suit in some areas to prevent wind
energy installations. Locally and even regionally via a grid (e.g. Denmark) wind
can be a significant electric power source. But wind is likely to be only a
modest help in the total world energy supply, and the end product is
electricity, no significant replacement for oil. As with solar energy, the
storage problem of large amounts of wind generated electricity is largely
Wind cannot provide a base load as winds are unreliable.
All sorts of installations have been tried to obtain
energy from this source, but with very modest results. Piston arrangements moved
up and down by waves which in turn move turbines connected to electric
generators have been tried in The Netherlands, but the project was abandoned.
Waves are not dependable, and the end product is electricity, and producing it
in significant quantities from waves seems a remote prospect.
It takes a high tide and special configuration of the
coastline, a narrow estuary which can be dammed, to be a tidal power site of
value. Only about nine viable sites have been identified in the world. Two are
now in use (Russia and France) and generate some electricity. Damming estuaries
would have considerable environmental impact. The Bay of Fundy in eastern Canada
has long been considered for a tidal power site, but developing it would have a
negative effect on the fisheries and other sea-related economic enterprises. It
would also disturb the habits of millions of birds which use the Bay of Fundy
area as part of their migration routes. Tidal power is not a significant power
source. The end product is electricity.
Fusion involves the fusion of either of two hydrogen
isotopes, deuterium or tritium. Deuterium exists in great quantities in ordinary
water, and from that perspective fusion is theoretically an almost infinitely
renewable energy resource. This is the holy grail of ultimate energy. Fusion is
the energy which powers the Sun, and that is the problem. The temperature of the
Sun ranges from about 10,000°C on its surface to an estimated 15 to 18 million
degrees in the interior where fusion takes place. Containing such a temperature
on Earth in a sustainable way and harnessing the heat to somehow produce power
has so far escaped the very best scientific talent. However, even if commercial
fusion were accomplished, the end product again is electricity, not a direct
convenient replacement for oil.
Within about 25 degrees each side of the equator the
surface of the ocean is warm, and the depths are cold to the extent that there
is a modest temperature differential. This can be a source of energy, using a
low boiling point fluid such as ammonia which at normal atmospheric temperature
of 70°F (21° C) is a gas, colder water can be pumped from the deep ocean to
condense the ammonia, and then let it warm up and expand to gas. The resulting
gas pressure can power a turbine to turn a generator. But the plant would have
to be huge and anchored in the deep open ocean or on a ship, all subject to
storms and corrosion, and the amount of water which has to be moved is enormous
as the efficiency is very low. How to store and transport the resulting
electricity would also be a large problem. OTEC does not appear to have much
potential as a significant energy source, and the end product is electricity.
Ocean Thermal Energy Conversion (OTEC)
Not Primary Energy Sources
References are sometimes made as to using these for
energy sources. Neither is a primary energy source. Hydrogen must be obtained by
using some other energy source. Usually it is obtained by the electrolysis of
water, or by breaking down natural gas (methane CH4). Hydrogen is
highly explosive, and to be contained and carried in significantly usable
amounts it has to be compressed or cooled to a liquid at minus 253°C. Hydrogen
is not easy to handle, and it is not a convenient replacement for pouring 10
gallons of gasoline into an automobile fuel tank.
Hydrogen and Fuel Cells
Fuel cells are being developed for use in transportation (automobiles,
trucks, buses, etc.) but fuel cells have to be fueled with hydrogen. Fuel cells
are not a source of energy in themselves, but are a possible ultimate substitute
for the internal combustion engine. However, putting the infrastructure in place
to effectively and economically produce and store hydrogen on the widespread
basis as oil and its derivatives are today, is an enormous, costly, and long
term task. The ultimate result can hardly be as versatile and convenient as is
the use of oil products today around the world.
Living Off Our Capital
And The Limits Of Technology
We now live in very fortunate times. In the combination of the versatility of
end uses, energy density, ease of handling and storage, and being now able to
produce it relatively inexpensively and in great volume, there is no energy
source comparable to oil. But living in a chiefly petroleum fueled economy and
in a fossil fuel economy in general, we are living off our capital, which is
In a very perceptive volume for the time it was written, British physicist C.
