Monolithic InP/Ga0.47In0.53As tandem solar cells for space

A review is provided of progress made in the development of InP/Ga(0.47)In(0.53)As monolithic tandem solar cells since the last SPRAT conference. Improved one-sun, three terminal tandem designs have resulted in Air Mass Zero (AM0) efficiencies as high as 23.9 pct. at 25 C. Additionally, high efficiency concentrator versions of the three terminal device were developed. The best concentrator tandem has a peak AM0 efficiency of 28.8 pct. under 40.3 suns at 25 C. For the concentrator tandems, the subcell performance parameter temperature coefficients are reported as a function of the concentration ratio. Results from a computer modeling study are presented which provide a clear direction for improving the efficiency of the concentrator tandem. The prospects for fabricating high efficiency, series connected (i.e., two terminal) InP/Ga(0.47)In(0.53)As monolithic tandem cells are also discussed

Stability of CIS/CIGS Modules at the Outdoor Test Facility over Two Decades: Preprint

This paper discusses examining the status and question of long-term stability of copper indium diselenide (CIS) photovoltaic (PV) module performance for numerous modules that are deployed in the array field, or on the roof of, the outdoor test facility (OTF) at NREL, acquired from two manufacturers

Generalized optoelectronic model of series-connected multijunction solar cells

The emission of light from each junction in a series-connected multijunction solar cell both complicates and elucidates the understanding of its performance under arbitrary conditions. Bringing together many recent advances in this understanding, we present a general 1-D model to describe luminescent coupling that arises from both voltage-driven electroluminescence and voltage-independent photoluminescence in nonideal junctions that include effects such as Sah-Noyce-Shockley (SNS) recombination with n ≠ 2, Auger recombination, shunt resistance, reverse-bias breakdown, series resistance, and significant dark area losses. The individual junction voltages and currents are experimentally determined from measured optical and electrical inputs and outputs of the device within the context of the model to fit parameters that describe the devices performance under arbitrary input conditions. Techniques to experimentally fit the model are demonstrated for a four-junction inverted metamorphic solar cell, and the predictions of the model are compared with concentrator flash measurements

Forward-Biased Thermal Cycling: A New Module Qualification Test

Following a proposal by BP Solarex to modify the standard module qualification sequence, we performed a forward-biased themal cycling on three types of commercial modules to evaluate the procedure. The total number of thermal cycles was doubled to 400 and maximum power measurements were made every 50 cycles

Comparison of Degradation Rates of Individual Modules Held at Maximum Power

States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States Government purposes. In this paper, we present a comparison of maximum power degradation rates of individual modules under out-door conditions in Golden, Colorado. Test modules in-clude single- and polycrystalline-Si (x-Si, poly-Si), amor-phous Si (a-Si, single, dual, and triple junction), CdTe, Cu-In-Ga-Se-S (CIS), and c-Si/a-Si heterostructure, from nine difference manufacturers. From monthly blocks of output power data, ratings were determined using multiple re-gressions to Performance Test Conditions (PTC). Plotting the power ratings versus time allowed degradation rates to be calculated from linear regressions. We also include a summary of module degradation rates obtained from the open literature over the past five years. Compared with the common rule-of-thumb value of 1 % per year, many modules are seen to have significantly smaller degrada-tion rates. A few modules, however, degrade significantly faster

Unit roots in periodic autoregressions

Abstract. This paper analyzes the presence and consequences of a unit root in periodic autoregressive models for univariate quarterly time series. First, we consider various representations of such models, including a new parametrization which facilitates imposing a unit root restriction. Next, we propose a class of likelihood ratio tests for a unit root, and we derive their asymptotic null distributions. Likelihood ratio tests for periodic parameter variation are also proposed. Finally, we analyze the impact on unit root inference of misspecifying a periodic process by a constant-parameter model

Towards improved cover glasses for photovoltaic devices

For the solar energy industry to increase its competitiveness there is a global drive to lower the cost of solar generated electricity. Photovoltaic (PV) module assembly is material-demanding and the cover glass constitutes a significant proportion of the cost. Currently, 3 mm thick glass is the predominant cover material for PV modules, accounting for 10-25% of the total cost. Here we review the state-of-the-art of cover glasses for PV modules and present our recent results for improvement of the glass. These improvements were demonstrated in terms of mechanical, chemical and optical properties by optimizing the glass composition, including addition of novel dopants, to produce cover glasses that can provide: (i) enhanced UV protection of polymeric PV module components, potentially increasing module service lifetimes; (ii) re-emission of a proportion of the absorbed UV photon energy as visible photons capable of being absorbed by the solar cells, thereby increasing PV module efficiencies; (iii) Successful laboratory-scale demonstration of proof-of-concept, with increases of 1-6% in Isc and 1-8% Ipm. Improvements in both chemical and crack resistance of the cover glass were also achieved through modest chemical reformulation, highlighting what may be achievable within existing manufacturing technology constraints

Column-integrated aerosol optical properties in Sodankylä (Finland) during the Solar Induced Fluorescence Experiment (SIFLEX-2002).

A study has been made of the column aerosols using solar irradiance extinction measurements at ground level in a boreal region (Sodankyla ̈, Finland) during spring 2002. The aerosol properties have been related to air mass origin. In general, the aerosol levels were observed to be very low, independent of the air mass origin, with an aerosol optical depth (AOD) value at 500 nm of less than 0.09 ± 0.03. Two characteristic patterns were observed depending on whether the air masses originated in the north and west or from the south and east. In the first case (north and west origins) the aerosol load was very small, with very low optical depths in the range 0.03 ± 0.02 to 0.09 ± 0.03 for 500 nm wavelengths. The size distribution usually showed two modes, with a strong contribution from the large-particle mode, probably a consequence of the presence of maritime-type particles originating in the ocean. When the air masses originated from a south or east direction, the behavior was the opposite to that noted before. In these cases the AOD was rather larger, above all for air masses originating in central Europe and Russia with an average value at 500 nm of 0.14 ± 0.02