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DOE OSTI2022

Molecular Doping Increases the Semitransparent Photovoltaic Performance of Dilute Bulk Heterojunction Film with Discontinuous Polymer Donor Networks

The semitransparent and colorful properties of organic solar cells (OSCs) attract intensive academic interests due to their potential application in building integrated photovoltaics, wearable electronics, and so forth. The most straightforward and effective method to tune these optical properties is varying the componential ratio in the blend film. However, the increase in device transmittance inevitably sacrifices the photovoltaic performance because of severe carrier recombination that originates from discontinuous charge-transport networks in the blend film. In this work, a strategy is proposed via the molecular-doping strategy to overcome these shortcomings. It is discovered that p-doping is able to release the trapped holes in segregated polymer domains leading to short-circuit current enhancement, while n-doping is more effective to fill the bandgap states producing a higher fill factor. More importantly, either type of doping improves the photovoltaic performance in the semitransparent photovoltaic devices. These discoveries provide a new pathway to breaking the compromise between the photovoltaic performance and optical transmittance in semitransparent OSCs, and hold promise for their future commercialization.

14 SOLAR ENERGY↗

NASA NTRS2012

Preliminary Design of a Solar Photovoltaic Array for Net-Zero Energy Buildings at NASA Langley

An investigation was conducted to evaluate photovoltaic (solar electric systems) systems for a single building at NASA Langley as a representative case for alternative sustainable power generation. Building 1250 in the Science Directorate is comprised of office and laboratory space, and currently uses approximately 250,000 kW/month of electrical power with a projected use of 200,000 kW/month with additional conservation measures. The installation would be applied towards a goal for having Building 1250 classified as a net-zero energy building as it would produce as much energy as it uses over the course of a year. Based on the facility s electrical demand, a photovoltaic system and associated hardware were characterized to determine the optimal system, and understand the possible impacts from its deployment. The findings of this investigation reveal that the 1.9 MW photovoltaic electrical system provides favorable and robust results. The solar electric system should supply the needed sustainable power solution especially if operation and maintenance of the system will be considered a significant component of the system deployment.

Cole, Stuart K.↗

DOE OSTI2021

Controlling distributed energy resources via deep reinforcement learning for load flexibility and energy efficiency

Behind-the-meter distributed energy resources (DERs), including building solar photovoltaic (PV) technology and electric battery storage, are increasingly being considered as solutions to support carbon reduction goals and increase grid reliability and resiliency. However, dynamic control of these resources in concert with traditional building loads, to effect efficiency and demand flexibility, is not yet commonplace in commercial control products. Traditional rule-based control algorithms do not offer integrated closed-loop control to optimize across systems, and most often, PV and battery systems are operated for energy arbitrage and demand charge management, and not for the provision of grid services. More advanced control approaches, such as MPC control have not been widely adopted in industry because they require significant expertise to develop and deploy. Recent advances in deep reinforcement learning (DRL) offer a promising option to optimize the operation of DER systems and building loads with reduced setup effort. However, there are limited studies that evaluate the efficacy of these methods to control multiple building subsystems simultaneously. Additionally, most of the research has been conducted in simulated environments as opposed to real buildings. This paper proposes a DRL approach that uses a deep deterministic policy gradient algorithm for integrated control of HVAC and electric battery storage systems in the presence of on-site PV generation. The DRL algorithm, trained on synthetic data, was deployed in a physical test building and evaluated against a baseline that uses the current best-in-class rule-based control strategies. Performance in delivering energy efficiency, load shift, and load shed was tested using price-based signals. The results showed that the DRL-based controller can produce cost savings of up to 39.6% as compared to the baseline controller, while maintaining similar thermal comfort in the building. The project team has also integrated the simulation components developed during this work as an OpenAIGym environment and made it publicly available so that prospective DRL researchers can leverage this environment to evaluate alternate DRL algorithms.

