Economic operation of high-efficiency concentrator solar cells require
s solar concentration ratios which up to now can only be achieved with
two-axis tracking. In this paper we present a two-stage concentrator
approaching concentration ratios up to 300X while being tracked around
only one polar axis. Its principle is as follows: a parabolic trough
focuses the direct solar radiation onto a line parallel to the polar t
racking axis. The half rim angle of this first concentrating stage is
chosen to be equal to the sun's maximum declination of 23.5 degrees. T
he second stage consists of a row of dielectric, nonimaging 3-D-concen
trators, which couple the concentrated light directly into square sola
r cells. In contrast to linear secondaries the 3-D-secondaries make us
e of the limited divergence of +/- 23.5 degrees in the NS-direction to
achieve additional concentration. The performance of the system depen
ds sensitively on how well the angular acceptance characteristic of th
e second stage matches with the square-shaped angular irradiance distr
ibution in the focal line of the parabolic trough. A new concentrator
profile has been found that exhibits an almost ideal square acceptance
characteristic with a very sharp cut-off. A prototype two-stage conce
ntrator has been constructed with a total geometrical concentration of
214X. In outdoor measurements a total optical efficiency of 77.5% was
obtained.