HYDRO ENERGY

  Hydraulic potential is the  combination of the possible flows 
  and distribution of gradients, and hydraulic resource is that 
  fraction of  hydraulic  potential  that  is  still accessible 
  after  economic  considerations. Hydropower owes its position 
  as  a  renewable  resource  to  the varying, but more or less 
  continuous  flow of a  certain  amount of water in the stream. 
  This  water, supplied by rain and  always  moving, constantly 
  flows from the  mainland to the sea, where it evaporates into 
  the  atmosphere  in  an  unending  cycle  controlled  by  two 
  opposing  forces, heat of  the sun  and  the  earth's gravity. 
  Hydropower is a precipitation  dependent resource, subject to 
  the  uncertainties which  it entails. Water  run off can vary 
  within wide limits. 

  The  harnessing  of  energy  of the  falling water to provide 
  mechanical  power has been one of man's greatest achievements. 
  Water  wheels  providing  mechanical  power  for grinding and 
  water  pumping  are  still  in  common  use.  The  industrial 
  revolution  created  new  requirements, which demanded larger 
  power  generating  capacities, which led to rapid improvement 
  in the  design  of water wheels, turbines and generators. The 
  capacities  of  hydropower  plants   became  very   large  as 
  electricity generation became common place by the end of 19th 
  century. The  position  has  ultimately reached a stage where 
  large-scale  hydroelectric plants contribute significantly to 
  the  State's and  the  National  energy demand. Unfortunately, 
  every  development has its  cost  and  the cost of exploiting 
  hydropower is vigilance  in  ensuring  the environment is not 
  irreparably  damaged  and  the life of the river continues to 
  flourish. This demands  considerable  care  and  attention in 
  planning. 

  A micro, mini or  small  hydropower  station  can divert only 
  potential  energy of the water which would have dissipated to 
  no  benefit in the natural  flow  along the water course. The 
  domain  where  these can have potential impact on development 
  is  domestic lighting and stationary motive power demand  for 
  such diverse productive uses as water pumping, wood and metal 
  work, grain mills, agro processing industries, etc. 
  
  Mini, micro  and small hydro plants combine the advantages of 
  large  hydro  plants  on  one  hand  and  decentralised power 
  supply on the other. The  disadvantages associated with large 
  hydropower plants,like high transmission costs, environmental 
  issues  like  submergence  of  forests  and  crop  lands, and 
  displacement  of  families, are  not  present in small plants. 
  Moreover, the  harnessing of local resources like small hydro 
  resources, being of a decentralised  nature, lends  itself to 
  decentralised utilisation,local implementation and management, 
  making rural  development possible based on self-reliance and 
  use of local natural resources.

  Potential energy of water at a certain height can be converted 
  into  mechanical energy by using a turbine.  The falling water 
  hits  or  exerts a pressure on the blades of the turbine.  The 
  power  available  is  proportional to the head and the rate of 
  discharge of the water. That is,
  
            P = h C H Q
  where     P = power available (kW)
            h = hydropower system efficiency (70 per cent)
            C = constant (=9.81 x 103 kg/m2s2)
            H = head of the water (m)
            Q = flow of the water (m3/s)
  The  flow  through the turbine is not independent of the water 
  head.  For  a  given  turbine  size, the flow will actually be 
  faster  if  the  head  is larger.  As a result, high heads are 
  favored  for  hydropower generation.  In practice, water heads 
  are  used  from less than one meter to several  hundred meters.  
  With low  heads, obviously, a large flow  must be available to 
  get a substantial amount of power.

  The capacity of hydropower plants can vary between a few kW to 
  about 1,000 MW.  The  appropriate  scale of a hydropower  unit 
  depends on local geographic and climatological conditions, and 
  the  characteristics  of  the demand for power.  The scale and 
  local  conditions also, to a large  extent, determine the type 
  of construction  and  machinery  required, and accordingly the 
  investments. Hydropower  generation  is  highly  site-specific.  
  This  implies  that  proper  attention  must be  given to site 
  selection and local  surveys.  For big hydro schemes, it would 
  require  elaborate feasibility studies that have to be done by 
  specialised  consultants.  For small hydro units simple survey 
  methods can be adequate.
  Another  classification  of hydro plants is based on different 
  systems of water usage. That is,
  i.    River  power  plants, where the head is created by weirs 
        or dams,
  ii.   Diversion  schemes  that   basically  utilize  naturally 
        available heads,
  iii.  Run - of - river  plants  with  little or no  control of 
        discharge, and
  iv.   Storage  power  plants with high dam and large reservoir 
        for flow regulation.

  The construction of a hydropower  unit essentially consists of 
  a water intake, a penstock that leads the water to the turbine, 
  a control  system, the turbine  itself, and except micro units, 
  a generator  to  convert the mechanical energy into electrical 
  energy. The hydropower  system also  includes civil works like 
  dams, weirs, canals, etc.
  Various  types of turbines  are available.  They can be of the 
  reaction  type,  like  the  Francis  turbine  and  the  Kaplan 
  turbines, where  the  turbine  is  completely submersed in the 
  water, or of the impulse  type, like the Pelton turbine, where 
  a jet of water hits the turbine blades.  The traditional water 
  wheel  can also be considered as an impulse  type system.  The 
  cross flow  turbine that is used for mini and micro units have 
  the  characteristics of both the types.  Special types are the 
  Segner  turbines  that  can  be  used  in micro units, and the 
  hydraulic  ram.  The latter  does not produce mechanical power, 
  but can be used to pump  relatively small  quantities of water 
  to relatively higher heights.

  Turbines for big hydro units are tailor made,i.e.,specifically 
  adapted  to the prevailing head, flow and local conditions. To 
  a  lesser  extent, the  same is true  for  smaller hydro units. 
  Such adaptations determine the efficiency that can be achieved.  
  Hydro technology is mature  technology and local manufacturing 
  is possible in many countries.  Turbines have a long life time 
  (30 years or more) with little maintenance  required and their 
  operation is relatively simple.