off grid solar earthing question

[michaelgoulden]

Hello all

I am trying to put a plan together for a solar off grid system with dc ac inverter set up.

There is no mains electric.

the nearest house with electric is 2 miles away.

My question is how do arrange earthing for the dc side and the ac side. 

Do I link -dc    and -ac to earth?

I cannot watch anymore utube.  so much conflicting  information. 

I just need a simple earthing plan.

Many thanks in advance for your replies.

[KhunLA]

Not an expert, but would think no different than if connected to PEA.  Your energy source / inverter will connect to your breaker box, assuming grounded / earthed, as it should be.  

 

Hope to be corrected, if mistaken.

[BritManToo]

Don't earth the DC, it'll break your inverter.

You can earth the PV frame if you want.

If you must have protection fuse and surge, but not needed if you're not putting in a lightning strike area. A lightning strike will kill the panels whatever you do.

 

https://www.lazada.co.th/products/applegreen-combiner-dc-box-3-1-mc4-dc-surge-1000v-dc-fuse-12a-25a-32a-dc-breaker-16a-32a-63a-i509418767-s904224453.html

Edited January 27, 2022 by BritManToo

[michaelgoulden]

this is a copy of my diy plan so far

[BritManToo]

34 minutes ago, michaelgoulden said:

this is a copy of my diy plan so far

 

3x 400w panels will only get you 5 units a day at best, you need more panels

I'd use something more standard (and integrated) than all your little parts.

 

Like this ..... 16Kbht

https://www.lazada.co.th/products/i2226480952-s9185383861.html

 

or this ....... 13k5bht

https://shopee.co.th/5.5KW-Hybrid-Off-Grid-Inverter-48V-MPPT-100A-Pure-Sine-Wave-รองรับโมดูล-WIFI-i.428988356.13409949302

 

48v seems to be the standard for batteries these days, 24v will restrict you.

You should also consider a generator for charging in emergencies/monsoon season.

Not expensive at all, 6kbht should be enough for occasional use.

 

No need for 4mm solar cable with that few panels.

2.5mm twin is a lot cheaper and good for 16A at 400V

Your specifications only call for 10A at 140V

(and the reality is 3 panels in series will be lucky to deliver 5A)

 

Edited January 27, 2022 by BritManToo

[Crossy]

Yeah ^^^. I would go with an integrated off-grid hybrid and 48V storage.

 

Also I'd go for a proper 48V pack with a single BMS.

 

For earthing, which was the original question, follow the recommendations of the inverter manufacturer.

[michaelgoulden]

thanks for your ideas

where would I find a 48volt pack? or can I just buy 4 batteries and put in series.

[michaelgoulden]

I have a generator for back up. I was hoping to build a system I could add more panels later.I know 3 panels is tiny for the system,but its what I have now,Looking at it an intergrated system looks a cheaper option and simpler to install.

thanks again 

[Crossy]

1 hour ago, michaelgoulden said:

where would I find a 48volt pack? or can I just buy 4 batteries and put in series.

 

Many 48V packs on Lazada in various sizes, or DIY a pack yourself.

 

Using series 12V packs can have pitfalls, many don't guarantee correct operation over 24V total (the BMS fries) and there's a risk if they get out of balance they will cut off charge / discharge early so you lose capacity. 

[michaelgoulden]

1 hour ago, Crossy said:

 

Many 48V packs on Lazada in various sizes, or DIY a pack yourself.

 

Using series 12V packs can have pitfalls, many don't guarantee correct operation over 24V total (the BMS fries) and there's a risk if they get out of balance they will cut off charge / discharge early so you lose capacity. 

the problem is many on lazada are unbranded and the prices are so much different 1000s baht difference its hard to choose one you can beleive in.Has anyone one bought a 48v system with bms on lazada they could recommend? Also many suppliers say its an order from china 15 days with ups or whatever do we end up paying more in import taxes.I would rather buy in thailand knowing the price is fixed.

[BritManToo]

4 hours ago, michaelgoulden said:

thanks for your ideas

where would I find a 48volt pack? or can I just buy 4 batteries and put in series.

This one is big, branded and expensive 10KWhr .... 78Kbht.

https://www.lazada.co.th/products/must-10kwh-ess-tesla-powerwall-48v-200ah-lifepo4-battery-hybrid-grid-home-solar-energy-storage-system-i2777108044-s10101632895.html

 

And there's guys building smaller ones at a more reasonable price 6KWhr .... 30Kbht.

https://www.lazada.co.th/products/i2646833087-s9512437008.html

 

Both these sellers get good reviews, and the products are in Thailand.

