  The potential of the Surface Brightness Fluctuations (SBF) method to
determine the membership of dwarf elliptical galaxies (dEs) in nearby galaxy
clusters is investigated. Extensive simulations for SBF measurements on dEs in
the I-band for various combinations of distance modulus, seeing and integration
time are presented, based on average VLT FORS1 and FORS2 zero points. These
show that for distances up to 20 Mpc (Fornax or Virgo cluster distance),
reliable membership determination of dEs can be obtained down to very faint
magnitudes -10<M_V<-12 mag (25 mag / arcsec^2) within integration times of the
order of 1 hour and with good seeing. Comparing the limiting magnitudes of the
method for the different simulated observing conditions we derive some simple
rules to calculate integration time and seeing needed to reach a determined
limiting magnitude at a given distance modulus for observing conditions
different to the ones adopted in the simulations. Our simulations show a small
offset of the order of 0.15 mag towards measuring too faint SBF. It is shown
that this is due to loss of fluctuation signal when recovering pixel-to-pixel
fluctuations from a seeing convolved image. To check whether our simulations
represent well the behaviour of real data, SBF measurements for a real and
simulated sample of bright Centaurus Cluster dEs are presented. They show that
our simulations are in good agreement with the achievable S/N of SBF
measurements on real galaxies.
