ENERGY ALTERNATIVES: RENEWABLE
ENERGY AND ENERGY CONSERVATION
Classification of Energy Sources
All the sources of energy, currently available for harnessing,
can be linked to two fundamental forces in nature-
gravitational and nuclear. Nuclear fusion is the source of
solar energy - the driving force for much of the energy
consumed on earth today.
Renewability or non-renewability of a solar driven process is
distinguished based on the energy storage or cycling time
involved. Renewable resources have a cycling time less than
100 years, while for non-renewable resources, it is greater
than a million years. The depletable resources are fossil
fuels, which are non - renewable since the rate of their
utilisation far exceeds the rate at which they are formed.
Examples of renewable resources are hydro energy, solar
energy, wind, biomass, and energy from wastes (such as biogas,
The renewable solar energy is subdivided into direct and
indirect types.Sunlight used directly can produce electricity,
heat or derive a chemical reaction. It is used indirectly
when it drives other processes, biological - chemical or
climatic - mechanical, which in turn are used as sources of
The energy sources can be classified in a number of ways
based on the nature of their transaction, as commercial and
noncommercial sources of energy . All energy resources,
particularly the commercial ones, are natural. Coal, oil and
nuclear sources constitute commercial sources, while firewood,
biomass and animal dung constitute non- commercial sources.
Also, the energy sources are classified based on animate and
Energy sources could also be classified as exhaustible/
depletable or non - depletable / renewable resources. The
distinguishing feature of an exhaustible resource is that, it
gets exhausted when used as an input of a production process,
and at the same time, its undisturbed role of growth is nil.
That is, the temporal services provided by a given stock of
an exhaustible resource are finite.
Further, based on conventionality in deriving energy, energy
sources could be classified as conventional (coal, oil, hydro,
nuclear, etc.) and non - conventional (solar, wind, tidal,
geothermal, biogas, etc.) sources.
They are also classified as primary or secondary types - coal,
firewood, etc., being primary sources and electricity, a
secondary source. Energy in its primary form can be of
different kinds. The main types are Chemical (fossil fuels-
coal, oil, natural gas, peat; biomass - wood, agricultural
residues, etc.),Potential (water at a certain height),Kinetic
(wind, waves), Radiation (sun), Heat (geothermal reservoirs,
ocean thermal reservoirs) and Nuclear (uranium). The primary
form of energy must generally be converted into secondary or
final forms of energy before it can be used. For instance,
the potential energy of a waterfall (primary energy) is
converted into electricity ( secondary energy), which is
transmitted and transformed to supply (final) energy to a
factory, where it is converted into mechanical energy (useful
energy) for productive operations.
Important types of secondary energy are electricity and
mechanical energy. But chemical energy is also important as
a secondary energy, for instance, in the form of refined oil
products. Final energy is the energy that reaches the
consumer. This can be electricity at a suitable voltage, or
chemical energy in kerosene or batteries. The consumer,
finally, uses certain equipment to convert the final energy
he buys, into useful energy for one of his end use activities,
e.g., irrigation, transport, cooking, etc.
Most of the energy sources are substitutable to each other
due to the fact that some form of energy can be converted to
other - such as coal to electricity, use of photo electricity
to drive a chemical reaction, wind energy to pump and store
water that could be used to produce electricity when required,
or solid biomass to produce liquid or gaseous fuels of higher
calorific value. All forms are ultimately converted into heat.
This gives rise to the inter-fuel substitution process with
which an economy can substitute its abundantly available
resources to the scarcely endowed one.