In this paper the solar thermal collector with spectrally selective
absorber with and without flat solar radiation reflectors has been
considered.
The changes of optimal positions of reflectors during the year
have been determined analytically and experimentally for collector
fixed at ˇ = 45◦ position in order to obtain the maximum concentration
of solar radiation intensity. Both numerical calculation and
experimental measurements indicated that optimal angle position
of the bottom reflector was the lowest (5◦) in December and
the highest (38◦) in June. Systematically good agreement between
numerical and experimental data during the year has been found,
which allowed us to predict reliable values for optimal position of
reflectors for different collector tilted plane angle.