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DOE OSTI2022

Multiport Control with Partial Power Processing in Solid-State Transformer for PV, Storage, and Fast-Charging Electric Vehicle Integration

This article proposes a multiport control method to enable partial power processing (PPP) in a medium-voltage (MV) multiport solid-state transformer (SST). MV multiport SSTs are promising in integrating low-voltage DC sources or loads such as solar photovoltaic, energy storage, and electric vehicles into smart grids without bulky line-frequency transformers. Compared to voltage-source SST, current-source (CS) SST features single-stage isolated bidirectional AC/AC, AC/DC, or DC/DC conversion using an inductive DC link. For a multiport CS SST, it is revealed in this article that the PPP capability can be enabled through the proposed control without extra hardware, different from the case of voltage-source converters where special hardware architecture is required for the PPP. With the PPP, most power exchange between LV ports is processed by only a fraction of the entire conversion stage, leading to reduced DC-link current, volume, loss, and improved efficiency. The proposed multiport PPP control scheme is analyzed to verify the advantages across a wide voltage and power range against conventional full power processing (FPP) multiport control, using the soft-switching solid-state transformer (S4T) with reduced conduction loss as an example. Comparative experimental results based on a SiC three-port S4T prototype verify the effectiveness of the proposed PPP scheme against the FPP scheme under both steady state and dynamic conditions. Here, the DC-link current reduction is measured to be more than 36%. Significantly, the proposed multiport PPP control scheme is generic and applicable to any hard-switching or soft-switching CS SSTs without extra hardware.

14 SOLAR ENERGY↗

DOE OSTI2015

Absorption enhancement through Fabry-Pérot resonant modes in a 430 nm thick InGaAs/GaAsP multiple quantum wells solar cell

We study light management in a 430 nm-thick GaAs p-i-n single junction solar cell with 10 pairs of InGaAs/GaAsP multiple quantum wells (MQWs). The epitaxial layer transfer on a gold mirror improves light absorption and increases the external quantum efficiency below GaAs bandgap by a factor of four through the excitation of Fabry-Perot resonances. We show a good agreement with optical simulation and achieve around 10% conversion efficiency. We demonstrate numerically that this promising result can be further improved by anti-reflection layers. This study paves the way to very thin MQWs solar cells.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2026

Upgrading Biogas through in situ Conversion of Carbon Dioxide to Biomethane in Anaerobic Digesters

Organic waste streams generated by wastewater treatment plants, agricultural operations, and food processing industries represent an important yet underutilized opportunity for renewable energy production in the United States. Through anaerobic digestion, these waste streams can produce biogas, a mixture primarily composed of methane (CH4) and carbon dioxide (CO2), that can be upgraded to pipeline-quality natural gas. However, most existing upgrading technologies remove CO2 from biogas rather than utilizing it, leaving a significant portion of the potential energy unused. This project investigates a novel biological upgrading approach that converts CO2 into additional CH4 by supplying hydrogen (H2) to specialized microorganisms capable of performing hydrogenotrophic methanation. The main challenges associated with biological biogas upgrading are related to hydrogen supply, gas-liquid mass transfer, and process stability. First, due to the high cost of hydrogen gas, it is preferable that H2 be produced on-site using renewable energy sources such as wind or solar power. Second, hydrogen has low solubility in liquids, which limits its availability to microorganisms and requires strategies to improve gas dissolution and transfer within the reactor. Third, process inhibition may occur as a result of increased pH caused by CO2 consumption or elevated H2 partial pressure, both of which can negatively affect methanogenic activity. Although research in these areas has advanced during the course of this project, these challenges have not yet been fully resolved. To date, the biological systems that have achieved the highest methane concentrations are typically ex-situ reactors, where operational conditions can be more easily controlled. For this reason, the findings of the present project remain highly relevant. The project goal was to develop an innovative system that can accomplish biogas upgrading via biological conversion of CO2 to CH4, in a novel hybrid approach that combines the advantages of both in-situ and ex-situ systems. The proposed system employs a three-phase upflow anaerobic bioreactor with H2 delivery through a gas-permeable membrane, enabling efficient hydrogen transfer and microbial conversion. Under optimized operating conditions, the system achieved 99% H2 consumption and 90% CO2 conversion. A subsequent gas cleaning stage was implemented to further improve gas quality and meet target purity standards. The upgraded gas composition reached 97.7% CH4, 2.2% CO2, and 0.97% O2, while H2S concentrations remained below detection limits. In addition, a flue gas-driven inorganic thermoelectric generator (TEG) system was designed and experimentally validated as a potential source of electricity for H2 production. The system consisted of six TEG modules connected in series and achieved an open-circuit voltage of 4.5 V and a maximum power output of 224 mW at a temperature difference of approximately 53.5 °C, demonstrating effective conversion of waste heat into electrical power under simulated flue gas conditions. Finally, a comprehensive techno-economic analysis was completed to evaluate the capital and operating costs associated with the proposed system. The results provide important insights to guide future scale-up, optimization, and potential deployment of integrated biological biogas upgrading technologies.