Lazada also guarantees all products sold through Lazada includes any taxes.

Best not to put them in or too near your house, shed in the garden job IMHO.

Edited January 27, 2022 by BritManToo

[willi2006]

If your system is isolated and the manufacturer of the inverter doesn't require earthing in this case, I wouldn't connect it to earth. Because touching any blank wire wouldn't result in an electric shock. An isolated, unearthed system is already what you achieve by using an "Isolation transformer" in an earthed system.

 

Earthing one wire and touching the other, the then "live wire", could give a shock.

Edited January 28, 2022 by willi2006
typo

[SomchaiDIY]

Some english video info here can help understand ground bond of inverter outputs

 

Bonding info can apply for the on or off grid type install

 

Video is inside thailand 3 phase to 1 phase system
 

 

 

 

 

[SomchaiDIY]

 

Sorry I forget to add video for dc side of solar system

 

 

 

 

[Crossy]

@SomchaiDIY Great videos, thanks for posting.

 

I'm somewhat intrigued as to why he places his surge suppression next to the panels, my mind places them next to the expensive inverter.

 

I also use 2-pole DC MCBs on the panel strings to ensure nothing is going to bite when I think about replacing failed MOV cartridges.

 

Thoughts??

 

[BritManToo]

8 minutes ago, Crossy said:

@SomchaiDIY Great videos, thanks for posting.

 

I'm somewhat intrigued as to why he places his surge suppression next to the panels, my mind places them next to the expensive inverter.

 

I also use 2-pole DC MCBs on the panel strings to ensure nothing is going to bite when I think about replacing failed MOV cartridges.

 

Thoughts??

 

I agree,

Most combiner boxes have a fuse on the + and the - coming from the PVs.

 

[SomchaiDIY]

53 minutes ago, Crossy said:

I'm somewhat intrigued as to why he places his surge suppression next to the panels, my mind places them next to the expensive inverter.

I see he has surge protection at each end of the dc line

 

One mov set at combine boxes and one mov set at the inverter board

 

Maybe this is good for the long line from solar panel to inverter

[Crossy]

18 minutes ago, SomchaiDIY said:

I see he has surge protection at each end of the dc line

One mov set at combine boxes and one mov set at the inverter board

Maybe this is good for the long line from solar panel to inverter

 

Thanks, I admit I didn't watch the videos in detail, most of these things are mind-bendingly boring, a simple diagram would do the job for the engineers here. 

 

It certainly cannot hurt and it's not like these beasts are particularly expensive.

 

But from personal experience these DC MOVs go leaky rather than actually tripping the "replace" window, leading to the inverter complaining about "leakage", just more things to check to get back online.

[SomchaiDIY]

28 minutes ago, Crossy said:

Thanks, I admit I didn't watch the videos in detail, most of these things are mind-bendingly boring, a simple diagram would do the job for the engineers here. 

Sorry for the boring video maybe my english confusion about this post area

 

I was thinking the person asking about ground was not tech engineer and looking for some basic idea

 

My mistakes sorry I did not understand this is a post area for tech engineer

[Crossy]

10 hours ago, SomchaiDIY said:

Sorry for the boring video maybe my english confusion about this post area

I was thinking the person asking about ground was not tech engineer and looking for some basic idea

My mistakes sorry I did not understand this is a post area for tech engineer

 

No, you get me wrong, the videos are fine and just right for this area of the forum. IMHO he would do well to include simple diagrams as well, but that's just me.

 

The "boring" bit is my personal feeling, I hate watching instructional videos which is why I skip-watched and missed the suppression at both ends (I'm still not really convinced but he does have fairly long runs).

 

 

 

[Muhendis]

15 hours ago, Crossy said:

Thanks, I admit I didn't watch the videos in detail, most of these things are mind-bendingly boring, a simple diagram would do the job for the engineers here. 

Yes I agree. These You Tube things are difficult to watch for engineers but they are useful for the non-technical person even if only to show how complex or, conversely, how simple some things can be.

Also the You Tuber gets paid for the video.

Don't forget to watch the video on how to understand a "simple diagram".

[BritManToo]

17 hours ago, Crossy said:

But from personal experience these DC MOVs go leaky rather than actually tripping the "replace" window, leading to the inverter complaining about "leakage", just more things to check to get back online.

If I were putting my PVs in a flat open field, I'd want protection against lightning strikes.

On a car port next to a house ..... pointless ..... lightning don't strike there.

For the site in the video a simple DC switch is enough.