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.
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