Ground Mount cable run questions!

[NikoV6]

Hi, I have constructed a fairly large "shed" to mount 10Kw of solar panels.

I have a choice of mounting the inverter in the new "shed" or 22m away in another outbuilding that has the battery storage and electricity meter.

Question is, what is preferable, mount inverter in new shed and run 6mm twin and earth to the battery or mount inverter in the outbuilding and run 6mm solar cable from the shed?

Preference is to mount inverter in the outbuilding so that I can CT clamp the exported solar energy in the electricity meter.

Problem with running the 6mm solar cable is I would like to take a power feed for lights and sockets to the shed in the same conduit, I don't think DC and AC should be near each other!

DIY solar install is easy!

[Stinsy]

There isn’t much in it. However assuming same-size cables then mounting the inverter in the shed would be (slightly) better for efficiency because the longer run is the higher voltage wires.

[Oldgreybeard]

With a 10kWp array the highest voltage cables will be the DC ones in all probability, so they will be carrying the lowest current and it would makes sense to send high voltage DC over that distance. It would need a multicore armoured cable, though, as with a 10kWp array you're going to have several strings and each string will need a pair of conductors in the cable. Aim for the highest string voltages you can (limited by the inverter input) to keep losses to a minimum.

[Mr Gus]

As as aside, has anyone spotted any keenly priced (but capable) SWA for solar installs / EV chargers lately? (Worth asking)
Cheers lads.

[NikoV6]

With a 10kWp array the highest voltage cables will be the DC ones in all probability, so they will be carrying the lowest current and it would makes sense to send high voltage DC over that distance. It would need a multicore armoured cable, though, as with a 10kWp array you're going to have several strings and each string will need a pair of conductors in the cable. Aim for the highest string voltages you can (limited by the inverter input) to keep losses to a minimum.

Two strings of 11 panels, 460V, 10.88A. Solis inverter has two inputs, one 25A the other 12.5.

I have 250m of 6mm cable supplied by the panel supplier, this will be run in twin wall plastic conduit. Is this not suitable and I should look to use armoured?

[Oldgreybeard]

Two strings of 11 panels, 460V, 10.88A. Solis inverter has two inputs, one 25A the other 12.5.

I have 250m of 6mm cable supplied by the panel supplier, this will be run in twin wall plastic conduit. Is this not suitable and I should look to use armoured?

That's fine in twin wall duct, no different to all the tens of thousands of miles of power distribution cable run in ducts under roads etc, none of which is usually armoured. You only need armoured cable when there's no other mechanical protection, usually.

[NikoV6]

Two strings of 11 panels, 460V, 10.88A. Solis inverter has two inputs, one 25A the other 12.5.

I have 250m of 6mm cable supplied by the panel supplier, this will be run in twin wall plastic conduit. Is this not suitable and I should look to use armoured?

That's fine in twin wall duct, no different to all the tens of thousands of miles of power distribution cable run in ducts under roads etc, none of which is usually armoured. You only need armoured cable when there's no other mechanical protection, usually.

Many thanks

Assume the power to the new shed to provide light and a socket would need to be run in a separate twin wall duct to keep the AC and DC apart?

[nowty]

Preferably I would run DC to the outbuilding because you want the inverter as close to the meter / consumer unit as possible. Because the longer the AC cable run, the higher the voltage drop at high output (you have an 8kW inverter ?), which translates into a higher operating voltage at the inverter end and may trip out the inverter. Also 6mm for a long AC connection would also exacerbate voltage drop, I'd be going for 10mm at least.

Voltage drop with DC is irrelevant as the inverter's MPPT will run at whatever the voltage is as their operating ranges are very high.

I would also preferably use armoured cable underground whether you decide to run either DC or AC, then you don't have to duct it.

[ALAN/ALAN D]

Fully agree with Mr Nowty. The best way to go.

I have had rats eat through plastic conduit / trunking. A little mouse had a go at this bit of wire.

[Oldgreybeard]

Fully agree with Mr Nowty. The best way to go.

I have had rats eat through plastic conduit / trunking. A little mouse had a go at this bit of wire.

I bet that was an older bit of cable that still used a vegetable oil as a release agent/lubricant during manufacture. There were a few years when this was a real problem with flexible cables, mice and rats were attracted to the smell of the minute oil residue on, or in, the cable sheath and would then nibble away at it. It was a major problem with some cars, mostly in the USA, where rodents often nest in engine bays. Cars were written off because of it, so the wire and cable manufacturers changed the stuff they use when making the cable and the problem went away. The same problem was seen here on outdoor cables, the stuff sold for use in cold weather.

Twin wall duct is specifically manufactured for underground cable protection and has the advantage that additional or replacement cables can always be pulled through later, as long as a draw cord is left in the duct. All our underground cables here are in twin wall duct, including the underground mains supply cables. The phone cables come in underground too, but in 50mm grey BT rigid ducting. None of the utility cables are armoured, although all the cables I ran in for garden lights, the shed, etc are. Bit belt and braces putting armoured cables in ducts, but it has allowed an extra cable to be run in when I put the greenhouse up. PITA pulling SWA cable through duct, though. Pulling a (non-armoured) data cable in down to the well shed was a great deal easier.