Power Sources

US Energy Consumption by Source

(click image to enlarge)

A power source is a fuel that returns more energy than is invested to produce it. The sun, our star, runs on the most powerful energy source known - nuclear fusion. It's a process scientists hope to harness one day. On earth it was the carbon-based fossil fuel, coal, that powered the Industrial Revolution from the 19th century. The U.S. depends largely on coal, natural gas and nuclear power to generate its essential electrical energy. Petroleum, the single most-consumed fuel, is the giant of transportation.

Fossil Fuels

Fossil fuels - coal, oil, natural gas. These fuels provide in excess of 80% of the power commercially produced in the United States. Without the carbon-based fossil fuels, the global economy would collapse. Petroleum fuels our cars and trucks; natural gas heats our homes; coal provides much of the energy used to run our factories. We rely on fossil fuels more than we do on any other source of power to sustain our global civilization.


All fossil fuels are the result of geological conditions that transformed massive deposits of plants and animals that lived and died millions of years ago into mostly hydrocarbon compounds of varying composition. Depending on the environment and nature of the forces that compressed and contained the deposits, some of them were transformed into coal, some into crude oil, and some into natural gas.


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Nuclear Power

Nuclear Power - Of all our current power generators, nuclear reactors produce greatest amount of energy per unit of fuel weight. They do this by splitting the atoms of specially processed uranium, releasing large amounts of energy, a process known as nuclear fission. Under the right conditions the splitting process can become a self-sustaining chain reaction, allowing a continuous flow of energy and power. The process is efficient, low in cost and emits no air pollution or carbon dioxide.


However, nuclear reactors are expensive to build, and the fission process results in highly radioactive waste products that must be isolated from human exposure in safe and secure storage conditions for many years. Nuclear produces 9% of our power, but no new plants have been built in the last several years, due to public fears of environmental and, more recently, security dangers. Improved technology and practical energy needs may change that, but transportation and long-term storage of used fuel rods have yet to be fully addressed.


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Renewable Power Sources

Hydroelectric, biomass, wind, geothermal and solar are classified as renewable power sources. Their use does not permanently deplete the primary sources of energy used to generate useable energy products (e.g. electricity). Currently, these power sources account for about 10% of our energy supply. However, they are the most hoped-for solution to our growing need for clean energy.

Wind

Wind is now producing 21% of renewable energy. That's just .51% of the total energy yield, but wind energy has nearly tripled in production since 2007. It works by using the wind to turn tall propeller-like turbines, whose spinning hubs connect to generators which convert mechanical to electrical energy. Wind is relatively cheap, very clean and a wind farm takes about 2 years to build. But it is intermittent as a power source, hurts birds, and neighbors say it's annoyingly noisy.


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Solar Power

Solar power currently comes in two forms: concentrated solar power (CSP) and photovoltaic (PV). Together, these sources of solar energy account for about 6% of renewable energy.


Concentrated solar power (CSP), presently the most practical method for large-scale solar power generation, concentrates the sun's heat on an absorbant surface, which transfers the heat to water. The resulting steam drives a turbine linked to an electric generator. CSP plants employ large reflective surfaces, which tilt with the movement of the sun to focus solar rays on absorber tubes, which contain a fluid that transfers the heat to the power plant's boilers. For smaller applications like heating and cooling buildings or heating water, flat heat-absorbent panels pass heat through to tubes of fluid which transfer it to an insulated water tank. The world's largest solar plant, built in the 1980's in the Mohave Desert of California, uses the CSP method.


Photovoltaic (PV) cells, when exposed to the radiant energy of the sun, produce an electrical voltage. At a photovoltaic power station, multiple panels of silicon-based PV cells covered by non-reflective glass collect electromagnetic energy directly from the sun. Electric fields within the cells force the sunlight electrons to move in a given direction, establishing direct current (DC) electricity. Photovoltaic energy must be stored in batteries or other special storage systems for use in cloudy conditions or darkness.


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Hydroelectric Power

Hydroelectric is the leading renewable source, responsible for 6% of overall electrical generation, and 24% of renewable power. A hydroelectric station is built by damming a river and installing turbines, which are run by falling water. The energy produced is cheap, clean and constant. But dams are costly to build, may cause flooding and can disrupt ecological plant and animal systems.


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Geothermal

Geothermal power stations tap into reservoirs of deep underground water heated by surrounding hotbeds of rock and volcanic magma. Steam from that water is what ultimately powers geothermal generators to produce 2% of renewable energy or .35% of total electrical generation. Small geothemal systems can heat and cool buildings efficiently, though at considerable installation cost.


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Biomass

Biomass accounts for 5% of renewable power. It is now used mostly for the transportation fuels ethanol and biodiesel. In addition, other biomass fuels (i.e. fast-growing "energy" crops, agricultural wastes and methane from landfills) may be burned, fermented or "digested" by bacteria to provide an inexpensive, relatively clean electrical power source.


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Urgent Concerns

During the 21st century emergent international, environmental, economic and political concerns - climate change, newly prosperous and competitive nations, dependence on other countries for critical fuel supplies - have pushed research on renewable sources of energy generation to a new level of national urgency in the U.S. and other nations. There are compelling forces at work on a global level, driving the world toward renewable energy sources. The environment issue is presently forefront in the concerns for our energy future. However, changing to mostly renewable power sources for a clean, affordable, sustainable future is necessary, expensive, controversial, transformative - and a long way off.