DC Homerun wire instead of AC wire

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inforaj

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Hello everyone,
It would be fantastic if you could give me some ideas for a DC home run instead of an AC cable from the rooftop to the ground.
The customer design engineer desires a DC homerun from the rooftops to the grounds. He prefers that all of the equipment be put on the ground rather than the roof.
We have seven 60KW AC inverters, each with eleven strings. I suggested putting all the inverters on the roof and running an AC wire instead of a DC cable. This will be less nos of conduit and cable and a cost-effective and low-voltage drop solution, but the customer's engineer declined and wants to run the DC cable from the rooftop to the grounds.

Does anyone know what the benefits of installing DC Homerun are?

I really appreciate any help you can provide.
 
inforaj said:
Hello everyone,
It would be fantastic if you could give me some ideas for a DC home run instead of an AC cable from the rooftop to the ground.
The customer design engineer desires a DC homerun from the rooftops to the grounds. He prefers that all of the equipment be put on the ground rather than the roof.
We have seven 60KW AC inverters, each with eleven strings. I suggested putting all the inverters on the roof and running an AC wire instead of a DC cable. This will be less nos of conduit and cable and a cost-effective and low-voltage drop solution, but the customer's engineer declined and wants to run the DC cable from the rooftop to the grounds.

Does anyone know what the benefits of installing DC Homerun are?

I really appreciate any help you can provide.
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As a compromise if your inverters can be wired this way, you could have DC combiners on the roof and run a single DC line from each one. 77 conduits is obviously going to be horrific, and if you combine DC wiring into fewer conduits you'll have to consider conduit loading derates to your ampacities.
 
A combiner would be the way to go. How are you meeting the requirements for rapid shutdown if the inverters are on the ground?

This was always my biggest headache with inverters on the ground without built in rapid shutdown
 
Yeah, this all depends on rapid shutdown and what options there are for the inverters you want.

In the US, DC from the roof is usually THWN-2 in EMT or FMC.
 
ggunn said:
As a compromise if your inverters can be wired this way, you could have DC combiners on the roof and run a single DC line from each one. 77 conduits is obviously going to be horrific, and if you combine DC wiring into fewer conduits you'll have to consider conduit loading derates to your ampacities.
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In any case, adding this DC combiner box will increase the price of the combiner box.
 
inforaj said:
THWN-2 and EMT or IMC conduits are most likely.
Click to expand...

That would be a good choice because it provides shielding to reduce radiation of RF interference that the DC/DC converter at the front end of the inverter can place on its DC input lines.
 
ggunn said:
As a compromise if your inverters can be wired this way, you could have DC combiners on the roof and run a single DC line from each one. 77 conduits is obviously going to be horrific, and if you combine DC wiring into fewer conduits you'll have to consider conduit loading derates to your ampacities.
Click to expand...
Most of these size installations I have seen that bring the DC off the roof use a cable tray system and a waterfall off the roof. This was quite popular in the old days when a central inverter was 500kW and too heavy for most roofs.
 
ggunn said:
As a compromise if your inverters can be wired this way, you could have DC combiners on the roof and run a single DC line from each one. 77 conduits is obviously going to be horrific, and if you combine DC wiring into fewer conduits you'll have to consider conduit loading derates to your ampacities.
Click to expand...
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The DC Combiners are not used. I just got the drawing, and the customer said that we need to run a String cable/conduit from the roof to the ground wall until we reach the inverter positions.
 
inforaj said:
View attachment 2564897
The DC Combiners are not used. I just got the drawing, and the customer said that we need to run a String cable/conduit from the roof to the ground wall until we reach the inverter positions.
Click to expand...
One quibble: You have drawn the modules connected to the P1101 in parallel instead of in series.
 
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