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, 
  agrowastes, etc.).

  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 
  inanimate characteristics. 
  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.