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2020

An improved method for direct incident solar radiation calculation from hourly solar insolation data in building energy simulation

Solar radiation considerably influences the energy consumption of buildings and the power production of building integrated photovoltaic (BIPV) systems. Hourly solar insolation (Wh/m 2 ), represented as the amount of solar irradiance collected on the ground during a 1-h period, is the most common solar radiation data available and widely used in weather files applied in building energy modeling programs (BEMPs). Because the solar beam and position vary over time, the use of hourly insolation data as the input might result in errors in the estimation of the direct incident solar radiation on a particular surface. In this study, methods used in BEMPs for direct incident solar radiation calculations are first analyzed, and an improved method adopting a new algorithm for estimating the solar irradiance is proposed. Furthermore, the algorithm assumes that the solar irradiance changes linearly within a 1-h period and can be estimated based on the solar irradiance at the half clock and slope. The collected direct normal solar irradiance data of 2016 from eight solar radiation stations in China were used to demonstrate the proposed method and evaluate its performance by comparing the results with those from three conventional methods used in BEMPs along with the ground truth measurements. In addition, in this study, factors affecting the accuracy of the calculation results are explored. The results of the estimated direct incident solar radiation show that the proposed method achieves the best accuracy, followed by the methods used in DOE-2, EnergyPlus, and DeST. The proposed method guarantees that the hourly direct solar insolation will remain the same and reflects the variation in the direct solar irradiance across a 1-h time frame. The proposed method can be adopted in BEMPs to improve the accuracy of the solar radiation calculation, thereby improving the accuracy of the simulated building performance and the BIPV production.

14 SOLAR ENERGY↗

DOE OSTI2020

On-device lead sequestration for perovskite solar cells

Perovskite solar cells, as an emerging high-efficiency and low-cost photovoltaic technology face challenges on their way towards commercialization. Substantial improvements have been made to device stability but potential issues with lead toxicity and leaching from devices remain relatively unexplored. The potential for lead leakage could be perceived as an environmental and public health risk when using perovskite solar cells in building-integrated photovoltaics. Here we present a chemical approach for on-device sequestration of more than 96 per cent of lead leakage caused by severe device damage. A coating of lead-absorbing material is applied to the front and back sides of the device stack. On the glass side of the front transparent conducting electrode, we use a transparent lead-absorbing molecular film containing phosphonic acid groups that bind strongly to lead. On the back (metal) electrode side, we place a polymer film blended with lead-chelating agents between the metal electrode and a standard photovoltaic packing film. The lead-absorbing films on both sides swell to absorb the lead, rather than dissolve, when subjected to water soaking, thus retaining structural integrity for easy collection of lead after damage.

