The food supply continues to sustain us. Farmers plant and harvest
their crops, including corn, soybeans, wheat, or other plant life. See
Figure 5-4. Some foods not only supply humans with energy, but are also
used to supply vehicles with energy. For example, gasohol is made from
grains to fuel automobiles. It is described more extensively in the section
on alcohol fuels. Food product waste can also be burned or converted into
fuel. Successful experiments in producing fuels from gardening and agri-
cultural wastes have been performed. They are described in the biocon-
version section later in this chapter.
Wood
Wood is a very old source of energy. It has been used as an energy
source since the prehistoric times, and it continues to be used as an energy
source today. For many years, it has been used to heat homes and for
cooking. By the early 1900s, the use of wood as a fuel declined. Other
sources of energy that offered more energy per volume, such as oil and
natural gas, were beginning to be used. Today, however, you can find
wood-burning stoves and fireplaces in modern homes. See Figure 5-5.
Wood pellet stoves are also a popular source of supplemental heat for
some people. Once again, wood has become a useful source of energy.
When harvesting wood, the wood must be split; transported; dried for
optimal efficiency; stacked; and manually loaded into a fireplace, stove, or
furnace. Burning wood requires periodic stoking of the fire, and tempera-
ture control within the structure can be difficult to regulate. Depending on
availability, wood can be an inexpensive energy source in comparison to
other fuels. Denser woods, like oak and hickory, tend to yield a greater
amount of energy per volume than many other species of wood.
Gasohol: An auto-
mobile fuel made
from grains.
Chapter 5
100
Figure 5-4. The yearly cycle of planting, growing, and harvesting crops
provides an abundant supply of food to serve as an energy source for people
and animals. Some crops, such as these soybeans, can be used to produce
other types of energy sources, such as biodiesel fuel for vehicles.
G R E E N T E C H
The practice of irre-
sponsible forestry
has irreversibly dam-
aged some of our
forests. Several orga-
nizations now exist to
monitor and regulate
every step of forestry
in order to sustain
forests.