Environmental Engineering Reference
In-Depth Information
bridged. The idea of generating solar energy in deserts and transporting it to urban areas
has been promoted, in particular, by the DESERTEC Foundation, a network of scientists
and business interests whose long-term goal is to meet most of the energy needs of North
Africa, and as much as 10 per cent of Europe's, through solar power plants installed in the
CSP-generated electricity is still expensive compared with fossil-fuelled power, and this
remains a major barrier to development. Somewhat ironically, dramatic reductions in the
installation costs of PV plants are challenging the CSP market in the United States and
Europe. In the last few years, several planned CSP projects have been redesigned to use
PV technologies instead. According to some experts, the rush towards PV may represent
a growing trend, while others believe that the provision of thermal storage will justify a
development phase, its future role in the global energy mix is uncertain.
4.7 Bioenergy
The Sun in a Teacup
The sugar that sweetened my tea this morning was a kind of stored solar energy, formed
months ago by plants. Although most of the solar energy that penetrates the Earth's
atmosphere is expended in warming the soil, air, and water, and in driving winds and
waves, a tiny fraction (about 0.1 per cent) is exploited by plants and algae to fuel
photosynthesis, in which atmospheric carbon dioxide and water are converted into glucose
(a simple form of sugar) and oxygen. Once produced, this glucose may take one of three
different paths: either it is consumed immediately within the plant's cells to provide energy
for metabolism; it is converted into sucrose or starch and stored as an energy reserve within
roots, fruits, or tubers; or it is converted into the cellulose and lignin that form the plant's
skeleton.
When plants and animals die, their biomass is decomposed by bacteria, the complex
organic molecules broken down into inorganic carbon dioxide and water, which re-enter
the photosynthetic cycle. 'Biomass' is the term given to all organic matter produced by
the food chain, but a part may be stored for a time in the form of peat or fossil fuels.
Fossil fuels have an organic origin but are not considered biomass because they have
left the photosynthetic cycle. This is an important distinction in energy terms. Biomass
fuels, as long as they are produced sustainably, avoiding forest destruction and lengthy
