  We analyze standard theoretical models of solar energy conversion developed
to study solar cells and photosynthetic systems. We show that the assumption
that the energy transfer to the reaction center/electric circuit is through a
decay rate or "sink", is in contradiction with the second law of
thermodynamics. We put forward a thermodynamically consistent alternative by
explicitly considering parts of the reaction center/electric circuit and by
employing a Hamiltonian transfer. The predicted energy transfer by the new
scheme differs from the one found using a decay rate, casting doubts on the
validity of the conclusions obtained by models which include the latter.
