Environmental Engineering Reference
In-Depth Information
windy regions, or from areas suited for massscale biomass production, to major
urban and industrial areas.
Table 5.2 Typical power density of energy sources
Presently new renewables (modern biomass energy, geothermal heat and electri-
city, small hydropower, low-temperature solar heat, and wind electricity) contrib-
ute approximately 2% to the world's total primary energy supply.
However, electricity production from solar photovoltaic systems as well as grid-
connected wind turbines has been growing at an impressive rate. Between 1998
and 2008 wind electricity grew at an average rate of approximately 30%, while
grid connected photovoltaic energy grew by almost 40%, bioethanol by 13%, and
geothermal heat production by 20%. Even so, it will likely be decades before new
renewables add up to a major fraction of total global energy use because they cur-
rently represent only a small percentage of total energy use. Nevertheless, a few
countries have adopted ambitious targets; Germany, for example, has a target of
50% renewables by 2050. Impressive growth rates have been achieved in recent
years for geothermal (in Iceland) and solar thermal heat production (in China).
Substantial cost reductions in the past few decades have made a number of re-
newable energy technologies competitive with fossil fuel technologies in certain
applications. Modern, distributed forms of biomass, in particular, have the potential
to provide rural areas with clean forms of energy based on the use of biomass re-
sources that have traditionally been used in inefficient, polluting ways. Biomass
can be economically produced with minimal or even positive environmental im-
