Contents
TOC \o “1-3” \h \z HYPERLINK \l “_Toc531089860” Introduction
PAGEREF _Toc531089860 \h 2
HYPERLINK \l “_Toc531089861” Wind Energy PAGEREF _Toc531089861 \h
2
HYPERLINK \l “_Toc531089862” Solar Energy PAGEREF _Toc531089862 \h
3
HYPERLINK \l “_Toc531089863” Geothermal Energy PAGEREF
_Toc531089863 \h 4
HYPERLINK \l “_Toc531089864” Biomass PAGEREF _Toc531089864 \h 6
HYPERLINK \l “_Toc531089865” Air Pollution PAGEREF _Toc531089865 \h
6
HYPERLINK \l “_Toc531089866” Greenhouse Gases PAGEREF _Toc531089866
\h 8
HYPERLINK \l “_Toc531089867” Implications for Agriculture and
Forestry PAGEREF _Toc531089867 \h 8
HYPERLINK \l “_Toc531089868” Hydropower PAGEREF _Toc531089868 \h 9
HYPERLINK \l “_Toc531089869” Conclusion PAGEREF _Toc531089869 \h
10
HYPERLINK \l “_Toc531089870” Sources PAGEREF _Toc531089870 \h 12
Introduction
To combat global warming and the other problems associated with fossil
fuels, the world must switch to renewable energy sources like sunlight,
wind, and biomass. All renewable energy technologies are not appropriate
to all applications or locations, however. As with conventional energy
production, there are environmental issues to be considered. This paper
identifies some of the key environmental impacts associated with
renewable technologies and suggests appropriate responses to them. A
study by the Union of Concerned Scientists and three other national
organizations, America’s Energy Choices, found that even when certain
strict environmental standards are used for evaluating renewable energy
projects, these energy sources can provide more than half of the US
energy supply by the year 2030.
Today the situation in fuel and industrial complexes round the world is
disastrous. Current energy systems depend heavily upon fossil and
nuclear fuels. What this would mean is that we would run out of mineral
resources if we continue consuming non-renewables at the present rate,
and this moment is not far off. According to some estimates, within the
next 200 years most people, for instance, seize using their cars for
lack of petrol (unless some alternatives are used). Moreover, both
fossil and nuclear fuels produce a great amount of polluting substances
when burnt. We are slowly but steadily destroying our planet, digging it
from inside and releasing the wastes into the atmosphere, water and
soil. We have to seize vandalizing the Earth and seek some other ways to
address the needs of the society some other way. That’s why renewable
sources are so important for the society. In fact, today we have a
simple choice – either to turn to nature or to destroy ourselves. I have
all reasons to reckon that most of people would like the first idea much
more, and this is why I’m going to inquire into the topic and look
through some ways of providing a sustainable future for next
generations.
Wind Energy
It is hard to imagine an energy source more benign to the environment
than wind power; it produces no air or water pollution, involves no
toxic or hazardous substances (other than those commonly found in large
machines), and poses no threat to public safety. And yet a serious
obstacle facing the wind industry is public opposition reflecting
concern over the visibility and noise of wind turbines, and their
impacts on wilderness areas.
One of the most misunderstood aspects of wind power is its use of land.
Most studies assume that wind turbines will be spaced a certain distance
apart and that all of the land in between should be regarded as
occupied. This leads to some quite disturbing estimates of the land area
required to produce substantial quantities of wind power. According to
one widely circulated report from the 1970s, generating 20 percent of US
electricity from windy areas in 1975 would have required siting turbines
on 18,000 square miles, or an area about 7 percent the size of Texas.
In reality, however, the wind turbines themselves occupy only a small
fraction of this land area, and the rest can be used for other purposes
or left in its natural state. For this reason, wind power development is
ideally suited to farming areas. In Europe, farmers plant right up to
the base of turbine towers, while in California cows can be seen
peacefully grazing in their shadow. The leasing of land for wind
turbines, far from interfering with farm operations, can bring
substantial benefits to landowners in the form of increased income and
land values. Perhaps the greatest potential for wind power development
is consequently in the Great Plains, where wind is plentiful and vast
stretches of farmland could support hundreds of thousands of wind
turbines.
In other settings, however, wind power development can create serious
land-use conflicts. In forested areas it may mean clearing trees and
cutting roads, a prospect that is sure to generate controversy, except
possibly in areas where heavy logging has already occurred. And near
populated areas, wind projects often run into stiff opposition from
people who regard them as unsightly and noisy, or who fear their
presence may reduce property values.
