реферат скачать
Главная | Карта сайта
реферат скачать

реферат скачать

реферат скачать
... А Б В Г Д Е Ж З И К Л М Н О П Р С Т У Ф Х Ц Ч Ш Щ Э Ю Я

реферат скачать
Введите фамилию автора:

Environmental impacts of renewable energy technologies

Environmental impacts of renewable energy technologies


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


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


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


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 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.


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


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



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.


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;

реферат скачать
НОВОСТИ реферат скачать
реферат скачать
ВХОД реферат скачать
забыли пароль?

реферат скачать    
реферат скачать
ТЕГИ реферат скачать

Рефераты бесплатно, курсовые, дипломы, научные работы, реферат бесплатно, сочинения, курсовые работы, реферат, доклады, рефераты, рефераты скачать, рефераты на тему и многое другое.

Copyright © 2012 г.
При использовании материалов - ссылка на сайт обязательна.