Solar doesn’t work that well in northern China during the winter because there is hardly any sun. Even discounting the pollution, the area would be mostly foggy and overcast, it would be like trying to use solar in Seattle.

An apartment complex I lived in had solar hot water and I absolutely hated it, I could never take a “hot” shower during Beijing’s cold winter, just a luke warm one.

For those that don't live in Seattle, tomorrow, on Winter Solstice, the sun will not rise more then 19° above the horizon.

You're not going to get much solar heating out of that... Unless you want to block your neighbor's solar heating array.

Implementation can make a huge difference, people do install these systems in Alasca and then supplement for a few weeks in the middle of winter which is still a huge fuel savings and cost reduction.

But, if your going to base this on a central location then sizing the system and maintain the desired temperature output is simplified.

There isn’t much space for solar panels, so sizing is intrinsically constrained. Also, these are 32 story towers with approximately 130 units...it’s not rocket science why it doesn’t work out.

They were definitely not supplementing enough.

Ouch, with 32 stories roof space is not good by to be nearly enough. But, if you're going off site you no longer space constrained.

Which is why I say implementation is so important. 90% reduction in fuel used and lower costs is IMO a better trade off than nuclear which is only useful ~9 months out of the year and has high ongoing costs.

Russia on the other hand is even further north and could probably see more value from such a system.

Do solar hot water heaters work when it isn't sunny?

Yes, the amount of solar heating is affected by the angle of insolation more than the amount of visible sun. They work when overcast just fine, but they won’t work so well in winter at higher latitudes - such as northern China.