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Solar pv panel earthing


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I have recently purchased an Axpert 3kva/2400w MKS inverter connected to 2 x 102ah batteries as a standalone unit currently only connecting to AC for charging of batteries. Using to run tv, dstv during load shedding via extension cable. I would like to make use of the solar charging capability and have a single 250w Renesola pv panel which i want to connect but not sure how to earth as well as the roof mounting rail.

I understand that both equipment and system earthing is required. Would appreciate any advice on how to do this please. For equipment grounding can i take to existing earth spike or does it require its own. For system grounding not sure at all how to do.

Thanks

Alistair

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This is from one of the previous post from Wetkit


 


 


 


Here is my shopping list for mounting the panels to the roof.


Planning two sets of four panels, but only installing 4 panels for now.


 


Hardware can be ordered from any electrical supplier. Part numbers from Cabstrut.


4 x P2000 (5m sections, 1mm thick)


20 x SN110/M10 (m10 spring nuts)


20 x P1063 (Square to hold 2 panels on the sides)


10 x P1026 (90 degree angle, to hold outside panels)


20 x M10 bolts, 80mm long


 


This time I will try and document the installation step for step.

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you can purchase "earth clips" from most solar suppliers, clips on the panel frame and you crimp the cable to it on each panel.. there are two trains of thought on earthing, some folks use the existing house earth and some add seperate earth rods for the solar system. I use the homes existing earth spike if it has good value else plant another spike.

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Its easy to buy a copper coated spike at the hardware and some copper wire

I'm just not sure what diameter wire you should use

I would recommend going to a electrical supplier ,they could give the info and hopefully a better price

 

I don't know but would it make sense to have more earth rods to help dissipate lightning ?

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  • 1 month later...

Hi Alistair

 

Have a look at this video (unfortunately it is an hour long) but give you an understanding of earthing. I found it helpful and very good. My internet is uncapped, due to a service provider using my mountain to beam internet to the surrounding rural area, so the length of the video was not an issue.

 

https://youtu.be/mpgAVE4UwFw

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I don't know but would it make sense to have more earth rods to help dissipate lightning ?

 Multiple earthing rods are generally a bad idea as a strike close to one earthing rod will set up a difference in ground potential and you will have an energy pulse travelling along you earth wire from one rod to the other. If you have multiple earth rods they must not be interconnected.  Three or four rods with cable in between still counts as 1 earthing. To have a earth rod on the southern side of the house because that is where your municipal supply enters the premises and to have a earth rod on the north side because that is where your PVs are (and the two are connected through your home) is asking for trouble. Earth your frames and panels to their own rod and then earth your inverter to you home's earth rod.

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Hi Chris, great video and thanks for posting the link on the forum.

 

I do however believe that you have misunderstood some key principles in the video.

 

Nowhere in the video does the presenter recommend that you use independent earth electrodes. In fact the video shows that it is independent earth electrodes that can cause problems.

 

If you have independent earth electrodes then it is important to bond them together. This can be achieved by not only direct metallic conductive paths, such as copper cabling but also by using cable trays, conduits, cable armouring, pipe work and other conductive paths.The more parallel paths created the better the bond will be. 

 

Lightning (as an example) can either strike your installation directly or indirectly and you have to design the earthing system to cater for both scenarios. Generally speaking you try and create a well defined, low impedance path for the fault current to return to the source.

 

 

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Hi Carl

 

I did not explain myself properly then. I am not advocating multiple earth rods I am just saying if you have two don't link them.

 

The earth is a poor conductor over a short distance; the same chap in a different video  put in a 3m long earthing rod and 1 m away there was still 3/4 of the potential between the grounding rod and the earth. They had not bonded well. He then  ran some tests and it is only once the ground rod is 10m long that you start getting good conductance.

 

From minute 49 in the video it shows what happens when you bond two electrodes that are some distance apart. The lightning strike sets up a gradient of potential radiating out from the point of strike. The impedance of your earthing is lower than that of the earth and some of that energy from the lightning pulse travels down your earth pathway from the electrode closest to the lightning strike to the electrode furthest from the strike, subjecting all you earthed appliances to several thousand joules. Therefore use only one grounding rod and a good one. Even with a  grounding  rod 15 m in length you are not going to get enough flow to cause 15 A circuit breakers to trip. I am not recommending independent ground rods but if you do feel you need two rods do not connect them. A cluster of rods joined by cable is still only effectively one earth electrode, just one is hoping to decrease the impedance to ground.  

 

A direct strike on your installation is going to fry just about everything in spite of surge protectors etc. Hopefully the stray voltages induced by a close strike will go to ground through your lightning surge protectors. 

 

When earthing the panels and frame the only stray voltage should be atmospheric (lighting).  I would rather not have that energy coming into my home. A short within the panel should blow your solar fuses at your combiner box as it will draw energy from the other strings and exceed the 12A which I have installed in my case and this should warn you you have a touch potential problem. . Stray voltages are trying to go to source. In the case of lightning that is ground or quite often in the Karoo, adjacent cloud. 

 

In the case of a short circuit in you house, the stray voltage needs to go to source (Eskom - generator in my case). That is why the earth wire is bonded to neutral in your DB. You are providing a pathway for stray voltages to go back to source. I just question the logic of running 23m (in my case) of earthing wire (which in all likelihood will only conduct energy from lighting) through my home to an earthing point on the southern side of my home. Therefore in my case I will have a separate earth for my PVs, frame and PV home run cables, which are all on the northern side, which will not be connected to the earthing rod on the southern side of the house (which is for our current electrical installation). At my inverter, the input earth and neutral will be bonded, as from there the cable run is direct from generator to inverter. You need to bond the output too since in battery mode your inverter is acting as the power source and you need to provide a pathway back to source for stray current. The earth and neutral in the Axpert do not seem to be bonded in the inverter but I will check finally when I put wires in. Terminals and their screws often do not make good contact until tightened. Strictly speaking the earth bond on the output should open if the inverter is in bypass mode perhaps by using a contactor.

 

 

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