This paper addresses the challenge of designing a cellular network that can meet a dynamic range of offered traffic loads at a low energy level. Cellular networks are conventionally deployed to meet a high traffic load and can be energy inefficient at lower loads. The paper proposes a novel cell expansion technique that can reduce total energy consumption by up to 46% depending on the offered load. Dynamic cell expansion switches off a certain pattern of cell-sites in accordance with traffic load and allows neighbouring cells to compensate by expanding their coverage. A key novelty is achieving this via creating inner and outer cell regions using vertical sectorization and adaptively tilting outer cell antennas to expand and contract cell coverage. Furthermore, a management service is proposed to handle contention between competing cells. The gains achieved compared to existing techniques is 22% higher and the results of this paper can have a profound impact both on the operators' revenue and global environment, reducing up to 11 power plants world wide.