Capacity planning of carbon-free microgrid with hydrogen storage considering robust short-term off-grid operation

Carbon-free microgrids (CFMs) composed of renewable energy and hydrogen energy storage systems (HESS) are a promising solution for low-carbon energy systems. However, when CFMs are off-grid, their reliability is frequently questioned, especially when renewable energy (RE) outputs are extremely low. To reduce the total cost and improve the off-grid reliability, this paper proposes a two-stage robust planning model for CFM with renewable energy and HESS that considers both grid-connected (GC) and short-term (several days) off-grid (OG) statuses. In the GC status, the target is to minimize the system expenses; while in the OG status, the optimization goal is not to lose the important loads in a short period of time considering the worst realization of days. The Nested-C&CG algorithm is employed to solve the robust planning model of CFM. Additionally, a new uncertainty set that takes terrible days into account for RE and loads is presented to make the decision robust. Finally, the numerical analysis based on the case studies shows that the HESS in CFM has the ability to support loads in OG status for a week. And the total cost of the CFM using HESS and batteries can be reduced by 11.83% compared with that using only batteries. In addition, the planning results with robust optimization can guarantee that all the important loads are satisfied.