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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 OSTI2022

Improved CdTe PLR Estimates: Self-Shading and Spectral Mismatch

The RdTools year-on-year method of estimating performance loss rate (PLR) employs a simple normalization to remove the confounding effect of irradiance and temperature variation. However, the normalization's assumption that PV production scales linearly with in-plane broadband irradiance is a worse approximation for CdTe and other technologies with larger spectral sensitivities than it is for the more common c-Si technology. Additionally, CdTe systems using single-axis trackers (-20% of installed US utility-scale capacity) are subject to self-shading in the morning and afternoon, introducing another nonlinearity between PV output and broadband irradiance. Ignoring these effects may subject the estimated PLR to increased uncertainty, and perhaps bias, depending on the character of their short- and long-term variability. In this work we show that including self-shading and spectral mismatch models in the normalization for tracking CdTe systems can result not only in tighter PLR confidence intervals but different median PLRs as well. The shading and spectral models are kept simple to maintain consistency with the RdTools ethos of not requiring detailed system metadata or unusual measurements.

CdTe↗
DOE OSTI2020

bifiPV2020 Bifacial Workshop: A Technology Overview

The virtual bifiPV Workshop was held in July 2020 to provide the solar industry with a forum for sharing and discussing research into bifacial photovoltaic (PV) technology. This report outlines major insights from the workshop to give the reader an overview of the latest developments in bifacial PV technology worldwide, from the lab to the field. Citations are drawn from this workshop unless otherwise noted, with all proceedings available online at bifipvworkshop. com. Presentations for the bifiPV2020 Workshop focused on the following areas: bifacial power plant modeling and simulation, albedo improvements, the development of encapsulants, the durability and reliability of current bifacial technologies, performance comparisons between glass-glass and glass-transparent backsheet configurations, the future of passivated emitter and rear contact (PERC) solar cells, and the growing adoption of n-type solar cells. With 650 GW total PV installed worldwide and 1 TW to come very soon, PERC is now the standard PV cell type produced en masse. However, it is already reaching 23% efficiency, the upper limit for this type of technology. PV modules breaking the 0.5-kW barrier are starting to appear, and the costs of standard PERC technology are already below 0.2 USD/Wp. In 2019, five GW of bifacial PV were installed worldwide. In 2020, the majority of bifacial installations are expected to be located in the United States, China, and Middle East and North Africa (MENA) states. N-type bifacial technologies are becoming increasingly viable and have huge potential to dominate the market in the coming years. With bifacial technology mounted on horizontal single-axis trackers (HSAT), bids below 10 USD/MWh will soon be observed in the MENA region, and later in Chile and the United States. Factory audits and reliability testing can reduce field failures by helping buyers to select producers that follow rigorous quality assurance and quality control processes.

14 SOLAR ENERGY↗
DOE OSTI2020

bifiPV2020 Bifacial Workshop: A Technology Overview

The virtual bifiPV Workshop was held in July 2020 to provide the solar industry with a forum for sharing and discussing research into bifacial photovoltaic (PV) technology. This report outlines major insights from the workshop to give the reader an overview of the latest developments in bifacial PV technology worldwide, from the lab to the field. Citations are drawn from this workshop unless otherwise noted. Presentations for the bifiPV2020 Workshop focused on the following areas: bifacial power plant modeling and simulation, albedo improvements, the development of encapsulants, the durability and reliability of current bifacial technologies, performance comparisons between glass-glass and glass-transparent backsheet configurations, the future of passivated emitter and rear contact (PERC) solar cells, and the growing adoption of n-type solar cells. With 650 GW total PV installed worldwide and 1 TW to come very soon, PERC is now the standard PV cell type produced en masse. However, it is already reaching 23% efficiency, the upper limit for this type of technology. PV modules breaking the 0.5-kW barrier are starting to appear, and the costs of standard PERC technology are already below 0.2 USD/Wp. In 2019, five GW of bifacial PV were installed worldwide. In 2020, the majority of bifacial installations are expected to be located in the United States, China, and Middle East and North Africa (MENA) states. N-type bifacial technologies are becoming increasingly viable and have huge potential to dominate the market in the coming years. With bifacial technology mounted on horizontal single-axis trackers (HSAT), bids below 10 USD/MWh will soon be observed in the MENA region, and later in Chile and the United States. Factory audits and reliability testing can reduce field failures by helping buyers to select producers that follow rigorous quality assurance and quality control processes.

