One of the key elements of a VPPA financial analysis is the estimate of future wholesale electricity prices at the point of sale. These future prices can then be compared with the expected PPA price to evaluate the overall VPPA profitability for your city. This process should ideally be conducted by an expert in energy markets; further, since modeling future energy prices is a notoriously difficult thing to do accurately, you may want to consider reviewing multiple forecasts and/or evaluating several scenarios.
There are a few common methods to estimate how future energy prices may change over time: