The student pilot reported that the flight began as a dual instruction flight with his flight instructor. They performed 6 or 7 landings, which included simulated engine failures. The instructor then exited the airplane and the student pilot performed 2 more takeoffs and landings to a full stop without incident. On the third solo takeoff the left wing dipped and contacted the ground. The airplane then began to skid to the left, off the runway to a stop. The airplane sustained substantial damage to the firewall. The student pilot listed no mechanical failure or malfunction of the airplane.