  Most evolutionary robotics studies focus on evolving some targeted behavior
without taking the energy usage into account. This limits the practical value
of such systems because energy efficiency is an important property for
real-world autonomous robots. In this paper, we mitigate this problem by
extending our simulator with a battery model and taking energy consumption into
account during fitness evaluations. Using this system we investigate how energy
awareness affects the evolution of robots. Since our system is to evolve
morphologies as well as controllers, the main research question is twofold: (i)
what is the impact on the morphologies of the evolved robots, and (ii) what is
the impact on the behavior of the evolved robots if energy consumption is
included in the fitness evaluation? The results show that including the energy
consumption in the fitness in a multi-objective fashion (by NSGA-II) reduces
the average size of robot bodies while at the same time reducing their speed.
However, robots generated without size reduction can achieve speeds comparable
to robots from the baseline set.
