  In this Letter we report on the results of our search for photons from a U(1)
gauge factor in the hidden sector of the full theory. With our experimental
setup we observe the single spectrum in a HPGe detector arising as a result of
the photoelectric-like absorption of hidden photons emitted from the Sun on
germanium atoms inside the detector. The main ingredient of the theory used in
our analysis, a severely constrained kinetic mixing from the two U(1) gauge
factors and massive hidden photons, entails both photon into hidden state
oscillations and a minuscule coupling of hidden photons to visible matter, of
which the latter our experimental setup has been designed to observe. On a
theoretical side, full account was taken of the effects of refraction and
damping of photons while propagating in Sun's interior as well as in the
detector. We exclude hidden photons with kinetic couplings chi > (2.2 x
10^{-13}- 3 x 10^{-7}) in the mass region 0.2 eV < m_gamma' < 30 keV. Our
constraints on the mixing parameter chi in the mass region from 20 eV up to 15
keV prove even slightly better then those obtained recently by using data from
the CAST experiment, albeit still somewhat weaker than those obtained from
solar and HB stars lifetime arguments.
