In this paper, Cyber-Physical-Social Systems (CPSS) explicitly refers to the collaborative robots for industry. Battery autonomy is a predominant factor that limits the operating time of a cobot. As a consequence, it becomes essential for it to minimize energy consumption while satisfying all its constraints including real-time ones. This paper reviews the current state-of-the-art relating to approaches for energy efficiency specifically dedicated to cobots. The analysis indicates that energy harvesting technology combined to energy-aware real-time schedulers and energy-efficient path planners could permit to build energy-neutral CPSS.