How much cleaner is solar thermal than PV? I assume that depends on how dirty it is to produce the metal for the turbines (steam or air, in the case of solar towers).

All of these are very clean compared to coal.

Solar thermal is vulnerable to attacks from media articles about dead birds and the fact that some of them have to burn natural gas to start the plant in the morning. You can find both varieties of article courtesy of Fox News:

https://www.foxnews.com/politics/taxpayer-backed-solar-plant...

https://www.foxnews.com/science/emerging-solar-plants-scorch...

Solar thermal does have one huge advantage over PV: the plants contain their own short-term energy storage and keep running well after dark. Unfortunately due to market forces solar thermal is currently dead in America. All planned plants have been canceled.

Not clean enough to offset the higher cost per kWh currently. The PV price collapse kneecapped several alternative power sources. Plus solar thermal requires big centralized power plants, where PV can be distributed easily.

Solar thermal has a larger footprint, considering turbines and such, but would tend to be more easily recyclable out of the waste stream.