The cold hard fact is that excel is not a very good tool for project finance modelling. This is because of natural circular references that occur in project finance structuring. For example, Interest During Construction (IDC) depends on debt which can depend on project cost. But IDC is a component of project cost. This is a classic circular reference.
The copy and paste and the iteration button fail miserably in solving circular references. Excel loses its ability to perform sensitivity analysis, target contract bids, and quickly demonstrate the effects of alternative structuring parameters.
The good news is that you can fix the circular reference with a user defined function (UDF).
The better news is the UDF can be used as a sophisticated method to audit many of the equations in your model.