Power Sources and Uses in Brief
U.S. primary energy consumption by source and sector, 2016
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. still depends to some extent on coal to generate its essential electrical energy, although in recent years coal has declined in its use and natural gas and nuclear power together now exceed coal in importance. Petroleum, the single most-consumed fuel, is the giant of transportation, but produces only 1% of our electricity.
For the 21st century, however, 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. Changing to mostly renewable power sources for a clean,affordable, sustainable future is expensive, controversial, transformative - and long way off.
Here's a brief overview of our power sources:
1. Fossil fuels - coal, oil, natural gas. Acid rain, smog, and smoke befouled the air of industrialized countries and large cities for more than a century. This visibly dirty air was the result of burning the carbon-based fossil fuels: oil for transportation fuel and coal for energy production. Much of this pollution has been remedied in the US, by legislation that requires energy companies to clean or sequester the waste products of energy production. However, the most important current problem with the use of fossil fuels is the over-production of carbon dioxide, the invisible "greenhouse gas" most closely associated with global warming.
The importance of fossil fuels, petroleum, coal and natural gas, in modern civilization presents the world with a dilemma.
On one hand, we have come to rely on large, consistent, instantly available supplies of fossil fuels for almost all our cars, trucks, trains, boats and airplanes. Many homes use oil for heating, and we use fossil-based chemicals to produce many of the products of our daily life, from our home furnishings to the clothes on our backs. Most of our electricity is generated by the burning of coal or natural gas. In addition, economic growth in countries around the world creates increasing demand for more and more of the energy so readily available from the plentiful supply of fossil fuels available on our planet.
At the same time, we have an increasing understanding that potentially harmful global climate change could result from our massive use of such fuels. Additionally, we know that all fossil fuels are finite as resources. They will eventually have to be replaced by other sources of energy, probably at considerably higher cost than we are paying today and perhaps sooner than we like to think, due to the impending, deeply destructive, profoundly negative impact they have on our global environment.
Given our current predicament, how do we successfully transition to cleaner, sustainable fuel(s)?
2. Nuclear fission. Of all our current power generators, nuclear reactors produce the 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. 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 a substantial portion of our power, but no new plants have been built in over 20 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.
3. Renewables - hydroelectric, biomass, wind, geothermal and solar. Currently, these power sources account for only about 10% of our energy supply. However, they are the most hoped-for solution to our growing need for clean energy.
Hydroelectric is the leading source of renewable power. A hydroelectric station is built by damming a river and erecting 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.
Biomass is now used mostly for the transportation fuels ethanol and biodiesel. However, 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.
Wind has increased substantially as a source of renewable power 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. It's drawbacks are that it is intermittent as a power source, hurts birds, and neighbors say it's annoyingly noisy.
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 renewable energy. Small geothermal systems can heat and cool buildings efficiently, though at considerable installation cost.
Solar power currently comes in two forms: concentrated solar power (CSP) and photovoltaic (PV).
Concentrated solar power (CSP) concentrates the sun's heat on an absorbent 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 absorbing 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. One of the world's largest solar plants, 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.