14 SOLAR ENERGY↗

NASA NTRS2014

Renewable Energy at NASA's Johnson Space Center

NASA's Johnson Space Center has implemented a great number of renewable energy systems. Renewable energy systems are necessary to research and implement if we humans are expected to continue to grow and thrive on this planet. These systems generate energy using renewable sources - water, wind, sun - things that we will not run out of. Johnson Space Center is helping to pave the way by installing and studying various renewable energy systems. The objective of this report will be to examine the completed renewable energy projects at NASA's Johnson Space Center for a time span of ten years, beginning in 2003 and ending in early 2014. This report will analyze the success of each project based on actual vs. projected savings and actual vs. projected efficiency. Additionally, both positive and negative experiences are documented so that lessons may be learned from past experiences. NASA is incorporating renewable energy wherever it can, including into buildings. According to the 2012 JSC Annual Sustainability Report, there are 321,660 square feet of green building space on JSC's campus. The two projects discussed here are major contributors to that statistic. These buildings were designed to meet various Leadership in Energy and Environmental Design (LEED) Certification criteria. LEED Certified buildings use 30 to 50 percent less energy and water compared to non-LEED buildings. The objectives of this project were to examine data from the renewable energy systems in two of the green buildings onsite - Building 12 and Building 20. In Building 12, data was examined from the solar photovoltaic arrays. In Building 20, data was examined from the solar water heater system. By examining the data from the two buildings, it could be determined if the renewable energy systems are operating efficiently. Objectives In Building 12, the data from the solar photovoltaic arrays shows that the system is continuously collecting energy from the sun, as shown by the graph below. Building 12 has two solar inverters, located on the second floor, that collected the data from the solar photovoltaic arrays. The data displayed here is the total energy produced by the system. These are cumulative amounts, so the last point on the graph shows all of the energy collected from the system since the start of its operation. The data shown here was manually collected from the solar inverters. However, the data is also automatically recorded through EBI. Through analysis of both sets of data it was determined that the EBI data was faulty. For example, from the manually collected data it can be determined that a total of 73 kWh of energy was collected between the dates of 1/16/2014 – 1/22/2014. The EBI data reports that approximately 17800 kWh of energy was collected during the same time frame. Not only does this exceed the time frame examined, but it also exceeds the total energy collected from the start of collection as recorded from the inverters. This leads to the belief that there is a malfunction with the automatic recording of the energy. In Building 20, data was examined from the solar water heater dating back many months and found that the pump for the solar water heater system was not operating properly, as exhibited in the graph shown below. The pump operates on a solar energy system, meaning that it collects energy throughout the day from the sun. Because of this, the system would stop operating shortly after the sun set because of a lack of sunlight. At that point, the graph should show a zero flow rate, but as exhibited in the graph below, that is not the case. It is clearly shown that the pump is continuously operating, even during the night. It was also observed that the majority of the time the pump would not turn on at all, despite good weather conditions. This led to the conclusion that the pump is malfunctioning, and needs to be examined and fixed.

McDowall, Lindsay↗

DOE OSTI2023

Observations and Lessons Learned in Residential Roofing Integrated Photovoltaics

The data file includes field observations of residential roofing integrated photovoltaics installation that happened between July 2021 and June 2022 in California. There are 21 observations - 2 in the re-roofing category and 19 in the new construction category. The file includes two time and motion forms (Re-Roofing & New Construction) we used to capture the time it takes for each activity in the rooftop solar and electrical installation process. You will see the duration for detailed steps along with activities that are included for total installation time for the paper. There are three parts to the time and motion form - Part 1 has project and crew characteristics, product information, and inspection and permitting data and can be filled before the installation. Part 2 has the actual installation time stamps and related notes. Part 3 has the crew information and can be filled on-site or off-site, but this section is optional. The re-roofing form has pre-solar activities and gutters and vents section in Part 2 of the form, whereas new construction form includes a section for capturing the time it took for rough wiring. The re-roofing form does not include rough wiring but instead includes the final electrical wiring process. These are the key differences in both the forms. Each day/step/installation activity needs to include the crew break time as they happen and there is space available to capture the crew breaks duration. In Table 1 below, the different terms used in the time and motion form are defined and their corresponding unit of measurement stated. We also highlight the optional sections. The data is captured in total mins, total hours, person mins, person hours. You can use this form or make edits to the form to recreate the study or make your own observations. The data herein was reviewed but may not be comprehensive. NREL invites questions and inputs to improve the data, including to: Correct erroneous information Fill in missing/updated information Clarifications on data and variables Updated information may be submitted to Sushmita Jena at sushmita.jena@nlr.gov.

14 SOLAR ENERGY↗

DOE OSTI2022

MgZnO High‐Voltage Transparent Thin‐Film Transistors Built on Glass

Recently, there has been increasing interest in building‐integrated photovoltaic (BIPV), which enables harvesting solar energy effectively. Large‐area glass components such as windows are widely used in modern constructions. In addition to the PV on opaque components such as walls and roofs, the transparent photovoltaic (TPV) directly built on glass is complementary to fully utilize the PV energy in BIPV. A high‐voltage transparent thin‐film transistor (HVTTFT) built on glass is an ideal option for distributed microinverters for TPV modules. A wide‐bandgap oxide‐based HVTTFT on glass for this purpose is reported. The HVTTFT on glass uses ZnO‐based materials with different functions for two roles: a semiconductor Mg 0.01 Zn 0.99 O (MZO) as TFT channel and Al‐doped ZnO (AZO) as transparent conductive oxide (TCO) electrodes. The centrosymmetric circular structure of the MZO HVTTFT with a high‐k‐stacking gate dielectric enables a blocking voltage as high as ≈1 kV and an on/off ratio of 10 6 . The device exhibits an average optical transmittance of 81% over the visible spectrum.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

