# DC Cabling of Large-Scale Photovoltaic Power Plants
## 3 Array Cabling on the DC Side
### DC Cabling  
The type of DC cable is selected according to the short-circuit current (\(I_{\rm SC}\)), the maximum system voltage (\(U_{\rm maxP}\)), the ambient conditions (\(T_{\rm a}\)), and according to the relevant standards [11]. The SP topology requires two types of cable: one that connects the solar modules in a string (S\({}_{1}\)) and another that connects the strings to the inverter input (S\({}_{2}\)).  
According to the standards, the cable cross-section has to be chosen so that value of its nominal current is 1.56 times the value of the short-circuit current of the solar module [11]. A temperature correction factor is also introduced. For an ambient temperature of 30 \({}^{\circ}\)C and a maximum temperature of 40 \({}^{\circ}\)C, a cable of 90 \({}^{\circ}\)C is chosen, and this factor is 0.58 [10].  
Figure 2: Block structure of large-scale FPV power plant.  
The required current capacity of the \(I_{\text{C1}}\) cable (for serial connections) can be determined as follows:  
\[I_{\text{C1}}=\frac{1.56\cdot I_{\text{SC}}}{0.58}. \tag{7}\]  
The required current capacity of the \(I_{\text{C2}}\) cable (for parallel connections) can be determined as follows:  
\[I_{\text{C2}}=N_{\text{S}}\cdot I_{\text{C1}}. \tag{8}\]  
In order to determine the lengths of DC cables, it is necessary to know the system's geometry, which is a function of the way the modules are placed. In this paper, only floating photovoltaic plants (FPV) are considered. FPVs are built on water surfaces such as water reservoirs, hydropower plant reservoirs, natural and artificial lakes, sea surfaces, and water channels [24]. Due to the stability of the pad that supports the solar modules, FPVs are usually realized with one solar module on the carrier. The solar module is mounted on a shorter side of the solar module and placed along the carrier's edge. In addition, the carriers are at the level of the base on which the cables are placed (Figure 3). Due to the vibration of the structure, the modules in the same string are spaced apart for \(L_{0}\).  
The distance between two arrays is determined by:  
\[D=W(\cos\alpha+\sin\alpha\cdot\cot\beta)=W(\cos\alpha+\sin\alpha\cdot\tan( \alpha_{\text{at}}+23.5^{\circ}), \tag{9}\]  
where \(\alpha_{\text{at}}\) is the latitude of the location. The cables lengths that connect the solar modules in strings and the solar modules between two strings are determined as follows:  
\[d_{\text{M-M}} = K_{\text{T}}\cdot(L+L_{0}), \tag{10}\] \[d_{\text{S-S}} = K_{\text{T}}\cdot(D+W\sin\alpha). \tag{11}\]  
The minimum required lengths are multiplied by the coefficient \(K_{\text{T}}\). This is due to the flexibility during installation and the shrinkage of the cables at low temperatures. In this paper, \(5\%\) of the length is added, i.e., \(K_{\text{T}}=1.05\).  
In the standard SP configuration, connecting the solar modules in a string where all the solar modules are arranged in one string requires a return cable that doubles the length of the cable per string. If the number of solar modules in the string is even, then the string is divided into two subsets, and the return cable is not required (Figure 4).  
Figure 3: Solar module position geometry in FPV plants.