Yes, this PowerCalc spreadsheet is a 'rough & ready' aid.
Before you enter a number into the 'wind' column, you have to assess the 'Effective' windspeed based on YOUR riding direction and the WIND direction.
Firstly, work out your 'Angle of attack', and then multiply the WIND speed by the Cosine of the Angle of attack.
So if it IS a true headwind, the wind will be 1.00 x windspeed, and if its 45 degrees attack, the wind will be 0.71 of the reported wind speed.
You power requirement is the appropriate value on the 'cook book' RoadLoad curve for the resultant windspeed added to your roadspeed.
PowerCalc spreadsheet has some 'generic' values for Xsection A, Cd and mass; and it has 'generic' Roadload curves for these examples.
You are encouraged to enter your own Xsection A, Cd and mass, but this requires some further data collection I have described on another thread many months ago.
PowerCalc is a good starter for Brainiacs.