  We study, by means of numerical simulations and analysis, the details of the
accretion process from a disc onto a binary system. We show that energy is
dissipated at the edge of a circumbinary disc and this is associated with the
tidal torque that maintains the cavity: angular momentum is transferred from
the binary to the disc through the action of compressional shocks and viscous
friction. These shocks can be viewed as being produced by fluid elements which
drift into the cavity and, before being accreted, are accelerated onto
trajectories that send them back to impact the disc. The rate of energy
dissipation is approximately equal to the product of potential energy per unit
mass at the disc's inner edge and the accretion rate, estimated from the disc
parameters just beyond the cavity edge, that would occur without the binary.
For very thin discs, the actual accretion rate onto the binary may be
significantly less. We calculate the energy emitted by a circumbinary disc
taking into account energy dissipation at the inner edge and also irradiation
arising there from reprocessing of light from the stars. We find that, for
tight PMS binaries, the SED is dominated by emission from the inner edge at
wavelengths between 1-4 and 10 $\mu$m. This may apply to systems like CoRoT
223992193 and V1481 Ori.
