Introduction
Energy from wind is one of the oldest energy harvesting technologies that is being used for centuries. Winds are caused by the rotation of the earth and the heating of its atmosphere by the sun. The total annual kinetic energy of air movement in the atmosphere is estimated to be about 3 x 105 kWh or about 0.2% of the solar energy reaching the earth. The maximum technically usable potential is estimated to be theoretically 30 trillion kWh per year, or about 35% of the world’s current total energy consumption [1]. The power in wind blowing at 25.6 km/h (7.1 m/s) is about 200 W/m2 of the area swept by the windmill. Approximately 35% of this power can be captured by a typical windmill and converted to electricity. The kinetic energy of air can be transformed to mechanical and then to electrical form of energy using fans, gears, turbines and a generator system. In the current scenario, windmills are electricity harvesting technologies which account for more than 280 GW installed capacity worldwide [2]. Electricity generation from wind is directly proportional to the air density, swept area of blades and cube of the wind velocity. Since, wind velocity is tentative, by optimizing the blade area, maximum energy can be extracted for any particular wind speed at a given place [3].
P = (1/2)* ρ*A*V3 ........ (1)
where, P – Wind power; ρ – Air mass density; A – Swept area (area of wind flow); V – Wind velocity
The annual wind speed at a location is an initial indicator of the value of wind resource. The relationships between the annual mean wind speed and the potential value of wind energy resource are listed below [4].
Table 1. Potential of wind energy corresponding to annual wind speed
| Annual Mean wind speed @ 10m Ht. (m/s) | Indicated value of wind resource |
| < 4.5 | Poor |
| 4.5 - 5.4 | Marginal |
| 5.44 - 5.7 | Good to Very Good |
| > 5.7 | Exceptional |
Uttara Kannada district, located in the west coast and in Western Ghats region of Karnataka state, is blessed with good wind potential. Harnessing of wind energy could play a prominent role in meeting the energy demand in the region since electricity supply is unreliable at most times. Wind energy potential in the district can cater to the regional electricity demand through wind energy conversion system (WECS), avoiding plenteous greenhouse gas (GHG) emission through burning of fossil fuels. It can be harnessed locally in a decentralized manner in rural and remote areas for applications such as water pumping for crops and plantations. Wind driven electricity generation can be utilized as an independent power source and for purposes of augmenting electricity supply from grids. In densely populated coastal taluks like Karwar, Kumta and Bhatkal in Uttara Kannada District, decentralized production of electricity would help local industries, especially seasonal agro processing industries of cashew, areca nut etc. WECS can be hybridized with solar, biomass or any other available local energy resource to provide reliable power for both domestic and industrial loads as wind flow is more during monsoon which would compensate for lower solar insolation and reduced dry biomass availability [5].
1. Wind resource assessment
Wind resource assessment aids in understanding the local wind dynamics of a region. In order to make an accurate assessment of wind resource of an area, wind data measurements of at least 10 years is essential; however wind data of a smaller duration would still provide an overview of the potential [6]. GIS (Geographic information system) based spatial assessment of wind resources helps in estimating the potential in the vicinity of wind monitoring stations. Knowledge of variations (spatial and temporal) in wind speed will help in economically viable installation of wind energy conversion system bearing disturbance free operation. It will also provide fundamental information about seasonal changes in wind speed which contributes to wind power potential [7]. Knowledge of constant annual average wind speed facilitates improvement of wind power harvesting plants and assures pre-decided annual generation. Wind flow developed due to the differential heating of earth is modified by its rotation and further influenced by local topography. This results in annual (year to year), seasonal, synoptic (passing weather), diurnal (day and night) and turbulent (second to second) changes in wind pattern [8]. Increased heat energy generated due to industries and escalating population in urban areas result in heat islands which affects the wind flow as well.