Environmental Engineering Reference
In-Depth Information
3
The world's energy system is very large: in 2008 it amounted to 492 exajoules, cor-
responding to 11.75 billion tons of oil equivalent (toe). With a population of almost
6.7 billion people, this corresponds approximately to 1.75 toe per capita per year
(
Figure 3.1
).
The primary energy sources are:
- Solar, responsible for hydropower, wind, photovoltaic, and solar thermal energy as well
as the production of biomass and, ultimately, the fossil fuels (coal, oil, and gas);
- Geothermal energy, originating in the molten core of the Earth;
- Tidal energy, originating in the gravitational attraction from the Moon; and
- Nuclear energy, originating in the nuclei of atoms.
Renewable energy sources are the ones produced from geophysical or biological
sources that are naturally replenished at the rate of extraction. Biomass, hydro-
power, wind energy, photovoltaic solar energy, high-temperature solar thermal en-
ergy, low-temperature solar energy, geothermal, and ocean energy in the form of
waves and tides are all renewable. Nuclear power is not strictly renewable because
uranium reserves (from which nuclear power is produced) are finite, although they
can last for a long time at the present rate of consumption.
