A fast and accurate algorithm for the computation of effective electri
c and mathematically equivalent properties of composites with nonsmoot
h interfaces is reported. The algorithm is based on an integral equati
on reformulation of the electrostatic partial differential equation an
d a fast hierarchical technique for potential field evaluation. In a n
umerical example, 200 large and strongly inhomogeneous aggregates of r
andomly overlapping disks are solved with a relative error of 0.0005.