Coal, oil, and natural gas
are "fossil fuels"
that have replaced
other energy sources
because they have
a higher power density
( except for nuclear power ),
are available,
and are inexpensive.
Fossil fuels
are so inexpensive
they make electricity
and transportation
affordable even for
low-income households.
Power density
is energy flow
per unit of time,
A natural gas well
is nearly 50 times
more power-dense
than a wind turbine,
more than 100 times
as dense as a
biomass-fueled
power plant,
and 1,000 times
as dense as
corn ethanol.
Coal has
an energy density
50% to 75% that of oil,
but still much more than
solar, wind, and biofuels.
Crude oil has,
at ambient pressure
and temperature,
the highest
energy density
of all fossil fuels.
High power density
explains why
a basket of coal
light enough
for a single person
to carry
can heat a home
for an entire day
and night,
even in winter.
A pipe less than
one inch in diameter
can provide
enough natural gas
to meet the cooking,
heating, and
hot water needs,
of even large homes.
The uranium used
in nuclear reactors .
has an energy density
even higher than
fossil fuels,
but the facilities needed
to harness that power,
reduce its power density
to closer to that
of fossil fuels.
Unjustified
public concerns
over the safety
of nuclear power,
has greatly slowed
the expansion
of nuclear power
in the United States,
and in most other
parts of the world,
although not in China.