## 3 Relevant Research in Wind Farm Design and Optimization
### Electromagnetic Interference (EMI)
#### 3.2.6 Economic Modeling of Wind Farms  
The total cost of a wind farm can be decomposed into two different kind of costs: fixed (or capital) and variable (or recurrent) costs. Fixed costs include the acquisition and installation of WTs, cost of the land, foundations, power lines, transformers, auxiliary roads and additional infrastructure as pointed out previously. Variable costs include O&M costs, costs of WT component degradation, costs for unexpected problems mitigation and taxation. In many approaches variable costs, such as O&M costs, has been considered constant over the optimization procedure. Only two works [166,279] tried to model the effect of fatigue degradation in the O&M costs. In addition, the energy price evolution, which plays an important role in the economic feasibility of the wind farm project, has been considered constant, or predefined with a linear evolution, over the project lifetime, with the exception of the works of [PERSON] _et al._[278] and the TOPFARM framework [306]. Some costs such as taxes have not been considered because of the different taxation legislation found in different countries. Cost of Energy (CoE)  
Several major European projects have looked at the cost scaling of wind farm components. The Structural and Economic Optimisation of Bottom-Mounted Offshore Wind Energy Converters Study (Opti-OWECS) [319,320] investigated the state of the art of offshore wind technologies from 1996 to 1997 and endeavored to determine methods by which to lower the CoE from offshore wind farms. The Opti-OWECS study covered the economics of offshore WTs, support structures, electrical interconnection, installation, siting, layout, and O&M. The Offshore Wind Energy Cost and Potential (OWECOP) project was focused on the development of a software tool to model offshore wind farm costs. The Dutch Offshore Wind Energy Converter (DOWEC) project, conducted from 1997 to 2003, looked at ways of improving offshore WT design and increasing their cost-effectiveness. The project identified approaches to design and build better, more reliable large WTs (e.g., 5-6 MW) for large wind farms, and further examined the electrical, O&M, support structure, and rotor-nacelle assembly (RNA) costs as well as WT wakes. The major findings of such works are summarized and adapted in the work of [PERSON] [55], who proposed the definition of Levelized Production Costs (LPC), as shown in Equation (11). The cost components of Equation (11) are briefly summarized here, while the full derivation and validation can be consulted in [55]. All cost functions are reported in 2006 U.S. dollars. The Rotor-Nacelle Assembly (RNA) cost [S] consist of an empirical function of the rated WT power (\(P_{\mathsf{rated}}\) [kW]), as shown in Equation (61):  
\[C_{\mathsf{RNA}}=1170\ P_{\mathsf{rated}} \tag{61}\]  
The cost of the support structure (\(C_{SS}\)), which consists of the tower, sub-structure, and foundation, depends on the type of support technology considered. The cost of the WT tower (\(C_{\mathsf{tower}}\)) is given next:\[C_{\rm tower}=1.5\ m_{\rm tower}=1.5\ \left(c_{\rm tower}\ D^{2.8}\left(\frac{Z_{\rm H }}{D}\right)^{1.7}\left(\frac{P_{\rm rated}}{A}\right)^{0.6}\right) \tag{62}\]  
where \(m_{\rm tower}\) [kg] is the mass of the tower, \(c_{\rm tower}=0.016\) is a constant determined in a validation study, \(D\) [m] is the rotor diameter, \(Z_{\rm H}\) [m] is the hub height and \(P/A\) [W/m\({}^{2}\)] is the rated power density of the WT. Three different support/foundation technologies were studied: the gravity (\(C_{\rm GB}\)), the monopile (\(C_{\rm pile}\)), and the tripod (\(C_{\rm tripod}\)) bases, and their costs are summarized in Equations (63)-(65) respectively.