The Chief of Safety for the operator reported that the student pilot was on a solo flight in a glider and on the return leg to the airport when he noticed that he "seemed to be sinking quickly." While talking with his instructor over the radio and scanning for an open field, he decided to land on a street in a nearby neighborhood. While on approach, the glider struck tree tops and then a power line. Subsequently, the glider rolled to the right and the right wing struck the ground. The glider came to rest on the right side of the fuselage and the student pilot exited the glider. The glider sustained substantial damage to both wings and fuselage. The Chief of Safety reported that there were no preaccident mechanical failures or malfunctions with the glider that would have precluded normal operation. The automated weather observation system about 8 nautical miles from the accident site reported, about the time of the accident, wind calm, temperature 91°F, dew point 75°F, and altimeter setting 30.04 inches of mercury.