17.2% Efficient CdSexTe1−x solar cell with (InxGa1−x)2O3 emitter on lightweight and flexible glass

High-efficiency, lightweight, and flexible solar cells are sought for a variety of applications particularly when high power density and flexible form factors are desired. Development of solar cells on flexible substrates may also offer production advantages in roll-to-roll or sheet-to-sheet processes. Here, we report device efficiencies of 17.2% and 14.6%, under AM1.5G and AM0 irradiances, respectively, for a flexible, lightweight, CdTe-based solar cell. To advance the efficiency relative to the highest previously reported AM1.5G value of 16.4%, we used an indium gallium oxide (IGO) emitter layer on a cadmium stannate (CTO) transparent conductor, which was deposited on 100-μm thick Corning® Willow® Glass. A sputtered CdSe layer was employed to incorporate Se into a CdTe absorber that was deposited by close-space sublimation, and CuSCN was used as a hole transport layer between the CdTe and the back metal electrode. The IGO and CTO layers remained intact during the high temperature film processing as seen in cross-sectional imaging and elemental mapping. This device configuration offers great promise for building-integrated photovoltaics, space applications, and higher rate manufacturing.

Physics↗

DOE OSTI2026

Performance Modeling of Tandem Photovoltaics: A Yearlong Outdoor Degradation Analysis of a Ga⁢As//Si Minimodule

We present a performance modeling and degradation analysis framework for tandem photovoltaic modules, building upon established procedures for crystalline silicon devices and adapting them to account for the spectral sensitivity of multijunction technologies. The methodology employs filter criteria to select outdoor measurements close to standard test conditions (STC) under stable spectral and ambient conditions, followed by normalization of power production data with corrections for temperature, irradiance, and precipitable water vapor. We demonstrate this framework using a mechanically stacked four-terminal gallium arsenide (Ga⁢As) // silicon (Si) tandem solar minimodule deployed outdoors from October 2019 to January 2021 in Golden, Colorado, USA. We determined degradation rates of −4.1 ±0.2%/year for the Ga⁢As subcell and −2.5 ±0.9%/year for the Si subcell, with analysis of individual performance metrics indicating that packaging degradation, particularly delamination, was the dominant failure mode. Simulations using PVcircuit, an open-source equivalent-circuit solver, confirmed these findings. The presented methodology provides a reproducible foundation for performance modeling and degradation analysis of emerging tandem technologies.

14 SOLAR ENERGY↗

DOE OSTI2022

Distribution System Research Roadmap; Energy Efficiency and Renewable Energy

The scope of the U.S. Department of Energy's Energy Efficiency and Renewable Energy (EERE) office covers a number of distributed energy resource (DER) technologies, including distributed photovoltaics, smart buildings, wind, water, behind-the-meter-storage, and electric vehicles. The impact of these technologies on the distribution system is often assessed with an individual technology focus. Similarly, different technology offices often leverage different sets of tools, leading to analyses that are not comparable. EERE sought the ability to assess the impact of integrating multiple DER technologies, and to comprehensively address DER integration challenges across the portfolio of EERE technologies. This project built on existing work understanding technical challenges, mapped out the key research questions, assessed relevant capabilities across the national laboratory network, identified key gaps, and produced a research roadmap to inform EERE investment decisions.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

NASA NTRS1973

NSF presentation

Wind energy conversion research is considered in the framework of the national energy problem. Research and development efforts for the practical application of solar energy -- including wind energy -- as alternative energy supplies are assessed in: (1) Heating and cooling of buildings; (2) photovoltaic energy conversion; (3) solar thermal energy conversion; (4) wind energy conversion; (5) ocean thermal energy conversion; (6) photosynthetic production of organic matter; and (7) conversion of organic matter into fuels.

