Environmental Engineering Reference
In-Depth Information
with only 13 watts of power per square meter, yet is far more useful, as we can convert it
relatively easily into electricity.
For energy to be useful, it must have at least one of three basic characteristics: it
must be sufficiently but not excessively concentrated; it must be storable; and it must be
transportable. Not all forms of energy (thermal, chemical, electrical, etc.) have the same
level of usability, and only chemical fuels meet all three requirements. Electricity meets
the first and the third conditions. Although it may be stored in sufficient quantity to power
small appliances, such as phones, laptops and flashlights, electricity storage at an industrial
scale is still a long way off. That is why hospitals rely on diesel generators rather than
batteries in case of blackouts. Thermal energy may satisfy the first condition but can be
stored and transported only at low intensity (e.g., in a thermos flask).
The Three Characteristics of Useful Energy
Concentrated:
The tide is able to raise and lower every vessel in a port, but is of little help
in raising even a small boat within a few minutes or maintaining that position for days. It
is often possible to alter the concentration of an energy supply, but it is far more difficult to
concentrate dispersed energy than to disperse concentrated energy.
Storable:
A conventional diesel-engine car can run for about 700 kilometres on a single
tank of fuel. This is the great advantage of fuel-based energy sources. Even the most efficient
electriccarscanonlymanageaboutathirdofthatdistanceonasinglecharge,andtheyrequire
several hours to recharge.
Transportable:
Natural gas or electricity can be channelled through pipes and cables for
thousands of kilometres, while losing very little of their energy. Heat, by contrast, is rapidly
dispersed and requires thick insulation for transport even over short distances.
1.5 The Biology of Energy
When we humans compare ourselves to other species, it is usually to emphasise our more
attractive qualities. Thus, a burly man may be compared to a lion or an oak, a beautiful
woman to a swan or a rose. Few humans would feel flattered at being compared to a
mushroom. Yet, in one very crucial respect, we have more in common with fungi than
with an oak or a rose. We humans - like all other animals, all forms of fungi, and some
types of bacteria - are heterotrophs. This means that we need to consume other organisms
