Has anyone ever used a roll of Solar screen on windows for cutting down the light instead of ND gel rolls, such as Rosco? I've been told that there is a possibility of moires in the mesh. I want to bring down the light coming through the glass of these back patio doors, but preferably on the cheap. Anyone with experience using the aforementioned screens (the kind you'd find, say, at Lowe's)?

Moire issues in these situations is largely a function of the depth of field you work with.

Screened windows that are in sharp focus often DO cause moire pattern problems.

If you can throw the screen even slightly out of focus then the problems disappear.

So the distance from the camera to the screen, compared to the camera to subject distence, and how much you can manage to open your iris to force a shallow depth of field while balancing the exposure of your subject and the window are the primary concerns.

Good luck.