  Transport properties of granular systems are governed by Coulomb blockade
effects caused by the discreteness of the electron charge. We show that, in the
limit of vanishing mean level spacing on the grains, the low-temperature
behavior of 1d and 2d arrays is insulating at any inter-grain coupling
(characterized by a dimensionless conductance g.) In 2d and g>>1, there is a
sharp Berezinskii-Kosterlitz-Thouless crossover to the conducting phase at a
certain temperature, T_{BKT}. These results are obtained by applying an
instanton analysis to map the conventional `phase' description of granular
arrays onto the dual `charge' representation.
