## 2 Overview of the Basic Concepts of Wind Farm Design and Optimization
### Wind Farm Planning--Guidelines and Standards  
In general, it is recommended to specify and design wind farm projects in accordance with the state-of-the-art standards of the International Electrotechnical Commission (IEC) [29] and the technical guidelines proposed by international wind energy associations. Some examples include, but are not limited to:  
* The European Wind Energy Association (EWEA): European Best Practice Guidelines for Wind Energy Development [30]. * The American Wind Energy Association (AWEA): Wind Energy Siting Handbook [31], the AWEA fact sheets and the standards for wind energy industry [32]. * The British Wind Energy Association (BWEA or RenewableUK): Best Practice Guidelines for Wind Energy Development [33]. * Global Wind Energy Council (GWEC): Global Wind Reports (2006-2012) [34]. * Sustainable Energy Authority of Ireland (SEAI): How to develop a Wind Farm [35]. * Wind Energy Handbook, Chapter 9: Wind-turbine Installations and Wind Farms [36]. Four general stages for wind farm planning and development are briefly summarized next:(1) _Wind Farm Site Selection_. The siting process [37; 38; 39; 40; 41] refers to the investigation of an area/region/district with the purpose of selecting the best location (site) for a wind farm. Wind farms are very versatile and can be integrated successfully into many types of landscapes, from agricultural fields to mountain ridges, among others. The selection of the wind farm location is commonly based on a hierarchy scheme including three general factors: (1) the available infrastructure (_i.e._, accounting for the current capacity of the electrical, civil engineering and communication infrastructure and its expansion plans); (2) the environmental suitability (e.g., accounting for restricted areas such as natural protected areas or bird conservation areas); and (3) the wind resource. The wind resource quantification [42; 43; 44; 45] is based on long-term records (each record being a 10-min averaged measurement obtained from sampling with a frequency of 1 Hz or higher) of atmospheric variables exhibiting temporal and spatial variations: wind speeds [m/s] at different heights, wind directions [\({}^{\circ}\)] at different heights, solar radiation [W/m\({}^{2}\)], temperatures [\({}^{\circ}\)C] at different heights, pressure [Pa], relative humidity [%], rain fall [mm], and sometimes even air quality. Since atmospheric variables are considered to be random on nature, further analyses are performed to study its statistical characteristics (e.g., determine its probability density functions), which allow the wind farm designer to quantify expected values at the potential wind farm site. Additional information that helps the designer to dimension the loads and stresses the potential WT will undergo while operating at the site can be obtained from statistical-dynamical analyses, which include the following measured variables: local ambient turbulence intensity [%], power and turbulence spectra and coherences, mean and maximum gusts [m/s], rain/ice/snow/hail [%], chemical effects (related to corrosion by salts and/or soiling), and atmospheric stability cycles [36]. In engineering practice, wind farm designers usually calculate the local 3D wind field of the site by means of commercial packages [46; 47; 48; 49; 50; 51; 52] that implement and numerically solve the governing equations of fluid mechanics. Different levels of sophistication exist for such calculations, with the approach that considers the Reynolds Averaged Navier-Stokes (RANS) equations, complemented with turbulence models, being widely used. It has been shown that the RANS-based models' predictions provide reasonable agreement with the experimental data measured at sites with complex topography [53]. The micro-scale flow modeling is usually based on high-resolution maps representing the topography, obstacles and roughness of the region.