ENERGY  ALTERNATIVES: RENEWABLE
ENERGY AND ENERGY CONSERVATION
TECHNOLOGIES



Mean Wind Speed and Energy Resource
  The annual wind  speed at a location  is useful as an initial 
  indicator of the value of the wind resource.The relationships 
  between  annual mean wind speed  and  potential  value of the 
  wind energy resource are listed below.

Anual mean wind speed @ 10 m Height
< 4.5 m/s
4.5 - 5.4 m/s
5.4 - 6.7 m/s
> 6.7 m/s

Indicated value of wind resource
Poor
Marginal
Good to Very Good
Exceptional
  In  locations  where  data  are not  available, a qualitative 
  indication of a high annual mean  wind speed can be  inferred 
  from  geographical  location,  topographical  features,  wind-
  induced  soil erosion, and deformation of vegetation. However, 
  accurate determination of the mean annual wind speed requires 
  anemometer data for at least  12 months. Earlier studies have 
  revealed that  the mean  wind  speed for a given  year varies 
  from  year to year  but  within ±10% of the long-term mean. A 
  ±10%  variation in mean wind  speed would show a variation in 
  energy content of ±30% or more. 

  Part of the kinetic energy of wind can be captured by a rotor 
  and converted into mechanical or potential energy.  The major 
  drawback of a wind  power system stems from the nature of the 
  source - wind has a  low  power  density, and wind  speed and 
  direction are highly variable.  Therefore, wind power systems 
  are  best  for applications  which can tolerate varying power 
  input, such as, pumping of water  from wells, the traditional 
  windmill  application in many  parts of the world.  The power 
  that can be  achieved by a wind system is proportional to the 
  cube of the  wind  speed  and  the  square  of  the  windmill 
  diameter. That is,
                    P = nCd2v3
    where,     P = theoretical wind power (kW)
                    d = windmill diameter (m)
                    v = wind speed (m/sec)
                    C = constant (5.104 kg/m3)
                    n = windmill efficiency (20-40 per cent)
There are three principle dimensions to wind energy technology, namely: (a) Type of machine - horizontal axis , from sail and multibladed to fast - running rotor types, and vertical axis from Savonius to fast - running Darrieus and variations, (b) Applications - water pumping , desalination , heating, cooling,autonomous power generation and power generation with grid connection, and (c) Size of machine - small (less than 10 kW), medium (10-100 kW), medium-large(100-1000 kW) and large (more than 1 MW).
  (i)   Wind Energy Driven Waterpumping Systems (Windpumps)
  (ii)   Wind Energy Driven Electricity Generation (Wind Generators)