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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Calibration and Rating of Photovoltaics: Preprint

Rating the performance of photovoltaic (PV) modules is critical to determining the cost per watt, and efficiency is useful to assess the relative progress among PV concepts. Procedures for determining the efficiency for PV technologies from 1-sun to low concentration to high concentration are discussed. We also discuss the state of the art in primary and secondary calibration of PV referencecells used by calibration laboratories around the world. Finally, we consider challenges to rating PV technologies and areas for improvement.

14 SOLAR ENERGY↗
DOE OSTI2024

Introducing the Baseline Performance Reference (BPR) for Irradiance in PV System Applications

Photovoltaic (PV) reference cells, modules, and arrays respond in a complex manner to the many variables that define their operating environment. PV reference cells for irradiance measurement have similarities but also differences to operational PV modules. For this reason, a more neutral and a well-defined generic PV reference cell is needed, whose characteristics are close enough to most operational PV devices to make stable performance indicators possible but whose characteristics are not necessarily identical to any of them. This poster describes a new well-defined reference quantity for outdoor PV measurements, called the baseline performance reference (BPR).

baseline performance reference↗
DOE OSTI2025

PV Reference Cells for Outdoor Use: Stability Over Four Years of Deployment

Photovoltaic (PV) reference cells are frequently used to evaluate the performance of PV power plants. They provide a measure of irradiance that strongly correlates with the electrical output of PV modules, which makes them very useful for detecting short-term anomalies or long-term degradation in PV power plant output. One very important quality is long-term stability. This report presents observations about the stability of a set of 22 commercial reference cells that have been in continuous operation for a period of four years at the Solar Radiation Research Laboratory (SRRL) site at the National Renewable Energy Laboratory (NREL). The 22 reference cells at the SRRL represent 10 different models from 6 manufacturers.

14 SOLAR ENERGY↗
DOE OSTI2018

Validation of reference genes for real-time PCR of cord blood mononuclear cells, differentiating endothelial progenitor cells, and mature endothelial cells

Highlights: • RT-qPCR was used to assess and follow the differentiation of EPCs. • A set of reliable and non-variable genes is key to obtain accurate RT-qPCR results. • The relative gene expression of CD34+ and differentiating endothelial progenitor cells was determined. • The optimal set of reference for the gene expression studies performed by RT-qPCR was determined. In the last ten years, endothelial progenitor cells (EPCs) have gained interest as an attractive cell population in regenerative medicine for vascular applications. This population is defined as the precursor of endothelial mature cells (ECs) through a process of differentiation. To our knowledge, no single marker can be used to discriminate them from mature ECs. To effectively study their differentiation kinetics, gene expression must be assessed. Quantitative real-time PCR (RT-qPCR) is widely used to analyze gene expression. To minimize the impact of variances from RT-qPCR, a rigorous selection of reference genes must be performed prior to any experiments due to variations in experimental conditions. In this study, CD34+ mononuclear cells were extracted from human cord blood and differentiated into EPCs after seeding for a maximum period of 21 days. To choose the best combinations of reference genes, we compared the results of EPCs, CD34+ mononuclear cells, and mature endothelial cells to ensure that the differentiation kinetics did not affect the expression of our selected reference genes. The expression levels of seven genes, namely, YWHAZ, GAPDH, HPRT1, RPLP0, UBC, B2M, and TBP were thus compared. The algorithms geNorm, NormFinder, BestKeeper, and the Comparative ΔCt method were employed to assess the expression of each candidate gene. Overall results reveal that the expression stability of reference genes may differ depending on the statistical program used. YWHAZ, GAPDH, and UBC composed the optimal set of reference genes for the gene expression studies performed by RT-qPCR in our experimental conditions. This work can thus serve as a starting point for the selection of candidate reference genes to normalize the levels of gene expression in endothelial progenitor cell populations.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

