Enhanced generation, energy storage and transmission expansion planning for renewables with operational flexibility through unit commitment

In this paper, we investigate the impact of operational flexibility in planning context considering four operational models; Economic Dispatch (ED), ED with ramping, Unit Commitment (UC) and UC with convex relaxation (UC-C). Using these operational models and three test cases; 6, 14, 24 bus systems, we quantify the error that occur due to exclusion or approximation of flexibility constraints. Numerical analysis reveals that this error in total cost can be as high as 8% and that approximated operational models such as ED, ED+R or UC-C could provide sub-optimal solutions with inefficient capacity mix. Even though the impact of sub-optimal solutions is minor in the observed set of experiments, this could be problem specific. As these solutions are driven by multiple factors such as network topology, candidate availability and other input parameters, a constrained system with limited options is more likely to be affected by approximated operational flexibility.