Place sweet potato slices in a 5 to 6 quart slow cooker. In a small bowl, stir together orange juice concentrate, brown sugar, salt, sage, and thyme. Pour over sweet potato slices; toss to coat. Dot with butter. Cover and cook on low-heat setting for 5 to 6 hours or on high-heat setting for 2½ to 3 hours. Before serving, stir to coat with orange juice mixture and sprinkle with crumbled bacon.