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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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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Reducing Residential PV System PII Costs

SolarPro article outlining the residential pv solar permitting landscape as it exists today, outlining inefficiencies and bottlenecks. Description of resources and best practices to help reduce current cost and resource contraints.

14 SOLAR ENERGY↗
DOE OSTI2018

A Coordinated Compensation Strategy for Module-Mismatch of CHB-PV Systems Based on Improved LS-PWM and Reactive Power Injection

Here, the cascaded H-bridge (CHB) converter has become a promising candidate topology for utility-scale photovoltaic systems thanks to merits like modular structure, distributed maximum power point tracking (MPPT), and direct distribution grid access without medium-voltage transformers, etc. However, module-mismatches arising from non-ideal elements like partial shading and parameter variations pose a technical challenge for such systems. If not dealt with properly, module-mismatches can lead to adverse effects like unbalanced dc-link voltages of the modules, distortion of grid current, reduced power generation, etc. Conventional methods, such as reactive power compensation and level-shifted pulse-width modulation (LS-PWM) based compensation, can alleviate this issue, but their performances are still limited by the allowable modulation range of power converters. In this paper, a compensation strategy combining reactive power compensation with a novel modulation method is proposed to extend the operating range in terms of module mismatch. Experimental results on a 2.4kW/208V single-phase setup are presented and have demonstrated that the proposed method can not only ride through a larger range of module-mismatches but also improve solar power utilization and system efficiency owing to reduced switching events, non-compromised MPPT, and less required reactive power.

42 ENGINEERING↗
DOE OSTI2022

Sizing battery energy storage and PV system in an extreme fast charging station considering uncertainties and battery degradation

In this paper, we present mixed integer linear programming (MILP) formulations to obtain optimal sizing for a battery energy storage system (BESS) and solar generation system in an extreme fast charging station (XFCS) to reduce the annualized total cost. The proposed model characterizes a typical year with eight representative scenarios and obtains the optimal energy management for the station and BESS operation to exploit the energy arbitrage for each scenario. Contrasting extant literature, this paper proposes a constant power constant voltage (CPCV) based improved probabilistic approach to model the XFCS charging demand for weekdays and weekends. This paper also accounts for the monthly and annual demand charges based on realistic utility tariffs. Furthermore, BESS life degradation is considered in the model to ensure no replacement is needed during the considered planning horizon. Different from the literature, this paper offers pragmatic MILP formulations to tally BESS charge/discharge cycles using the cumulative charge/discharge energy concept. McCormick relaxations and the Big-M method are utilized to relax the bi-linear terms in the BESS operational constraints. Finally, a robust optimization-based MILP model is proposed and leveraged to account for uncertainties in electricity price, solar generation, and XFCS demand. Case studies were performed to signify the efficacy of the proposed formulations.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2016

PV Systems Reliability Final Technical Report: Ground Fault Detection

We have examined ground faults in PhotoVoltaic (PV) arrays and the efficacy of fuse, current detection (RCD), current sense monitoring/relays (CSM), isolation/insulation (Riso) monitoring, and Ground Fault Detection and Isolation (GFID) using simulations based on a Simulation Program with Integrated Circuit Emphasis SPICE ground fault circuit model, experimental ground faults installed on real arrays, and theoretical equations.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2025

Cost-optimized energy storage operation for a grid-connected solar PV system at community and individual scales

This study provides a comparative analysis of grid-connected PV-integrated battery storage at individual and community scales. The paper addresses the challenge of managing energy demand-generation mismatch by using a battery energy storage optimization algorithm, which minimizes operational costs while accounting for battery degradation. Also, this work introduces a broader evaluation basis that includes seasonal variability, grid exchange smoothness, and scalability across different battery capacities. Results show that community-scale storage more effectively dampens grid exchange power fluctuations and reduces system costs, particularly with moderate price differences between electricity buying and selling prices and low battery capacities. The paper also analyzes the impacts of static control versus cost-optimized battery system management. Here, it is shown that the gap in system costs between the cost-optimized and static control scenarios widens as the price difference increases.

