Testing the 'Segmented Dish' Piecewise-Focusing Solar Collector

The concept of a piecewise-focusing solar collector is proposed and investigated. The scales
of vertical and horizontal sun-tracking motion are separated. The concept is realised as a
‘segmented dish’ with cavity receiver, in which about 100 reflectors mounted on a base-frame
track the sun’s elevation, and the entire base-frame tracks the sun in azimuth. The
reflectors approximate the surface of a paraboloid tilted at a fixed angle. Each reflector
rotates about a single nearly-horizontal axis attached at a particular angle to the base frame,
such that it is perfectly aimed at three sun elevations and only slightly mis-aimed otherwise.

A 3.6 m diameter partial physical model was constructed, equipped with ten mirror units in
‘worst-case’ positions, focusing on a flat target. A corresponding numerical model allowed
greater precision in results and a greater range for analysis; the models agreed within the
limits of the physical model’s precision. A concentration ratio of at least 2000 can be achieved at the entrance to a cavity receiver.

It is suggested that because of its non-elevating framework the segmented dish could be built
economically in sizes an order of magnitude larger than for a paraboloidal dish. The concept
may be capable of reducing the overall cost of concentrating solar thermal power stations.