I found a few postmortems related to failover between power sources: it’s one thing to have UPS, generators and utility power, but you do have to switch cleanly between them.
2012, amazon:
2011: colo4
2005: serverbeach
http://forums.serverbeach.com/showthread.php?5123-Post-Mortem-of-Virginia-Power-outage
2013: superbowl (not quite the same, I think)
http://www.reuters.com/article/2013/02/08/entergy-superbowl-idUSL1N0B83N620130208