A new design for a photovoltaic concentrator, the most recent advance based on the Kohler concept, is presented. The
system is mirror-based, and with geometry that guaranties a maximum sunlight collection area (without shadows, like
those caused by secondary stages or receivers and heat-sinks in other mirror-based systems). Designed for a concentration of 1000x, this off axis system combines both good acceptance angle and good irradiance uniformity on the solar cell. The advanced performance features (concentration-acceptance products –CAP- about 0.73 and affordable peak and average irradiances) are achieved through the combination of four reflective folds combined
with four refractive surfaces, all of them free-form, performing Köhler integration 2. In Köhler devices, the irradiance uniformity is not achieved through additional optical stages (TIR prisms), thus no complex/expensive elements to manufacture are required. The rim angle and geometry are such that the secondary stage and receivers are hidden below the primary mirrors, so maximum collection is assured. The entire system was designed to allow loose assembly/alignment tolerances (through high acceptance angle) and to be manufactured using already well-developed methods for mass production, with high potential for low cost. The optical surfaces for Köhler integration, although with a quite different optical behavior, have approximately the same dimensions and can be manufactured with the same techniques as the more traditional secondary optical elements used for concentration (typically plastic injection molding or glass molding). This paper will show the main design features, along with realistic performance simulations considering all spectral characteristics of the elements involved.
Development of a novel HCPV nonimaging concentrator with high concentration (>500x) and built-in spectrum splitting
concept is presented. It uses the combination of a commercial concentration GaInP/GaInAs/Ge 3J cell and a
concentration Back-Point-Contact (BPC) silicon cell for efficient spectral utilization, and external confinement
techniques for recovering the 3J cell's reflection. The primary optical element (POE) is a flat Fresnel lens and the
secondary optical element (SOE) is a free-form RXI-type concentrator with a band-pass filter embedded in it - Both the
POE and SOE performing Köhler integration to produce light homogenization on the receiver. The band-pass filter
transmits the IR photons in the 900-1200 nm band to the silicon cell. A design target of an "equivalent" cell efficiency
~46% is predicted using commercial 39% 3J and 26% Si cells. A projected CPV module efficiency of greater than 38%
is achievable at a concentration level larger than 500X with a wide acceptance angle of ±1°. A first proof-of concept
receiver prototype has been manufactured using a simpler optical architecture (with a lower concentration, ~100x and
lower simulated added efficiency), and experimental measurements have shown up to 39.8% 4J receiver efficiency using
a 3J cell with a peak efficiency of 36.9%.
Here we present a novel optical design of the high concentration photovoltaics (HPCV) nonimaging concentrator
(>500x) with built-in spectrum splitting concept. The primary optical element (POE) is a flat Fresnel lens and the
secondary optical element (SOE) is a free-form RXI-type concentrator with a band-pass filter embedded in it, both POE
and SOE performing Köhler integration to produce light homogenization on the target. It uses the combination of a
commercial concentration GaInP/GaInAs/Ge 3J cell and a concentration Back-Point-Contact (BPC) silicon cell for
efficient spectral utilization, and external confinement techniques for recovering the 3J cell's reflection. Design targets
equivalent cell efficiency ~46% using commercial 39% 3J and 26% Si cells, and CPV module efficiency greater than
38%, achieved at a concentration level larger than 500X and wide acceptance angle (±1°). A first proof-of concept
receiver prototype has been manufactured using a simpler optical architecture (with a lower concentration, ~100x and
lower simulated added efficiency), and experimental measurements have shown up to 39.8% 4J receiver efficiency using
a 3J with peak efficiency of 36.9%.
The XR-Köhler concentrator1 is a design that has the possibility to work under high concentration, maintaining the high
acceptance angle and high irradiance uniformity on the solar cell. It is an on-axis free-form design that consists of a
reflective (X) and refractive (R) surface. For a geometrical concentration of about 800x the simulated results show an
acceptance angle of ±1.79deg with high irradiance uniformity on the solar cell. This article shows the design results of
the XR-Köhler and also a novel passive cooling system (LPI patented) that keeps the solar cell operation temperature
under 100°C at extreme conditions (wind speed = 0 m/s, module tilt angle = 45deg and Ta = 50°C). The results of using
the XR-Köhler device as a collimator when the light source has very high non-uniform luminance distribution, i.e.
multichip LEDs, are also here presented.
Conventional incandescent light bulbs have a wire filament acting as an extended light source with nearly constant intensity throughout its quasi-spherical emission pattern. Here we present a novel family of optical devices that make use of commercially available Lambertian or near-Lambertian LED light sources, in conjunction with tailored optical element bonded to the top surface of the LED. These hybrid devices can emulate the output of traditional incandescent filaments, or can be designed to produce a wide range of light output beam patterns. We call these new devices Virtual Filaments, as they can be designed to appear the same as an incandescent filament, with a similar light output pattern, and having a similar focal position above the base. These new lamps can then be used in the same applications as those they replace, thus eliminating the need to redesign or replace the original luminaire. We present several possible optical designs that can be used with a number of standard LEDs to replace standard incandescent bulbs. In one example we show a design that provides an output with near-uniform intensity across a full beam angle of 300 degrees, from a focal position 20 mm above an LED. Other major advantages of these new devices include their ability to be given sharp cutoffs, to homogenize non-uniform LED light sources and to color-mix the output of RGB LEDs.
Simple optics composed of a spherical lens and a conic mirror are described and the relation between the radius of the lens and height of the cone on far field illuminance performance is analyzed for a fixed exit aperture dimension. Ray sets for real LEDs were used to simulate the performance of the hybrid optics and it is shown that there are combinations of values for the lens radius and cone height for which the optic produces an approximately constant illuminance pattern on a distant target. The effects of varying the lens radius while keeping the cone height constant, and of varying the cone height while keeping the lens radius constant, are also presented, as these variations result in beams of varying angular spread. It is shown that a relatively course two parameter optimization can find near optimum solutions, where the optimization is carried out using ray sets of commercially available LEDs and the merit function is constant illuminance.
For reasons both fluid-dynamic and stylistic, volumetric constraints on vehicular luminaires grow more exacting. For full design-freedom of luminaire placement and shape, new designs are needed that have shallow depth and are capable of emitting a beam that makes a net angle with the local surface normal. Automotive headlamps, fog-lamps, and daylight-running lamps may need to project their illumination patterns onto the road from a position on sloped front surfaces. A conventional paraboloid, however, must be recessed behind a sloped window, thus using up space inside the vehicle-skin. A conventional TIR lens, with its output beam centered on its axis of circular symmetry, will also have to intrude into the vehicle interior, and shine through a sloped window. Instead, the luminaire should be thin enough to mount on a vehicle’s skin without needing a hole to be cut into it, a luminaire also capable of emitting its beam substantially off the local normal. To this end, two new TIR lenses are introduced here that generate off-normal beams. In one, a circular TIR lens takes on an internal tilt of its symmetry axis to produce a collimated output beam with high tilt, nearly 45° from the surface normal of the lens exterior. In the other, an off-axis linear TIR lens can be made with an internal tilt to the reflected rays. When used with LEDs, this new linear lens can be combined with exterior transverse lenslets, tailored to meet an intensity prescription.
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.
At every conference since 1995 we have reported on work in- progress to find a consistent formalism connecting the radiance concept with measurement of radiance, even under conditions where wave effects are important. In such circumstances, classical radiometry no longer provides an adequate description. In this conference we report on measurements of radiance that are well modeled by our theory, but would not be adequately described by classical radiometry.
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