REVIEW OF RENEWABLE SOURCES OF ENERGY

  The  main  types  of  useful energy are heat  and  mechanical 
  energy. Heat though predominant in household  activities like 
  cooking  and  water  heating, is also  needed  for productive 
  activities like drying and industrial applications.Mechanical 
  power is predominant in the productive sectors, e.g.,industry, 
  agriculture and transport.

  Efficient  use of energy is achieved  when unnecessary energy 
  conversions  are  avoided, as  each  conversion  has  limited 
  efficiency  and, therefore, implies a certain  loss of energy 
  as  wasted  heat.  For  instance,  if  secondary  energy  can 
  immediately  serve  as final energy, or even as useful energy, 
  substantial  losses  can   be  avoided .  Examples  are  wind 
  machines  in  irrigation  or  hydro turbines powering a shaft.  
  This  principle favors decentralised energy generation and is 
  particularly  relevant with new and renewable  energy sources.  
  Very  high  efficiencies  can be achieved  with  cogeneration, 
  where heat as a by-product of power is not wasted, but put to 
  good  use  on the  spot.  This  can be  applicable to biomass 
  gasification. The counterbalance originates from economics of 
  scale which generally favor large-scale energy conversion.

  The  foregoing  sections  make  clear  that  renewable energy 
  technologies cannot be limited to the technologies per se. It 
  is therefore important as to what form of energy is  provided, 
  and  how  the  technology  can  serve  a  particular  end use 
  activity. Sometimes, a combination of technologies would give 
  an  optimum  energy  mix, to secure a continuous and reliable 
  energy supply. In the following section,some renewable energy 
  technologies, such  as,   wind  energy, hydro  energy,  solar 
  energy,  geothermal  energy  and  draught  animal  power  are 
  reviewed.