Window solar panels: useful in one specific situation

Window solar panels work. They just don’t work well enough to matter for most people.

A decent 100W rooftop panel in direct sun might produce 300–400Wh on a good day. A window panel of the same rated wattage, mounted vertically behind glass, might produce 60–80Wh on that same day.

The use case where they make sense: renters who can’t mount panels externally and need to trickle-charge a small battery for phone/laptop power. For anything beyond that, the math stops working.