Photovoltaics

[PaulWDent]

I don't rememeber if it is the NEC code or NABCEP that now specifies the following: If your solar panels would be grounded to a point more than 6' away from house ground, they must have their own grounding electrodes.

This is completely wrong. Think of this: You have a microphone at the end of a 50' length of coax. One terminal of the microphone connects to the inner and the other terminal to the sheath. Would it be better if instead we disconnected the latter from the sheath and connected it with a piece of #14 to the ground terminal of the nearest receptacle? Try it! The hum will blow your speaker cone!

The problem is, having wires from the solar panels to equipment grounded at the house ground and another wire from the solar panel frame to a separate grounding system creates a huge loop antenna. This will increase the radiation of inverter hash, as well as inducing an enormous transient into the current carrying wires from the solar panel to the rest of the equipment when there are neighboring lightning strikes.

If lightning hits the panel frame, your'e going to get creamed with ths method, because a 25 ohm solar panel ground will do nothing to hold down the voltage. You will have a million volts on the panel frame relative to the solar cells, it will arc across from frame to cells, and thence to the inverter. If however you ground the frame via the conduit that carries the cell output to the inverter, they will all go up to a million volts together, with little potential difference to cause damage.
Coax is King!

The manuacturer's recommendations for my Xantrex inverter installation recommend exactly the opposite of this new code. Everything should go back to the same ground, and ground wires should run in the same conduit as hot and neutral wires. The frame of solar panels should be grounded via the conduit and/or this ground wire.

The code needs to be changed pronto.

 

[gndrod]

I don't rememeber if it is the NEC code or NABCEP that now specifies the following: If your solar panels would be grounded to a point more than 6' away from house ground, they must have their own grounding electrodes.

This is completely wrong. Think of this: You have a microphone at the end of a 50' length of coax. One terminal of the microphone connects to the inner and the other terminal to the sheath. Would it be better if instead we disconnected the latter from the sheath and connected it with a piece of #14 to the ground terminal of the nearest receptacle? Try it! The hum will blow your speaker cone!

The problem is, having wires from the solar panels to equipment grounded at the house ground and another wire from the solar panel frame to a separate grounding system creates a huge loop antenna. This will increase the radiation of inverter hash, as well as inducing an enormous transient into the current carrying wires from the solar panel to the rest of the equipment when there are neighboring lightning strikes.

If lightning hits the panel frame, your'e going to get creamed with ths method, because a 25 ohm solar panel ground will do nothing to hold down the voltage. You will have a million volts on the panel frame relative to the solar cells, it will arc across from frame to cells, and thence to the inverter. If however you ground the frame via the conduit that carries the cell output to the inverter, they will all go up to a million volts together, with little potential difference to cause damage.
Coax is King!

The manuacturer's recommendations for my Xantrex inverter installation recommend exactly the opposite of this new code. Everything should go back to the same ground, and ground wires should run in the same conduit as hot and neutral wires. The frame of solar panels should be grounded via the conduit and/or this ground wire.

The code needs to be changed pronto.

Hi Paul,
Is there a reference Section to Article 690 that should be addressed that you can cite? I have been tracking the last two cycles for Solar Array grounding and if the panel frames are isolated from the dc energy output, the frame grounding would normally have a connection to the Grounding Electrode System. If the inverter modules grounding are bonded together integral with the array panel dc return, then I would agree.

The 2008 Article 690.45 conductor sizing and 690.47 GES have been expanded to include field pole mounted arrays that would require electrode grounding in the field. The 2011 Article 690.47 GES has extensive revisions that include permitting one single dc GEC bonding to for multiple inverter use. This may be due to parallel inverter design is due to each solar panel can now include having it's own inverter in the panel circuitry for an ac source output.

Could this be what you are referring to? There would be an interface isolation bonding condition in each panel...not including the frame I believe?

 

[Peterp]

There are some good safety tips on installing solar panels, and connecting them up to the grid. You always have to be careful, as people tend to forget how much current a solar installation can actually produce. Its actually scary if you think about it. Here are some DIY Solar Panels plans i found that were useful in helping me with my installation. A number of things have to be considered, from the inverter type, to the gauge of cable, etc

 

[gndrod]

A DIY panel/inverter?

A DIY panel/inverter?

There are some good safety tips on installing solar panels, and connecting them up to the grid. You always have to be careful, as people tend to forget how much current a solar installation can actually produce. Its actually scary if you think about it. Here are some DIY Solar Panels plans i found that were useful in helping me with my installation. A number of things have to be considered, from the inverter type, to the gauge of cable, etc

Hi Peter,
Did each panel have their own inverter? If so, how are the array panels framing connected together? Were these rack or pole mounted?

 

[Smart $]

I don't rememeber if it is the NEC code or NABCEP that now specifies the following: If your solar panels would be grounded to a point more than 6' away from house ground, they must have their own grounding electrodes.

...

What code cycle are you on... 2008?

FWIW, what you stated is sort of the inverse perspective of an exception. 690.47(D) Exception No. 2 syas you don't have to install the additional electrodes if within 6' of the premises wiring electrode (I have to ask who actually wrote this exception... the NEC does not use that term in the grounding section, so how is one to correlate 250 terminology with 690 terminology if it is different)... but don't fret. For one, that entire paragraph and its exceptions have been removed from the 2001 NEC edition.

Additionally, if one understand the full scope of grounding in 690, you will figure out that the "local electrodes" are still bonded through EGC's to the premises GES...

 

[PaulWDent]

Array frame bonding

Array frame bonding

I was citing the 2008 code and have yet to check if the 2011 code says the same thing.
There might be different concerns for a residential system as compared to a solar farm.
One difference (and I am still on 2008 code) is that when PV is installed on a residential house (and not an outbuilding like a barn), it has to have GFDI on the DC side. Grounding the array frame by a separate path can prevent this from working by causing spurious tripping due to noise. My main concern would however be that it would worsen electrical storm damage potential. Many installers like to use liquidtight metal to wire up the PV panels to the combiner and inverters, and this is my favorite solution too. The array frame should be grounded via the liquidtight metal sheath to the same ground source as the other equipment - but put another green wire in the conduit too for security! I particularly like liquidtight metal rather than bare metal conduit for this because the insulated outer jacket discourages any future electricain from thinking they can pick up a ground there - which they shoud not, due to the GFDI operation.
This "coax" solution is better for noise and better for lightning protection and we need to make sure that future versions of the code at least allow it, if not recomnmend it.

Now, large solar farms can be very spatially dispersed, but they do not require GFDI. In the case they comprise a set of separate arrays, each with an associated inverter, it might make a lot of sense than to have one ground rod per array/inverter combination. The inverter output is generally floating (two hot legs and no neutral) and sees ground only through the utility transformer when connected to the utility in the service panel.