25 ENERGY STORAGE↗
DOE OSTI2021

Ganged-PV System Evaluation

The following report contains data and data summaries collected for the SkySun LLC elevated Ganged PV arrays. These arrays were fabricated as a series of PV panels in various orientations, suspended by cables, at the National Solar Thermal Test Facility (NSTTF) at Sandia National Laboratories (SNL). Starting in February of 2021, Sandia personnel have collected power and accelerometer data for these arrays to assess design and operational efficacy of varying ganged- PV configurations. The purpose of this power data collection was to see how the various array orientations compare in power collection capability depending on the time of day, year, and the specific daily solar direct normal irradiance (DNI). The power data was collected as a measurement of the power output from the various series strings. The project team measured direct current (DC) voltage and current from the respective arrays. The accelerometer data was collected with the purpose of demonstrating potential destructive mode shapes that could take place with each of the arrays when exposed to high winds. This allowed the team to evaluate whether impacts with respect to specific array orientations using suspended cables is a safe design. All data collection was performed during calendar year 2021.

14 SOLAR ENERGY↗
DOE OSTI2013

High Energy Yield Distributed Architecture for Large Commercial and Utility-Scale PV Systems

Photovoltaic energy has come a long way from its early days when small cells were fabricated in the labs in the early 50s. While it took a long time for PV modules to mature into what we now see in the market and in rooftops across the world, the power electronics has been lagging behind & was always the weakest point in the PV plant, being responsible for the majority of failures & robbing the PV plants of their full potential by losing precious Watts in the process of converting power from DC to AC. Since the early days of PV power, it has been recognized that the modules need to operate at their maximum power point in order to extract as much power as is available from the PV modules at a given time of day and year. Numerous maximum power point devices were developed to do just this. While effective at extracting as much power as they can, soon after there was a realization that in a PV installation where a central inverter is used, many losses occur, hence energy yield losses. This has led to thinking about alternative architectures where the maximum power point tracking (MPPT) is performed much closer to the modules rather than at a central inverter. Several architectures were proposed ranging from a microinverter, microconverter, string inverter, string optimizer, and to a multi-string inverter or optimizer. While these architectures promise to increase the energy yield by 5% to 25% (depending where MPPT is located), & recovering losses due to shading, soiling, mismatch … there were no real studies and implementations in the field to corroborate these numbers. The program that GE Global Research proposed & received funding for is aimed at a type of distributed architectures, namely the dc architectures where only the MPPT function is distributed across the PV plant. Further, the project is concerned with choosing the right architecture for large scale commercial & utility scale plants but not residential installations. Findings from Task 1- Define Requirements & Develop Architecture- showed that for large scale commercial & utility PV plants, locating the MPPT at the string level with a string size of >3kW is the most cost effective solution & that the increase in energy yield of 6% to 8% is more than enough to make up for the increased cost due to additional power electronics. Our study also shows that in addition to an increase in energy yield, having a dc/dc converter at the string level brings additional benefits such as increased array visibility, allowing for increased monitoring and diagnostics; high and constant dc bus voltage which allows for reducing losses further and optimizing the inverter; and ability to detect ground and arc faults. Task 2 focused on designing a suitable dc/dc converter that meets the requirements defined in Task 1: Efficiency, Cost, & Reliability. For this task, we surveyed and simulated all candidate topologies known by the practitioners in the field. We also generated a novel topology, simulated it, & compared it to existing topologies. Our novel topology being a partial power processing converter came out on top due to its simplicity (fewer parts), it high efficiency, its reliability, and its lower cost. In the remaining tasks of the project, we built the hardware, tested it first in the lab, then in the field and once we worked out all the bugs and issues and were confident our system was robust, we installed it on the rooftop and started collecting the data by mid-Q3 2012. We shared our work with the scientific community in the form of conference & Journal papers, hence contributing to the general understanding of this technology area. The methods, techniques, and hardware developed under this project have all been tested in the field over long periods of time, and under many conditions and have been shown to be robust and reliable. The converters built and developed under this program have been in operation in the field since mid-June 2012, and no hardware failures have been recorded. While some software issues have been seen, none have been showstoppers. The cost analysis of the hardware showed that it meets the cost target set in the requirement document developed in the trade-off study. Improving the performance of solar installations for commercial and utility scale plants contributes to reducing their cost of ownership, hence spreading them to a larger section of the society and making them affordable. Our project contributed to the understanding of the distributed architectures, showed that PV plants’ cost of electricity can be reduced through additional power electronics which allows for harvesting more energy from the plant. When the project started in 2009, the cost of PV energy was still high, hence there was a real need to increase the energy yield, hence reduce the levelized cost of electricity (LCOE). While costs have come down significantly, the need for increasing the energy yield is still relevant, hence the project results, hardware, and techniques developed are still pertinent today. By taking this project from concept to rooftop demonstration, we showed that the technology is mature enough, robust enough, and has the potential to be used by many more customers, hence benefiting the public in general through the spread of PV energy, which ultimately contributes to reducing our dependency on fossil fuel, improving the environment, and creating more jobs.