14 SOLAR ENERGY↗
DOE OSTI2022

PV Reference Cells for Outdoor Use: Comparison of First-Year Field Measurements

Reference cells are widely used in the photovoltaic (PV) industry to measure irradiance. For field applications and outdoor use, a variety of products are on the market, and they are often perceived as low-cost alternatives to thermopile pyranometers. But reference cell characteristics, such as directional and spectral response, fundamentally differ from pyranometers, and measurements made by the former cannot be substituted for or directly compared with the latter. The National Renewable Energy Laboratory's (NREL's) Solar Radiation Research Laboratory is currently in a multiyear effort to develop guidance and recommendations for the design and use of outdoor reference cells, with a view to reducing inconsistencies and measurement uncertainty. The core of this effort is the long-term deployment of multiple products from different manufacturers that are mounted at a fixed tilt, on a single-axis tracker, and on a dual-axis tracker. This report provides an analysis of the data collected during the first year of operation at the NREL location. An overall assessment is made by comparing the total energy measured by each instrument to the other instruments having the same orientation. These totals are calculated for three different scenarios: (1) using the factory calibration factors, (2) using the previously determined NREL Cell Lab calibration factors, and (3) using the newly determined field calibration factors derived from the recorded measurements. Because the true or correct measurement values are unknown, pair-wise comparisons are made. The results show that the difference between the highest and lowest measured energy can exceed 3% when using the factory calibration factors. Consistency among instruments improves when Cell Lab calibrations are used, and it further improves when using field calibration factors.

14 SOLAR ENERGY↗
DOE OSTI2023

Bifacial PV Module Energy Modeling Validation Study

The cost delta between monofacial and bifacial photovoltaic (PV) modules was decreasing in 2018 when this study was initially proposed, making bifacial modules an attractive offering. However, there were limited field studies available that could be considered utility-scale representative, and PV module manufacturers were stating large ranges for the expected energy yield improvements of bifacial technology. This generated uncertainties regarding bifacial performance gains and the actual LCOE (levelized cost of energy). There was also relatively low confidence in the industry’s energy modeling tools’ ability to accurately predict bifacial energy yield, meaning that early adopters of bifacial modules were not able to fully account for the increased energy yield in their energy and financial models. The intent of this project was to provide the solar industry with greater certainty on the energy yield gains of bifacial modules and provide higher confidence in the ability for different energy modeling software to model bifacial PV site performance. Achieving this would allow for bifacial technology to become bankable (i.e. accepted by Independent Engineers, site financiers and other PV site stakeholders), offering a step change in PV site performance that had not been seen since the widespread adoption of the single-axis tracker. Over the course of this study other economic factors including a significant tariff exemption for bifacial modules resulted in accelerated adoption of bifacial technology throughout the US utility scale solar segment. The number of early adopters increased rapidly, and with many investors accepting this module choice the question of bifacial bankability was seemingly answered faster than expected. However, PVEL’s study has still achieved significant accomplishments in demonstrating the accuracy of bifacial modeling across three different software platforms. The results of this study have shown that the mean biased error (MBE) between the field data and the predicted values from all three software platforms were aligned with a maximum MBE of 1.3% and a minimum MBE of -1.8%.

