Understanding of Selection of cable and cable size for a solar PV Plant


In a solar PV plant selection of cable, cable size and its layout are as important as selection of modules and inverter. Cables are the medium to transfer electricity from module to inverter. Even scientists has take science to another level but still its is not possible on the industrial scale to transfer a good amount of electricity without wire/cable. So, selection of cable  and cable size is very important while designing a solar PV plant. 

It may be noted that a typical 5 MW solar project use about 5 KM of solar cable, hence optimizing cable size and cable routing becomes important for system designer. Even if we say, 1% of energy saved through reduces cable losses; it generated extra energy worth 25 Lac per annum. While selecting cable, it’s important, that we do a right selection of conductor size. For solar projects both copper and aluminum conductors are used, however, using aluminum has its own demerits such as low bending strength, higher thickens and higher losses. Although we can save bit of money while using aluminum conductor, but it becomes, difficult to change broken cable In the solar field and the loss of generation due to cable failures become critical which should be consider while selecting a cable conductor type. 

The operating temperature of cable affects its current carrying capacity and hence, the local site conditions play very important role while selecting right size of cable. Typically, the cable should be design consider the highest temperature observed at the site (worst case scenario). It has been observed that cable sizing is done at STC of the 25o C, however, we have seen in various sites, the operating temperature of cable goes as high as 75o C.  The system voltage is also an important factor while deciding the cable size.

If a system voltage is 600 V, the cable size for a 8 A current and losses are 2% then cable size is of the order of 6 mm2 and if with the same voltage and current value but with only 1% of loss, if the system voltage is increased to 1000V DC cable size can be reduced to 2.5mm2 to carry the same power.

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