Before last summer, I had never actually stood in front of a utility-scale solar thermal plant. We simply didn’t have any (at the time) that had finished being constructed yet in California! While photovoltaic (PV) utility-scale solar facilities are, by their very nature, quiet, solar thermal facilities are a different story. All solar thermal, be it parabolic trough, power tower, or even the mythical Stirling engine, operate on the same basic principle as every conventional power plant humanity has ever designed: heat up a liquid to its boiling point, and use the steam generated to spin a turbine. Which leaves us with either billowing clouds of steam (not very efficient) or re-condensed and extremely hot liquid, requiring some form of cooling, typically in the form of what are essentially giant air conditioners.
Thus, a utility-scale solar thermal plant is actually extremely noisy! Listen to this brief video from the Solnova Parabolic Trough facility, part of the Plataforma Solúcar, owned by Abengoa, near Sanlucar la Mayor, Andalucía, Spain (map link). The whine could be heard from over a kilometer away.
(If the embedded video isn’t working, click here)