40m DC run to inverter?

Zenith74 · 03-07-2023 7:48am #1

Hey all, looking for some thoughts on my plan for a PV installation.

I have a garage with a South facing roof that will take 9 panels. There’s a new fuseboard in the garage with a 10sqmm cable back to the main board and a 16kW heatpump in the garage. So it’s an ideal spot for the inverter to go to, well connected, plenty of indoor space, out of the house for (minor) safety reasons.

Before the heatpump went in we were using 1000kWh a month on two EVs and household appliances, so I’m sure it will be much higher now. So I’d love to put in more like 20 panels.

While there is some space around the house for a ground array, including near the garage, they’d catch some shading from various sheds/fences and they’re not too attractive either (according to my wife, I think they look awesome, obviously!).

The other option is to put 10 more panels on the South facing roof of the house and use an underground duct (already in-place) to bring them back to the inverter in the shed. It’s about 20m to the garage from the house, but adding in a few meters internally at both sides it would be just short of 40m total. Any thoughts on this? I’m not certain of my figures, but it looks to me like if we used a pair of 10sqmm cables we’d have a voltage drop of <1% which seems like not a big deal at all?

Cheers for any thoughts!

graememk · 03-07-2023 9:19am

https://www.boards.ie/discussion/2058303437/40m-dc-run-to-inverter

20m run is fine, each string(about 10-12 p panels) are separate

The standard 4mm² is fine for that.

I have 24 panels 50-60m away from my inverter but that is on a 6mm2 5 core swa as it's running though multiple sheds to get back to the inverter.

Buffman · 03-07-2023 1:18pm

Your plan sounds fine. Presumably you'll be using a maximum size inverter so 9 & 10 panel strings sound ideal without knowing exact specs.

Zenith74 · 03-07-2023 10:10pm

Sorry my wording wasn’t too clear there, the run will be 40m. I confusingly included the irrelevant detail of the underground duct length.

Why the 5 core, + and - for two strings and an earth? Wonder if I’ll need earth from the inverter to the panels or is two cores enough? I don’t recall the panels in my last house being earthed.

Guessing a 5 or 6kW inverter. Willing to accept quite a bit of clipping on the sunniest days in the height of summer, hoping the 20 panels will give me a better chance of having some half decent generation in the spring/autumn when the heatpump will be busy.

graememk · 03-07-2023 10:17pm

Yep 2 strings + an earth. They have the earth on one of the rails.

Comes down from the roof to the fireman switch(needed it for the grant) on 4mm2 and then from the switch to a junction box into the SWA. SWA goes into the DC isolator beside the inverter where it reverts back to 4mm2 with MC4 connectors.

Zenith74 · 04-07-2023 8:22am

Does anybody have panels on their roof and knows if the frames are earthed or not?

It would make life much easier if I only have to pull two cores rather than three, but it will need to be safe and pass an SEAI inspection obviously!

@graememk that fireman switch I assume is manual, rather than an automatic one that cuts the DC if the mains electric goes off? I’m wondering if because I’ll be running the DC through the house on its way to the garage do I need to put an automatic fireman switch up in the attic close to the panels and before I go onto the 6sqmm to head to the garage.

To be clear I’ll be getting the system professionally installed, I’m just trying to understand what will be required so I can plan for routes etc as we work on the house.

graememk · 04-07-2023 9:29am

Automatic, I've also a 3 core 1.5mm taking the power to the fireman switch.

Although in a house it's usually inside beside the inverter.

Mine and my parents are all earthed.

AmpMan · 04-07-2023 10:20am

rails should be earthed with 10sq

allinthehead · 09-07-2023 9:06am

https://www.boards.ie/discussion/comment/120802964#Comment_120802964

Can you explain the rationale behind this statement?

slave1 · 09-07-2023 5:10pm

10sq, jeez, never heard that before

AmpMan · 10-07-2023 7:08am

https://www.boards.ie/discussion/comment/120824651#Comment_120824651

Its in the regs section 544 Equipotential bonding conductors

Main bonding conductors shall connect extraneous conductive parts of the main engineering services in a building.

Main bonding conductors provided for the main bonding system according to 411.3.2 shall have a conductivity but shall not be less than:

- 10 mm2 copper

allinthehead · 14-07-2023 1:10pm

https://www.boards.ie/discussion/comment/120828379#Comment_120828379

Not sure if it would be considered main bonding, I've seen in some documents 4mm2 mentioned as supplementary bonding but I've also seen 6mm2.

It's 16sq if the building has lightning protection.

AmpMan · 14-07-2023 1:18pm

https://www.boards.ie/discussion/comment/120850827#Comment_120850827

Its right there in the text I quoted from the regs.

Main bonding conductors shall connect extraneous conductive parts of the main engineering services in a building.

https://electricalreview.co.uk/2023/06/22/cea-finds-97-of-rooftop-solar-installations-had-major-safety-concerns/

allinthehead · 14-07-2023 2:01pm

https://www.boards.ie/discussion/comment/120850882#Comment_120850882

That doesn't tell us that it even needs bonding, let alone that it's main bonding. You're talking about equipotential bonding, equipotential with what? Unless the roof is steel or there're steel downpipes nearby then why are you bonding at all?

Not trying to be argumentative or saying that you're wrong here btw, just trying to understand your rationale.

AmpMan · 14-07-2023 2:20pm

I asked safe electric.

allinthehead · 14-07-2023 2:29pm

https://www.boards.ie/discussion/comment/120851260#Comment_120851260

So did I, and that's not the answer I got.

allinthehead · 14-07-2023 2:39pm

https://www.boards.ie/discussion/comment/120802460#Comment_120802460

You will need Dc surge protection where the cables enter the building as the dc run is more than 10 meters from the inverter. This will mean running a 10 sq earth to that point too. Make sure they install surge protection at your distribution board too. Most don't, but it's a regulation.

40m DC run to inverter?

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