Explicit Expressions for Solar Panel Equivalent Circuit Parameters Based on Analytical Formulation and the Lambert W-Function

Due to the high dependence of photovoltaic energy efficiency on environmental conditions (temperature, irradiation...), it is quite important to perform some analysis focusing on the characteristics of photovoltaic devices in order to optimize energy production, even for small-scale users. The use of equivalent circuits is the preferred option to analyze solar cells/panels performance. However, the aforementioned small-scale users rarely have the equipment or expertise to perform large testing/calculation campaigns, the only information available for them being the manufacturer datasheet. The solution to this problem is the development of new and simple methods to define equivalent circuits able to reproduce the behavior of the panel for any working condition, from a very small amount of information. In the present work a direct and completely explicit method to extract solar cell parameters from the manufacturer datasheet is presented and tested. This method is based on analytical formulation which includes the use of the Lambert W-function to turn the series resistor equation explicit. The presented method is used to analyze commercial solar panel performance (i.e., the current-voltage–I-V–curve) at different levels of irradiation and temperature. The analysis performed is based only on the information included in the manufacturer’s datasheet.

Explicit expressions for solar panel equivalent circuit parameters based on analytical formulation and the Lambert W - Function

Due to the high dependence of photovoltaic energy efficiency on environmental conditions (temperature, irradiation...), it is quite important to perform some analysis focusing on the characteristics of photovoltaic devices in order to optimize energy production, even for small-scale users. The use of equivalent circuits is the preferred option to analyze solar cells/panels performance. However, the aforementioned small-scale users rarely have the equipment or expertise to perform large testing/calculation campaigns, the only information available for them being the manufacturer datasheet. The solution to this problem is the development of new and simple methods to define equivalent circuits able to reproduce the behavior of the panel for any working condition, from a very small amount of information. In the present work a direct and completely explicit method to extract solar cell parameters from the manufacturer datasheet is presented and tested. This method is based on analytical formulation which includes the use of the Lambert W-function to turn the series resistor equation explicit. The presented method is used to analyze the performance (i.e., the I - V curve) of a commercial solar panel at different levels of irradiation and temperature. The analysis performed is based only on the information included in the manufacturer's datasheet.

Two-photon photocurrent and voltage up-conversion in a quantum dot intermediate band solar cell

It has been proposed that the use of self-assembled quantum dot (QD) arrays can break the Shockley-Queisser efficiency limit by extending the absorption of solar cells into the low-energy photon range while preserving their output voltage. This would be possible if the infrared photons are absorbed in the two sub-bandgap QD transitions simultaneously and the energy of two photons is added up to produce one single electron-hole pair, as described by the intermediate band model. Here, we present an InAs/Al 0.25Ga 0.75As QD solar cell that exhibits such electrical up-conversion of low-energy photons. When the device is monochromatically illuminated with 1.32 eV photons, open-circuit voltages as high as 1.58 V are measured (for a total gap of 1.8 eV). Moreover, the photocurrent produced by illumination with photons exciting the valence band to intermediate band (VB-IB) and the intermediate band to conduction band (IB-CB) transitions can be both spectrally resolved. The first corresponds to the QD inter-band transition and is observable for photons of energy mayor que 1 eV, and the later corresponds to the QD intra-band transition and peaks around 0.5 eV. The voltage up-conversion process reported here for the first time is the key to the use of the low-energy end of the solar spectrum to increase the conversion efficiency, and not only the photocurrent, of single-junction photovoltaic devices. In spite of the low absorption threshold measured in our devices - 0.25 eV - we report open-circuit voltages at room temperature as high as 1.12 V under concentrated broadband illumination.

Stacked GaAs(Sb)(N)-capped InAs/GaAs quantum dots for enhanced solar cell efficiency

Different approaches have arisen aiming to exceed the Shockley-Queisser efficiency limit of solar cells. Particularly, stacking QD layers allows exploiting their unique properties, not only for intermediate-band solar cells or multiple exciton generation, but also for tandem cells in which the tunability of QD properties through the capping layer (CL) could be very useful.

Stacked GaAsSbN-capped InAs/GaAs quantum dots for enhanced solar cell efficiency

Different approaches have recently arisen aiming to exceed the Shockley-Queisser efficiency limit. Particularly, the use of self-organized quantum dots (QD) has been recently proposed in order to introduce new states within the barrier material, which enhances the subband gap absorption yielding a photocurrent increase. Stacking QD layers allows exploiting their unique properties for intermediate-band solar cells (SC) or tandem cells.In all these cases, tuning the QD properties by modifying the capping layer (CL) can be very useful.

