  We assess the detectability of baryonic acoustic oscillations (BAO) in the
power spectrum of galaxies using ultra large volume N-body simulations of the
hierarchical clustering of dark matter and semi-analytical modelling of galaxy
formation. A step-by-step illustration is given of the various effects
(nonlinear fluctuation growth, peculiar motions, nonlinear and scale dependent
bias) which systematically change the form of the galaxy power spectrum on
large scales from the simple prediction of linear perturbation theory. Using a
new method to extract the scale of the oscillations, we nevertheless find that
the BAO approach gives an unbiased estimate of the sound horizon scale.
Sampling variance remains the dominant source of error despite the huge volume
of our simulation box ($=2.41 h^{-3}{\rm Gpc}^{3}$). We use our results to
forecast the accuracy with which forthcoming surveys will be able to measure
the sound horizon scale, $s$, and, hence constrain the dark energy equation of
state parameter, $w$ (with simplifying assumptions and without marginalizing
over the other cosmological parameters). Pan-STARRS could potentially yield a
measurement with an accuracy of $\Delta s/s = 0.5-0.7 % $ (corresponding to
$\Delta w \approx 2-3% $), which is competitive with the proposed WFMOS survey
($\Delta s/s = 1% $ $\Delta w \approx 4 % $). Achieving $\Delta w \le 1% $
using BAO alone is beyond any currently commissioned project and will require
an all-sky spectroscopic survey, such as would be undertaken by the SPACE
mission concept under proposal to ESA.
