## 2 Overview of the Basic Concepts of Wind Farm Design and Optimization
### Visual Impact  
Compared to other electricity-producing technologies, wind farms produce relatively small visual impacts. Visual impacts are site-specific and can be determined from the size and relative proximity between the observer and the WTs, the spread or extend of WTs, the WTs view orientation, local topography, the position of nearby buildings, and the local vegetation. Global public surveys have reported strong support for having WTs installed close to urban areas [108]. However, local opposition to wind farms may arise depending on the wind farm location and the relatively closeness of WTs to human settlements, rural and/or urban zones. Visual Impact Assessments (VIA) [109, 110, 111, 112, 113] essentially consist in documenting the baseline conditions of the potential site, perform accurate visualizations of the proposed wind farm layout with a photo simulation or a three-dimensional planning software, and analyze the changes compared to the baseline situation. The metrics used within the VIA process includes a measure of the visual contrast that WTs introduce to the landscape. Proper micro-siting helps to improve the visual integration of WTs, cables, substations and access roads in the landscape [31]. However, the decision whether WTs intrude on the landscape is highly subjective. Therefore, variations on VIA are commonly encountered depending on human perception of visual effects, and sometimes it is not simply a function of size, number, color or distance between WTs and observers.  
WT rotors are prominent objects whose rotational movement induces attention. In special situations, WT blades may interrupt the sunlight or moonlight producing a flicker of light that can affect illumination in nearby areas. This effect is commonly known as shadow flicker or stroboscopic effect. WT shadow flicker has the potential to induce photosensitive epilepsy seizures [114], however, the risk is minimized with a proper wind farm layout planning. Shadow flicker is predictable and can occur only in specific conditions, locations and time of day. The recommended shadow flicker setback distance between WTs and residences is 1 km [94]. However, greater setback distances may be required when WTs are sited on elevated ridges, as the shadow flicker can be cast over larger distances.  
(e.g., WT blade composite materials, the shape, size and material of the WT tower and nacelle, transformers, _etc._), the signal frequency and the geometric factors such as the relative position between the WTs and the communication systems. The basic parameter used to measure EMI effects on a given communication system is the ratio of the amplitude of the scattered or secondary signal to the amplitude of the desired ambient or primary signal. Any possible EMI related problems can be prevented by properly designing the wind farm layout. However, other technical solutions or mitigation techniques such as the installation of amplifiers, re-transmitters, transmitting antennas or even repeater stations could reduce the amount of unwanted EMI. EMI can be minimized by ensuring that all equipment complies with relevant electromagnetic compatibility standards, by following any national legislations and by performing EMI assessments [131,132].