Abstract: A method for determining a power outage probability of an electrical power grid for a time period, the method comprising the following steps carried by a processor of a data processing unit: dividing the time period into several time intervals, determining a power generation capacity of a power generation facility and an energy storage unit size for an energy storage unit for said time period, determining an effective load unit demand for each time interval from a load unit demand of a load unit for each time interval, and computing the power outage probability using a grid parameter that comprises the power generation capacity, the energy storage unit size and the effective load unit demand, wherein the grid parameter is optimized for its maximum value with respect to all time intervals of the time period