09 BIOMASS FUELS↗

DOE OSTI2017

Demonstrating Hybrid Heat Transport and Energy Conversion System Performance Characterization Using Intelligent Control Systems

The debate continues on the magnitude and validity of climate change caused by human activities. However, there is no debate about the need to make buildings, modes of transportation, factories, and homes as energy efficient as possible. Given that climate change could occur with the wasteful use of fossil fuel and the fact that fossil energy costs could and will swing wildly, it is imperative that every effort be made to utilize energy sources to their fullest. Hybrid energy systems (HES) are two or more separate energy producers used together to produce energy commodities. The HES this report focuses on is the use of nuclear reactor waste heat as a source of further energy utilization. Nuclear reactors use a fluid to cool the core and produce the steam needed for the production of electricity. Traditionally this steam, or coolant, is used to convert the energy then cooled elsewhere. The heat is released into the environment without being used further. By adding technologies to nuclear reactors to use the wasted heat, a system can be developed to make more than just electricity and allow for loading following capabilities.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2015

Study on limiting efficiencies of a-Si:H/μc-Si:H-based single-nanowire solar cells under single and tandem junction configurations

Detailed balance calculations are presented for a-Si:H/μc-Si:H-based single- and tandem-junction single-nanowire solar cells (S- and T-SNSCs). Our study is based on three-dimensional finite-element electromagnetic simulation and thermodynamic balanced analysis, which includes radiative and Auger recombinations simultaneously. We quantify and compare the limiting short-circuit current densities, open-circuit voltages, and light-conversion efficiencies of these highly compact photovoltaic cells, addressing especially the effect of Auger recombination on the open-circuit voltages of SNSCs. Results show that tandem design leads to much higher light-conversion capability than μc-Si:H S-SNSCs, but exhibits superior performance than a-Si:H S-SNSCs only for cells with large radii.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2022

Nanostructured carbon as highly efficient and stable anodes for ethylene production and power generation in protonic ceramic electrochemical cells

Protonic ceramic electrochemical cells (PCECs) have the potential in reducing the energy input and carbon emissions in ethylene production from ethane dehydrogenation. The performance of conventional perovskite-based anode materials for ethane conversion in PCECs is limited by their low active surface area and proneness to coke deposition. In this work, for the first time, we demonstrate the use of aligned carbon nanotube forests (CNTFs) as a novel anode material for an ethane fueled PCEC to co-produce ethylene and electricity. The CNTF electrode was grown on the electrolyte by the chemical vapor deposition (CVD) method. Highly dispersed iron carbide nanoparticles are formed in situ on the CNTFs during the CVD process, acting as highly active catalysts for ethane dehydrogenation. The novel PCECs show superior catalytic and electrochemical performances to that using conventional perovskite-based anodes. The cell also exhibits excellent durability and anti-coking abilities within 100 h test. This work showcases the promising application of nanostructured carbon, a new class of non-perovskite materials, as the multifunctional electrode materials for PCECs.

