GodMark2
Master Poster
Three words.
External isolation switch.
Our residential solar has a number of them fitted, including a smart switch that the power company can operate by sending signals down the gird.
Initially I was a little nonplussed when told that if there is a blackout, our brand new household solar system would not be of any use to us.
The explanation is, of course, quite logical.
The power company shuts down residential solar systems so that generated power from them is not fed to the grid while work needs to be done.
Isolation switches disconnect you from the mains. If you have no batteries (or limited load-balance batteries), this will put your PV system into a 'down' mode, unless it has provisions for 'critical systems' output that never shuts down. If you have full storage batteries, it will happily continue producing power to the house, even while the mains are disconnected.
http://www.solarabcs.org/utilitydisconnect/pdfs/ABCS-05_studyreport.pdf
http://www.aeesolar.com/grid-tied-solar-systems-with-backup-power