Environmental Engineering Reference
In-Depth Information
manufacturing cost penalty that will be offset in part by fuel cost savings. Automobiles promise to
be one of the more cost-effective ways for reducing oil consumption and carbon emissions.
1.2.3
Energy as a Commodity
Because of the ubiquitous need for energy, combined with the ability to store and utilize it in
many forms, energy is marketed as a commodity and traded internationally at more or less well
established prices. For example, in recent years the world crude oil price has ranged from about
15-35 $/barrel, or about 2-5 $/GJ.
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Coal is generally cheaper than oil, whereas natural gas is more
expensive. The difference in price reflects the different costs of recovery, storage, and transport.
Nuclear fuel refined for use in nuclear electric power plants is less expensive than fossil fuels, per
unit of heating value.
Coal is the cheapest fuel to extract, especially when mined near the earth's surface. It is also
inexpensive to store and transport, both within and between continents. But it is difficult to use
efficiently and cleanly, and in the United States it is used mainly as an electric utility fuel. Oil
is more expensive than coal to recover, being more dispersed within geologic structures, but is
more easily transported by pipeline and intercontinentally by supertanker. It is almost exclusively
the fuel of transportation vehicles, and it is also the fuel of choice for industrial, commercial, and
residential use in place of coal. Like oil, natural gas is recovered from wells, but is not easily stored
or shipped across oceans. It commands the highest price because of the greater cost of recovery, but
is widely used in industry, commerce, and residences because of its ease, efficiency, and cleanliness
of combustion.
In contrast with fossil and nuclear fuels, renewable energy is not transportable (except in
the form of electric power) or storable (except in hydropower and biomass systems). Renewable
hydropower electricity is a significant part of the world electric power supply and is sold as a
commodity intra- and internationally.
Synthetic fuels, such as hydrogen, ethanol, and producer gas, are manufactured from other
fossil fuels. By transforming the molecular structure of a natural fossil fuel to a synthetic form
while preserving most of the heating value, the secondary fuel may be stored or utilized more
easily, or provide superior combustion characteristics, but is inevitably more expensive than its
parent fuel.
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On the time scale of centuries, the supplies of fossil and nuclear fuels will be severely depleted,
leaving only deposits that are difficult and expensive to extract. The only sources that could supply
energy indefinitely beyond that time horizon are nuclear fusion and renewable energy. These are
both capital-intensive technologies. Their energy costs will inevitably be competitive with fossil
and fission fuels when the latter become scarce enough.
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10
A barrel of crude oil contains about 6 GJ (6 MBtu) of fuel heating value.
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Plutonium-239, a fissionable nuclear fuel, is formed from uranium-238, a nonfissionable natural mineral, in
nuclear reactors. In this sense it is a synthetic nuclear fuel, which can produce more energy than is consumed
in its formation, unlike fossil fuel-based synthetic fuels.
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If fusion power plants will be no more expensive than current fission plants, at about 0.3-1 dollar per thermal
watt of heat input, then the capital cost of supplying the current U.S. energy consumption of about 3 TW
would be 1-3 trillion dollars (T$). The cost of this energy would be several times current costs.
