Environmental Engineering Reference
In-Depth Information
2
Where Does Energy Come From?
2.1 Energy Commodities
Every form of energy that we currently use comes from the sun. The sun emits the light and
heat that powers solar panels and water heaters, causes the air movements that drive wind
turbines,replenishestheriversthatfeedhydroelectricreservoirsandstimulatesbiofuelcrops
to grow, as it did the plants and algae whose fossilised remains form the coal, oil and gas in
the Earth's crust. The sole exception to this rule is uranium, which did not so much come
from
as
with
the sun, having been present in the primordial nebula that gave rise to our solar
system.
When we talk about energy sources, we are not describing their scientific origin as much
as the form the different energy carriers take. That is why coal, wind and light are regarded
as different energy sources. But because energy is big business, we also talk about energy
commodities can be divided into three main categories: heat, electricity and fuels.
While it is possible to obtain heat directly from the Earth and the sun, most of the
heat we use in homes, offices and factories was obtained indirectly, usually by burning
fuel. Sometimes, at a domestic scale, heat is generated using electricity; for example, in
electric boilers or heat pumps. This method is, of course, highly inefficient as it represents a
threefold energy conversion; fuel to heat, heat to electricity and electricity back to heat.
Electricity is the most versatile of all energy carriers. It is used to power a vast array
of machines, from factory robots to domestic appliances. Its only limitation is storability,
which is why we still don't have electric trucks or airplanes. It powers most of the
conveniences of modern life, from electric lighting and food processing to televisions and
computers. Electricity that is obtained directly from natural sources - such as hydro, wind,
solar, tidal and wave power - is referred to as primary electricity, while electricity produced
in nuclear or fossil-fuelled power plants by heating water to drive steam turbines is known
as secondary electricity.
In many languages the word for fuel is closely related to combustion. After all, the ability
to extract energy from fuels without burning them - through nuclear fission or fuel cells
- is a recent discovery. Fuels that are sourced directly from nature, including wood, oil,
coal, natural gas and uranium, are referred to as primary fuels. They may be used as they
