Environmental Engineering Reference
In-Depth Information
5
Renewables, by definition, are forms of energy that are not exhaustible, as are
fossil fuels. All renewables originate in the Sun and will last as long as the Sun it-
self. Most of them, such as wind, waves, hydroelectric, solar thermal, and biomass,
originate in the radiation incident on the Earth. Tidal energy is due to the gravita-
tional attraction between the Earth, the Sun, and the Moon, and geothermal energy
originates from the center of the Earth, which has not yet cooled.
Biomass is the generic name given to material generated by living organisms
such as wood, charcoal, and organic residues from agriculture and animals—all of
which can be used as energy sources. About 45% of biomass matter in weight is
composed of carbon usually in the form of carbohydrates composed by carbon, hy-
drogen, and oxygen. It is abundant and, up to the middle of the 19th century, it was
the dominant form of energy used by humans for home heating and cooking and
heat for industrial processes. It is a renewable energy resource like all the energies
originating from the Sun.
Biomass is produced continuously through photosynthesis, and one estimates
that 200 billion dry tons of biomass are produced per year, of which a small fraction
is used for energy purposes.
In many developing countries biomass continues to be used mainly for cooking,
in very inefficient and primitive cook stoves. Still, approximately 6% of all energy
consumed in the world is used for this purpose, generating some health problems
related to the soot produced in inefficient burning.
The basic problem in using fuel wood to cook is its low efficiency, which is
usually below 10%. This is the case of the three-stone cooking stove, widely used
by low-income populations in developing countries. Although the energy produced
is cheap, these stoves are very polluting and prone to accidents. Simple improve-
ments in primitive stoves are inexpensive and may considerably increase the effi-
