Реферат: Environmental impacts of renewable energy technologies
Реферат: Environmental impacts of renewable energy technologies
Contents
Introduction 2
Wind
Energy 2
Solar
Energy 3
Geothermal
Energy 4
Biomass 6
Air
Pollution 6
Greenhouse
Gases 8
Implications
for Agriculture and Forestry 8
Hydropower 9
Conclusion 10
Sources 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;
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