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

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

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

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

Validation of a Photovoltaic Module Energy Ratings Procedure at NREL

The procedure determines the energy production of a PV module for five reference days. The reference days represent possible operating environments and are qualitatively described as Hot Sunny, Cold Sunny, Hot Cloudy, Cold Cloudy, and Nice. Based on statistical weather criteria, these days were selected from the National Solar Radiation Database (NSRDB). Besides the hourly solar radiation and meteorological data from the NSRDB, the reference days include air mass, angle of incidence, plane of array, and spectral irradiance for a south-facing PV module at latitude tilt, battery-charging voltage, and parameters f1 and f2 for determining PV module temperature. Indoor I-V curve measurements over a range of temperatures and irradiances characterize the electrical performance of a PV module and are used to determine factors to correct for non-linear performance when irradiance and temperature vary. They also serve as a matrix of reference I-V curves for translating to reference-day condition s. The sensitivity of a PV module to variations in the spectral distribution of the incident radiation is accounted for by using an incident irradiance. Differences in PV module thermal characteristics are accounted for by using a PV module's installed nominal operating cell temperature (INOCT) for input to the Fuentes temperature model. The procedure does not consider radiation and transmittance losses at large incident angles. These losses were judged too small, and not sufficiently different, for various PV modules to justify the complexity of their measurement and inclusion in the procedure. PV performance measurements from NREL's Outdoor Test Facility during calendar-year 1998 were used to validate the procedure by comparing modeled and measured maximum power values for seven flat-plate PV modules representing different technologies. On an annual basis, modeled values compared within 5% of measured values. Taking into account reproducibility errors from ratings being performed by different facilities and the modeling errors, the following statement applies to the ability of this procedure to show relative differences in the energy production of two PV modules: ''Because of errors in measurements and energy rating methodology, differences of 8% or less in the energy ratings of two PV modules are not significant. If one of the PV modules is amorphous silicon, differences of 13% or less in the energy ratings of two PV modules are not significant.'' This work was performed to develop and validate a PV module energy rating procedure for incorporation into IEEE PAR1479, ''Recommended Practice for the Evaluation of Photovoltaic Module Energy Production.'

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

Common Trends and Common Cycles in Canada: Who Knew So Much Has Been Going On?

It is generally accepted that convergence is well established for regional Canadian per capita outputs. The authors present evidence that long-run movements are driven by two stochastic common trends in this time series. This evidence casts doubt on the convergence hypothesis for Canada. Another prevalent belief is that Canada forms an optimal currency area (OCA). The authors uncover three serially correlated common cycles whose asymmetries suggest Canada is not an OCA. Their common trend-common cycle decomposition of regional outputs also reveals that trend shocks dominate fluctuations in Ontario, Quebec, and the Maritimes in the short run and long run but not in British Columbia and the Prairie region. Thus, regional Canadian economic fluctuations are driven by a rich, diverse, and economically important set of propagation and growth mechanisms