Need Advice- Upgrading my off-grid solar system in Ohio

Re: Need Advice- Upgrading my off-grid solar system in Ohio

My two cents: :roll:

Heisenberg wrote: »

Okay, So for now I will run the 6awg from panel frames/mounts to earth ground

The new inverter will be the Morningstar 300 true sine. It indicates a 3a inline fuse on the Black Ac output line, so I shouldn't have an issue wiring it to a standard plug then I assume.

I don't see a need for the 3 amp fuse--And that fuse is under rated for inverter that is spec'ed for 600 Watts @ 10 minutes (~5.2 amps @ 115 VAC).

Does the neutral ground/bond already exist within this (morningstar 300) inverter itself, or does that occur if and when I would connect earth ground to the neutral ac output on the inverter as the diagram indicates?

No--As far as I know, the output of the MorningStar 300 TSW inverter is floating... You can let it float or tie it to your "local" ground (99% of the time, it will not matter what you do--In a very few cases, you may have problems starting tube type florescent fixtures in cold weather or poor function from AC powered automatic spark ignitors in Stoves, etc. Both tend to use a Grounded Neutral for best operation).

In theory, floating AC output power supplies are less of a shock hazard. However, because a wire can be shorted to ground at any time/any where--It best not to assume "safety" of a floating AC output (in a factory, this would be "inspected" once a day or once a week to ensure the output is "really" floating).

What if I just earth ground the panels (frame) and do not ground any equipment? Is this what they call a "floating system"?

You are "earthing" or grounding the metal frames to reduce the chance of lighting energy choosing its own path (through the wooden structure, or through your wiring). Also, during some conditions, you can have high static charges build up on the ground frames--So that can be a shock hazard (if you are working on the roof).

My solar "utility room" is approx 30ft from the ground in the cabin loft. It would get pretty expensive to "single point ground" each unit that has a grounding lug.

Several grounds we are talking about here... First there is the "main ground" which is usually just outside the exterior wall nearest to your "main panel" (whatever that is) and where power "enters" the home.

A second ground (rod) maybe that at a solar array XX feet or more from the home that is used to connect just the solar panel frames (and metal structure) to earth ground. I like to tie a ~6 AWG wire from the remote ground rod to the main ground rod. This ground connection is to provide "solid" grounding if you have power at the array (say you brought out AC power for a local AC outlet). If there is a short to the solar array assembly, it will trip the breaker/inverter back at the home.

Next. "Single Point Grounding" may not mean what you think it does (at least to me). A single point ground is a connection from the ground rod to (for example) your battery Ground Bus (negative bus typically).

You can have a second wire from the main ground rod to the AC Neutral (either at the inverter or the main AC Panel).

The point is not to have other ground wires going to a DC ground elsewhere (say at the inverter DC negative connection or a second Neutral White wire to ground connection) back to the Main Ground Rod (as an example). This would allow parallel current paths for the return current--And grounds are supposed to be for "safety" and not a parallel current path (in normal operation).

Notice that in the above "simple" grounding scheme--The "Main Ground Rod" has three connections--One from the Remote ground rod, a second to the Battery negative bus, and a third to the AC Neutral / White Wire common/bus point.

You will probably have other safety green wires that can all run to the DC negative Bus for safety ground (say the Solar Charge Controller "earth ground", the AC Inverter's "earth ground"... And you can run other grounds (like the third green wire ground in your AC outlets) to the Neutral/White Earth Ground common / bus point.

More or less, I would suggest keeping the DC "safety ground" separate from the AC "safety round"... Generally, with batteries you can be looking at 100-400 amp circuits. And on the AC side you may be looking at 3-50 amp circuits--Much less current (you don't want to dump a Hot to Metal Case short in your AC inverter to a 14 AWG wire in your AC grounding system)... You want to take that Inverter safety ground (with 6 AWG or heavier wire) directly to the Battery Bank Negative Bus (so you an pop the inverter "200 amp" branch circuit Fuse/Breaker).

If you are in a lightning area, you may want to add lighting/surge suppressors where the DC PV wires enter the building (J box of some sort) and add some suppressors on the Inverter AC output too (watch the suppressors' ratings so that you got the AC and DC voltage ratings correct).

We do have some links on lightning control:

BB. wrote: »

A couple threads about Lightning:

Off Grid Grounding Technique?
Another Question, this time about Lightning

Note, the above are discussions, not a do A, B, and C--and you will be "safe". There probably is no such thing with lightning. Several different techniques are discussed--and a few of those posters even have experience with lightning. :cool:

And our host's consolidated FAQ page:

www.windsun.com
Lightning Protection for PV Systems

From other past posts here, Windsun (admin/owner of NAWS), he said that most of lighting induced failures he saw were in the Inverters' AC output section.

Towards the end of this thread is a very nice discussion of proper generator grounding.

Since those above posts, Midnite has come out with some newer surge suppressors which may work much better than the standard Delta brand versions:

Surge Protection Devices
Metal Oxide Varistors mounted in PV junction box? (one of the threads where we discussed Delta/Midnite suppressors)

I am no expert at this--So, doing some research and/or finding a HAM radio person with lightning experience will be helpful.

-Bill