03 NATURAL GAS↗

DOE OSTI2016

Solution-based electrical doping of semiconducting polymer films over a limited depth

Solution-based electrical doping protocols may allow more versatility in the design of organic electronic devices; yet, controlling the diffusion of dopants in organic semiconductors and their stability has proven challenging. Here we present a solution-based approach for electrical p-doping of films of donor conjugated organic semiconductors and their blends with acceptors over a limited depth with a decay constant of 10–20 nm by post-process immersion into a polyoxometalate solution (phosphomolybdic acid, PMA) in nitromethane. PMA-doped films show increased electrical conductivity and work function, reduced solubility in the processing solvent, and improved photo-oxidative stability in air. Here, this approach is applicable to a variety of organic semiconductors used in photovoltaics and field-effect transistors. PMA doping over a limited depth of bulk heterojunction polymeric films, in which amine-containing polymers were mixed in the solution used for film formation, enables single-layer organic photovoltaic devices, processed at room temperature, with power conversion efficiencies up to 5.9 ± 0.2% and stable performance on shelf-lifetime studies at 60 °C for at least 280 h.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Engineering Design of Advanced H 2 – CO 2 Pd and Pd/Alloy Composite Membrane Separations and Process Intensification

The integrated gasification combined cycle (IGCC) process is a way to co-produce synthesis gas, electricity, hydrogen, fuels and chemicals from coal and coal/biomass-mix in an environmentally responsible manner. The production of hydrogen via the water-gas shift (WGS) reaction is a key part of this process. Pd and Pd/Alloy-based catalytic membrane reactors used in the WGS process could significantly improve the efficiency of the IGCC process with a great potential for process intensification. Membrane reactors enable reaction, separation and product concentration to take place in a single unit operation, leading to conversion levels beyond thermodynamic equilibrium due to the continuous removal of H 2 . Worcester Polytechnic Institute (WPI) has developed composite Pd and Pd/alloy composite hydrogen separation membranes with high H 2 flux, excellent selectivity and long-term durability for this membrane reactor process. WPI membranes used in a natural gas reforming operation were stable for over 6,000 hours (>8 months) at 500°C and 40 bar. Under the DOE Hydrogen Pathway Program (DE-FC-26-07NT43058) Pd membranes prepared by WPI exceed the DOE 2015 targets for H 2 flux, selectivity and stability. Furthermore, the scalability of the WPI technology has been shown to be relatively easy, and composite Pd/Cu and Pd/Au alloy membranes have been shown to be sulfur resistant and permeance recoverable.

42 ENGINEERING↗

DOE OSTI2016

Engineering Bioelectronic Signal Transduction Using the Bacterial Type III Secretion Apparatus

Engineering efficient methods for living systems to transfer electrical energy to non-living systems, at relevant size scales, continues to challenge our knowledge of materials and biology. Our goal was to enable signal transduction between cells and inorganic materials, using controlled electron transport as the energy transfer mechanism. We envision using the cell as a living battery, providing a set of environmental signals to trigger synthetic biological networks that divert intracellular electron transport pathways to inorganic extracellular structures. Conversely, changing electron influxes could guide cellular responses. It is challenging, however, to precisely engineer nanostructured materials to achieve controllable catalytic or electronic properties and connect them with biological energy sources. Our approach to this problem is to engineer protein scaffolds, taking advantage of the native recognition, selectivity and self-assembly properties of these nano-scale building blocks as well as their native intracellular localization patterns. We are using a type III secretion system (T3SS) needle protein from Salmonella enterica, PrgI, as a template for metal nanowire synthesis for biosensing and bioenergy applications. We demonstrate that purified PrgI monomers spontaneously self assemble into long filaments, and that high-affinity peptide tags specific for attachment to functionalized particles can be integrated into the N-terminal region of PrgI. The resulting filaments selectively bind to gold, whether the filaments are assembled in vitro, sheared from cells, or remain attached to live S. enterica cell membranes. Chemical reduction of the gold modified PrgI variants results in structures that are several microns in length and which incorporate a contiguous gold surface.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2023

