What is It?
In simple words, it is often said to be the ability to do work. It
exists in many different forms, and it is measured with many different
units. Some of the different forms are: heat; kinetic, potential,
nuclear, chemical, mass, and electromagnetic. But the simple statement
is way too simple. It is incomplete and wrong.
On a much deeper level,
There is a fact, or if you wish, a law,
governing all natural phenomena that are known to date. There is
no known exception to this law–it is exact so far as we know.
The law is called the conservation of energy.
It states that there is a certain quantity, which we call energy,
that does not change in the manifold changes which nature undergoes.
That is an abstract idea, because it is a mathematical principle;
it says there is a numerical quantity which does not change when
something happens. It is not a description of a mechanism, or anything
concrete; it is just a strange fact that we can calculate some number
and when we finish watching nature go through her tricks and calculate
the number again, it is the same...
It is important to realize that in physics today,
we have no knowledge of what energy is.
We do not have a picture that energy comes in little blobs of a definite
amount. It is not that way. However, there are formulas for calculating
some numerical quantity, and when we add it all together it gives "28"—always
the same number. It is an abstract thing in that it does not tell us
the mechanism or the reason for the various formulas.
et al (page 4-1, 2006).
Carl Nave of Georgia State University has published a useful hypertext
resource for Physics called HyperPhysics,
especially his pages on energy.
Because energy is so important in so many different ways
for so many different industries, many different units are used for energy.
- Joule is the scientific unit of energy. It is the work needed to
push an object one meter with a force of one newton in the direction
of the movement.
- Calorie is used to measure heat energy.
- It is the amount of heat needed to raise the temperature of
one gram of water at 15 degrees celsius at a constant pressure
of 101.325 kPa (1 atmosphere) by one degree celsius.
- 1 Calorie = 4.1855 Joules.
- The calorie used to measure the energy content of food is the
kilocalorie = 1000 calories.
- Note, however, other, slightly different definitions of the calorie
are used, ranging from 4.182 to 4.190 Joules/calorie. See the entry
for Calorie in
- BTU is the British Thermal Unit, the English equivalent of the calorie.
- It is the heat needed to raise the temperature of one pound
of water at 39.1 degrees Fahrenheit by one degree Fahrenheit.
- 1 BTU = 1055 Joules.
- Note, however other, slightly different definitions of the BTU
are used, ranging from 1054.3 to 1059.67 Joules/BTU. See the entry
for BTU in the Wikipedia.
- 1 quad = 1015 BTU.
- One barrel of oil, when burned, releases about 5,800,000 BTU = 6,100,000,000
J = 6.1 Giga Joules = 6.1 GJ.
- One cubic foot of gas (natural gas), when burned, releases about
1,300 BTU = 1,400,000 J = 1.4 Mega Joules = 1.4 MJ.
- One ton (British) TNT = 4,184,000,000 J.
Because energy values are often very large, we use the following prefixes
for units in science. The letter in parentheses is the abbreviation for
- kilo (k) = 103 = thousand
- Mega (M) = 106 = million
- Giga (G) = 109 = billion (US)
- Tera (T) = 1012 = trillion (US)
Sometimes called a billion (UK)
- Peta (P) = 1015 = quadrillion (US).
- 1 quadrillion BTU = 1015 BTU = 1 Quad = 1.055
X 1018 Joules.
- 1 Quad ∼ 1018 Joules.
- Exa (E) = 1018
- Zeta (Z) = 1021
Why are we concerned about energy?
- Most of the energy we use in daily life is produced by burning
of fossil fuels.
- The energy is used by automobiles and to generate electricity.
- The burning releases CO2 into the atmosphere possibly
causing global warming.
- We use so much energy that any source or sources will be so large
that they will cause environmental problems. For example, windmills
can be noisy and ugly, nuclear power plants produced long-lived radioactive
How much energy do we use?
See the Statistical
Review of World Energy 2005 by British Petroleum. Here is the powerpoint
presentation (2.6 MB).
- Global energy use in 2003 was 4.1 X 1020 Joules which
is equivalent to 13 Terawatts.
- 1 Terawatt (TW) = 1012 Joules/second= 1012 Watts.
- The global energy use is equivalent to 71,000,000,000 barrels
of oil equivalent used at the rate of 196,000,000 barrels of oil
equivalent per day or the energy in 4.6 metric tons of mass converted
- Global energy use from fossil fuels was approximately 8,260 million
metric tons oil equivalent, which is approximately 9,623 X 106 m3 =
a cube of oil 2.12 km on a side.
- Global oil consumption in 2003 was 76,800,000 barrels of oil per
- Most of the remainder of our energy comes from natural gas
- All are fossil fuels.
- The per capita consumption of energy in the United States is about
57 barrels of oil equivalent per year or 11 kW continuously.
- The energy is used to heat and light homes, offices, and stores,
to power trucks and automobiles, and to operate machinery.
- 57 barrels of oil at $50/barrel = $2,850.
- If the energy were used entirely as electricity, it would cost
about $7,300 per person per year.
