  We consider the repulsive Hubbard model on a class of lattices or graphs for
which there is a large degeneracy of the single particle ground states and
where the projector onto the space of single particle ground states is highly
reducible. This means that one can find a basis in the space of the single
particle ground states such that the support of each single particle ground
state belongs to some small cluster and these clusters do not overlap. We show
how such lattices can be constructed in arbitrary dimensions. We construct all
multi-particle ground states of these models for electron numbers not larger
than the number of localized single particle eigenstates. We derive some of the
ground state properties, esp. the residual entropy, i.e. the finite entropy
density at zero temperature.
