# DC Cabling of Large-Scale Photovoltaic Power Plants
## 1 Introduction  
One of the most significant advantages of Floating Solar Photovoltaic (FPV) power plants is that they do not occupy land that could be used for other purposes; thus, they eliminate the need for vegetation removal. Nevertheless, they still occupy large areas that vary from 7500 m\({}^{2}\) to 15,000 m\({}^{2}\) for 1 MW of installed capacity [1]. Solar modules that usually produce between 250 W and 550 W of power per module are installed on this surface. The average surface area of solar modules used in such installations is approximately 1.5 m\({}^{2}\) to 2.5 m\({}^{2}\). A fundamental task for any PV power plant designer is to connect the solar modules in a string so that the string voltage corresponds to the input voltage range of the inverter. Modern inverters operate with maximum voltages of up to 1500 V DC, while the optimal operating voltage ranges from 320 V to 1300 V DC [2; 3; 4]. Inverters available on the market are typically rated from a few kW to a few hundred kW [3; 4; 5]. For maximum PV array output, the power must optimally match the rated power of a PV array with the inverter's rated power. Therefore, it is common for several strings to be connected in parallel at the inverter input. The inverter output is AC three-phase low voltage (usually a line voltage from 220 V to 760 V) [3; 4; 6; 7]. A transformer is generally used for grid integration to step-up the low output voltage to a medium or high voltage level [1; 3; 8; 9]. Several configuration schemes for PV arrays are described and discussed in the literature [3; 10]. The serial-parallel (SP) topology is the suitable configuration for FVP power plants with a high installed capacity, and is therefore considered in this paper [9]. The SPtopology for such power plants is characterized by many inverters. In this configuration, several parallel arrays of solar modules are connected to each inverter. The wiring of the solar modules to the inverter is performed on the DC side and is called DC cabling. The cabling process is characterized by a lot of technical requirements and constraints. All requirements should consider the cost of cabling and the losses in the cables. The characteristics of the cables are selected according to the maximum currents in the system, which has to comply with the technical characteristics of the solar modules and inverters [11; 12]. In the cable selection process, the power plant's voltage range and temperature range should be essential factors [11; 12]. Both the price and resistance of the cable are a function of length. Therefore, when a cable is selected according to the technical requirements of the equipment, the costs and losses are lower when the cable length is shorter. A review of up-to-date literature clearly shows that the cabling process is insufficiently considered. Cabling in PV power plants is considered in just a few papers. In [10], a mathematical model for calculating cable lengths and the required cable cross-sections for different topologies was given, and the calculation of the voltage drop on the DC side was performed. Comparative analyses of capital investments in cable systems for various architectures and potential payback periods were created. The problem analyzed in [10] was related to the selection of topology to reduce losses due to the influence of partial shadow on the power plant. In [13; 14], the problem of energy losses on DC and AC cables was analyzed. An approximate expression was obtained, yielding the relation between the installed capacity, the location of the power plant, and the annual losses. A comparison of the results was performed with the measured losses. The cable length problem was not considered. The authors of [15] reviewed the overcurrent occurrence at partial shading and analyzed the minimum requirements for wiring and protection based on valid standards of PV systems. It also proposed to change the standard that defines the required current capacity of a DC cable. In [16], the cable was selected to minimize the objective function.