Annual Energy Cost Escalation

This calculation for LEED is typically based on the virtual rate from the energy model if you are pursuing Option 1 for EAp2/EAc1. This is based on the rate used without any escalation. Technically the PPA does not even enter into the equation as the "savings" are solely based on avoided energy cost.

In PPA part of the cost that is not reflected in the rate paid is the land use agreement. The seller/owner is required to maintain land rights to allow operation, access and use of a PPA project.

Use the virtual rate as suggested by Marcus Sheffer. That is the only option that, more or less, accounts for costs that are not obvious in a PPA.

I should note, that for a recent project, certified as LEED NC GOLD, a few months ago, we used TOU (Time of use) for renewables rather than virtual rate for electricity.

You should only spend the effort on figuring out TOU for on-site renewables, if you are just below the threshold to earn an additional energy efficiency point. Otherwise, claiming TOU does not make a significant difference. In the case of the project needed the extra point because the LEED review was exceptionally onerous.

If you don't use the virtual rate you will need to make the case to the reviewer that another rate is more appropriate to your situation as Hernando suggests. If you feel that another rate is more appropriate I would suggest that you calculate it both ways and if it makes a substantial difference, justify the deviation. This way the reviewer can see the calculation based on the virtual rate and will not ask you to redo the calculation if they do not agree with your justification for another rate.