The risk of electricity outages caused by natural disasters, cyberattacks, or physical attacks seems to increase, despite high standards for security of supply in Western Europe. At the same time the importance of electricity for public, economic, and social well-being has increased during the last decade with accumulative dependencies on IT-systems. Proven methods of blackout prevention or mitigation focus on short period of power outages experienced by households and business in the local distribution network. The more unlikely event of a large-scale blackout for a period of days brings traditional methods including emergency diesel generators sets to its limits. Renewable energy microgrids can improve the resilience of critical infrastructure, assets with greatest importance for the public and national security, and reduce the impact of blackouts. Under certain conditions the additional investment in distributed energy resources, storage and microgrid management systems could contribute to operational improvements. For a hypothetical military base of the Austrian Armed Forces with critical infrastructure the thesis investigates under which conditions it is feasible to build and operate a renewable energy microgrid to provide sufficient generation for its electrical load and remain islanded in the event of blackout for ten days and to reduce operational cost during standard grid-connected operation.