We present work at the Steward Observatory Solar Lab on a high concentration photovoltaic system in which sunlight focused by a single large paraboloidal mirror powers many small triple-junction cells. The optical system is of the XRX-Köhler type, comprising the primary reflector (X) and a ball lens (R) at the focus that reimages the primary reflector onto an array of small reflectors (X) that apportion the light to the cells. We present a design methodology that provides generous tolerance to mis-pointing, uniform illumination across individual cells, minimal optical loss and even distribution between cells, for efficient series connection. An operational prototype has been constructed with a 3.3m x 3.3m square primary reflector of 2m focal length powering 36 actively cooled triple-junction cells at 1200x concentration (geometric). The measured end-to-end system conversion efficiency is 28%, including the parasitic loss of the active cooling system. Efficiency ~32% is projected for the next system.

Abstract.A REhnu CPV module uses a 2.6 m 2 , back-silvered glass reflector to focus sunlight into a 150 mm diameter receiver housing 36 multijunction cells. Current modules use commercially available 8.8 mm cells operated at 950x concentration with a cell efficiency of 41% for an AM1.5 solar spectrum. Optics in the receiver format the sunlight to illuminate the cells which are mounted slightly apart on four flat circuit boards. Active cooling is provided by liquid circulated to a radiator which can easily be configured to also provide thermal energy in the form of hot fluid at an adjustable temperature up to 80 °C. Modules mounted in pairs on a dual axis tracker have been tested in the field. Module conversion efficiency, corrected to 25 °C cell temperature (CSTC), is found to peak at 31.2% for air mass 2.75. The I-V curve shows that the concentrated sunlight is distributed between the cells with a uniformity of ±7%. Steps are now being taken to improve uniformity, to reduce infrared losses caused by iron absorption in the reflector glass and by the receiver's antireflection coatings, and to upgrade to 42% efficient cells. Overall efficiency is projected to then increase to 35%. In hybrid mode (electrical + thermal) the total efficiency approaches 80%. REhnu's basic generator unit to be replicated for large scale installations has eight modules in a 2 x 4 array on a dual axis tracker. The first of these 6 kW units with mirrors of very low iron absorption glass has now been installed in the field, and 16 more units are under construction for a 100 kW, grid-connected plant at the Solar Zone of the University of Arizona Tech Park.

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Lucy MacGregor highlights her 2021 Distinguished Lecture, “Multiphysics analysis: Extracting the most from diverse data sets.” She discusses how combining data sets can compensate for weaknesses in each, how utilizing gravity data improves the seismic image, the biggest obstacle in utilizing data sets, and more. Hear the full episode at https://seg.org/podcast/post/11276 .

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