Environmental impacts of renewable energy technologies
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;