Environmental Engineering Reference
In-Depth Information
do it. You do not have to replace everything with solar
power or windmills.
The distinction between primary energy and the
energy directly used by us is important. Emissions come
mainly from primary energy while what we use is a mix
of primary and secondary energy. For example, electri-
city is a secondary form of energy and has to be made
from something else
there are no electricity mines.
Electricity is made at power plants that use some pri-
mary fuel, coal or natural gas, or nuclear reactors, or
wind, or water, etc. Electricity, then, is not primary
energy. If you drove an electric car you would use no
gasoline and emit no greenhouse gas directly, but pro-
ducing the electricity you used to charge your batteries
to run the car would produce greenhouse gases, and how
much depends on the mix of fuels used to generate the
electricity. On the other hand, if you use natural gas to
heat your home, you are directly using one of the pri-
mary energy sources. To reduce our greenhouse gas
emissions we have to reduce the emissions from the
primary fuel supply. So, if someone tells you of the
marvels of hydrogen as a motor fuel because using it
emits no greenhouse gases, ask how the hydrogen was
made and what those emissions were.
The primary energy supply consists of six main fuels:
oil, coal, natural gas, nuclear energy, large hydroelectric
energy plants, and combustibles (mostly forest and agri-
cultural waste material). What are called
-
“
Other
”
in
Table
below include wind, solar, geothermal, small-
scale hydropower, and biofuels which together only
amount to about
.
% of TPES. The breakdown by fuel
is important because their use in the economy differs and
