انرژی ها نو

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Problems with Tidal Turbines?

Some environmentalists worry that the newer forms of water
power could create problems, too. The large underwater
turbines used to create wave and tidal power are very new.
Scientists have not had much time to study how they will
affect fi sh. Some people worry that the spinning blades could
kill fi sh or force them from their usual paths. The fi sh might
have trouble swimming to the areas where they normally have
babies. Also, if fewer fi sh than usual are living in an area, birds
that feed on them will have less food. Fishers also fear they will
have a harder time making a living if the turbines affect fi sh
that live near the coasts.
Some scientists worry about whales and other sea
mammals. The cables used to hold buoys or carry electricity
could block their paths. In addition, the animals might not see
the cables and be injured by them

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Another concern is pollution. Many of the buoys and other
devices used to generate wave power contain liquid chemicals.
Some scientists fear these chemicals could leak and kill life in
the oceans. The equipment used to generate electricity also
makes noise. Scientists wonder if the noise might scare fish
looking for food and upset their usual patterns.
Ocean thermal energy conversion (OTEC) systems—which
are expensive to build and maintain—might have their own
problems. Using warm ocean water to create electricity removes
heat from the water. This could harm plants and animals that
need the warmth to survive. It could also affect plants and
animals that live in the cold waters below.

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انرژی فسیلی

Biofuels

The world gets its energy from many
different sources. In the United States,
approximately 85 percent of the energy
supply comes from coal, oil, and natural gas.
Nuclear power provides another 8 percent. All other
sources—including solar and wind energy—add up to no more
than 7 percent.
Depending so heavily on coal, oil, and natural gas poses a
serious problem. These fuels were formed many millions of
years ago. They cannot last forever. Supplies of coal, oil, and
natural gas are going to run low. To satisfy the world’s growing
energy needs, scientists are looking at

renewable fuels—fuels
that cannot be used up. Many scientists believe that biofuels

may help the world meet this challenge.

What Are Biofuels?

Biofuels are renewable energy sources that come from living
things. Some of these fuels have been used for a very long
time. For example, have you ever gathered branches to build
a campfi re? If so, you have already handled one of the oldest
biofuels—wood. In many countries, wood is still used daily for
cooking and home heating.
Another very ancient biofuel is

dung. Dung is a common
name for animal droppings. If you live on a street where dog
owners fail to pick up after their dogs, you probably think of

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dung as a major annoyance or health hazard. Much of the
world, however, sees dung as a valued resource. Farmers and
gardeners use dung (also called manure) as fertilizer to help
crops and plants grow. People in many countries use dried cow
dung as a fuel for cooking.

Modern Biofuels

The use of biofuels has expanded beyond these ancient
resources. Today, many cars run on

ethanol, usually blended
with gasoline. Ethanol is a form of alcohol. This liquid fuel is
made from corn, sugarcane, or other crops. Two of the world’s
major ethanol producers are the United States and Brazil.
Vehicles can also run on biodiesel. This fuel is made from
vegetable oils or animal fats. It can be used as a substitute for

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diesel fuel made from

crude oil. Some drivers have stopped
buying diesel at service stations. Instead, their cars and trucks
run on used frying oil that they get from restaurants. Country
singer Willie Nelson, who is a biodiesel user, says his car smells
like French fries!
Scientists are working on advanced ways to make biofuels
from grasses and garbage. In a decade or two, whole cities may
get their power from giant tanks filled with algae. (Algae are
plantlike life forms that usually grow in water.) Many experts
believe that biofuels will have a growing role in the world’s
energy future

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Biofuels and Fossil Fuels

Coal, oil, and natural gas are known as

fossil fuels. Fossil

comes from a Latin word meaning “dug up.” Fossil fuels are the
remains of plants and animals that have been dead for many
millions of years. The fossil fuels we use today took more than
300 million years to make. They cannot last forever. People are
using them much faster than Earth can produce them.
Biofuels and fossil fuels are similar in some ways. Both
types of fuel come from living things. The difference is that the
supply of fossil fuels will run out. The supply of biofuels will
not. Biofuels are renewable. As long as we have sunlight, soil,
air, and water, we can always grow more biofuels

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The Challenge of Climate Change

A major problem with fossil fuels is their effect on

climate.
When fossil fuels are burned, they produce substances that are
called greenhouse gases. Greenhouse gases trap heat energy
from the Sun. They cause heat to build up in the atmosphere.
Many scientists say that the buildup of greenhouse gases causes
global warming. Global warming poses many different dangers.
If climate change continues, for example, some regions of
the world may have terrible storms, while other regions will
get very little rain. Without enough water, crops will wither
and food supplies will run short. This will lead to dangerous

famine

, which will likely hit the world’s poor countries and
poor people hardest.
Global warming has other effects as well. Ice may melt at
the North and South Poles. This would pose dangers to polar
bears, who depend on the ice in the Arctic region to live. The
melting of the ice would also cause sea levels to rise. As a
result, people who live in coastal areas may experience severe
floods. In addition, major storms could leave whole cities under
water. If current trends continue, major U.S. cities could be in
danger. Threatened cities include New York, Baltimore, San
Francisco, and New Orleans.
The burning of fossil fuels also causes air pollution. Various
substances that are released into the air lead to the formation
of smog—an unhealthy mixture of fog, dust, and fumes that
can blanket a city. The substances also cause such problems
as asthma and lung damage. Fossil fuels have also been linked
to acid rain, which has harmful effects on rivers, lakes, crops,
plants, and animals.

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Can Biofuels Help?

Could using biofuels instead of fossil fuels reduce the amount of
pollution and the threat of climate change? That depends. Some
biofuels used today have serious problems. Like fossil fuels,
wood produces greenhouse gases when it is burned. The same
is true of ethanol, dung, and some other biofuels.
A major problem with wood is that harvesting too much of it

can threaten the world’s forests. This can make global warming

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worse, because forests and jungles absorb greenhouse gases.
A similar problem happens when jungles are cut down to grow
biofuel crops. Farmers in Brazil have cut down some of the
Amazon jungle to grow sugarcane for ethanol.
Energy researchers recognize these problems. They are
developing new ways to make and use biofuels. These methods
would not involve burning. They would not cut down precious
forest lands. They would not add more greenhouse gases to
the atmosphere. Someday, these new biofuels may help solve
both the world’s energy supply problem and the problem of
global warming

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Nature’s
Storage Battery

Today, the world gets about 8 percent
of its energy from traditional biofuels
such as wood and dung. Wood cut for fuel
is a very important source of energy in some
African countries. Africa as a whole gets more than
20 percent of its energy from wood. In the United States, on the
other hand, wood fuel makes up only about 2 percent of the
energy supply. About 800,000 U.S. homes burn wood as their
main source of heat.
About 2 percent of the world’s energy supply comes from
modern biofuels such as ethanol. This percentage is likely to
increase in the future, as researchers fi nd new ways to replace
fossil fuels with renewable fuels.

Understanding Carbon

To understand how biofuels work, you need to understand the

carbon cycle

. The carbon cycle is the process by which living
things collect, store, and use energy. Life on Earth could not
exist without it.
Carbon is found in all living things. It is also found in the air
you breathe and the food you eat. Biofuels contain carbon. So
do fossil fuels. In fact, biofuels and fossil fuels are often called
carbon-based fuels.
Your body contains carbon along with oxygen and hydrogen.
More than 90 percent of the human body consists of these