An acquaintance of the pilot had expressed an interest in learning to fly the pilot’s newly purchased airplane, and the pilot agreed to provide a demonstration/introductory flight. The acquaintance had no prior flight experience. On the morning of the planned flight, the pilot discovered that the airplane battery was dead and decided to hand-prop the engine to start it. He instructed the passenger, seated in the left seat, how to operate the brakes and throttle. The engine was hand-propped and started successfully by the pilot, but the airplane began to move forward. The pilot was unable to board the airplane, and the passenger was unable to control or stop the airplane, or shut down the engine. The airplane departed its parking spot, crossed a runway, and struck a ground-mounted solar panel array located about 200 feet away. An eyewitness reported that the engine rpm increased and the airplane accelerated as it traversed the airport. The airplane sustained damage to the propeller, engine mount, firewall, windscreen, wings, and nose landing gear. Four solar panels were also damaged. The passenger stated that due to inexperience, he was unable to properly operate the brakes, but he could not recall whether he attempted to manipulate the throttle during the event.