Morse, F. H.↗

NASA NTRS1996

Mir Cooperative Solar Array Project Accelerated Life Thermal Cycling Test

The Mir Cooperative Solar Array (MCSA) project was a joint U.S./Russian effort to build a photovoltaic (PV) solar array and deliver it to the Russian space station Mir. The MCSA will be used to increase the electrical power on Mir and provide PV array performance data in support of Phase 1 of the International Space Station. The MCSA was brought to Mir by space shuttle Atlantis in November 1995. This report describes an accelerated thermal life cycle test which was performed on two samples of the MCSA. In eight months time, two MCSA solar array 'mini' panel test articles were simultaneously put through 24,000 thermal cycles. There was no significant degradation in the structural integrity of the test articles and no electrical degradation, not including one cell damaged early and removed from consideration. The nature of the performance degradation caused by this one cell is briefly discussed. As a result of this test, changes were made to improve some aspects of the solar cell coupon-to-support frame interface on the flight unit. It was concluded from the results that the integration of the U.S. solar cell modules with the Russian support structure would be able to withstand at least 24,000 thermal cycles (4 years on-orbit). This was considered a successful development test.

Hoffman, David J.↗

NASA NTRS1997

Thermal Cycling of Mir Cooperative Solar Array (MCSA) Test Panels

The Mir Cooperative Solar Array (MCSA) project was a joint US/Russian effort to build a photovoltaic (PV) solar array and deliver it to the Russian space station Mir. The MCSA is currently being used to increase the electrical power on Mir and provide PV array performance data in support of Phase 1 of the International Space Station (ISS), which will use arrays based on the same solar cells used in the MCSA. The US supplied the photovoltaic power modules (PPMs) and provided technical and programmatic oversight while Russia provided the array support structures and deployment mechanism and built and tested the array. In order to ensure that there would be no problems with the interface between US and Russian hardware, an accelerated thermal life cycle test was performed at NASA Lewis Research Center on two representative samples of the MCSA. Over an eight-month period (August 1994 - March 1995), two 15-cell MCSA solar array 'mini' panel test articles were simultaneously put through 24,000 thermal cycles (+80 C to -100 C), equivalent to four years on-orbit. The test objectives, facility, procedure and results are described in this paper. Post-test inspection and evaluation revealed no significant degradation in the structural integrity of the test articles and no electrical degradation, not including one cell damaged early as an artifact of the test and removed from consideration. The interesting nature of the performance degradation caused by this one cell, which only occurred at elevated temperatures, is discussed. As a result of this test, changes were made to improve some aspects of the solar cell coupon-to-support frame interface on the flight unit. It was concluded from the results that the integration of the US solar cell modules with the Russian support structure would be able to withstand at least 24,000 thermal cycles (4 years on-orbit).

Hoffman, David J.↗

NASA NTRS2012

Nanotube Production Devices Expand Research Capabilities

In order for the Hubble Space Telescope to take incredible, never-seen-before shots of celestial bodies and then send them back to Earth, the spacecraft needs power. While in orbit, Hubble cannot plug into an electrical outlet or stop at a store for some batteries. One of the ways NASA supplies power aboard a spacecraft is by harnessing energy from the most powerful entity in the solar system: the Sun. Since the 1960s, photovoltaic technology, or technology that converts sunlight into electricity, has been instrumental in the exploration of space. To build upon existing photovoltaic technology, NASA s Glenn Research Center has worked on a variety of innovative designs and materials to incorporate into photovoltaic cells, the building blocks of solar power systems. One of these materials is the carbon nanotube - a tiny structure about 50,000 times finer than the average human hair, with notably high electrical and thermal conductivity and an extreme amount of mechanical strength. Such properties give carbon nanotubes great potential to enhance the reliability of power generation and storage devices in space and on Earth. Dennis J. Flood, the branch chief of the photovoltaic division at Glenn in the 1990s, was looking into using carbon nanotubes to improve the efficiency of solar cells when he ran into a major roadblock - high-quality carbon nanotubes were not readily available. To address this problem, one of the chemists in Flood s group came up with a process and system for growing them. A senior chemist at Glenn, Aloysius F. Hepp, devised an injection chemical vapor deposition process using a specific organometallic catalyst in a two-zone furnace. Hepp's group found the unique process produced high-quality carbon nanotubes with less than 5 percent metal impurity. In addition, the process was more efficient than existing techniques, as it eliminated pre-patterning of the substrate used for growing the nanotubes, a timely and cost-prohibitive step.

