According to the pilot of the glider, he released from the tow airplane at 2,000 feet above ground level and turned to the south toward a ridge in search of orographic lift. The pilot reported that he found "weak lift" in the vicinity of the ridge and when he reached the south end of the ridge, he turned back to the departure airport because he could not maintain altitude. The pilot recalled that while in route back to the airport, he encountered sink, descended below the glide path to the airport and initiated an off airport landing to a large field. The pilot reported that during approach, he over flew a set of powerlines that were perpendicular to his glide path and noticed a second set of powerlines ahead that were also perpendicular to his glide path. The pilot recalled that he turned to avoid the powerlines, encountered more sink, leveled the wings and landed hard in the field. The glider sustained substantial damage to the tailboom. The pilot reported that there were no mechanical malfunctions or anomalies during the flight that would have prevented normal flight operations.