Determination of spectral variations by means of component cells useful for CPV rating and design

A methodology is presented to determine both the short-term and the long-term influence of the spectral variations on the performance of Multi-Junction (MJ) solar cells and Concentrating "This is the peer reviewed version of the following article: R. Núñez, C. Domínguez, S. Askins, M. Victoria, R. Herrero, I. Antón, and G. Sala, “Determination of spectral variations by means of component cells useful for CPV rating and design,” Prog. Photovolt: Res. Appl., 2015., which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/pip.2715/full. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving [http://olabout.wiley.com/WileyCDA/Section/id-820227.html#terms]." Photovoltaic (CPV) modules. Component cells with the same optical behavior as MJ solar cells are used to characterize the spectrum. A set of parameters, namely Spectral Matching Ratios (SMRs), is used to characterize spectrally a particular Direct Normal Irradiance (DNI) by comparison to the reference spectrum (AM1.5D-ASTM-G173-03). Furthermore, the spectrally corrected DNI for a given MJ solar cell technology is defined providing a way to estimate the losses associated to the spectral variations. The last section analyzes how the spectrum evolves throughout a year in a given place and the set of SMRs representative for that location are calculated. This information can be used to maximize the energy harvested by the MJ solar cell throughout the year. As an example, three years of data recorded in Madrid shows that losses lower than 5% are expected due to current mismatch for state-of-the-art MJ solar cells.

Spectral study and classification of worldwide locations considering several multijunction solar cell technologies

Multi-junction solar cells are widely used in high-concentration photovoltaic systems (HCPV) attaining the highest efficiencies in photovoltaic energy generation. This technology is more dependent on the spectral variations of the impinging Direct Normal Irradiance (DNI) than conventional photovoltaics based on silicon solar cells and consequently demands a deeper knowledge of the solar resource characteristics. This article explores the capabilities of spectral indexes, namely, spectral matching ratios (SMR), to spectrally characterize the annual irradiation reaching a particular location on the Earth and to provide the necessary information for the spectral optimization of a MJ solar cell in that location as a starting point for CPV module spectral tuning. Additionally, the relationship between such indexes and the atmosphere parameters, such as the aerosol optical depth (AOD), precipitable water (PW), and air mass (AM), is discussed using radiative transfer models such as SMARTS to generate the spectrally-resolved DNI. The network of ground-based sun and sky-scanning radiometers AERONET (AErosol RObotic NETwork) is exploited to obtain the atmosphere parameters for a selected bunch of 34 sites worldwide. Finally, the SMR indexes are obtained for every location, and a comparative analysis is carried out for four architectures of triple junction solar cells, covering both lattice match and metamorphic technologies. The differences found among cell technologies are much less significant than among locations.

Improving Optical Performance of Concentrator Cells by Means of a Deposited Nanopattern Layer

Multijunction solar cells (MJSC) use anti-reflective coatings (ARC) to minimize Fresnel reflection losses for a family of light incidence angles. These coatings adapt the refractive index of the cell to that of the surrounding medium. Patterns with sizes in the range of the light wavelength can be used to further reduce reflections through diffraction. Transparent nanopatterns with a gradual profile, called moth-eye nanostructures, can adapt the refractive index of the optical interfaces (often with n∼1.5) used to encapsulate concentrator solar cells to that of the air (n air∼1). Here we show the effect of a nanometric moth-eye ARC with a round motif deposited on commercial MJSC that achieves short-circuit current (I SC) gains greater than 2% at normal incidence and even higher in the case of tilted illumination. In this work, MJSC with different moth-eye ARC are characterized under quantum efficiency (QE) as well as under concentrated illumination I-V in order to assess their potential. Simulations based on coupled wave analysis (RCWA) are used to fit the experimental results with successful results.

Three-terminal heterojunction bipolar transistor solar cell for high-efficiency photovoltaic conversion

Here we propose, for the first time, a solar cell characterized by a semiconductor transistor structure (n/p/n or p/n/p) where the base-emitter junction is made of a high-bandgap semiconductor and the collector is made of a low-bandgap semiconductor. We calculate its detailed-balance efficiency limit and prove that it is the same one than that of a double-junction solar cell. The practical importance of this result relies on the simplicity of the structure that reduces the number of layers that are required to match the limiting efficiency of dual-junction solar cells without using tunnel junctions. The device naturally emerges as a three-terminal solar cell and can also be used as building block of multijunction solar cells with an increased number of junctions.

