A technique for calculating étendue from flowlines is proposed for both Lambertian and non-Lambertian light fields. Hyperbolic curve fitting from flowline measurements is proposed as a means of extrapolating flowlines to the far-field for improved calculation of étendue. The technique is applicable to rotationally symmetric light fields, and to specific asymmetric light fields where analytic viewfactor calculations exist.
Freeform optics has great potential for delivering highly effective solar concentrators and lighting systems, but in some cases it can be challenging to implement. A numerical method is described for calculating 3D flowline concentrator shapes in a way that provides complete freedom over the specification of arbitrary source and receiver objects. This lends the approach to a range of practical design problems involving asymmetric systems, non-lambertian and extended light sources. The method reproduces the hyperbolic and hyperparabolic concentrator geometries identified in the literature, operating close to the thermodynamic limit of concentration. A practical example is given in the optimisation of a secondary concentrator for a concentrator photovoltaic array receiving light from a field of heliostats. The secondary improves the overall capture efficiency of the photovoltaic receiver at noon, and is expected to deliver further improvement at other times of day.
High efficiency solar conversion requires collection of a broad spectrum of wavelengths from the ultra-violet into the infrared. Solar collector mirrors must provide high reflection across this spectral band without degrading over time. This work presents the results of a high-performance 200 mm parabolic mirror coated with an ultra-wide broadband dielectric reflector. The mirror was developed to demonstrate high efficiency broadband solar collection and power conversion. Mirror reflection was measured within the limits of NIST capabilities, and averaged over 99.65% from 400 to 1800 nm with an acceptance angle of 30°. Plasma-assisted reactive magnetron sputtering was used to produce these high density and environmentally stable films. These hard oxide films can be repeatedly cleaned in the field. Salt spray, humidity and angle performance results are presented.
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