Abstract: An air heating system is for use with a mechanism for flowing air. The system includes a plenum and a solar absorber. The solar absorber defines a first boundary of the plenum. The solar absorber is permeable to air. The mechanism for flowing air is for pulling air into the plenum through the permeable solar absorber. The plenum has an axial direction, wherein along a cross section of said plenum normal to the axial direction the permeable absorber has an average shape that is substantially convex when the permeable absorber is viewed from outside of the plenum.