The advanced grid module will be available with HOMER Pro 3.1 on January 19, 2015. Initially, it will be similar to the advanced grid in HOMER 2, with a few changes to the way structured rates (time of use charges) are defined to make it more flexible and easier to use. It will be possible to schedule a grid outage with the options in the structured rates, but such outage would occur the same time every day.
Random outages will be added in the future -- probably in version 3.2 planned for release in April 2015. I can let you in on a secret, though -- once you have version 3.1 (Jan 2015), you can use "Real Time Rates" to simulate grid outage. Real time rates works by importing a time series (8,760 lines, one for each hour of the year, in a text file with two values per line: power price and sellback rate). If you specify a value of "-999.0" for the grid power price in that file in any row, the grid will be turned off for that corresponding time step.
Until version 3.1, we recommend that users who need advanced grid features continue to use HOMER 2.