As the field of nonimaging optics has developed over the last 50 years, among its many applications, the best known and
recognized is probably in solar energy. In particular, the approach provides the formalism that allows the design of
devices that approach the maximum physically attainable geometric concentration for a given set of optical tolerances.
This means that it has the potential to revolutionize the design of solar concentrators. Much of the experimental
development and early testing of these concepts was carried out at the University of Chicago by Roland Winston and his
colleagues and students. In this presentation, some of many embodiments and variations of the basic Compound
Parabolic Concentrator that were developed and tested over a thirty-year period at Chicago are reviewed. Practical and
economic aspects of concentrator design for both thermal and photovoltaic applications are discussed. Examples
covering the whole range of concentrator applications from simple low-concentration non-tracking designs to ultrahigh-concentration
multistage configurations are covered.
We report results of a study our group has undertaken under NREL/DOE auspices to design a solar concentrator with uniform irradiance on a planar target. This attribute is especially important for photovoltaic concentrators.
We experimentally tested the operator formalism of radiative transfer on the response of an instrument to partially coherent wavefield produced by radiation emitted by distant and extended blackbody sources. The predictions of the formalism are found to agree well with the experiments. Phase space parameters are identified that characterize a measurement as well as indicating when the formalism will be useful, when we are not in the regime of geometrical optics or plane wave diffraction.
We report results of a study our group has undertaken to design a solar concentrator with uniform irradiance on a planar target. This attribute is especially important for photovoltaic concentrators. We find that a variety of optical mixers, some incorporating a moderate level of concentration, can be quite effective in achieving near uniform irradiance.
In this paper, we discuss the features of different types secondary concentrators used in solar energy for dish- thermal and high flux applications. We include a preliminary comparison of a new type of nonimaging concentrator with the more traditional ideal concentrators.
We have designed a Nd:YAG laser to be pumped by the High-Flux Solar Furnace (HFSF) at the National Renewable Energy Laboratory. Based on the unique features of the HFSF, the design objectives are high brightness and superior efficiency in primary mirror area utilization. The HFSF has a primary mirror of 11.5 m2 and a 1.85 f-number. With such a high f-number, the target is set off-axis and does not block incoming solar flux. Moreover, large f-number enables concentration which approaches the theoretical limit, and a two- dimensional non-imaging concentrator deposits the solar flux onto the internal part of a 10 mm diameter laser rod. For high brightness, we plan a wide low-loss fundamental mode and a laser rod aperture that suppresses high order modes. To get a fundamental mode, of up to a 2.5 mm waist, we have designed a convex-concave resonator, following well-known g1g2 equals 0.5 design for resonators with internal beam focusing. We have used the edge ray principle to design the concentrator, and ray traced the deposited power inside the laser rod. A 1.3% Nd doping level supports a maximal power deposition inside a 5 mm diameter.
A non imaging integrated evacuated solar collector for solar thermal energy collection is discussed which has the lower portion of the tubular glass vacuum enveloped shaped and inside surface mirrored to optimally concentrate sunlight onto an absorber tube in the vacuum. This design uses vacuum to eliminate heat loss from the absorber surface by conduction and convection of air, soda lime glass for the vacuum envelope material to lower cost, optimal non imaging concentration integrated with the glass vacuum envelope to lower cost and improve solar energy collection, and a selective absorber for the absorbing surface which has high absorptance and low emittance to lower heat loss by radiation and improve energy collection efficiency. This leads to a very low heat loss collector with high optical collection efficiency, which can operate at temperatures up to the order of 250 degree(s)C with good efficiency while being lower in cost than current evacuated solar collectors. Cost estimates are presented which indicate a cost for this solar collector system which can be competitive with the cost of fossil fuel heat energy sources when the collector system is produced in sufficient volume. Non imaging concentration, which reduces cost while improving performance, and which allows efficient solar energy collection without tracking the sun, is a key element in this solar collector design.
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