  We study thermal conductance and thermopower of a metallic single-electron
transistor beyond the limit of weak tunnel coupling. Employing both a
systematic second-order perturbation expansion and a non-perturbative
approximation scheme, we find, in addition to sequential and cotunneling
contributions, terms that are associated with the renormalization of system
parameters due to quantum fluctuations. The latter can be identified by their
logarithmic temperature dependence that is typical for many-channel Kondo
correlations. In particular, the temperature dependence of thermopower, which
provides a direct measure of the average energy of transported particles,
reflects the logarithmic reduction of the Coulomb-blockade gap due to quantum
fluctuations.
