Nick Waite

Improved outdoor measurements for Very High Efficiency Solar Cell sub-modules

Very High Efficiency Solar Cell (VHESC) program is developing integrated optical/photovoltaic modules for portable applications that operate at 50 percent efficiency. Test sub-modules incorporating four p-n junctions and corresponding optics have been realized and are predicted to realize efficiency greater than 40%. Phased implementation requires corresponding measurement to inspect accomplished work and provide improvement direction for the next step. The comparison between the real performance of the four-junction test sub-module and the theoretical prediction of its efficiency is a significant indication of the realizability of the final VHESC module including six junctions which is designed to achieve 50% efficiency. For the sub-module measurement, a test bed was set up for outdoor test. Previous outdoor measurements of the VHESC test sub-modules resulted in a preliminary sub-module efficiency of 36.2% [1]. As solar cells with better performance were fabricated, the measurement methodology was refined and corresponding improvements were made to the initial test bed. Three test sub-modules containing new solar cells were measured with the new test setup for three different concentration levels at University of Delaware (UD). One test sub-module demonstrated efficiency as high as 39.5%, coupled with 44.3% efficient solar cells and 89.1% efficient optics, at 30.48X concentration. The measurements were taken when the direct light intensity was over 860W/m2 and the Isc was not calibrated to 1000W/m2. Another two test sub-modules including solar cells in the same batch as the ones tested at UD were taken to National Renewable Energy Laboratory (NREL). The Isc data of the two test sub-modules were recorded outdoors at NREL when the direct light intensity was over 970 W/m2. In addition, the Isc was calibrated to the standard spectrum condition using ASTM G173 direct data. Comparison of the results shows the difference between the test sub-module efficiency measured at UD and NREL is less than 4%.

Initial test bed for Very High Efficiency Solar Cell

Very High Efficiency Solar Cell (VHESC) program is developing integrated optical system—photovoltaic modules for portable applications that operate at greater than 50 percent efficiency. We are integrating the optical design with the solar cell design, and we have entered previously unoccupied design space [1]. A test bed for rapid development and verification of performance of subsystems is also being developed. The results and analysis of the first complete integrated optics and solar cells on this test bed are reported. The demonstration has achieved efficiency greater than 36%. Analysis shows a direct path to efficiencies greater than 40%. These initial results have not been verified by NREL or any other 3rd party. We have previously reported the sum of the solar cell efficiencies to be over 42%, and optical subsystem efficiency greater than 93% [2]. Our approach is driven by proven quantitative models for the solar cell design, the optical design and the integration of the two.

System for driving 2-D infrared emitter arrays at cryogenic temperatures

Large IR detector arrays, particularly ones intended for military and aerospace applications, are often difficult and expensive to directly test. These detectors require an IR projector for scene simulation. Current methods for testing such sensors rely heavily on expensive field test programs and/or utilize lower performance thermal emission-based IR scene projectors. Recently there has been increased interest and development of seminconductor-based infrared (IR) LED-based emitter array devices (e.g. SLEDS), due to their ability to produce higher apparent temperatures, lower background temperatures, and much faster rise and fall times than thermal emission techniques. These devices flip-chip a large CMOS driver chip onto a two-dimensional array of IR emitter devices typically fabricated on a GaSb substrate. Several testing sessions showed the unique functionality and capabilities in several important areas such as: apparent temperature exceeding 1000 Kelvin, rise and fall time of 3–4 microseconds, and low apparent background temperatures. Unfortunately, SLEDS arrays require the removal of kW-level heat fluxes while being maintained at liquid-nitrogen temperatures. Although multiple project for construction of these IR emitter arrays are underway, currently there appears to be no cooling system available to operate these arrays at the performance level that they are capable of achieving.