  Current risk assessment ignores the stochastic nature of energy storage
availability itself and thus lead to potential risk during operation. This
paper proposes the redefinition of generic energy storage (GES) that is allowed
to offer probabilistic reserve. A data-driven unified model with exogenous and
endogenous uncertainty (EXU & EDU) description is presented for four typical
types of GES. Moreover, risk indices are proposed to assess the impact of
overlooking (EXU & EDU) of GES. Comparative results between EXU & EDU are
illustrated in distribution system with day-ahead chance-constrained
optimization (CCO) and more severe risks are observed for the latter, which
indicate that system operator (SO) should adopt novel strategies for EDU
uncertainty.
