This invention is a trough solar collector that uses inexpensive aluminized plastic films as the reflecting surface. The films are held in proper shape by stretching them between rigid ribs that are spaced apart along the length of the collector. The structure of the trough is held rigid by a unique sun-tracking system that not only guides a whole of array of troughs on a field to point them toward the sun, but also maintains the whole length of each trough in rigid configuration. It is not necessary to extend rigid metal beams along the trough to maintain the rigidity of the trough. Small-diameter cables are wrapped around rotatable pipes that extend along the east and west sides of the field. The cables extend over the field of the troughs and are attached to connecting points above the troughs in such a way that when the rotatable pipes rotate, the cables move, the troughs move with them, and the cables provide the rigidity of the troughs. The troughs are supported by support posts that are driven into the ground. Since the support posts do not have to supply torque to rotate the troughs, no concrete foundations are necessary.