  In the context of driven diffusive systems, for thermodynamic transformations
over a large but finite time window, we derive an expansion of the energy
balance. In particular, we characterize the transformations which minimize the
energy dissipation and describe the optimal correction to the quasi-static
limit. Surprisingly, in the case of transformations between homogeneous
equilibrium states of an ideal gas, the optimal transformation is a sequence of
inhomogeneous equilibrium states.