14 SOLAR ENERGY↗
DOE OSTI2024

Quantifying and Valuing Fundamental Characteristics and Benefits of Floating PV Systems

This project undertook the first systematic and comprehensive collection of Floating Photovoltaic (FPV) related techno-ecological data across diverse geographic regions of the United States. It examined FPV performance, assessed potential environmental risks and benefits, and provided data to support the development of research protocols for better understanding the impacts of FPV. As part of this process, we conducted a detailed study of four existing FPV sites and three land-based PV (LPV) sites in Florida and California.

14 SOLAR ENERGY↗
DOE OSTI2013

Low Cost Arc Fault Detection and Protection for PV Systems

Final report for Tigo Energy Incubator project. The specific objective of this 18-month research effort was to develop an off-the-shelf arc-fault detector. The starting point of the project was a prototype detector that was constructed using discrete components and laboratory equipment. An intermediate objective was to build a technically viable detector using programmable components in the detector circuitry. The final objective was to build a commercially viable detector by reducing the cost of the circuitry through the use of more sophisticated programmable components and higher levels of integration.

14 SOLAR ENERGY↗
DOE OSTI2015

Real-time Series Resistance Monitoring in PV Systems; NREL (National Renewable Energy Laboratory)

We apply the physical principles of a familiar method, suns-Voc, to a new application: the real-time detection of series resistance changes in modules and systems operating outside. The real-time series resistance (RTSR) method that we describe avoids the need for collecting IV curves or constructing full series-resistance-free IV curves. RTSR is most readily deployable at the module level on apply the physical principles of a familiar method, suns-Voc, to a new application: the real-time detection of series resistance changes in modules and systems operating outside. The real-time series resistance (RTSR) method that we describe avoids the need for collecting IV curves or constructing full series-resistance-free IV curves. RTSR is most readily deployable at the module level on micro-inverters or module-integrated electronics, but it can also be extended to full strings. Automated detection of series resistance increases can provide early warnings of some of the most common reliability issues, which also pose fire risks, including broken ribbons, broken solder bonds, and contact problems in the junction or combiner box. We describe the method in detail and describe a sample application to data collected from modules operating in the field.

14 SOLAR ENERGY↗
DOE OSTI2021

Mismatch losses in a PV system due to shortened strings

Numerous events may require intentional removal of one or more photovoltaic modules from a string, shortening the length of the string relative to others within the array, resulting in a string length mismatch. The impact of such a mismatch is not well understood either in measurable operational effects (voltage, current, power) or in the potential effects on long-term module health. It is impractical to solely approach this problem experimentally due to the size and complexity of arrays that may experience string length shortening. Here this work presents simulations, validated through limited field experiments on a two string array, providing a basis from which more complex arrays and scenarios may be explored. Refinement of the simulation achieves an overall error in IMPP for the nominal (S 1 ) and test strings (S 2 ) between the simulation and experimental values, through all test conditions, of +0.35 ± 1.46% and -0.36 ± 1.58% respectively. Shortening one of two strings by one module results in a power loss greater than the power contribution of the module alone (1.29 module equivalents); the impact increases through the maximum test case of a six module mismatch with a power loss equivalent to more than 11 modules. The impact of using string-end blocking diodes is presented with an emphasis at the array maximum power point and at open circuit. Implications are discussed for arrays of higher complexity.

14 SOLAR ENERGY↗