In California, bird deaths from electrocution or collisions with
spinning rotors have emerged as a problem at the Altamont Pass wind
“farm,” where more than 30 threatened golden eagles and 75 other raptors
such as red-tailed hawks died or were injured during a three-year
period. Studies under way to determine the cause of these deaths and
find preventive measures may have an important impact on the public
image and rate of growth of the wind industry. In appropriate areas, and
with imagination, careful planning, and early contacts between the wind
industry, environmental groups, and affected communities, siting and
environmental problems should not be insurmountable.
Solar Energy
Since solar power systems generate no air pollution during operation,
the primary environmental, health, and safety issues involve how they
are manufactured, installed, and ultimately disposed of. Energy is
required to manufacture and install solar components, and any fossil
fuels used for this purpose will generate emissions. Thus, an important
question is how much fossil energy input is required for solar systems
compared to the fossil energy consumed by comparable conventional energy
systems. Although this varies depending upon the technology and climate,
the energy balance is generally favorable to solar systems in
applications where they are cost effective, and it is improving with
each successive generation of technology. According to some studies, for
example, solar water heaters increase the amount of hot water generated
per unit of fossil energy invested by at least a factor of two compared
to natural gas water heating and by at least a factor of eight compared
to electric water heating.
Materials used in some solar systems can create health and safety
hazards for workers and anyone else coming into contact with them. In
particular, the manufacturing of photovoltaic cells often requires
hazardous materials such as arsenic and cadmium. Even relatively inert
silicon, a major material used in solar cells, can be hazardous to
workers if it is breathed in as dust. Workers involved in manufacturing
photovoltaic modules and components must consequently be protected from
exposure to these materials. There is an additional-probably very
small-danger that hazardous fumes released from photovoltaic modules
attached to burning homes or buildings could injure fire fighters.
None of these potential hazards is much different in quality or
magnitude from the innumerable hazards people face routinely in an
industrial society. Through effective regulation, the dangers can very
likely be kept at a very low level.
The large amount of land required for utility-scale solar power
plants-approximately one square kilometer for every 20-60 megawatts (MW)
generated-poses an additional problem, especially where wildlife
protection is a concern. But this problem is not unique to solar power
plants. Generating electricity from coal actually requires as much or
more land per unit of energy delivered if the land used in strip mining
is taken into account. Solar-thermal plants (like most conventional
power plants) also require cooling water, which may be costly or scarce
in desert areas.
Large central power plants are not the only option for generating energy
from sunlight, however, and are probably among the least promising.
Because sunlight is dispersed, small-scale, dispersed applications are a
better match to the resource. They can take advantage of unused space on
the roofs of homes and buildings and in urban and industrial lots. And,
in solar building designs, the structure itself acts as the collector,
so there is no need for any additional space at all.
Geothermal Energy
Geothermal energy is heat contained below the earth’s surface. The only
type of geothermal energy that has been widely developed is hydrothermal
energy, which consists of trapped hot water or steam. However, new
technologies are being developed to exploit hot dry rock (accessed by
drilling deep into rock), geopressured resources (pressurized brine
mixed with methane), and magma.
The various geothermal resource types differ in many respects, but they
raise a common set of environmental issues. Air and water pollution are
two leading concerns, along with the safe disposal of hazardous waste,
siting, and land subsidence. Since these resources would be exploited in
a highly centralized fashion, reducing their environmental impacts to an
acceptable level should be relatively easy. But it will always be
difficult to site plants in scenic or otherwise environmentally
sensitive areas.
The method used to convert geothermal steam or hot water to electricity
directly affects the amount of waste generated. Closed-loop systems are
almost totally benign, since gases or fluids removed from the well are
not exposed to the atmosphere and are usually injected back into the
ground after giving up their heat. Although this technology is more
expensive than conventional open-loop systems, in some cases it may
reduce scrubber and solid waste disposal costs enough to provide a
significant economic advantage.
Open-loop systems, on the other hand, can generate large amounts of
solid wastes as well as noxious fumes. Metals, minerals, and gases leach
out into the geothermal steam or hot water as it passes through the
rocks. The large amounts of chemicals released when geothermal fields
are tapped for commercial production can be hazardous or objectionable
to people living and working nearby.
