  With the invention of new far-infrared (FIR) and radio mm and sub-mm
instruments (DESIR on SMESE satellite, ESO-ALMA), there is a growing interest
in observations and analysis of solar flares in this so far unexplored
wavelength region. Two principal radiation mechanisms play a role: the
synchrotron emission due to accelerated particle beams moving in the magnetic
field and the thermal emission due to the energy deposit in the lower
atmospheric layers. In this contribution we explore the time-dependent effects
of beams on thermal FIR and radio continua. We show how and where these
continua are formed in the presence of time dependent beam heating and
non-thermal excitation/ionisation of the chromospheric hydrogen plasma.
