What is renewable energy?
Renewable energy comes from sources so huge that they’re virtually unlimited. Sunlight, wind and water all provide us with energy today.
Where does U.S. renewable energy come from?
50% Biomass
41% Hydroelectric
5% Geothermal
3% Wind
1% Solar
U.S. Electricity Generation by Energy Source , 2004
Contribution of Renewable Energy to U.S. Consumption, 2004
Renewable energy sources include the following:
BIOMASS
Provides 50% of renewable energy in the US (2007)
The term “biomass” covers many individual fuel sources.
Generating energy from biomass involves the burning of:
wood (and its byproducts and waste).
agricultural crops and crop residue (called “feedstock”).
residential, commercial and industrial waste.
methane from landfills.
alcohol fuels, such as ethanol.
Truck unloading wood chips which will fuel the Tracy Biomass Plant, Tracy, California.
Advantages
Availability: Burnable fuels related to plant materials are some of the most abundant materials on earth. Because of the many forms in which it’s available and the flexibility of its use, it’s the most important of renewable fuels. In less economically developed countries, biomass may provide 80% of energy, often from the burning of crop residue and locally available woody material.
Landfills: In the U.S., material which formerly went into landfills can now be converted to energy. Although this technology is not widespread in the U.S., its use is increasing.
Disadvantages
Carbon dioxide, one of the major products of the burning of biomass in less-developed countries is this human-produced greenhouse gas of main concern in global warming.
Forest depletion- As increasing amounts of plants and trees are burned for fuel, in addition to adding carbon dioxide to the atmosphere, the means for cleaning carbon dioxide from the atmosphere is reduced.
HYDROELECTRIC POWER
Provides 41% of renewable energy in the US (2007)
Advantages
Hydroelectric energy creates very little pollution because it requires no burning of fuel. Dams for electricity production are hugely expensive to build, but once constructed the power to spin generators which produce electricity is virtually free for the life of the dam.
Dams provide huge benefits in addition to power, including:
water supply for drinking.
irrigation and industrial uses.
flood control.
recreation.
Disadvantages
Good sites are difficult to find. They require a river with a large drop in elevation over a short distance and an upstream area remote enough that the flooding which takes place as the dam fills will not cause extensive economic damage or widespread hardship for many residents. The reservoir footprint of some dams is over 100 miles long.
Dams across the US are aging, with some approaching the 100-year mark. In 2002, a Task Committee of the Association of State Dam Safety Officials estimated that $36.2 billion dollars are needed to rehabilitate non-federal dams and that $10.1 billion dollars are needed over the next 12 years for repairs to the nation’s most critical dams.
U.S. hydroelectric power will probably not expand much in the foreseeable future.
GEOTHERMAL ENERGY
Provides 5% of renewable energy in the US (2007)
Geothermal energy refers to heat energy stored within the earth’s crust. For the most part, this heat is released over a wide area of the earth’s surface, but in some areas, especially in Western states, this heat is near the earth’s surface and concentrated.
High temperature sources in the earth are used to generate electricity. Total U.S. geothermal electrical production is now approximately 2200 Megawatts (MW), or about the same as four large nuclear power plants.
Low and medium temperature sources are used directly as a heating source for buildings, industrial processes, greenhouses, aquaculture and at resorts.
Low and medium temperature sources may also be used by ground-source heat pumps, which remove heat from the ground during the heating season and use the ground as a heat sink during the cooling season.
WIND ENERGY
Provides 3% of renewable energy in the US (2007)
Wind energy refers to air movement across the earth caused by uneven heating of the earth’s surface by the sun and by the earth’s rotation. Energy contained in wind is harvested with turbine generators, which produce electricity. Groups of turbines are erected in appropriate areas to create wind farms.
U.S. total electricity production from wind power was 11,600 MW at the end of 2006. This is equivalent to the amount of energy used by 3 million American homes, or about the same as 20 large nuclear power plants.
Wind power generating capacity increased by 27% in 2006 and is expected to increase an additional 26% in 2007. Wind power is believed to be capable of supplying up to 20% of U.S. electricity needs.
Advantages
Almost no pollutants are produced by wind power generation after construction of the turbines is complete. The net environmental result is definitely positive using this power source.
Wind power has the potential to provide a large percentage of the emission reductions needed to meet future targets for carbon dioxide levels.
Disadvantages
Developing infrastructure will be expensive. Carrying electricity from windy areas with good potential for wind farms to areas (mostly cities) where electricity is needed will require the construction of transmission lines or “infrastructure.”
Wind energy is limited by the number of geographical areas having enough wind to make production profitable. Most turbines operate at full power only about 10% of the time due to lack of wind.
SOLAR ENERGY
Provides 1% of renewable energy in the US (2007)
The sun provides us with energy in two ways:
Photovoltaics (PV): Photovoltaic modules convert sunlight into electricity. They have no moving parts, have 20-year lifespans and no negative environmental impact once they’re installed.
The most widespread use of PV in the U.S. is in small systems designed to satisfy all or part of the electricity demand of one home site. Increasingly companies or organizations are being formed to erect PV farms in which a large number of modules, called “arrays,” are erected to provide electrical power for a number of consumers.
Solar Thermal: Solar collectors are used to gather heat from the sun which can then be used for heating water or the home interior. These systems are typically used for residential or light commercial buildings.
Summary
Although solar energy will continue to grow as a means of providing heating and electricity, its share of total U.S. energy production/consumption will probably not grow much in the near future.
NUCLEAR ENERGY
Provides 20% of US electrical power Nuclear reactors produce electricity by spinning steam turbines. Steam is generated through a controlled, self-sustaining nuclear chain reaction called “fission” which occurs when atoms are split apart, releasing enormous amounts of energy.
The fission process is fueled by uranium 235, a rare metal which must be extracted from common uranium before being processed for use as a nuclear fuel.
Advantages
Nuclear power production puts no pollutants into the air. Each year, nuclear power plants in the U.S. prevent emissions of about 700 million metric tons of carbon dioxide. This is almost as much carbon dioxide as is released from all U.S. passenger cars combined.
Fewer fossil fuels will be burned and greenhouse gas emissions by will be lowered by increasing the share of U.S. electric power produced using nuclear fuels.
Nuclear power production produces less waste than fossil fuel production and it is more closely managed.
Disadvantages
Radioactive waste is produced. The half-life of Uranium 235 is over 700 million years. As of 2007, no permanent disposal site has been settled upon and almost all nuclear waste produced, from the start of nuclear energy production to the present, is in storage.
The outflow of heated water, the result of cooling processes necessary for controlling the fission process, may have a negative effect on nearby bodies of water. In some cases, it may also be beneficial.
Summary
High construction and operating costs have resulted in the building of fewer nuclear power plants in the U.S., with the last one completed in 1996. These costs will need to drop in order for nuclear power to be competitive with other energy sources.
The U.S. leads the world in total power produced through nuclear energy, although other nations with fewer natural resources have a higher national percentage of nuclear-produced power.
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