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 .
Electricity demand changes over time .