G. Darwin (1952) recounts the several "revolutions" which have taken
place in the progress of human history, such as the most recent one, the
Industrial Revolution. He states there is one more revolution coming:
The fifth revolution will come when we have spent the
stores of coal and oil that have been accumulating in the earth during
hundreds of millions of years ... it is obvious that there will be a very
great difference in ways of life ... a man has to alter his way of life
considerably, when, after living for years on his capital, he suddenly finds
he has to earn any money he wants to spend … The change may justly be called
a revolution, but it differs from all the preceding ones in that there is no
likelihood of its leading to increase in population, but even perhaps to the
There is a popular belief that somehow technology can indefinitely rescue the
human race from whatever predicament it may get itself into —solve all
problems. Pimentel and Giampietro (1994) have warned:
Technology cannot substitute for essential natural
resources such as food, forests, land, water, energy, and biodiversity...we
must be realistic as to what technology can and cannot do to help humans feed
themselves and to provide other essential resources.
Bartlett (1994) has observed:
There will always be popular and persuasive technological
optimists who believe that population increases are good, and who believe that
the human mind has unlimited capacity to find technological solutions to all
problems of crowding, environmental destruction, and resource shortages. These
technological optimists are usually not biological or physical scientists.
Politicians and business people tend to be eager disciples of the
This is not to say that technology cannot continue to produce many good
things in the future. But we must not confuse technology which uses resources
with creating the resources. The world is finite; there are limits. Nature has
given us a great inheritance formed in the Earth by myriad geological processes
over millions of years consisting of a huge variety of resources, including,
importantly now, fossil fuels. This is a nonrenewable bank account against which
we have been writing larger and larger checks as the needs of an increasingly
industrialized growing world population have been supplied.
But eventually this account will be exhausted, and we will have to bestir
ourselves to get out and live on current income, the first need of which
apparently will be to replace oil. How many people can a renewable energy
resource income support? And what will be the resources we will use to do this?
Cohen (1995) has discussed this, as is the title of his book, "How Many
People Can the Earth support?" But, perhaps the question should be phrased
"how many people should the Earth support?"
The optimum size of this population can hardly be estimated now with any
great degree of accuracy, but some suggestions have been made. Pimentel and
Pimentel (1996) believe that a world population of two billion might be
sustained in some reasonable degree of affluence. Other estimates have been made
and it is significant that most of them determine a figure which is
substantially smaller than is the size of today's population.
Trainer (1995), in a comprehensive study of renewable energy sources, has
made a well-supported clear statement:
Figures commonly quoted on costs of generating energy from renewable sources
can give the impression that it will be possible to switch to renewables as the
foundation for the continuation of industrial societies with high material
living standards. Although renewable energy must be the sole source in a
sustainable society, major difficulties become evident when conversion, storage
and supply for high latitudes are considered. It is concluded that renewable
energy sources will not be able to sustain present rich world levels of energy
use and that a sustainable world order must be based on acceptance of much lower
per capita levels of energy use, much lower living standards and a zero growth
Transition to an entirely renewable sustainable energy resource economy with
resulting changes in lifestyles is inevitable. Will it be done with intelligence
and foresight or will it be done by harsh natural forces? This is one of the
main challenges which lie before us.
It seems likely that a sustainable energy mix will be broader that it is
today where oil and natural gas make up more than 50 % of our supplies. And
energy in total will likely be more costly than our energy bill today. The
transition to this wider diversity of energy sources will proceed slowly and
probably be somewhat provincial depending on what regional resources are
Energy is the key which unlocks all other resources, and it will continue to
be the key to human physical prosperity. It is significant that both the per
capita use of oil; and the per capita use of energy in total both peaked in 1979
and have been falling ever since (Duncan, 2000). We may already be seeing the
beginning of the fifth revolution to which Darwin referred.
The British scientist and statesman, Sir Crispin Tickell (1994) has clearly
summed up our situation:
We have done remarkably little to reduce our dependence on
a fuel [oil] which is a limited resource and for which there is no
comprehensive substitute in prospect.
The challenge of conversion to alternative energy sources with the concurrent
problems of population size and stabilization, and adjustment of economies and
lifestyles is clearly at hand. A realistic appraisal of the future encourages
people to properly prepare for the coming events. Delay in dealing with the
issues will surely result in unpleasant surprises. Let us get on with the task
of moving orderly into the post-petroleum paradigm.
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