I did a couple of autoplays. It seems the only improvement built, anywhere, is solar farms. This plus the right civic gives 4 hammers on any tile, and it seems to me that the total hammers of cities is quite huge.
This is probably partly because the tech changes have not happened yet; before then, the solar plant and turbine are in separate techs (wind power, solar power), and you only need research one or other. With the tech changes, they are merged into the same tech, which should make both available. But until then they may not be researching the turbine tech (wind power).
Solar farms should be giving 1h1c, eventually rising with tech to 2h1c in the midgame and then 3h1c in the very late game.
Solar farms are buildable on flat and graben, and turbines are 2h rising to 3h and then 4h, but buildable only on mesa. So what we should observe is a mix of windtraps and turbines on mesa, and a mix of cottages and solar farms on flatland, and then bonuses. Mines should be worth building only on bonuses or in the very early game, or with slavery civic (though I was investigating slavery changes).
There are no civics (that I recall??) that boost solar farms.
So I don't see how you could be getting 4h on any tiles until the extremely late-game (military industrial complex tech), unless there is a typo in my files. You used to be able to get this from solar farms too, its just that the AI wouldn't do it because of the -1 water penalty, it didn't understand that the penalty had no impact on tiles that had zero water yield.
Unfortunate though if the AI is only building solar farms. They give 1h1c, whereas a cottage adjacent to a well gives 2c rising eventually up to 5 commerce, with further boosts from civics.
When I did a few tests, the AI was still building plenty of cottages.
But the AI has a known issue to over-value hammers.