The generation expenditures vary in each of the scenarios change for at least three  (1) the size of the allowance bank made possible by early reductions driven, in part, by program spending prior to the introduction of the caps; (2) the varying levels of demand for electricity over time, resulting in changes in the overall mix of generation resources; and, (3) the gradual reduction in the banked allowances available for withdrawal necessitating additional actions to reduce emissions.