14 SOLAR ENERGY↗
DOE OSTI2024

An Updated Life Cycle Assessment of Utility-Scale Solar Photovoltaic Systems Installed in the United States

Given the high deployment targets for solar photovoltaics (PV) needed to meet U.S. decarbonization goals, and the limited carbon budget remaining to limit global temperature rise, accurate accounting of the energy-use and greenhouse-gas emissions over the life-cycle of PV systems is needed. In the United States, most PV systems are large utility-scale systems which use single-axis trackers and central inverters, which are not commonly examined in existing life-cycle assessment (LCA) literature. In this study, we present a cradle-to-grave LCA of a typical silicon U.S. utility PV (UPV) installation which is consistent with the utility system features documented in the annual NREL PV system cost benchmark reports. We analyze and present results for four main metrics: cumulative energy demand (CED), greenhouse gas (GHG) emissions, energy payback time (EPBT), and carbon payback time (CPBT). We consider six primary manufacturing options: three based on an imported PV module supply chain (comparing low-carbon imports, high-carbon imports, and average imports), and three based on a potential domestic PV module supply chain (comparing low-carbon U.S. regions, high-carbon U.S. regions, and average U.S. regions). These manufacturing options were then paired with installation locations to create six main cases: low-carbon options were installed in Phoenix (Arizona), high-carbon options were installed in Seattle (Washington), and average options were installed in Fredonia (Kansas). These locations were selected to represent a range of irradiance and grid mixes in the United States, in order to illustrate the likely range of EPBTs and CPBTs possible across the United States. For all six cases, a sensitivity analysis for end-of-life (EOL) handling was explored to capture current and future management options: landfilling, partial recycling, and high-quality recycling. For the purposes of this report, the benchmark system was defined to use an average imported supply chain with partial recycling, installed in Fredonia (Kansas). CED results show ratios at or below 0.1 MJ oil-eq /MJgenerated which demonstrates efficient use of primary energy resources (below a 1:1 ratio), and represents a slight improvement over previous results in literature. GHG emissions per kWh range from 10-36 g CO 2 e, which are consistent with or lower than previous results published by NREL and IEA-PVPS. We use a graphical approach for calculating EPBT and CPBT in this report, which improves upon methods typically used in literature by accounting for non-linearity and avoiding data quality issues associated with long-term projections. EPBT was determined to vary from 0.5 to 1.2 years, with a benchmark EPBT of 0.6 years; CPBT was shown to vary from 0.8 to 20 years, with benchmark CPBT of 2.1 years, which is lower than other estimates from recent literature (typically >2 years).

14 SOLAR ENERGY↗
DOE OSTI2026

PV Systems Modelling with Python

PVSC tutorial demonstrating how to download irradiance data and sun position for a specific location, determine the orientation of a single-axis tracker system, calculate Plane of Array irradiance, and estimate the power output of a PV system.

14 SOLAR ENERGY↗
NASA NTRS1973

Evaluation of the electro-optic direction sensor

Evaluation of a no-moving-parts single-axis star tracker called an electro-optic direction sensor (EODS) concept is described and the results are given in detail. The work involved experimental evaluation of a breadboard sensor yielding results which would permit design of a prototype sensor for a specific application. The laboratory work included evaluation of the noise equivalent input angle of the sensor, demonstration of a technique for producing an acquisition signal, constraints on the useful field-of-view, and a qualitative evaluation of the effects of stray light. In addition, the potential of the silicon avalanche-type photodiode for this application was investigated. No benefit in noise figure was found, but the easily adjustable gain of the avalanche device was useful. The use of mechanical tuning of the modulating element to reduce voltage requirements was also explored. The predicted performance of EODS in both photomultiplier and solid state detector configurations was compared to an existing state-of-the-art star tracker.

Johnson, A. R.↗
NASA NTRS1979

Single-axle, double-axis solar tracker

Solar concentrator tracking mechanism consisting of angular axle and two synchronized drive motors, follows seasonal as well as diurnal changes in earth's orientation with respect to incoming sunlight.

