Measurements are reported of the irradiance produced by a two-stage solar concentrator designed to approach the thermodynamic limit. Sunlight is collected by a 40.6-cm diam parabolic primary which forms a 0.98-cm diam image. The image is reconcentrated by a nonimaging refracting secondary with index n = 1.53 to a final aperture 1.27 mm in diameter. Thus the geometrical concentration ratio is 102, 000. The highest irradiance value achieved was 4.4 +/- 0.2 kW cm(-2), or 56,000 +/- 5000 suns, relative to a solar disk insolation of 800 W m(-2). This is greater than the previous peak solar irradiance record by nearly a factor of 3, and it is 68% of that existing at the solar surface itself. The efficiency with which we concentrated 55 W of sunlight to a small spot suggests that our two-stage system would be an excellent candidate for solar pumping of solid state lasers.
The commercial rooftop environment poses difficult challenges for concentrating photovoltaic (CPV) systems. Rooftop CPV must not only meet low cost and high energy production targets common to ground mounted systems but also must solve safety, wind loading, and area usage requirements in ways that are compatible with the rooftop environment. To meet these requirements we have developed a low-profile carousel-mounted array of Fresnel concentrators using triple junction solar cells. In this paper we describe the key features of the opto-mechanical and thermal design for manufacturability and reliability. These features include the concentration level, the mechanical drive scheme, the configuration of the lens with secondary optical element, and passive cooling. Also described are elements of the optical component testing and assembly methods. We present exemplary results of environmental testing and measurements of electro-optical performance.
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