  We provide a thermodynamically consistent description of energy, charge and
spin transfers in a thermoelectric quantum-dot spin valve in the collinear
configuration based on nonequilibrium Green's function and full counting
statistics. We use the fluctuation theorem symmetry and the concept of entropy
production to characterize the efficiency with which thermal gradients can
transduce charges or spins against their chemical potentials, arbitrary far
from equilibrium. Close to equilibrium, we recover the Onsager reciprocal
relations and the connection to linear response notions of performance such as
the figure of merit. We also identify regimes where work extraction is more
efficient far then close from equilibrium.
