  We consider the capacity region of a $K$-user multiple access channel (MAC)
with energy harvesting transmitters. Each user stores and schedules the
randomly arriving energy using an energy buffer. Users can also perform energy
cooperation by transmitting energy to other users or receiving energy from
them. We derive the capacity region of this channel and show that 1) the
capacity region coincides with that of a traditional $K$-user Gaussian MAC with
energy cooperation, where the average power constraints are equal to the
battery recharging rates of the energy harvesting case; 2) each rate on the
capacity region boundary can be achieved using the save-and-forward power
control and a fixed energy cooperation policy.
