concentration only in one dimension, so that the concentration factor is less
than for a paraboloid dish. On the other hand, the one-dimensional arrangement
is mechanically simpler. Similarly, it is usual to have a trough collector
track the Sun only in one dimension. The axis is aligned north–south, and
the trough rotated (automatically) about its axis to follow the Sun in tilt
only. The power absorbed by the absorbing tube is