Exterior Day Rear Projection

[Lluis Moreno]

Good evening from Spain! 

I have a shooting in two weeks where they want a rear projection, it's an exterior day and we have a 6500 lumens projector and a 300x225 cm retroprojectable screen. Will I need more lumen output in the projector in order to have my image sharp?

I've done this before but not in shootings, just in live events, where the projection quality is not mandatory to be clean and sharp. 

I will pack some additional large black cloth to try blocking sun going through the screen, but I'd appreciate some more tricks! 

Thanks a lot and happy new year!