What are the dangers of sharing the AC and DC grounds on a charger/inverter system powered by a backup generator?
Grounds are the negative from the batteries (DC) and the dedicated ground from the inverter.
Usually when I've done a solar system I don't ground the negative of the battery
The solar panels normally have a ground connection - and the controller
Grounds should normally all be tied together then down to the earth rod
usually in a star configuration - ie all equipment grounded seperately back to the main ground point
not looped from one item to another
Here are links to the wiring diagrams for my PV system.
rough sketches
http://countryplans.com/smf/index.php?topic=6059.msg119820#msg119820
neater drawing
http://countryplans.com/smf/index.php?topic=6059.msg120194#msg120194
Introducing a generator into the system can be a problem at times. How it is grounded or not depends on how the generator manufacturer designed the generator system. There is some info on that someplace here but I can't find the link right now d* and have to go do my 4 hours of real work today.
All equipment grounds should be connected as UK indicates. That way any one piece of equipment can be removed from the system and not interrupt the path to ground for any other piece of equipment. Using buss bars makes connecting easier.
My inverter has one chassis ground, I tied that to the buss bar that serves all the DC equipment. That is connected to two earth grounds; two because I wanted to measure the resistance in the ground and you need two rods for that. They are connected together. That's okay. There should not be two ground rods connected to two different pieces of equipment that are also connected by a ground wire. Hope that is clear.
My ground off the AC service panel is separate. That's partly because it was installed first and partly because I was unsure of connecting it to the DC side, and partly because the DC rods are at the other side of the cabin.
IIRC, the issue at the generator stems from whether or not the generator has the ground and the neutral bonded within the generator system. If it is that can be a problem if the service panel the generator is connected to is also bonded, neutral to ground within the panel. Only one of those bonds permitted by NEC.
Gotta go.