Analysis of SOFCs Using Reference Electrodes

Reference electrodes are frequently applied to isolate the performance of one electrode in a solid oxide fuel cell. However, reference electrode simulations raise doubt to veracity of data collected using reference electrodes. The simulations predict that the reported performance for the one electrode will frequently contain performance of both electrodes. Nonetheless, recent reports persistently treat data so collected as ideally isolated. This work confirms the predictions of the reference electrode simulations on two SOFC designs, and to provides a method of validating the data measured in the 3-electrode configuration. Validation is based on the assumption that a change in gas composition to one electrode does not affect the impedance of the other electrode at open circuit voltage. This assumption is supported by a full physics simulation of the SOFC. Three configurations of reference electrode and cell design are experimentally examined using various gas flows and two temperatures. Impedance data are subjected to deconvolution analysis and equivalent circuit fitting and approximate polarization resistances of the cathode and anode are determined. The results demonstrate that the utility of reference electrodes is limited and often wholly inappropriate. Reported impedances and single electrode polarization values must be scrutinized on this basis.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2016

Tuning back contact property via artificial interface dipoles in Si/organic hybrid solar cells

Back contact property plays a key role in the charge collection efficiency of c-Si/poly(3,4-ethylthiophene):poly(styrenesulfonate) hybrid solar cells (Si-HSCs), as an alternative for the high-efficiency and low-cost photovoltaic devices. In this letter, we utilize the water soluble poly (ethylene oxide) (PEO) to modify the Al/Si interface to be an Ohmic contact via interface dipole tuning, decreasing the work function of the Al film. This Ohmic contact improves the electron collection efficiency of the rear electrode, increasing the short circuit current density (J{sub sc}). Furthermore, the interface dipoles make the band bending downward to increase the total barrier height of built-in electric field of the solar cell, enhancing the open circuit voltage (V{sub oc}). The PEO solar cell exhibits an excellent performance, 12.29% power conversion efficiency, a 25.28% increase from the reference solar cell without a PEO interlayer. The simple and water soluble method as a promising alternative is used to develop the interfacial contact quality of the rear electrode for the high photovoltaic performance of Si-HSCs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Examining Effects of Negative to Positive Capacity Ratio in Three-Electrode Lithium-Ion Cells with Layered Oxide Cathode and Si Anode

The negative to positive electrode capacity ratio (N:P) is crucial for lithium-ion cell design because it affects both energy density and long-term performance. Here, the effect of N:P ratio on electrochemical performance has been investigated for NMC 532 /Si cells containing a reference electrode. By monitoring individual electrode potentials, depths of lithiation/delithiation at the anode and cathode could be determined. The superior performance of the higher N:P cell, including greater reversibility, better capacity retention and lower impedance rise, can be attributed to smaller volume changes in the silicon particles during electrochemical cycling.

25 ENERGY STORAGE↗
DOE OSTI2025

Photovoltaic Mini-Module Soiling Stations: Cooperative Research and Development (Final Report)

Photovoltaic (PV) panels can become soiled due to a variety of environmental factors. This soiling reduces the amount of light reaching the cells and thus their energy output. The ratio of actual output of the soiled device that of a clean device is known as the soiling ratio. The daily change in soiling ratio is known as the soiling rate. To study soiling for different glass coatings. Two soiling stations were fabricated. The stations were designed to monitor the short-circuit current of PV cells encapsulated with glass featuring different coatings and measure the daily soiling ratio with a pair of reference cells, one of which is automatically brushed daily. This work meets the need to understand how the glass coatings perform in additional environments. The stations are designed to quantify both the soiling ratio (the ratio between actual/expected photovoltaic panel power output) as well as differences in anti-soiling performance of different glass coatings. The design of the dirty/clean reference cell system is described by Toth et al. The soiling ratio is calculated by calculating the average irradiance measured within one hour of solar noon by each of the reference cells and then taking the ratio of these daily near-noon averages. The soiling ratio time series for the station deployed in Georgia is shown in Figure 1. This figure shows that the soiling ratio at the site has not yet fallen below 0.99, indicating that peak daily soiling losses have been below 1%. The site was chosen because it is thought to be affected by pollen soiling. With continued monitoring over the course of at least a full year, we expect to be able to observe and quantify pollen soiling events.

