Images Formed by a Piecewise-Focusing Solar Collector

The concept of the piecewise-focusing (PWF) solar collector for use in concentrating solar
thermal (CST) power stations, realised as a ‘segmented dish’, is analyzed experimentally and
numerically. A scale model of one reflector gave corner-ray intersections on the target plane
that agreed quite well with the numerical model over a wide range of sun elevations. Applied
to a representative group of reflectors, the numerical model shows that focus quality at a
concentration ratio of 2000 (required for a cavity receiver) is satisfactory at all except very
low sun elevations. For adequate focusing at all elevations the number of reflectors per
PWF collector must be increased from 80 to 200-300. Compared to a large central receiver
CST plant with a surround-field of heliostats, a PWF-based CST plant with cavity receivers requires
only 70% of the mirror area for the same heat rate.