In a parabolic trough plant like Solana, the mirrors are curved inward, with a glass tube running along the deepest point, or trough, of each mirror. The tube is full of synthetic oil (also known as heat transfer fluid, or HTF). The concave mirrors concentrate light onto this HTF, heating it to 740 degrees Fahrenheit. The system is extremely efficient in collecting heat and concentrating it to a blistering level; when I asked what would happen if I touched the tube, the reply was a curt “Trust me, you definitely don’t want to do that.”

Once the oil is up to temperature, about 270 miles of pipe transport it to the power block, where the HTF takes one of two pathways, depending on Solana’s current needs.

via Who needs sunlight? In Arizona, solar power never sleeps | Ars Technica.