Source record↗

NASA NTRS1978

The application of photovoltaic roof shingles to residential and commercial buildings

The recent development of a shingle-type solar-cell module makes it possible to incorporate easily photovoltaic power generation into the sloping roofs of residential or commercial buildings. These modules, which use a closely packed array of nineteen 53-mm-diameter circular solar cells, are capable of producing 101 watts/sq m of module area under standard operating conditions. This module performance is achievable by the use of solar cells with an average efficiency of 13.3 percent at 1 kW/sq m air-mass-1.5 insolation and at a cell temperature of 28 C. When these modules are mounted on a sloping south-facing roof which is insulated on the rear surface, the annual energy generated at the maximum power operating point will vary from 255.6 to 137.3 kWh/sq m of module area depending on the site location, with Albuquerque, NM, and Seattle, WA, representing the highest and lowest values of the thirteen sites considered.

Shepard, N. F., Jr.↗

DOE OSTI2024

DuraMAT: Building a Consortium to Accelerate the Photovoltaic Module Reliability Learning Cycle

Durable and reliable photovoltaic (PV) modules are critical to enabling an efficient transition to sustainable energy generation. The rate at which new module designs and materials are developed and deployed currently outpaces the rate at which we can identify failure mechanisms and understand degradation rates. Increasing the service life of PV modules, and our ability to predict performance over time, requires more durable materials and designs, better durability testing, more extensive material characterization, robust modeling, and methods to cross-examine historical performance data to extract meaningful results. This is a multidisciplinary challenge that requires expertise from a broad range of fields and, therefore, benefits significantly from a collaborative approach. In this Perspective, we outline the approach taken by the Durable Module Materials Consortium (DuraMAT), present a few case studies where our approach was successful, and provide an outlook on where this approach might be applied as the PV technology landscape continues to rapidly evolve. Published by the American Physical Society 2024

14 SOLAR ENERGY↗

DOE OSTI2024

Modeling Distributed Generation in California

In support of analysis for the biennial Integrated Energy Policy Report, the California Energy Commission and the National Renewable Energy Laboratory have partnered to study the growth of distributed energy resources in California. This study involves the use of National Renewable Energy Laboratory's Distributed Generation Market Demand model, available at https://www.nrel.gov/analysis/dgen/, to project statewide adoption of distributed photovoltaics and paired storage. Key outcomes of the collaboration include: • Improved representation of California building stock, load profiles, historical adoption, and tariffs, including the net billing tariff, in the dGen model; • Trained CEC staff members to use and adapt the dGen model for their specific needs; • Developed a methodology for representing emerging consumer segments to potentially adopt distributed energy resources, including low-income, multifamily, and renter-occupied buildings; • Forecasted solar photovoltaic and paired storage growth in California using a common set of modeling parameters. This report describes the multiyear effort, which includes a discussion of: • Methodology and data employed in adapting the Distributed Generation Market Demand model for California to forecast solar photovoltaic and storage statewide through 2040; • Steps taken to modify the base model to forecast solar photovoltaic adoption in emerging market segments such as multifamily or renter-occupied homes or both; • Future enhancements of the model.

14 SOLAR ENERGY↗