14 SOLAR ENERGY↗
DOE OSTI2015

Hydrogenated indium oxide window layers for high-efficiency Cu(In,Ga)Se{sub 2} solar cells

High mobility hydrogenated indium oxide is investigated as a transparent contact for thin film Cu(In,Ga)Se{sub 2} (CIGS) solar cells. Hydrogen doping of In{sub 2}O{sub 3} thin films is achieved by injection of H{sub 2}O water vapor or H{sub 2} gas during the sputter process. As-deposited amorphous In{sub 2}O{sub 3}:H films exhibit a high electron mobility of ∼50 cm{sup 2}/Vs at room temperature. A bulk hydrogen concentration of ∼4 at. % was measured for both optimized H{sub 2}O and H{sub 2}-processed films, although the H{sub 2}O-derived film exhibits a doping gradient as detected by elastic recoil detection analysis. Amorphous IOH films are implemented as front contacts in CIGS based solar cells, and their performance is compared with the reference ZnO:Al electrodes. The most significant feature of IOH containing devices is an enhanced open circuit voltage (V{sub OC}) of ∼20 mV regardless of the doping approach, whereas the short circuit current and fill factor remain the same for the H{sub 2}O case or slightly decrease for H{sub 2}. The overall power conversion efficiency is improved from 15.7% to 16.2% by substituting ZnO:Al with IOH (H{sub 2}O) as front contacts. Finally, stability tests of non-encapsulated solar cells in dry air at 80 °C and constant illumination for 500 h demonstrate a higher stability for IOH-containing devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Comparable Senescence Induction in Three-dimensional Human Cartilage Model by Exposure to Therapeutic Doses of X-rays or C-ions

Purpose: Particle therapy using carbon ions (C-ions) has been successfully used in the treatment of tumors resistant to conventional radiation therapy. However, the potential side effects to healthy cartilage exposed to lower linear energy transfer (LET) ions in the beam track before the tumor have not been evaluated. The aim of the present study was to assess the extent of damage after C-ion irradiation in a 3-dimensional (3D) cartilage model close to human homeostasis. Methods and Materials: Primary human articular chondrocytes from a healthy donor were cultured in a collagen scaffold to construct a physioxic 3D cartilage model. A 2-dimensional (2D) culture was used as a reference. The cells were irradiated with a single dose of a monoenergetic C-ion beam with a LET of approximatively 30 keV/μm. This LET corresponds to the entrance channel of C-ions in the shallow healthy tissues before the spread-out Bragg peak (∼100 keV/μm) during hadron therapy protocols. The same dose of X-rays was used as a reference. Survival, cell death, and senescence assays were performed. Results: As expected, in the 2D culture, C-ions were more efficient than X-rays in reducing cell survival with a relative biological effectiveness of 2.6. This correlated with stronger radiation-induced senescence (two-fold) but not with higher cell death induction. This differential effect was not reflected in the 3D culture. Both ionizing radiation types induced a comparable rate of senescence induction in the 3D model. Conclusions: The greater biological effectiveness of C-ions compared with low LET radiation when evaluated in treatment planning systems might be misevaluated using 2D culture experiments. Radiation-induced senescence is an important factor of potential cartilage attrition. The present data should encourage the scientific community to use relevant models and beams to improve the use of charged particles with better safety for patients.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

Comparison of Pyranometers and Reference Cells on Fixed and One-Axis Tracking Surfaces: Preprint

A wide variety of sensors are used to monitor the irradiance incident on solar modules to evaluate the performance of photovoltaic (PV) systems. These instruments range from secondary standard pyranometers to photodiode-based pyranometers to reference cells. Although instruments are mounted in the plane of array of the modules, a wide range of results have been obtained. Some of these difference have been assumed to come from systematic uncertainties associated with the irradiance sensors. This study is an attempt to quantify these differences by comparing the output of selected thermopile pyranometers to photodiode-based pyranometers and reference cells on a horizontal surface, a fixed-tilt surface, and a one-axis tracking surface. This analysis focuses on clear-sky results from two sites with different climatic conditions. Several important features were observed. Photodiode-based pyranometers and reference cells produce widely different results under clear skies, especially at larger angles of incidence, even though both instruments are based on measuring the short-circuit current of solar cells. The difference is caused by the scattering of light as it passes through the glazing of the reference cell or the diffuser lens of the photodioded-base pyranometer. Both instruments are shown to have similar response to the spectral distribution of the irradiance when compared to the thermopile-based pyranometer, which has a response nearly independent of the wavelength of light used by PV modules.

