Environmental impacts of renewable energy technologies - Экология - Скачать бесплатно
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
1. "Biomass fuel." DISCovering Science. Gale Research, 1996. Reproduced in
Student Resource Center College Edition. Farmington Hills, Mich.: Gale
Group. September, 1999;
2. "Alternative energy sources." U*X*L Science; U*X*L, 1998;
3. Duffield, Wendell A., John H. Sass, and Michael L. Sorey, 1994, Tapping
the Earth’s Natural Heat: U.S. Geological Survey Circular 1125;
4. Cool Energy: Renewable Solutions to Environmental Problems, by Michael
Brower, MIT Press, 1992;
5. Powerful Solutions: Seven Ways to Switch America to Renewable
Electricity, UCS, 1999;
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