How to select right wind turbine ?

Electrical System
Sample Wind farm

Wind turbines are commonly used for renewable power generation. With the improvement in wind technology the Plant load factor for wind turbines have improved drastically. Now it is common to get turbines with more than 43 % of plant load factor which makes it more economical. Life of wind turbine is considered as 25 years and it is important to select right turbine for your project, for understanding how wind turbine works click here

Lets understand how to select right wind turbine :

  1. Wind Velocity : Wind velocity is important factor to consider while considering turbines, Wind velocity help us to estimate hourly power generation throughout the year. There are no of companies who monitor wind condition and help in estimating right wind velocity for future. After project location identification it is important to take help of any of the good wind resource company and get your wind data assessed. As we know simulation is done with past data and future data is estimated statistically, therefore wind resource company will give estimate with certain probability. It is important to consider right probably to estimate payback 99% probability shall be too conservative and 50% shall be moderate. Normally people use 75% or 90% probable data for driving project payback. These probability are generally mentioned as P50, P75, P90, P99 nos. Considering periodic change in wind pattern P75 may be considered as optimistic probability of power generation.
  2. Wind flow pattern : Wind flow varies from time to time, generally wind turbines are designed to operate between certain min- max limit say 3m/s to 12m/s. It is important to have wind flow above 3 m/s to start power generation from turbine. Beyond 12 m/s power generation shall be consistent at full load condition till the max wind velocity tripping point say 20 m/s . Therefore at the time of finalization of wind turbine it is important to get wind flow pattern and get power generated at the operating range condition only. This help us to select right wind turbine.
  1. Impact of other towers : As wind turbines are installed in dedicated wind farms, it is important to simulate impact of each turbine on another turbine to find wake effect. Wake effect is nothing but the aggregated influence on the wind farm, which results from the changes in wind speed caused by impact of the turbines on each other, Due to presence of no of turbine wind flow pattern may get disturbed and estimated result may not be achieved, Therefore not only wind farm but nearby wind farm needs to be considered while estimating power generation.
  1. Reference tower: for estimating right wind velocity it is important to collect data from nearby area, Generally mast is installed and wind reading is recorded, It is essential to have Mast tower installed near by project site. Data with less than 10 KM area are considered to be more reliable.
  2. Size of Wind Turbine : Size of wind turbine matters considering power output and converting wind energy to electrical energy, Higher rotor dia can harvest higher energy. With the use of higher size say above 120 meter, higher plant loading factor can be achieved. In general turbine with capacity more than 2 MW are energy efficient and economically viable.
  3. Height of hub from ground level : Air velocity increases with the increase in height, Therefore it is recommended to increase the height of tower for getting higher air velocity and higher output generation. Also it is to be noted that as height of tower increases the construction cost of turbine also increases. The economy of project is important and therefore most of the projects are installed at height of 120 to 150 mtrs.
  1. Turbine Losses : just like any other machines turbines are also having various losses which impacts the power generation. below are the major losses must be considered while estimating power
    • Availability : Machine availability is important for power generation and in case of wind turbine availability can be categorized as Turbine availability, Grid availability, Balance of plant availability. Turbine availability is the time available for turbine to generate power excluding maintenance, shutdown or breakdown time. Grid availability indicates grid availability of take power. similarly balance of plant is important to feeding power generated to grid.
    • Curtailment : Lower and higher wind can make turbine shut and therefore it is important to estimate curtailment losses accurately over past data. High temperature may be one of the reason for curtailment therefore it is important to consider ambient temperature before turbine selection.
    • Wakes: Wake effect is nothing but the aggregated influence on the wind farm, which results from the changes in wind speed caused by impact of the turbines on each other, Wakes can be internal ( because of operation of other turbines in same farm) or external (due to other wind farms located in nearby region. Wakes are also estimate based on future projects for long term power estimation. These wakes are termed as future wakes.
    • Electrical efficiency : As power is generated and transmitted to grid, there are electrical losses due to transformer and transmission lines from turbine to metering points.
    • Turbine efficiency : Turbine efficiency depend on the material of construction, blade profile, turbulence and its capability to convert max wind energy to electrical energy. It is warranted by manufacturer.
    • Environmental condition : Environmental condition may cause blade soiling or degradation, Extreme weather condition like thunderstorms, Icing may damage blades.
  2. Uncertainties : As the power estimates are based on past data there are no of uncertainties for power generation estimates like Measurement uncertainties ; vertical extrapolation of wind data, generally wind data is not available till the hub height and it is extrapolated from available data; long term correction uncertainties ; Climate variation uncertainties; Power modeling uncertainties etc, considering all uncertainties help to select right wind turbine with long term benefit.

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