At The Geysers, the largest geothermal development, steam vented at the
surface contains hydrogen sulfide (H2S)-accounting for the area’s
“rotten egg” smell-as well as ammonia, methane, and carbon dioxide. At
hydrothermal plants carbon dioxide is expected to make up about 10
percent of the gases trapped in geopressured brines. For each
kilowatt-hour of electricity generated, however, the amount of carbon
dioxide emitted is still only about 5 percent of the amount emitted by a
coal- or oil-fired power plant.
Scrubbers reduce air emissions but produce a watery sludge high in
sulfur and vanadium, a heavy metal that can be toxic in high
concentrations. Additional sludge is generated when hydrothermal steam
is condensed, causing the dissolved solids to precipitate out. This
sludge is generally high in silica compounds, chlorides, arsenic,
mercury, nickel, and other toxic heavy metals. One costly method of
waste disposal involves drying it as thoroughly as possible and shipping
it to licensed hazardous waste sites. Research under way at Brookhaven
National Laboratory in New York points to the possibility of treating
these wastes with microbes designed to recover commercially valuable
metals while rendering the waste non-toxic.
Usually the best disposal method is to inject liquid wastes or
redissolved solids back into a porous stratum of a geothermal well. This
technique is especially important at geopressured power plants because
of the sheer volume of wastes they produce each day. Wastes must be
injected well below fresh water aquifers to make certain that there is
no communication between the usable water and waste-water strata. Leaks
in the well casing at shallow depths must also be prevented.
In addition to providing safe waste disposal, injection may also help
prevent land subsidence. At Wairakei, New Zealand, where wastes and
condensates were not injected for many years, one area has sunk 7.5
meters since 1958. Land subsidence has not been detected at other
hydrothermal plants in long-term operation. Since geopressured brines
primarily are found along the Gulf of Mexico coast, where natural land
subsidence is already a problem, even slight settling could have major
implications for flood control and hurricane damage. So far, however, no
settling has been detected at any of the three experimental wells under
study.
Most geothermal power plants will require a large amount of water for
cooling or other purposes. In places where water is in short supply,
this need could raise conflicts with other users for water resources.
The development of hydrothermal energy faces a special problem. Many
hydrothermal reservoirs are located in or near wilderness areas of great
natural beauty such as Yellowstone National Park and the Cascade
Mountains. Proposed developments in such areas have aroused intense
opposition. If hydrothermal-electric development is to expand much
further in the United States, reasonable compromises will have to be
reached between environmental groups and industry.
Biomass
Biomass power, derived from the burning of plant matter, raises more
serious environmental issues than any other renewable resource except
hydropower. Combustion of biomass and biomass-derived fuels produces air
pollution; beyond this, there are concerns about the impacts of using
land to grow energy crops. How serious these impacts are will depend on
how carefully the resource is managed. The picture is further
complicated because there is no single biomass technology, but rather a
wide variety of production and conversion methods, each with different
environmental impacts.
Air Pollution
Inevitably, the combustion of biomass produces air pollutants, including
carbon monoxide, nitrogen oxides, and particulates such as soot and ash.
The amount of pollution emitted per unit of energy generated varies
widely by technology, with wood-burning stoves and fireplaces generally
the worst offenders. Modern, enclosed fireplaces and wood stoves pollute
much less than traditional, open fireplaces for the simple reason that
they are more efficient. Specialized pollution control devices such as
electrostatic precipitators (to remove particulates) are available, but
without specific regulation to enforce their use it is doubtful they
will catch on.
Emissions from conventional biomass-fueled power plants are generally
similar to emissions from coal-fired power plants, with the notable
difference that biomass facilities produce very little sulfur dioxide or
toxic metals (cadmium, mercury, and others). The most serious problem is
their particulate emissions, which must be controlled with special
devices. More advanced technologies, such as the whole-tree burner
(which has three successive combustion stages) and the
gasifier/combustion turbine combination, should generate much lower
emissions, perhaps comparable to those of power plants fueled by natural
gas.
Facilities that burn raw municipal waste present a unique
pollution-control problem. This waste often contains toxic metals,
chlorinated compounds, and plastics, which generate harmful emissions.
Since this problem is much less severe in facilities burning
refuse-derived fuel (RDF)-pelletized or shredded paper and other waste
with most inorganic material removed-most waste-to-energy plants built
in the future are likely to use this fuel. Co-firing RDF in coal-fired
power plants may provide an inexpensive way to reduce coal emissions
without having to build new power plants.
