Romanian

Wind Energy

History

Wind power was used by people over 3000 years ago; windmills were used for pumping water or grinding. Even today, in the century of information, wind power is exploited to obtain electricity.

Demand and consumption of increasingly high electricity had led to the need of developing new methods of obtaining energy. Scientists had found the solution in the old windmills that have a great advantage, that it doesn’t pollute, and the fuel (wind) is free.

Attempts to obtain power from wind dates back over a hundred years ago. A true blossoming of this technology was achieved in the last 30 years after the 1973 oil crisis when the price of oil barrel increa

causing many countries to invest in renewable energy research, one of

these energies being wind.

Technology

Wind energy is directly linked to sun activity on Earth. This creates differences in atmospheric pressure and temperature thus determines the movement of air currents that is captured with wind turbines. Wind turbines convert the kinetic From the old windmills, which grind grain or pump water, the design of wind turbines has reached a huge capacity to produce electricity energy of air flow in mechanical energy, and then, using a generator, into electricity. The energy of an air flux that moves at a linear velocity V is determined by the kinetic energy expression:

Where: m- air mass [kg]

v- wind speed [m/s]

The power of aero generator

is determined by the relation:

Cp - power factor

ρ - air density [kg/m³]

v - wind speed [m/s]

A- blades’ swept out area [m²]

For greater efficiency of wind turbine it is very important the intensity with which the wind blows. According to the Beaufort scales, drawn intensity is divided into 13 different categories.

This scale goes from 0 when the wind intensity is between 0 and 0,2 m/s and reaches an intensity of 12 when the wind speed is 32,7 m/s (117,72 km/h).

Capturing energy efficiency and air flow into electrical energy conversion depends on wind speed, number of turbine blades, aero generator construction and especially the orientation of the turbine.

Wind speed is important as Betz's research shows us that an ideal wind turbine can extract only 59.3% of airflow, hence resulting in major wind turbine construction.

To obtain maximum efficiency of energy conversion, the rotation speed of the rotor must be correlated with wind speed. This correlation is obtained by an optimum number of blades. Researchers had found that the optimum number of blades is 3.

To characterize the different aerodynamic characteristics of wind turbines we use the dimensionless parameter called the turbine speed (λ). The speed of turbines ties into one formula three important variables:

ω, rotation speed [rad/s]

R, rotor radius [m]

v, wind speed [m/s]

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