According to the pilot of the motorized glider, he was flying at an altitude of 6,000 feet en route to his home airport when he noted an episode of turbulence on the avionics logs for his flight path. He climbed to an altitude of 6,500 feet and continued to his destination; however, the glider subsequently encountered severe turbulence that lasted for a few seconds. The pilot heard a cracking noise and thought it was a quart of oil loose in the baggage compartment. He continued the flight and landed at his home airport uneventfully. While cleaning the glider after the flight, the pilot noted substantial damage to the empennage, which included a 12-inch crack to the composite structure under the right side of the vertical stabilizer. The pilot reported no mechanical malfunctions or failures that would have precluded normal operation prior to the turbulence encounter and noted that the glider remained controllable as normal after the turbulence encounter.