One of the major problems with non-vertical windows of every sort is that any dirt which accumulates blocks the normal drainage channels which they incorporate. This frequently leads to a dam effect whereby rainwater is trapped and overflows the lip of the window -into the building itself.
These windows are usually on rooves or out of sight and the problem is not dealt with until water ingress has caused expensive damage.
Today’s invention is a simple device which will sweep dirt from an unattended window before this situation arises. I noticed, when driving my car in winter, that a substantial block of snow was spinning on the rear window: in the grip of a stable vortex (the real streamlines don’t resemble those in the brochure, it seems).
I propose to equip all skylight-type windows with a thin disc of translucent plastic (PTFE, with a small boss on the rear face perhaps would minimise friction).
Powered only by the wind, this would carry some small vanes on the outer surface and be constrained to spin across the face of the window, spitting dirty water off before any residual clag could be deposited.