14 SOLAR ENERGY↗
DOE OSTI2023

The Baseline Performance Reference for Irradiance in PV System Applications

This report proposes the definition of a new baseline performance reference (BPR). The definition goes beyond existing standards pertaining to photovoltaic (PV) reference cells and devices to define the response under all possible operating conditions in the field. Field evaluations using BPR devices will be more sensitive to performance anomalies than pyranometers because they track PV system power output more closely. At the same time, they will be able to detect a broader range of performance anomalies than traditional matched reference devices, which might have matching defects. The BPR definition also opens the door to new practices in resource assessment and yield prediction. Solar resource data can be collected or modeled and validated directly as BPR irradiance, and PV system simulations based on BPR irradiance need fewer assumptions and less processing to obtain the effective irradiance on modules. As a result, lower uncertainty in yield assessments can be expected.

14 SOLAR ENERGY↗
DOE OSTI2012

Pyranometers and Reference Cells: Part 2: What Makes the Most Sense for PV Power Plants?

As described in Part 1 of this two-part series, thermopile pyranometers and photovoltaic (PV) reference cells can both be used to measure irradiance; however, there are subtle differences between the data that are obtained. This two-part article explores some implications of uncertainty and subtleties of accurately measuring PV efficiency in the field. Part 2 of the series shows how reference cells can be used to more confidently predict PV performance, but how this could best be accomplished if historic irradiance data could be available in PV-technology-specific formats.

14 SOLAR ENERGY↗
DOE OSTI2021

Spectral Effects in Albedo and Rearside Irradiance Measurement for Bifacial Performance Estimation

We investigate the impact of spectral dependence of ground surface reflectivity on albedo and rearside irradiance measurements necessary for bifacial photovoltaic (PV) module performance estimation and monitoring. Because PV modules are spectrally selective, albedo and irradiance measurements performed with common irradiance sensors may require spectral mismatch corrections when used for performance prediction. We investigate via simulation the differences in spectrally responsive albedo measured with thermopile pyranometers and crystalline silicon PV reference cells in comparison to a typical crystalline-silicon bifacial PV module. Simulations are performed for nine different representative ground surface materials using simulated solar spectra together with spectral reflectivity data distributed with the SMARTS simulation software. For the materials considered, the results show that albedo spectral mismatch relative to the bifacial module is distributed over a range of ±9.2% for thermopile pyranometers versus only ±3.7% for a typical PV reference cell. We consider the impact of this spectrally-responsive albedo mismatch on bifacial PV module rearside irradiance measurements. Using synthesized rearside spectral irradiance distributions, we find that for the nine different ground surface materials the predicted rearside irradiance measurement deviates from the effective irradiance observed by the PV module by on the order of 16.5 W/m 2 for the pyranometer and 3.6 W/m 2 for the PV reference cell. We discuss the implications for bifacial albedo and irradiance measurement.

41 EE - Solar Energy Technologies Office (EE-4S)↗
DOE OSTI2026

scPlantAnnotate: an accurate and robust transformer-based model for plant cell type annotation