Inhibition of DNA methyltransferase stimulates the expression of signal transducer and activator of transcription 1, 2, and 3 genes in colon tumor cells

Inhibitors of DNA methyltransferase, typified by 5-aza-2′-deoxycytidine (5-Aza-CdR), induce the expression of genes transcriptionally down-regulated by de novo methylation in tumor cells. We utilized gene expression microarrays to examine the effects of 5-Aza-CdR treatment in HT29 colon adenocarcinoma cells. This analysis revealed the induction of a set of genes that implicated IFN signaling in the HT29 cellular response to 5-Aza-CdR. Subsequent investigations revealed that the induction of this gene set correlates with the induction of signal transducer and activator of transcription (STAT) 1, 2, and 3 genes and their activation by endogenous IFN-α. These observations implicate the induction of the IFN-response pathway as a major cellular response to 5-Aza-CdR and suggests that the expression of STATs 1, 2, and 3 can be regulated by DNA methylation. Consistent with STAT’s limiting cell responsiveness to IFN, we found that 5-Aza-CdR treatment sensitized HT29 cells to growth inhibition by exogenous IFN-α2a, indicating that 5-Aza-CdR should be investigated as a potentiator of IFN responsiveness in certain IFN-resistant tumors.

Genetic evidence for the involvement of DNA ligase IV in the DNA-PK-dependent pathway of non-homologous end joining in mammalian cells

Cells of vertebrates remove DNA double-strand breaks (DSBs) from their genome predominantly utilizing a fast, DNA-PKcs-dependent form of non-homologous end joining (D-NHEJ). Mutants with inactive DNA-PKcs remove the majority of DNA DSBs utilizing a slow, DNA-PKcs-independent pathway that does not utilize genes of the RAD52 epistasis group, is error-prone and can therefore be classified as a form of NHEJ (termed basic or B-NHEJ). We studied the role of DNA ligase IV in these pathways of NHEJ. Although biochemical studies show physical and functional interactions between the DNA-PKcs/Ku and the DNA ligase IV/Xrcc4 complexes suggesting operation within the same pathway, genetic evidence to support this notion is lacking in mammalian cells. Primary human fibroblasts (180BR) with an inactivating mutation in DNA ligase IV, rejoined DNA DSBs predominantly with slow kinetics similar to those observed in cells deficient in DNA-PKcs, or in wild-type cells treated with wortmannin to inactivate DNA-PK. Treatment of 180BR cells with wortmannin had only a small effect on DNA DSB rejoining and no effect on cell radiosensitivity to killing although it sensitized control cells to 180BR levels. This is consistent with DNA ligase IV functioning as a component of the D-NHEJ, and demonstrates the unperturbed operation of the DNA-PKcs-independent pathway (B-NHEJ) at significantly reduced levels of DNA ligase IV. In vitro, extracts of 180BR cells supported end joining of restriction endonuclease-digested plasmid to the same degree as extracts of control cells when tested at 10 mM Mg2+. At 0.5 mM Mg2+, where only DNA ligase IV is expected to retain activity, low levels of end joining (∼10% of 10 mM) were seen in the control but there was no detectable activity in 180BR cells. Antibodies raised against DNA ligase IV did not measurably inhibit end joining at 10 mM Mg2+ in either cell line. Thus, in contrast to the situation in vivo, end joining in vitro is dominated by pathways with properties similar to B-NHEJ that do not display a strong dependence on DNA ligase IV, with D-NHEJ retaining only a limited contribution. The implications of these observations to studies of NHEJ in vivo and in vitro are discussed.

Advanced photovoltaic concentrator cells : quarterly technical progress report no. 5 for period September 1 - November 30, 1980 /

"Work Performed Under Contract No. AC02-77CH00178."

Commercialization of a thick film solar cell : quarterly technical progress report for April 1 - June 30, 1980 /

"Work Performed Under Contract No. AC02-77CH00178."

Commercialization of a thick film solar cell : quarterly technical progress report for period September 1 - October 1, 1980 /

"Work Performed Under Contract No. AC02-77CH00178."

Low-cost process for P-N junction-type solar cell : quarterly report 4 for May 30 - September 1, 1980 /

"Work Performed Under Contract No. AC02-77CH00178."