Grid-tied only vs Battery Backup Question, when grid goes down

 I've gotten the impression that if you have a grid-tied only system, then if
the grid goes down, your house also goes down - even on a bright sunshiny
day when the PV is putting out a lot of juice.  Is this true?  Is it true
for some inverters and not others?

Also, I've looked at setup designs, such as one at homepower magazine
http://www.homepower.com/basics/solar/   Since the batteries are between the
PV and the inverter, how does the invertor know if it's getting power from
the batteries or from the PV?  Or am I wrong in thinking that the house
stays up with battery backup when the grid goes down?

Thanks.

  Here's a quote from the installation guide for the SMA 6000U inverter:

"Note: Anytime the AC power is disconnected from the inverter, either
manually or as a result of an AC disturbance, the inverter will wait 5
minutes after the AC power has been restored to reconnect."  So if the
grid goes down, the house goes down.

I assume it applies to any inverter.  "The inverter has to sync itself
to the current line voltage and frequency supplied by the grid. By
code, it has to match the line voltage."  So that's why the inverter
goes down.  Doug, I apologize for plagiarizing the last quote from
you, but at least I'm crediting you :)

How does the inverter know where the power is coming from?  Why should
it care?  The house will stay up with battery backup when the grid
does down.  Provided you have enough batteries.


magazinehttp://www.homepower.com/basics/solar/  Since the batteries are between
the

 
I see that there's a problem with that last sentence.  Why does a
"Grid-Intertied Solar-Electric Systems with Battery Backup" stay on
when the grid goes out if the inverter ceases to function when the
grid goes out?  Hmm -- I'm sure a light bulb will go on soon, but
probably in someone else before me.


magazinehttp://www.homepower.com/basics/solar/Since  the batteries are between the

 The grid-tied inverter section ***disconnects***.

 

All inverters can tie to the grid.  It's just a question of how.
By definition a "Grid-Tie" inverter doesn't have batteries.  So
when it's generating more power than the home uses, it pushes the
excess out onto the grid.  This is a problem when the grid goes
down since it can energize the outside wires.  This is a safety
hazard to crews working on the lines. So by code, they have to
shut down.  Under certian conditions they can be "islanded".
That is, opperated separetly from the grid.

A conventional system doesn't push power back into the grid.
If it is connected to the grid, it is only to provide suplemental
power for cloudy days.  Typicly excess power is stored in batteries.


It doesn't, it doesn't care, and it doesn't matter.


See comments above.