- Consumption of energy in the United States was approximately:
- 39.1% oil
- 25.9% natural gas
- 24.4% coal
- 8.1% nuclear energy
- 2.5% hydroelectric, or
- 89.4% from fossil fuel consumption.
- The United States used approximately 24% of all the world's energy,
although we are only 4.6% of the world's population.
Pathways of energy use in the United States in 2005. More than half
of the energy produced is wasted (gray paths). Click on image for a
zoom. Units are in quads: 1 quad = 1015 British thermal
units = 1.055 exajoules = 1.0055 × 1018 Joules.
Why do we use so much fossil fuel?
We use fossil fuel because it is cheap relative to alternate sources
of energy. Gasoline is cheaper than bottled water. Gasoline price in
2005 was just approaching the peak price of 1981.
Price is determined by:
- Availability: Fossil fuels are abundant
and easily extracted. The important question is: How long will they
be abundant? The amount of known reserves divided by the rate of use
has remained constant at around 40 years for more than 150 years. More
recently, production has declined in many areas including the United
States, Mexico, and western Europe. Many experts now claim world oil
production has peaked and will begin to decline. This is known as Peak
- Economics: Supply relative to demand
- As supply drops and demand increases, price increases.
- Demand for oil is rising. The growth of the Chinese and Indian
economies, and the increased use of oil by oil-exporting countries,
has increased demand and reduced the supply of oil, driving up
prices since 2005.
- If oil and gas become even scarcer in the next few decades,
and if world demand continues to rise, the price will increases
greatly. As a result, use will drop, and release of CO2 will
drop, reducing the threat of global warming.
- Also, as prices rise, more sources are found, demand drops, conservation
and efficient use increase, and alternate fuels are used. As a
result, we never run out of a commodity.
- Politics: Political decisions and laws
have a strong influence on price:
- The Kyoto Protocol is a political solution to the CO2 problem,
and if implemented, it will increase costs.
- Governments tax fossil fuels to raise revenues and to reduce
- Many governments own oil companies and use the revenue to help
run their countries.
- Some governments limit the availability of fossil fuels.
- Some governments regulate the use of the fuels.
- In the United States, Congress mandated in 2005 that ethanol
be used in all gasoline. Ethanol is expensive, and not readily
available. This raised gasoline prices in 2006.
- In the United States, many local and state governments have not
allowed the construction of oil refineries. This limited the availability
of gasoline and drove up price.
Alternative Sources of Energy
To avoid the high cost of oil, and to reduce the emissions of greenhouse
gases, governments are seeking alternate sources of energy. In the short
term the outlook is bleak. Hoffert
et al (2002) summarized the possibility of replacing fossil fuels
with alternative sources of energy. Here is part of their abstract.
Here we survey possible future energy sources,
evaluated for their capability to supply massive amounts of carbon
emission-free energy and for their potential for large-scale commercialization.
Possible candidates for primary energy sources include terrestrial
solar and wind energy, solar power satellites, biomass, nuclear fission,
nuclear fusion, fission-fusion hybrids, and fossil fuels from which
carbon has been sequestered. Non-primary power technologies that could
contribute to climate stabilization include efficiency improvements,
hydrogen production, storage and transport, superconducting global
electric grids, and geoengineering. All of these approaches currently
have severe deficiencies that limit their ability to stabilize global
climate. We conclude that a broad range of intensive research and development
is urgently needed to produce technological options that can allow
both climate stabilization and economic development.
From Hoffert (2002).
The important points made in the article are:
- "Energy sources that can produce 100 to 300% of present world
power consumption without greenhouse emissions do not exist operationally
or as pilot plants."
- Improved efficiency in use of fuels is possible, although many uses
are already very efficient.
- "10 TW from biomass requires >10% of Earth's land surface,
comparable to all of human agriculture." And, we are now using
12 TW, and we will use around 30 TW by mid century. Already, by 2008
the demand for biofuels collided with the demand for more and better
food in developing countries leading to soaring food prices and food
riots in many countries.
- "The electrical equivalent of 10 TW requires a surface array
[of photocells] ~470 km on a side (220,000 km2). However,
all the PV cells shipped from 1982 to 1998 would only cover ~3 km2"
- "The main problem with fission for climate stabilization is
fuel...Current estimates of U in proven reserves and (ultimately recoverable)
resources are 3.4 and 17 million metric tons, respectively ...At 10
TW, this would only last 6 to 30 years--hardly a basis for energy policy.
A second article by Pacala
and Socolow (2004) noted "A portfolio of technologies now
exists to meet the world's energy needs over the next 50 years and
limit atmospheric CO2 to a trajectory that avoids a doubling
of the preindustrial concentration..." Here is the abstract of
Humanity already possesses the fundamental scientific,
technical, and industrial know-how to solve the carbon and climate
problem for the next half-century. A portfolio of technologies now
exists to meet the world's energy needs over the next 50 years and
limit atmospheric CO2 to a trajectory that avoids a doubling
of the preindustrial concentration. Every element in this portfolio
has passed beyond the laboratory bench and demonstration project; many
are already implemented somewhere at full industrial scale. Although
no element is a credible candidate for doing the entire job (or even
half the job) by itself, the portfolio as a whole is large enough that
not every element has to be used.
and Socolow (2004).
