With these two regulators, the PV array is therefore to be divided into two subgroups of seven or eight panels. The power of a group of seven panels in parallel would be 7 x 2.85 = 20 A, and for another group of eight panels, 8 x 2.85 = 23 A. With the help of Table 5.19, the online losses between the components can be calculated. For 10 mm2 section wiring, with 1 A current, 4 mV/m in double wiring are lost. Using this 2 x 10 mm2 cable, for 23 A (eight panels), 92 mV/m would be lost between the modules and the regulator, or around 0.92 V if there are 10 m of wiring.
On the appliance side, power of the milking machine on its own is already 47 A (= 1120 W/24 V). If it is supplied from the battery with 10m of 2 x 10 mm2
cable, the loss will be 1.80 V: if the distance is reduced to 3 m, the loss will reduce to only 0.56 V.
The physical installation and the distance between the equipment will therefore be crucial in this project. In practice, the battery, the regulator and the inverter will be located in the goat shed with the milking machine, since it is the latter device that consumes the most. So these sensitive components will be under cover. Good ventilation is essential (for possible discharge of hydrogen in case of accidental overcharge). The PV array will be situated as near as possible to those so that there will be less than 10 m of cable length (general layout in Figure 5.60).
Scale -<- ►
Figure 5.60 General situation of the farm and its main power distribution
The house will have its own 24 V DC domestic distribution wired from the regulator, plus a 230 V AC cable from the inverter to supply the computer.