Accurate cell type annotation remains a major bottleneck in plant single-cell RNA sequencing (scRNA-seq), where existing tools are often adapted from animal studies and perform sub-optimally on plant data. The lack of plant-specific computational frameworks limits the construction of plant cell atlases and downstream biological discovery. We develop and evaluate scPlantAnnotate, a Transformer-based reference annotation framework tailored for plant scRNA-seq data, and benchmark it against state-of-the-art deep learning and conventional methods across multiple plant species. Species-specific scPlantAnnotate models were trained using curated datasets from Arabidopsis thaliana, Zea mays, Oryza sativa, and Glycine max. We compared scPlantAnnotate with leading baselines under both standard random-split evaluation and a more stringent leave-one-dataset-out setting, which tests robustness to completely unseen datasets and tissue types. scPlantAnnotate consistently outperforms existing approaches across all four species under random-split evaluation. In the leave-one-dataset-out setting for A. thaliana, where performance drops markedly for all methods due to strong batch effects and dataset heterogeneity, scPlantAnnotate nonetheless achieves the highest Accuracy, Macro-F1, Balanced Accuracy, and Macro-AUROC on average and ranks first on most held-out datasets. These results demonstrate improved robustness to dataset shifts, a critical yet underexplored challenge in plant scRNA-seq analysis. A freely accessible web server enables users to annotate their own datasets using pretrained models. scPlantAnnotate provides a plant-specific, Transformer-based framework for single-cell annotation that delivers state-of-the-art performance and enhanced robustness to unseen datasets. By addressing limitations of existing tools and enabling scalable reference-based annotation, scPlantAnnotate supports the development of comprehensive plant cell atlases and facilitates broader use of single-cell genomics in plant biology.

Bioinformatics↗
DOE OSTI2018

A Comparison of Machine Learning Techniques to Extract Human Settlements from High Resolution Imagery

Two machine learning techniques were developed to extract human settlements from very high resolution (VHR) satellite images of 3 provinces in Afghanistan: Logar, Panjsher, and Wardak. The results were then compared with analyst verified reference data information known as the LandScan Settlement Layer (LandScan SL).[1] This study attempts to compare settlement mapping results from a support vector machine (SVM) classifier specifically integrated in a current settlement mapping framework and a deep learner utilizing a convolutional neural network (CNN) approach. By comparing the results from the SVM and the CNN to the reference data information we demonstrate that the CNN yields more accurate results overall, in terms of overall pixel cells, and the SVM performs more accurately in omission, based on derived statistics against the reference data information.

Weaver, Jeanette E↗
DOE OSTI2012

Pyranometers and Reference Cells, What's the Difference?: Preprint

As the photovoltaic industry has grown exponentially in the past decade, large photovoltaic (PV) fields have become more common. The investors for these projects calculate the expected return on investment based on expected electricity generation and adjust the interest rates and other financial terms according to the perceived risk. These calculations usually assume worst case according to thelisted warranty and any uncertainty in the measurement is translated directly into a reduced predicted performance. Because a 1% difference in predicted output could represent a large fraction of the expected return on investment, a small reduction in uncertainty translates into a much larger value to the entity making investment decisions. To reduce perceived risk in large-scale solarinvestments power plant performance (or production) guarantees have become increasingly common. This two part article explores some subtleties of accurately measuring PV efficiency in the field.

14 SOLAR ENERGY↗
DOE OSTI2019

Evaluating the Accuracy of Various Irradiance Models in Detecting Soiling of Irradiance Sensors: Preprint

We evaluate the feasibility of using various clear-sky models or purchased satellite data for estimating the soiling of a reference cell irradiance sensor. We find results to be more accurate for models that consider local meteorological conditions. We conclude that given the data sets considered, and depending on the requirements of the data analyst, choosing to use purchased satellite irradiance data from Solargis to estimate the soiling of a reference cell sensor tends to yield more accurate results, although there are instances where a clear-sky model performs better. The SOLIS clear-sky model in PVLIB with variable Pwat provided useful soiling results, implying that the general method of using a clear-sky model with local meteorological data may provide a low-cost tool for detecting soiling of irradiance sensors. irradiance data from Solargis to estimate the soiling of a reference cell sensor tends to yield more accurate results, although there are instances where a clear-sky model performs better. The SOLIS clear-sky model in PVLIB with variable Pwat provided useful soiling results, implying that the general method of using a clear-sky model with local meteorological data may provide a low-cost tool for detecting soiling of irradiance sensors.

14 SOLAR ENERGY↗