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Реферат: Environmental impacts of renewable energy technologies

Contents

Introduction 2

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;