Exergy Analysis of Single Array Wind Farm Using Wake Effects

Abstract

The influence of wake parameters on the exergy analysis of single array wind farm is studied in this paper. Key parameters which influence wake effects in a wind farm are wind velocity, tip speed ratio, number of blades, rotor speed, rotor diameter and hub height. Three different models namely power, wake and exergy model were used in estimating the exergy efficiency of the single array wind farm. Even though it is ideal for wind farms to fix the wind turbines in rows and columns the conditions of the site may not always be conducive for it. Hence analysis has been done keeping the wind turbines at random in a row and the effect of positioning on the performance is analyzed. Energy and exergy efficiency calculations were made for different cases by varying the positions of wind turbines in the single array wind farm. Standard relations were used in estimating the energy deficit in the wind farm due to wake effects. The wake effects were found to have an aggregated influence on the energy production of the wind farm, which results from the changes in the key parameters mentioned above. Potential areas for reducing energy losses by proper location and selection of turbines based on rating are highlighted. The influence of individual parameters contributing to the wake effect were analyzed and discussed in detail.

Applied Second Law of Thermodynamics on the Wind Energy Over Iraq

“…The wind velocity increasing by 33% when the turbine height become 50 m for all regions, while its increasing by 45% when the turbine height become 100 m for all regions. 14) and (15), as the different between inlet and outlet wind chill temperature was increase due to increase in exergy flow and causing to decreases in exergy efficiency according to equation (2). It is can be seen that the smaller value was 27.07, 26.51, and 26.24 (°C) in Basra at (12,50, and 100) m height respectively while the highest value was 28.33, 27.91, and 27.68 (°C) in Mosul at (12,50, and 100) m height respectively, this result represent the equation ( 14) where at wind velocity increase led to decrease in wind chill temperature, also can be notes that wind chill temperature value of Basra and Anbar was close together.…”

“…The useful output work of the wind turbine depends on. The model that used for useful work output of the wind turbine ( ) is given by Abdel Hamid (2009) [15] this model is depended on cut-in speed (u c ), rated wind speeds (u r ), furling speed (u f ) and on specific site, such as the Weibull distribution parameters k-Shape parameter and c (m/sec) scale parameter:…”

“…Where is the mechanical energy is the power coefficient of a wind turbine are the mechanical and alternator efficiency, that's equal to 0.98 and 0.97 respectively [4] The mechanical energy can be calculated from [8] (5) Where A is the swept area of the turbine is the density of air V 1 is the upwind velocity of turbine V 2 is the final velocity of turbine The density of air depended on temperature and pressure of air and was calculated using the ideal gas law Equation [15] (6) Where P is the pressure of air T is the temperature of air The final wind velocity (V 2 ) is equal to one third of the upwind velocity (V 1 ) [16] (7)…”

“…The power coefficient of a wind turbine ( ), was determined as a function of the tip speed ratio (λ), number of blades (Nb) [15] ( )…”

“…The wind turbines that have two blades must operate at a higher tip speed ratio than three bladed turbines to maintain the same power coefficient. While the tip speed ratio can be expressed in terms of tip speed and free stream wind velocity [15] (9) Where is the angular velocity (rad/s) is the radius e of the turbine is the stream wind velocity The Energy of the wind stream ( ) describes the total kinetic power of a wind stream and can be found [1] (10) Where is the density of air, can be estimated from equation ( 6) A is the swept area of the turbine is the wind velocity The exergy of flow Ex f , is the maximum achievable work gained as the air flows through the turbine. This term includes physical exergy (Ex Ph ) and kinetic exergy (Ex Ke ) [8] (11) Physical exergy incorporates the enthalpy and entropy changes related to the turbine operation as [8] ̇ * ( ( )…”