Off Grid Grounding

As a general proposition, the controller etc. could go to the same ground point as the AC, and the two grounds rods should be tied together.  Always check manuals for specific grounding instructions though.

The simple explanation is in an ungrounded PV system, both positive and negative legs have to be fused. Just grounding one side of the battery is easier. Must have a single ground connection point. Additional ground rods may be connected at each building structure.

Another off grid grounding question: 

How to ground the propane tank connected via a 50 foot copper pipe buried inside a poly pipe conduit in a trench that will be backfilled?   I have a wire run in the trench to the tank, but am not sure of where to route the wire from the tank.

Our electrician told us that we should ground the propane tank legs to the AC panel ground. Our panel ground goes to a standard AC ground plate on the other side of the house via the typical large bare Cu ground wire.   

Since the tank is bolted to concrete foundations set in the ground it is "slightly grounded" already.  I gather that it probably won't create too much of a problem to have these two routes to earth and there isn't much that could be done to isolate the tank from the earth.

The only other option would be to connect the tank to the AC ground plate directly with another wire run to the plate.

LIkely, the object of grounding the tank to the panel ground or ground plate is so that the propane piping does not carry all of the induced current and currents resulting from differences in ground potential in the event of a nearby strike.  Since we have have plastic water pipes there is no other interconnection between plumbing or gas pipes and the electrical ground.  Our propane appliances are all connected via copper pipe.  The gas kitchen range has no electrical ground as it is a battery powered Unique spark ignition range.

Does anyone know the proper way to do this?

Thanks!

Copper is pretty much standard around here for propane, but there are some that use poly jacketed thinwall SS or even polymer lines (must be protected).  Some jurisdictions worry about the Sulphur in propane reacting with copper and require internally tinned propane lines.

Probably best to run tank ground to panel ground which goes to earth plate as that keeps area between copper pipe and ground wire small in my case, reducing induced potentials from circulating currents.

My understanding though is that generally you want to have the straightest, shortest path to ground to have the lowest inductance and best chance of current following grounding conductor as the leading edge of the strike is a high frequency component that reacts strongly to conductor self inductance.  Larger flatter conductors are better than small wires as this component of the current doesn't have much surface area to travel on in a small wire.

Graham Parkinson said:

Another off grid grounding question: 

How to ground the propane tank connected via a 50 foot copper pipe buried inside a poly pipe conduit in a trench that will be backfilled?   I have a wire run in the trench to the tank, but am not sure of where to route the wire from the tank.