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Title: Spectral binning for energy production calculations and multijunction solar cell design

Abstract

Currently, most solar cells are designed for and evaluated under standard spectra intended to represent typical spectral conditions. However, no single spectrum can capture the spectral variability needed for annual energy production (AEP) calculations, and this shortcoming becomes more significant for series-connected multijunction cells as the number of junctions increases. For this reason, AEP calculations are often performed on very detailed yearlong sets of data, but these pose 2 inherent challenges: (1) These data sets comprise thousands of data points, which appear as a scattered cloud of data when plotted against typical parameters and are hence cumbersome to classify and compare, and (2) large sets of spectra bring with them a corresponding increase in computation or measurement time. Here, we show how a large spectral set can be reduced to just a few 'proxy' spectra, which still retain the spectral variability information needed for AEP design and evaluation. The basic 'spectral binning' methods should be extensible to a variety of multijunction device architectures. In this study, as a demonstration, the AEP of a 4-junction device is computed for both a full set of spectra and a reduced proxy set, and the results show excellent agreement for as few as 3more » proxy spectra. This enables much faster (and thereby more detailed) calculations and indoor measurements and provides a manageable way to parameterize a spectral set, essentially creating a 'spectral fingerprint,' which should facilitate the understanding and comparison of different sites.« less

Authors:
ORCiD logo [1]; ORCiD logo [2];  [2];  [2];  [2];  [2];  [2]
  1. National Renewable Energy Laboratory, Golden CO 80401 USA; Instituto de Energía Solar, Univ. Politécnica de Madrid, Avda. Complutense s/n Madrid 28040 Spain
  2. National Renewable Energy Laboratory, Golden CO 80401 USA
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S)
OSTI Identifier:
1415018
Report Number(s):
NREL/JA-5J00-68331
Journal ID: ISSN 1062-7995
DOE Contract Number:
AC36-08GO28308
Resource Type:
Journal Article
Resource Relation:
Journal Name: Progress in Photovoltaics; Journal Volume: 26; Journal Issue: 1
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; energy harvesting efficiency; multijunction solar cells; spectral binning

Citation Formats

Garcia, Iván, McMahon, William E., Habte, Aron, Geisz, John F., Steiner, Myles A., Sengupta, Manajit, and Friedman, Daniel J. Spectral binning for energy production calculations and multijunction solar cell design. United States: N. p., 2017. Web. doi:10.1002/pip.2943.
Garcia, Iván, McMahon, William E., Habte, Aron, Geisz, John F., Steiner, Myles A., Sengupta, Manajit, & Friedman, Daniel J. Spectral binning for energy production calculations and multijunction solar cell design. United States. doi:10.1002/pip.2943.
Garcia, Iván, McMahon, William E., Habte, Aron, Geisz, John F., Steiner, Myles A., Sengupta, Manajit, and Friedman, Daniel J. 2017. "Spectral binning for energy production calculations and multijunction solar cell design". United States. doi:10.1002/pip.2943.
@article{osti_1415018,
title = {Spectral binning for energy production calculations and multijunction solar cell design},
author = {Garcia, Iván and McMahon, William E. and Habte, Aron and Geisz, John F. and Steiner, Myles A. and Sengupta, Manajit and Friedman, Daniel J.},
abstractNote = {Currently, most solar cells are designed for and evaluated under standard spectra intended to represent typical spectral conditions. However, no single spectrum can capture the spectral variability needed for annual energy production (AEP) calculations, and this shortcoming becomes more significant for series-connected multijunction cells as the number of junctions increases. For this reason, AEP calculations are often performed on very detailed yearlong sets of data, but these pose 2 inherent challenges: (1) These data sets comprise thousands of data points, which appear as a scattered cloud of data when plotted against typical parameters and are hence cumbersome to classify and compare, and (2) large sets of spectra bring with them a corresponding increase in computation or measurement time. Here, we show how a large spectral set can be reduced to just a few 'proxy' spectra, which still retain the spectral variability information needed for AEP design and evaluation. The basic 'spectral binning' methods should be extensible to a variety of multijunction device architectures. In this study, as a demonstration, the AEP of a 4-junction device is computed for both a full set of spectra and a reduced proxy set, and the results show excellent agreement for as few as 3 proxy spectra. This enables much faster (and thereby more detailed) calculations and indoor measurements and provides a manageable way to parameterize a spectral set, essentially creating a 'spectral fingerprint,' which should facilitate the understanding and comparison of different sites.},
doi = {10.1002/pip.2943},
journal = {Progress in Photovoltaics},
number = 1,
volume = 26,
place = {United States},
year = 2017,
month = 9
}
  • This paper re-examines the impact of atmospheric absorption bands on series-connected multijunction cell design, motivated by the numerous local efficiency maxima that appear as the number of junctions is increased. Some of the local maxima are related to the bottom subcell bandgap and are already well understood: As the bottom subcell bandgap is varied, a local efficiency maximum is produced wherever the bottom cell bandgap crosses an atmospheric absorption band. The optimal cell designs at these local maxima are generally current matched, such that all subcells have nearly the same short-circuit current. We systematically describe additional local maxima that occurmore » wherever an upper subcell bandgap encounters an atmospheric absorption band. Moreover, these local maxima are not current matched and become more prevalent as the number of junctions increases, complicating the solution space for five-junction and six-junction designs. A systematic framework for describing this complexity is developed, and implications for numerical convergence are discussed.« less
  • NREL has demonstrated a 45.7% conversion efficiency for a four-junction solar cell at 234 suns concentration. This achievement represents one of the highest photovoltaic research cell efficiencies ever achieved across all types of solar cells. NREL's new solar cell, which is designed for operation in a concentrator photovoltaic (CPV) system where it can receive more than 1,000 suns of concentrated sunlight, greatly improves earlier designs by adding an additional high quality absorber layer to achieve an ultra-high efficiency.
  • Tandem solar cells can have significantly higher efficiencies than single-junction solar cells because they convert a larger fraction of the incident solar spectrum to electricity. For the design of tandem solar cells the spectral p-n junction model is proposed. It is based on tabulated standard spectra, on the fit of experimentally achieved open-circuit voltages, and assumes a quantum efficiency of unity. By consistent treatment of the energy gap in the diode equation, the model can be quantitatively applied to all tandem solar-cell systems. The special form and use of the reverse saturation current density is discussed in detail. The spectralmore » p-n junction model is rigorously applied based on accepted standard spectra. The tandem solar-cell performance limits based on the model are calculated. A quantitative expression for the increase in efficiency under concentration is derived. The limits predicted by the model are discussed for tabulated standard spectra. The highest achievable efficiency is 57.3 percent (AM1.5 global) without concentration of the incident light. The increase in efficiency under concentration is evaluated, and it is found that the relative change of the efficiency at any concentration X is linear with In (X).« less