Brantley, L. W.↗
NASA NTRS1976

Advanced application flight experiments precision attitude determination system. Volume 2: System tests

The performance capability of each of two precision attitude determination systems (PADS), one using a strapdown star tracker, and the other using a single-axis gimbal star tracker was measured in the laboratory under simulated orbit conditions. The primary focus of the evaluation was on the contribution to the total system accuracy by the star trackers, and the effectiveness of the software algorithms in functioning with actual sensor signals. A brief description of PADS, the laboratory test configuration and the test facility, is given along with a discussion of the data handling and display, laboratory computer programs, PADS performance evaluation programs, and the strapdown and gimbal system tests. Results are presented and discussed.

Source record↗
NASA NTRS1977

Performance tests of two precision attitude determination systems

Results of laboratory performance tests of two satellite attitude determination systems are given. One system employed a strapdown star tracker and gyro assembly, the other a single axis, gimballed star tracker and a gyro assembly. The laboratory tests simulated those orbit conditions which would be experienced on a three axis stabilized, earth pointed satellite in geosynchronous orbit. A ground-fixed laboratory test was performed in which system axes remained stationary in the laboratory coordinates while revolving star beams stimulated the star trackers. The laboratory instrumentation techniques used to meet the stringent accuracy requirements are described. Results are presented which show both systems met the performance goal of 3.6 arc seconds. Comparative analyses of both systems are also discussed.

Mcaloon, K. J.↗
NASA NTRS1987

An approach to conducting observations of non-trackable objects utilizing the Spartan spacecraft

The approach taken in the design of the guidance and navigation system for a 48-hour observation of Halley's Comet near perihelion passage, utilizing the SPARTAN 200 series carrier, is discussed. Autonomous vehicle navigation techniques that utilized solar sensors, a single star tracker, a 3-axis gyro package, and two independent cooperative microprocessors are described. While the Spartan-Halley spacecraft was destroyed during the Space Shuttle Challenger explosion, it is believed that the present approach has considerable potential for application to future missions that require autonomous control to perform scientific observations of nontrackable moving targets.

Watzin, James G.↗
NASA NTRS2023

Earth/Moon System Star Tracking Sensor for Improved Deep Space Laser Communications

The goal of this research is to improve deep space communication links by exploring a new concept in stellar navigation that uses images of the Earth/Moon system to obtain precise pointing information so that the laser signal from the satellite can be directed at the ground station with unprecedented accuracy. Currently, the concept for satellite pointing relies on a dual axis star tracker that compares images of the celestial sphere to a star catalog to obtain a 3-axis orientation solution. Most star trackers are designed with a wide field of view (required to obtain enough bright starts to achieve a navigational fix) and only provide reliable pitch and yaw estimates thus necessitating the use of a second star tracker looking at an axis perpendicular to the first one to obtain an accurate estimate of the roll of the spacecraft. In the new concept the optical design will be modified to ensure that both the Earth and the Moon will be within a narrow field of view centered on Earth relative to the field of view of most star tracking systems. Because of the proximity of the bodies, it is possible to obtain highly accurate estimates of the pitch, yaw and roll of the spacecraft relative to the Earth/Moon system. The new tracker will allow for accurate 3-axis control of the spacecraft from a single tracker thus allowing the second star tracker, which would normally be pointed in a direction perpendicular to the one pointed at earth, to obtain the spacecraft roll estimate. This wide field star tracker facilitates functions like the initial satellite pointing during the acquisition phase of establishing the laser communication link or solving the lost in space problem should the system need to be reset. This new design will be tested in simulation and compared for 3-axis pointing accuracy against a standard commercial star tracker.

Star tracker↗
NASA NTRS2008

An ATP System for Deep-Space Optical Communication

An acquisition, tracking, and pointing (ATP) system is proposed for aiming an optical-communications downlink laser beam from deep space. In providing for a direction reference, the concept exploits the mature technology of star trackers to eliminate the need for a costly and potentially hazardous laser beacon. The system would include one optical and two inertial sensors, each contributing primarily to a different portion of the frequency spectrum of the pointing signal: a star tracker (<10 Hz), a gyroscope (<50 Hz), and a precise fluid-rotor inertial angular-displacement sensor (sometimes called, simply, "angle sensor") for the frequency range >50 Hz. The outputs of these sensors would be combined in an iterative averaging process to obtain high-bandwidth, high-accuracy pointing knowledge. The accuracy of pointing knowledge obtainable by use of the system was estimated on the basis of an 8-cm-diameter telescope and known parameters of commercially available star trackers and inertial sensors: The single-axis pointing-knowledge error was found to be characterized by a standard deviation of 150 nanoradians - below the maximum value (between 200 and 300 nanoradians) likely to be tolerable in deep-space optical communications.