Using biomass-derived methanol and ethanol as vehicle fuels, instead of
conventional gasoline, could substantially reduce some types of
pollution from automobiles. Both methanol and ethanol evaporate more
slowly than gasoline, thus helping to reduce evaporative emissions of
volatile organic compounds (VOCs), which react with heat and sunlight to
generate ground-level ozone (a component of smog). According to
Environmental Protection Agency estimates, in cars specifically designed
to burn pure methanol or ethanol, VOC emissions from the tailpipe could
be reduced 85 to 95 percent, while carbon monoxide emissions could be
reduced 30 to 90 percent. However, emissions of nitrogen oxides, a
source of acid precipitation, would not change significantly compared to
gasoline-powered vehicles.
Some studies have indicated that the use of fuel alcohol increases
emissions of formaldehyde and other aldehydes, compounds identified as
potential carcinogens. Others counter that these results consider only
tailpipe emissions, whereas VOCs, another significant pathway of
aldehyde formation, are much lower in alcohol-burning vehicles. On
balance, methanol vehicles would therefore decrease ozone levels.
Overall, however, alcohol-fueled cars will not solve air pollution
problems in dense urban areas, where electric cars or fuel cells
represent better solutions.
Greenhouse Gases
A major benefit of substituting biomass for fossil fuels is that, if
done in a sustainable fashion, it would greatly reduce emissions of
greenhouses gases. The amount of carbon dioxide released when biomass is
burned is very nearly the same as the amount required to replenish the
plants grown to produce the biomass. Thus, in a sustainable fuel cycle,
there would be no net emissions of carbon dioxide, although some
fossil-fuel inputs may be required for planting, harvesting,
transporting, and processing biomass. Yet, if efficient cultivation and
conversion processes are used, the resulting emissions should be small
(around 20 percent of the emissions created by fossil fuels alone). And
if the energy needed to produce and process biomass came from renewable
sources in the first place, the net contribution to global warming would
be zero.
Similarly, if biomass wastes such as crop residues or municipal solid
wastes are used for energy, there should be few or no net greenhouse gas
emissions. There would even be a slight greenhouse benefit in some
cases, since, when landfill wastes are not burned, the potent greenhouse
gas methane may be released by anaerobic decay.
Implications for Agriculture and Forestry
One surprising side effect of growing trees and other plants for energy
is that it could benefit soil quality and farm economies. Energy crops
could provide a steady supplemental income for farmers in off-seasons or
allow them to work unused land without requiring much additional
equipment. Moreover, energy crops could be used to stabilize cropland or
rangeland prone to erosion and flooding. Trees would be grown for
several years before being harvested, and their roots and leaf litter
could help stabilize the soil. The planting of coppicing, or
self-regenerating, varieties would minimize the need for disruptive
tilling and planting. Perennial grasses harvested like hay could play a
similar role; soil losses with a crop such as switchgrass, for example,
would be negligible compared to annual crops such as corn.
If improperly managed, however, energy farming could have harmful
environmental impacts. Although energy crops could be grown with less
pesticide and fertilizer than conventional food crops, large-scale
energy farming could nevertheless lead to increases in chemical use
simply because more land would be under cultivation. It could also
affect biodiversity through the destruction of species habitats,
especially if forests are more intensively managed. If agricultural or
forestry wastes and residues were used for fuel, then soils could be
depleted of organic content and nutrients unless care was taken to leave
enough wastes behind. These concerns point up the need for regulation
and monitoring of energy crop development and waste use.
Energy farms may present a perfect opportunity to promote low-impact
sustainable agriculture, or, as it is sometimes called, organic farming.
A relatively new federal effort for food crops emphasizes crop rotation,
integrated pest management, and sound soil husbandry to increase profits
and improve long-term productivity. These methods could be adapted to
energy farming. Nitrogen-fixing crops could be used to provide natural
fertilizer, while crop diversity and use of pest parasites and predators
could reduce pesticide use. Though such practices may not produce as
high a yield as more intensive methods, this penalty could be offset by
reduced energy and chemical costs.
Increasing the amount of forest wood harvested for energy could have
both positive and negative effects. On one hand, it could provide an
incentive for the forest-products industry to manage its resources more
efficiently, and thus improve forest health. But it could also provide
an excuse, under the “green” mantle, to exploit forests in an
unsustainable fashion. Unfortunately, commercial forests have not always
been soundly managed, and many people view with alarm the prospect of
increased wood cutting. Their concerns can be met by tighter government
controls on forestry practices and by following the principles of
“excellent” forestry. If such principles are applied, it should be
possible to extract energy from forests indefinitely.
