Environmental Engineering Reference
In-Depth Information
Figure 2.17
Energy transfers involving water.
RENEWABLE ENERGY FROM THE ENVIRONMENT
applications
Energy is vital to sustain civilization. Energy in some form is required whether it is in the
home, at work or getting from one place to another using transport rather than on foot.
Demand for energy is still increasing, with coal, oil and gas being the main sources
contributing about 80 per cent of the global total primary energy supply (1996). Such
sources are classed as non-renewable, as on the human time scale they are not replaced.
As indicated in this chapter Earth receives energy from the sun. We also have flows of
energy as wind in the atmosphere, water flowing downhill on the lithosphere and tides in
the oceans. Attempts have been made to extract energy from these sources. Whilst being
technically possible, their use is not always cost-effective and subsidies have been required
to sustain them.
The most widespread method of energy production from renewable resources is
hydropower. In its earliest days the power was usually generated by flowing water causing
a wheel to turn but the amounts of energy produced were small. More effectively, energy
can be extracted where water is at different levels, as in a dam, or between high-level lakes
and a lower-level river. Often this is linked with pumped storage where water is used to
generate electricity during high peak demand and is then pumped back to the higher level
at times of lower demand, using energy generated by fossil fuel systems where it is more
difficult to stop and start generation.
