Environmental Engineering Reference
In-Depth Information
Almost all the oxygen in the earth's atmosphere is formed through oxygenic pho-
tosynthesis. Therefore, the oxygen we need in order to breathe is a pure by-product
of biomass production.
Biomass is distributed in many different forms throughout earth. In addition to solar
energy, water is essential for the growth of biomass. Even the solar energy in the
northernmost regions of the world is suffi cient to create biomass. Regions with water
shortages, however, have low biomass growth (Figure 12.3).
Figure 12.3 The view from space - vast areas of water cover the globe. Source: NASA.
Plants therefore convert sunlight into biomass using natural chemical processes. An
effi ciency can also be established for this process. As a result, land usage for
biomass cultivation is comparable to other renewable energy technologies such as
solar systems. A plant 's effi ciency is determined by dividing the calorifi c value of
dried biomass by the solar energy that reached the plant during its growth phase.
On average, including deserts and oceans, the effi ciency of biomass production on
earth is 0.14% [Kleemann and Meliß, 1993]. Despite the comparatively low effi -
ciency, biomass is created worldwide with an energy content that corresponds to
about ten times our entire primary energy requirements.
Yet not all biomass can be used as energy. Human beings currently use around 4%
of new biomass. Two percent goes into food and fodder production and one percent
ends up as wood products, paper or fi bre. Around 1% of newly created biomass is
used as energy - usually in the form of fi rewood - and it therefore covers about
one-tenth of the world's primary energy demand.
The plants that reach the highest effi ciency during the conversion of sunlight into
biomass are C4-plants. These plants have a rapid photosynthesis and, as a result,
use solar energy particularly effectively. C4-plants include amaranth, millet, corn,
Search WWH ::

Custom Search