Techno-Economic Analysis of a Thermally Integrated Solid Oxide Fuel Cell and Compressed Air Energy Storage Hybrid System

Natural-gas-fueled solid oxide fuel cell (SOFC) systems have the potential for high-efficiency conversion of carbon to power due to the underlying electrochemical conversion process while readily facilitating carbon capture through the separation of the fuel and oxidant sources. Compressed air energy storage (CAES) technology can potentially store significant quantities of energy for later use with a high round-trip efficiency and lower cost when compared with state-of-the-art battery technology. The base load generation capability of SOFC can be coupled with CAES technology to provide a potentially flexible, low-carbon solution to meet the fluctuating electricity demands imposed by the increasing share of intermittent variable renewable energy (VRE) production. SOFC and CAES can be hybridized through thermal integration to maximize power output during periods of high electrical demand and then store power when either demand is low or renewable generation reduces power prices. The techno-economics of a low-carbon hybrid SOFC and CAES system was developed and investigated in the present study. The proposed hybrid system was found to be cost-competitive with other power-generating base-load facilities when power availability was considered. The hybrid system shows increased resilience to changes in a high VRE grid market scenario.

25 ENERGY STORAGE↗

NASA NTRS2001

A 3-D Magnetic Analysis of a Stirling Convertor Linear Alternator Under Load

The NASA Glenn Research Center (GRC), the Department of Energy (DOE), and the Stirling Technology Company (STC) are developing Stirling convertors for Stirling Radioisotope Power Systems (SRPS) to provide electrical power for future NASA deep space missions. STC is developing the 55-We Technology Demonstration Convertor (TDC) under contract to DOE. Of critical importance to the successful development of the Stirling convertor for space power applications is the development of a lightweight and highly efficient linear alternator. This paper presents a 3-dimensional finite element method (FEM) approach for evaluating Stirling convertor linear alternators. The model extends a magnetostatic analysis previously reported at the 35th Intersociety Energy Conversion Engineering Conference (IECEC) to include the effects of the load current. STC's 55-We linear alternator design was selected to validate the model. Spatial plots of magnetic field strength (H) are presented in the region of the exciting permanent magnets. The margin for permanent magnet demagnetization is calculated at the expected magnet operating temperature for the near earth environment and for various average magnet temperatures. These thermal conditions were selected to represent a worst-case condition for the planned deep space missions. This paper presents plots that identify regions of high H where the potential to alter the magnetic moment of the magnets exists.

Geng, Steven M.↗

NASA NTRS2008

Single-mode, All-Solid-State Nd:YAG Laser Pumped UV Converter

In this paper, the status of a high-energy, all solid-state Nd:YAG laser pumped nonlinear optics based UV converter development is discussed. The high-energy UV transmitter technology is being developed for ozone sensing applications from space based platforms using differential lidar technique. The goal is to generate greater than 200 mJ/pulse with 10-50 Hz PRF at wavelengths of 308 nm and 320 nm. A diode-pumped, all-solid-state and single longitudinal mode Nd:YAG laser designed to provide conductively cooled operation at 1064 nm has been built and tested. Currently, this pump laser provides an output pulse energy of >1 J/pulse at 50 Hz PRF and a pulsewidth of 22 ns with an electrical-to-optical system efficiency of greater than 7% and a M(sup 2) value of <2. The single frequency UV converter arrangement basically consists of an IR Optical Parametric Oscillator (OPO) and a Sum Frequency Generator (SFG) setups that are pumped by 532 nm wavelength obtained via Second Harmonic Generation (SHG). In this paper, the operation of an inter cavity SFG with CW laser seeding scheme generating 320 nm wavelength is presented. Efforts are underway to improve conversion efficiency of this mJ class UV converter by modifying the spatial beam profile of the pump laser.