Lee, Shinhak↗
DOE OSTI2026

Solar-Tracker Diffuse-Response Algorithm for Balancing Energy Gain and Mechanical Wear in Photovoltaic Systems

Single-axis solar tracking maximizes photovoltaic energy production under clear-sky conditions; however, its effectiveness decreases under cloudy and overcast skies, where diffuse irradiance dominates and the optimal module orientation changes. Conventional tracking algorithms either neglect sky conditions or rely on simplified diffuse-response strategies that may trigger frequent tracker repositioning under variable cloud cover, leading to increased mechanical wear with marginal energy gains. This work proposes an enhanced diffuse-response tracking algorithm that explicitly accounts for both the intensity and temporal persistence of cloudiness. By requiring overcast conditions to persist for a minimum duration before reorienting the tracker to a diffuse-stow position, the proposed approach reduces unnecessary movements while preserving the benefits of diffuse-response operation. The algorithm is evaluated through numerical simulations based on historical meteorological data and validated using field measurements on monofacial and bifacial photovoltaic strings. The results show that the proposed strategy reduces excess tracker movement from 114% to 0.16% while maintaining nearly the same energy yield. Compared to a conventional diffuse-response algorithm, the associated energy reduction is minimal (≈0.17%) relative to the ≈0.37% yield gain observed at the studied location. These findings demonstrate that incorporating cloudiness duration enables a practical compromise between energy performance and tracker durability, particularly for monofacial photovoltaic systems.

14 SOLAR ENERGY↗
NASA NTRS2005

Attitude Control System Design for the Solar Dynamics Observatory

The Solar Dynamics Observatory mission, part of the Living With a Star program, will place a geosynchronous satellite in orbit to observe the Sun and relay data to a dedicated ground station at all times. SDO remains Sun- pointing throughout most of its mission for the instruments to take measurements of the Sun. The SDO attitude control system is a single-fault tolerant design. Its fully redundant attitude sensor complement includes 16 coarse Sun sensors, a digital Sun sensor, 3 two-axis inertial reference units, 2 star trackers, and 4 guide telescopes. Attitude actuation is performed using 4 reaction wheels and 8 thrusters, and a single main engine nominally provides velocity-change thrust. The attitude control software has five nominal control modes-3 wheel-based modes and 2 thruster-based modes. A wheel-based Safehold running in the attitude control electronics box improves the robustness of the system as a whole. All six modes are designed on the same basic proportional-integral-derivative attitude error structure, with more robust modes setting their integral gains to zero. The paper details the mode designs and their uses.

Starin, Scott R.↗
DOE OSTI2024

Simulating Wind-Driven Loading on PV Systems

As PV modules continue to trend toward larger, thinner, and more flexible forms they grow more susceptible to damage from dynamic wind loading. As a result, understanding the impact of wind on PV systems, particularly when mounted on compliant solar-tracking hardware, and identifying robust, stable array layouts and stow strategies is becoming increasingly important for the PV community. We are developing an open-source software package, PVade (PV aerodynamic design engineering), to simulate the cascading fluid-structure interaction that occurs within single-axis, solar-tracking arrays to enable researchers to test hardware, layout, and tracker control changes, leading to enhanced stability and a reduction in wind-driven damage. We will give an overview of the PVade software and present the latest outcomes from our ongoing validation campaign in which we compare time series and statistical structural responses with field data. From there, we will present simulated results from a larger, multi-row array and highlight the effect of varying tracker angles on stability and the differences between positive and negative tilt angles.

fluid↗