Most of rural Ukraine already uses or can use solid fuel (firewood, coal) for heating. The article is about flats, not off-grid houses.

Adding some supplemental solar that will move the needle a drop in a brown-out isn't absolutely nothing I suppose, but really for immediate war-time resiliency you would be using solar for off-grid purposes (even if during grid blackouts only).

If your goal is to stay on grid the payoff on solar isn't really realized for 10+ years, when not only are the panels paid off but the accumulation factor of a country full of people with solar panels reduces the grid strain on the conventional sources you list. Adding them for war-time reasons is overall a net negative vs just buying diesel heaters, distributing solar for actual off-grid purposes so people have communications, etc. It is not going to meaningfully reduce dependency on those sources during the period of the war -- that's why I assumed it had to be for off-grid alternative because in that case it would achieve that goal.

Of course it is better than nothing, assuming they did not waste too many domestic resources doing this Greenpeace stunt. But this on-grid solar component is not a serious proposition for wartime demand, and you would be WAY better off donating to maintaining/defending the existing hydro/nuclear/coal generation than trying to deploy enough solar to move the needle for solar grid resiliency within the timespan of the war. I guess I just assumed they were acting rationally and that is why I thought it might be used in off-grid scenarios, but you've disillusioned me of that.