On July 26, 2018, about 1900 eastern daylight time, a Cessna 150B, N1193Y, was substantially damaged during a precautionary landing in Matthews, North Carolina. The student pilot was not injured. The airplane was operated by the pilot under the provisions of Title 14 Code of Federal Regulations part 91 as a solo-instructional flight. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight that originated at Wilgrove Air Park (8A6), Charlotte, North Carolina at 1810.The pilot reported that the preflight procedures, taxi, takeoff, and departure were uneventful. The fuel tanks were full and no water was noted. About 40 minutes into the flight, about 1,800 feet above mean sea level, he noticed that the airplane was "sluggish" and would not "maintain lift." The engine indications were normal with no sputtering or hesitation noted. He applied carburetor heat and the engine speed dropped about 300 rpm. The airplane was still sluggish, so he turned off the carburetor heat. Since the airplane continued to fly sluggishly, the pilot decided to land the airplane in a grass field adjacent to a church. During the landing rollout, the airplane nosed over and came to rest, inverted. The pilot reported in a postaccident interview and a written statement that there were no mechanical issues with the airplane in flight, and the engine would produce 2,750 rpm at full power. He also reported that the high ambient temperature (100°F) and the full fuel tanks may have contributed to the airplane's sluggishness. An inspector with the Federal Aviation Administration (FAA) responded to the accident site and examined the wreckage. He reported that the wings and fuselage sustained structural damage. His examination of the airframe and engine did not reveal evidence of a mechanical malfunction or failure that would have precluded normal operation. The pilot held a student pilot certificate and reported 3.1 hours of dual instruction and 15 hours of solo flight time. He did not have an instructor's endorsement to operate the airplane in solo flight. The FAA inspector reviewed his pilot logbook and reported that there were "severe training deficiencies."