Hydropower
The development of hydropower has become increasingly problematic in the
United States. The construction of large dams has virtually ceased
because most suitable undeveloped sites are under federal environmental
protection. To some extent, the slack has been taken up by a revival of
small-scale development. But small-scale hydro development has not met
early expectations. As of 1988, small hydropower plants made up only
one-tenth of total hydropower capacity.
Declining fossil-fuel prices and reductions in renewable energy tax
credits are only partly responsible for the slowdown in hydropower
development. Just as significant have been public opposition to new
development and environmental regulations.
Environmental regulations affect existing projects as well as new ones.
For example, a series of large facilities on the Columbia River in
Washington will probably be forced to reduce their peak output by 1,000
MW to save an endangered species of salmon. Salmon numbers have declined
rapidly because the young are forced to make a long and arduous trip
downstream through several power plants, risking death from turbine
blades at each stage. To ease this trip, hydropower plants may be
required to divert water around their turbines at those times of the
year when the fish attempt the trip. And in New England and the
Northwest, there is a growing popular movement to dismantle small
hydropower plants in an attempt to restore native trout and salmon
populations.
That environmental concerns would constrain hydropower development in
the United States is perhaps ironic, since these plants produce no air
pollution or greenhouse gases. Yet, as the salmon example makes clear,
they affect the environment. The impact of very large dams is so great
that there is almost no chance that any more will be built in the United
States, although large projects continue to be pursued in Canada (the
largest at James Bay in Quebec) and in many developing countries. The
reservoirs created by such projects frequently inundate large areas of
forest, farmland, wildlife habitats, scenic areas, and even towns. In
addition, the dams can cause radical changes in river ecosystems both
upstream and downstream.
Small hydropower plants using reservoirs can cause similar types of
damage, though obviously on a smaller scale. Some of the impacts on fish
can be mitigated by installing “ladders” or other devices to allow fish
to migrate over dams, and by maintaining minimum river-flow rates;
screens can also be installed to keep fish away from turbine blades. In
one case, flashing underwater lights placed in the Susquehanna River in
Pennsylvania direct night-migrating American shad around turbines at a
hydroelectric station. As environmental regulations have become more
stringent, developing cost-effective mitigation measures such as these
is essential.
Despite these efforts, however, hydropower is almost certainly
approaching the limit of its potential in the United States. Although
existing hydro facilities can be upgraded with more efficient turbines,
other plants can be refurbished, and some new small plants can be added,
the total capacity and annual generation from hydro will probably not
increase by more than 10 to 20 percent and may decline over the long
term because of increased demand on water resources for agriculture and
drinking water, declining rainfall (perhaps caused by global warming),
and efforts to protect or restore endangered fish and wildlife.
Conclusion
So, no single solution can meet our society’s future energy needs. The
solution instead will come from the family of diverse energy
technologies that do not deplete our natural resources or destroy our
environment. That’s the final decision that the nature imposes. Today
mankind’s survival directly depends upon how quickly we can renew the
polluting fuel an energy complex we have now with sound and
environmentally friendly technologies.
Certainly, alternative sources of energy have their own drawbacks, just
like everything in the world, but, in fact, they seem minor in
comparison with the hazards posed by conventional sources. Moreover, if
talking about the dangers posed by new energy technologies, there is a
trend of localization. Really, these have almost no negative global
effect, such as air pollution.
Moreover, even the minor effects posed by geothermal plants or solar
cells can be overseen and prevented if the appropriate measures are
taken. So, when using alternatives, we operate a universal tool that can
be tuned to suit every purpose. They reduce the terrible impact the
human being has had on the environment for the years of his existense,
thus drawing nature and technology closer than ever before for the last
2 centuries.
Sources
“Biomass fuel.” DISCovering Science. Gale Research, 1996. Reproduced in
Student Resource Center College Edition. Farmington Hills, Mich.: Gale
Group. September, 1999;
“Alternative energy sources.” U*X*L Science; U*X*L, 1998;
Duffield, Wendell A., John H. Sass, and Michael L. Sorey, 1994, Tapping
the Earth’s Natural Heat: U.S. Geological Survey Circular 1125;
Cool Energy: Renewable Solutions to Environmental Problems, by Michael
Brower, MIT Press, 1992;
Powerful Solutions: Seven Ways to Switch America to Renewable
Electricity, UCS, 1999;
PAGE
PAGE 2
Нашли опечатку? Выделите и нажмите CTRL+Enter
