Since it’s all classified o honestly don’t have a clue. But passive radar is also a thing and something that the Swedish defense industry is fairly good at https://en.wikipedia.org/wiki/Passive_radar.
It probably has more to do with the fact that solar that far north is a non-starter. Any PV installed there will actually make AGW and carbon emissions worse, not better. Basically, the amount of carbon emitted due to manufacturing is greater than the carbon savings over the lifetime of the panel in those locations.
That makes sense but my first thoughts were that panels wouldn't be oriented so that the majority of that flat surface was perpendicular to the radar but instead much closer to parallel, and that aviation radar would be higher up than a house roof to avoid ground clutter.
