the collector
can be stationary or tracking. A CPC concentrator can be
orientated with its long axis along either the north–south or
the east–west direction and its aperture is tilted directly
towards the equator at an angle equal to the local latitude.
When orientated along the north–south direction the
collector must track the sun by turning its axis so as to
face the sun continuously. As the acceptance angle of the
concentrator along its long axis is wide, seasonal tilt
adjustment is not necessary. It can also be stationary but
radiation will only be received the hours when the sun is
within the collector acceptance angle. When the concentrator is orientated with its long axis along the east–west
direction, with a little seasonal adjustment in tilt angle the
collector is able to catch the sun’s rays effectively through
its wide acceptance angle along its long axis. The minimum
acceptance angle in this case should be equal to the
maximum incidence angle projected in a north–south
vertical plane during the times when output is needed
from the collector. For stationary CPC collectors mounted in
this mode the minimum acceptance angle is equal to 478.
This angle covers the declination of the sun from summer to
winter solstices (2 £ 23.58). In practice bigger angles are
used to enable the collector to collect diffuse radiation at the
expense of a lower concentration ratio. Smaller (less than 3)
concentration ratio CPCs are of greatest practical interest.