Long run Ground Mount Solar DC considerations

[ThomasGB]

Hi all,

I am in the process to configure an 18 kW ground mount install in the backyard. The run to the house will be about 400 feet and based on my calculations it seems that it would be more cost effective to run a series of DC wires to the house (6 wires ~400 V/10A), perhaps to a small structure just to mount the inverters close to the house, and then a short AC run to the house into a subpanel and then the utility grid tie-in. Does that make sense?

Also, with regards to NEC 2017 what kind of rapid shut down configurations would apply for a design like that?

Many thanks

[bcroe]

Making that long run at higher DC voltage is the way to go. I suppose you will
have 2 inverters? Do calculate your losses in wire resistance, 2% might be a
reasonable trade off against wire cost. 6 pairs could work, you might spend
less by combining them into 2 much larger pairs, possibly using aluminum wire.

A ground mount may be built to require minimum effort for snow clearing, if
you are expecting any. Read about that in the sticky SNOW TOLERANT PV
MOUNTING under SOLAR PANELS FOR YOUR HOME. Bruce Roe

[ThomasGB]

Hi Bruce,

thank you for your reply. I planned 3 inverters 6 kW each (Fronius Primo) because of the 600V restriction for residential and the MPPT voltage limit (480V) of the inverter. Thank you for the snow tolerance tip! A 10 AWG wire would give me a voltage drop of 1.9%, 8 AWG 1.25%.

Do you have any advice on the second part: Installing the inverters at the house versus a short distance away? Does that have any implications for the rapid shut down requirements?

Many thanks
Thomas

[bcroe]

Generally rapid shutdown does not apply to ground mounts, not used here. But
others may give a more authoritative input based on your location. Bruce Roe

[ThomasGB]

Ok, thank you. I am in Maryland, Baltimore County

[Mike90250]

first, 18Kw is a really large system. Have you obtained preliminary approval from your power company and local building department? Your insurance company ? I ask because generally, systems over 10kw are licensed as Commercial Power. and I don't want you to get a rude surprise .

second, your local building department may have their own variations from NEC, they would be your authority.