I. INTRODUCTION

II. THE BIG PICTURE

III. ENERGY CONSUMPTION OF NETWORK ELEMENTS
A. Base stations
B. End devices

IV. ENERGY EFFICIENCY TECHNIQUES
A. Network energy efficiency
B. End-devices

V. WIRELESS POWER TRANSFER
A. Wireless Energy Transfer
B. Simultaneous Wireless Information and Power Transfer

VI. ENERGY COOPERATION
A. Energy sharing
B. Communication cooperation

VII. ENERGY TRADING
A. A review of energy trading in Smart Grids
B. Cellular networks meet SG

VIII. CONCLUSIONS