Renewable
Energy Sources
Source:
U.S. Department of Energy
Concern over the
environmental impact of burning fossil fuels has
helped spur interest in alternative fuels that are less polluting. And
since the supply of fossil fuels is finite and diminishing, there is
interest in "renewable" sources that do not deplete existing supplies.
However, renewable energy sources still make up only a small share of
U.S. domestic energy production (about 6%, or excluding hydropower,
about 3.5%). The major reason for this is their relatively higher cost
(in some cases 2 to 4 times that of power obtained from traditional
fuels). The following are the major renewable energy sources available.
Renewable Energy's Role in Nation's Energy Supply (2008)
Source:
Energy Information Administration
Biomass
is plant-derived
material usable as a renewable energy source,
including wood energy crops such as hybrid poplars and willow trees,
agricultural crops including soybeans and corn, and animal and other
wastes. Biomass is one of the two most common energy sources in the
U.S. today along with hydropower. Forms of biomass such as wood can be
burned to produce heat and generate electricity. Agricultural crops can
be chemically converted into fuels such as ethanol and biodiesel; these
are the only known renewable liquid energy sources, and may one day
replace petroleum and fossil-fuel produced diesel. But bringing ethanol
and biodiesel into wide use would require more energy-efficient methods
of production and transportation, Overall, biomass fuels are much
cleaner-burning than fossil fuels, though biomass fuels do produce
carbon dioxide and other pollutants.
Geothermal
energy is
generated from heat from inside Earth. This form
of energy is both clean and renewable, The technology has caught on in
countries with substantial geothermal activity such as Iceland, where
it accounts for 16% of electricity output and 86% of all energy used
for home heating. In the U.S. the best sources for geothermal power are
in the west, where there are many underground lakes of heated water;
however, large-scale access would require drilling. A major goal in
this field is to find a way to harness energy directly from magma
(molten rock material), which has great potential because of its high
temperature.
Hydrogen
is the 3rd most
abundant element on Earth. It does not
naturally occur on Earth as a pure gas or liquid, but is always
combined with other elements (such as with oxygen to form water or
carbon to form methane). For energy use it is produced from
hydrocarbons using heat, bacteria or algae through photosynthesis, or
by using sunlight or electricity to split water into hydrogen and
oxygen, Hydrogen batteries or "fuel cells" are already used by NASA on
the space shuttle, In a fuel cell. electrons are released from the
hydrogen atoms in a chemical reaction and flow through an external
circuit as electricity. The protons then combine with oxygen (and some
of the electrons in the electric current) to make heat and waiter
suitable for drinking. Fuel cells do hot run down, but work as long as
hydrogen is supplied. Some experts think hydrogen will be the power
source of the future. However, an infrastructure would need to be
created for safe and cost-effective transportation and storage of
hydrogen.
Hydropower,
or
hydroelectric power, is generated by water flowing
through turbines. With biomass fuels, it is one of the two most common
renewable energy sources in the U.S. today. A dam on a river is a
common hydropower producer. No harmful greenhouse gases are produced,
but the dams needed to generate the power can harm river ecosystems.
Researchers are working on turbine technologies that may maximize use
of hydropower and reduce adverse environmental effects.
Ocean energy is generated
in two ways. Thermal ocean energy uses the
heat that the ocean absorbs from the sun to power generators, and
sometimes drinkable desalinated water is a by-product. Mechanical ocean
energy is generated by the movement of tides and waves through a
turbine, In both cases, power generation is not very efficient with
current technology, Much more research is needed to make thermal ocean
energy generation a reality. Mechanical ocean energy requires large
dams or breakwater-type structures called "tidal barrages" to be built,
which could cause harm to coastal ecosystems.
Solar energy is generated
using heat and light from the sun, Solar
energy is an increasingly common source of electricity. Photovoltaic
(PV) solar cells arc made of semi-conducting materials that can
directly convert sunlight to electricity without any harmful waste
product: Solar collectors are made more efficient by using arrays of
mirrors to concentrate the sun's rays onto PV panels. Another way of
using sunlight is to heat water directly. According to the DOE, homes
incorporating solar heating designs can save as much as 50% on heating
bills. The downside to solar energy is that it depends heavily on a
range of factors including location, time of year and weather.
Wind energy uses wind
turbines to produce energy. They are perched on
high towers, usually 100 feet or higher, and often placed in large
groups ("farms") to generate electricity for towns and cities. On a
much smaller scale, stand-alone turbines are sometimes used by farmers
and homeowners to generate supplemental electricity. In the past 20
years, government incentives in the form of tax credits to producers
and incentives for homeowners have helped lower the price of wind power
by 85%, making it a more feasible option, Some people object to wind
farms because of their appearance or the noise the turbines make. Wind
power raises few other environmental problems; but the turbines can
pose a danger to birds. In addition, because weather is involved,
consistent generation is a challenge. |
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