  In this paper, a method to evaluate the flexibility of aggregates of domestic
electric water heaters is proposed and applied to the Italian case. Flexibility
is defined as the capability of the aggregate to vary its power demand for a
given time interval. The evaluation method consists of a Monte Carlo analysis,
that uses the thermal model of electric water heaters and a proper elaboration
of the external inputs, such as ambient and cold water temperatures, and hot
water demand. The case of large aggregates defined along the Italian territory
has been studied showing the dependence of flexibility on seasons and on time.
