  This letter introduces a method to manage energy storage in electricity
grids. Starting from the stochastic characterization of electricity generation
and demand, we propose an equation that relates the storage level for every
time-step as a function of its previous state and the realized surplus/deficit
of electricity. Therefrom, we can obtain the probability that, in the next
time-step: (i) there is a generation surplus that cannot be stored, or (ii)
there is a demand need that cannot be supplied by the available storage. We
expect this simple procedure can be used as the basis of electricity
self-management algorithms in micro-level (e.g. individual households) or in
meso-level (e.g. groups of houses).