Still, even this will not be easy:
To put the stabilization challenge in stark terms,
under Pacala and Socolow's most optimistic assumptions for stabilization
at 550 p.p.m., the world will need to reduce its projected business-as-usual
emissions by about 1,000 gigatonnes of carbon over the next century.
Seven stabilization wedges worth would achieve 175 gigatonnes, leaving
a considerable gap, even if the total business-as-usual emissions have
been overestimated by a factor of two or more.
Many believe that if climate change can be dealt
with relatively easily, then there would also be little need to adapt
to it. This sort of thinking may explain why the issue of adaptation
plays no role in the book. Overlooking adaptation in any discussion
of climate policy is a sign that the challenge posed by climate change
has been fundamentally mischaracterized — not only because the
world is already committed to some degree of climate change, but also
because adaptation makes sense under any future climate scenario.
In the words of Hardin in The
Tragedy of the Commons, we must change our behavior to solve
One alternate source of energy that may be must useful for the next
few decades may be nuclear fission, used by nuclear power plants. All
power sources contribute to greenhouse gases, either directly through
burning of fossil fuels, or indirectly through construction of facilities.
But nuclear, wind, and hydro power contribute least.
Greenhouse gas (GHG) emissions from various power sources, including
direct and indirect sources. * means projections are not available.
From Greening of the Nuclear Age by
the American Nuclear
Society, adapted from the International Atomic Energy Agency.
The cost of producing energy from alternative sources varies greatly,
Nuclear energy is slightly more expensive than wind, geothermal, and
Price of energy from alternative sources compared with cost from fossil
From Forbes Magazine
(24 November 2008: page 64).
We can reduce present fuel use by using more efficient systems such
as mass transportation. But consider this editorial:
There are just two problems with mass transit
[in the US in 2005]. Nobody uses it, and it costs like hell. Only
4% of Americans take public transportation to work. Even in cities
they don't do it. Less than 25% of commuters in the New York metropolitan
area use public transportation. Elsewhere it's far less -- 9.5% in
San Francisco-Oakland-San Jose, 1.8% in Dallas-Fort Worth. As for
total travel in urban parts of America -- all the comings and goings
for work, school, shopping, etc. -- 1.7 % of those trips are made
on mass transit. ... Heritage cites the Minneapolis "Hiawatha" light
rail line, soon to be completed with $107 million from the transportation
bill. Heritage estimates that the total expense for each ride on
the Hiawatha will be $19. Commuting to work will cost $8,550 a year.
If the commuter is earning minimum wage, this leaves about $1,000
a year for food, shelter and clothing. Or, if the city picks up the
tab, it could have leased a BMW X-5 SUV for the commuter at about
the same price. We don't want minimum-wage workers driving BMW X-5s.
That's unfair. They're already poor, and now they're enemies of the
From: O'Rourke (2005).
Historical experience since 1800 shows that increased energy efficiency
usually leads to more energy consumption. Clearly, we have a long way
to go to solve the problem of too many people driving cars.
What would be the effect of the Kyoto Protocol on
the US Economy?
See the Energy Information Agency's Kyoto
Testimony. The complete Briefing
Paper is here.
Please read Introduction and Total
Energy from Energy
in the US: 1635-2000 produced by the US Department
of Energy's Energy Information
Energy efficiency of freight transportation
This table summarizes the efficiency of the three main
modes of transport of freight: by barge, rail, or truck.
|Fuel Efficiency (1)
|Barge Equivalents (2)
|Tow Equivalents (3)
||1 15-barge tow
||870 large semis
|EMISSIONS RATIOS (4)
|Hydrocarbons plus Nitrogen Oxides
|| These are the miles one ton of cargo can be
transported on one gallon of fuel.
|| One Mississippi barge can transport 1,500 tons
of cargo. This is equivalent to 52,500 bushels of wheat or 453,600
gallons of fuel.
|| One tow, consisting of a boat and fifteen barges
is 0.25 miles in length, whereas 2.25 100 car train units is 2.75
miles in length, and 870 trucks spaced bumper to bumper is 11.5 miles
|| Eastman Data Emissions Comparison: This is the
ratio of emissions for trucks and rail on a ton-mile basis relative
From Iowa Department of Transportation and
Feynman, R., R. Leighton, et al. (2006). The
Feynman Lectures on Physics, Addison Wesley.
Hoffert, M. I., K. Caldeira, G. Benford and many others (2002). "Advanced
technology paths to global climate stability: energy for a greenhouse
planet." Science 298 (5595): 981-987.
O'Rourke, P.J. (2005). Mass Transit Hysteria. Wall
Street Journal, 16 March 2005, A24.
Pielke, R. A. (2006). What just ain't so. Nature 443
Pacala, S. and R. Socolow (2004). "Stabilization
Wedges: Solving the Climate Problem for the Next 50 Years with Current
Technologies." Science 305 (5686): 968-972.
24 March, 2009