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).
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.