The room block has now closed and the hotel may be full.  As you know, cancellations occur.  I advise you to call and you may get in.  If not, I would use one of the travel sites to see what you can get nearby.  Expedia, Hotels, etc. may be able to help you.

The host property for the Clearwater Clean Energy Conference is the Sheraton Sand Key.  Sand Key is one of the 20 Best U.S. Beaches, according to many travel and tourism organizations.

A personalized Web site for Clearwater Clean Energy Conference occurring
 (June 3 to 7, 2018) is listed below.

https://www.starwoodmeeting.com/events/start.action?id=1804117026&key=2C7DFCFC

The Sheraton Sand Key is located at 1160 Gulf Boulevard, Clearwater, FL  33767; phone:  727-595-1611.  Please use the code CE29AA when you call in.  You may also FAX:  727-596-1711.