Installing long DC Cable homeruns fromd string to inveerter
My question is not so much about amperes and voltages but about the most efficient method for connecting a high volume of DC PV Strings cables.
It concerns a project of 3.5 MW in total divided over 3 phases. The first phase consists of:
• 2,766 solar panels
• 156 Strings
• 13 x 60KW Inverter / inverter
It is a large factory hall. The panels are mounted on the roof in a String Layout of 156 Strings. The roof is inclined approximately 6 degrees.
Now I am looking for the best way to run the DC String cables between the PV Strings and the Inverter. The cable reels are large, each 1000 meters. A cable tray is mounted on the roof to guide the DC cabling. The cable trays meet on the roof where there is a feed-through to the room with all inverters.
Roughly speaking, I've actually seen, heard of two different methodologies:
1. String by string
2. Combine multiple strings
1 String for string
The method is as follows. The cable reel is placed in a metal frame so that it can be unwound freely. On the roof is someone who takes the cable by the hand and sound it through the DC cable tray until you reach the right string. Downstairs he is helped by someone who ensures that the cable is sufficiently unwound. On the roof, the cable is labeled with inverter number and string number. At the bottom, the cable is unrolled to the correct inverter and there it is cut and also labeled with inverter number and string number. This operation is repeated until all DC cabling has been installed / pulled.
1. Combine multiple strings
The method is as follows. You measure with a tape measure string 1 to 12. (Each inverter has 12 strings). So these lengths are measured manually. The cable reel is placed in a metal frame so that it can be unwound freely. Then I roll off the 12 measured distances for string 1 to 12. Each string is labeled on the ground at the end and at the beginning with the correct inverter number and string number. Fixed on the ground with also the MC4 connectors to the cables for connection to the string on the roof. These 12 cables are bundled together and these 12 cables are pulled from the inverter room to the strings on the roof in 1 go.
Which of you has experience with such large installations and would like to share knowledge about the best way to implement them?