Hi Mike,
The PBI amount variables are not available as inputs for stochastic simulations because they are arrays of values rather than a single value. Any input variable in the SAM user interface that has a little blue and grey button next to it is one that you can assign either a single value or more than one value. For example, SAM allows you to assign either a single value to the PBI $/kWh amount, or a value to specific years in the analysis period. The algorithm that generates input distributions for the stochastic simulations can only work with single values, so any input that can be entered as an array with multiple values is excluded from the list of available values. Other examples of those inputs are degradation rate, PTC amount, O&M costs, etc. Parametric simulations are more flexible and do not have that limitation.
We are considering making some improvements to the parametric and stochastic simulations, and will keep your comments in mind as we do.
Best regards,
Paul.