  In this paper, we address the long-term system's requirement reserve sizing
due to the high-level of variable renewable energy (VRE) sources penetration,
inside the expansion planning model. The increase in the insertion of this kind
of energy source will also bring an increase in the reserve requirements. A
higher requirement will be translated into additional costs to the system since
the system operator will need to allocate generators for reserve purposes. The
VRE sources implicitly cause these costs, so besides the investment cost, the
expansion planning models should consider those costs on the expansion decision
process. The methodology proposed here aims to provide a probabilistic and
dynamic evaluation of the forecast errors of VRE sources generation,
translating these errors into the system's requirement reserve. This evaluation
is done inside the expansion planning optimization model, treating the reserve
requirement as an endogenous variable. Finally, a real case study of the
Mexican system is presented, so that we can analyze the results of the
methodology and the impacts of considering the reserve requirement along with
the expansion planning decision.
