Context : Aims : The statistical equilibrium of neutral and ionised silicon in the solar photosphere is investigated . Line formation is discussed and the solar silicon abundance determined . Methods : High-resolution solar spectra were used to determine solar \log gf \varepsilon _ { Si } values by comparison with Si line synthesis based on LTE and NLTE level populations . The results will be used in a forthcoming paper for differential abundance analyses of metal-poor stars . A detailed analysis of silicon line spectra leads to setting up realistic model atoms , which are exposed to interactions in plane-parallel solar atmospheric models . The resulting departure coefficients are entered into a line-by-line analysis of the visible and near-infrared solar silicon spectrum . Results : The statistical equilibrium of Si i turns out to depend marginally on bound-free interaction processes , both radiative and collisional . Bound-bound interaction processes do not play a significant role either , except for hydrogen collisions , which have to be chosen adequately for fitting the cores of the near-infrared lines . Except for some near-infrared lines , the NLTE influence on the abundances is weak . Conclusions : Taking the deviations from LTE in silicon into account , it is possible to calculate the ionisation equilibrium from neutral and ionised lines . The solar abundance based on the experimental f -values of Garz corrected for the Becker et al. ’ s measurement is 7.52 \pm 0.05 . Combined with an extended line sample with selected NIST f -values , the solar abundance is 7.52 \pm 0.06 , with a nearly perfect ionisation equilibrium of \Delta \log \varepsilon _ { \odot } ( { Si \textsc { ii } } / { Si \textsc { i } } ) = -0.01 .