  The flux of hypothetical "hidden photons" from the Sun is computed under the
assumption that they interact with normal matter only through kinetic mixing
with the ordinary standard model photon. Requiring that the exotic luminosity
is smaller than the standard photon luminosity provides limits for the mixing
parameter down to 10^-14, depending on the hidden photon mass. Furthermore, it
is pointed out that helioscopes looking for solar axions are also very
sensitive to hidden photons. The recent results of the CAST collaboration are
used to further constrain the mixing parameter at low masses m<1 eV where the
luminosity bound is weaker. In this regime the solar hidden photon flux has a
sizable contribution of longitudinally polarized hidden photons of low energy
which are invisible for current helioscopes.
