  Dark (hidden) photons are widely recognised as well motivated candidates for
physics beyond the standard model, and have been invoked for the solution of
several outstanding problems, including to account for the dark matter in the
universe. In this paper, we consider a simple model for dark photons, which is
coupled to ordinary matter only through kinetic mixing with ordinary photons.
Within this framework, we calculate the flux of solar dark photons on Earth and
revise the potential to detect it with the next generation of axion
helioscopes, particularly with the International AXion Observatory (IAXO). This
paper extends on previous theoretical analyses in two main ways. Firstly, it
includes a more complete analysis of the possible sources of dark photons from
the sun, including the contribution of the solar magnetic field and of nuclear
processes, and secondly it includes predictions on the parameter space
accessible in the gas-filled phase of IAXO.
