[hinkley]

Years ago I fantasized about making a transformer designed to pass through a window. One coil on the outside, one on the inside. Unfortunately I don’t think you can split the core of a transformer and still get anywhere near the efficiency

Also more recently I learned that these things can vibrate. Which would not be good for a window.

You’d be better off passing a wire ribbon around the sash.

[Animats]

Split transformers for power transmission exist, but are rare. Here's a 3 KW system used for non-contact charging of electric forklifts, industrial mobile robots, and such.[1] 93% efficiency claimed. Probably not worth the trouble just to get power through a window.

[1] https://www.wiferion.com/us/

[hinkley]

Witricity is trying to do the same with electric cars.