Prasad, Narasimha S.↗

NASA NTRS2008

Supporting Technology at GRC to Mitigate Risk as Stirling Power Conversion Transitions to Flight

Stirling power conversion technology has been reaching more advanced levels of maturity during its development for space power applications. The current effort is in support of the Advanced Stirling Radioisotope Generator (ASRG), which is being developed by the U.S. Department of Energy (DOE), Lockheed Martin Space Systems Company (LMSSC), Sunpower Inc., and the NASA Glenn Research Center (GRC). This generator would use two high-efficiency Advanced Stirling Convertors (ASCs) to convert thermal energy from a radioisotope heat source into electricity. Of paramount importance is the reliability of the power system and as a part of this, the Stirling power convertors. GRC has established a supporting technology effort with tasks in the areas of reliability, convertor testing, high-temperature materials, structures, advanced analysis, organics, and permanent magnets. The project utilizes the matrix system at GRC to make use of resident experts in each of the aforementioned fields. Each task is intended to reduce risk and enhance reliability of the convertor as this technology transitions toward flight status. This paper will provide an overview of each task, outline the recent efforts and accomplishments, and show how they mitigate risk and impact the reliability of the ASC s and ultimately, the ASRG.

Schreiber, Jeffrey G.↗

NASA NTRS2009

Supporting Technology at GRC to Mitigate Risk as Stirling Power Conversion Transitions to Flight

Schreiber, Jeffrey G.↗

DOE OSTI2016

Theory of photovoltaic characteristics of semiconductor quantum dot solar cells

We develop a comprehensive rate equations model for semiconductor quantum dot solar cells (QDSCs). The model is based on the continuity equations with a proper account for quantum dots (QDs). A general analytical expression for the total current density is obtained, and the current-voltage characteristic is studied for several specific situations. The degradation in the open circuit voltage of the QDSC is shown to be due to strong spontaneous radiative recombination in QDs. Due to small absorption coefficient of the QD ensemble, the improvement in the short circuit current density is negligible if only one QD layer is used. If spontaneous radiative recombination would be suppressed in QDs, a QDSC with multiple QD layers would have significantly higher short circuit current density and power conversion efficiency than its conventional counterpart. The effects of photoexcitation of carriers from discrete-energy states in QDs to continuum-energy states are discussed. An extended model, which includes excited states in QDs, is also introduced.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

Optical, Electrical, and Magnetic Studies of Organic Solar Cells Based on Low Bandgap Copolymer with Spin ½ Radical Additives

The charge photogeneration and recombination processes in organic photovoltaic solar cells based on blend of the low bandgap copolymer, PTB7 (fluorinated poly‐thienothiophene‐benzodithiophene) with C60‐PCBM using optical, electrical, and magnetic measurements in thin films and devices is studied. A variety of steady state optical and magneto‐optical techniques were employed, such as photoinduced absorption (PA), magneto‐PA, doping‐induced absorption, and PA‐detected magnetic resonance (PADMR); as well as picosecond time‐resolved PA. The charge polarons and triplet exciton dynamics in films of pristine PTB7, PTB7/fullerene donor–acceptor (D–A) blend is followed. It is found that a major loss mechanism that limits the power conversion efficiency (PCE) of PTB7‐based solar cell devices is the “back reaction” that leads to triplet exciton formation in the polymer donor from the photogenerated charge‐transfer excitons at the D–A interfaces. A method of suppressing this “back reaction” by adding spin½ radicals Galvinoxyl to the D–A blend is presented; this enhances the cell PCE by ≈30%. The same method is not effective for cells based on PTB7/C70‐PCBM blend, where high PCE is reached even without Galvinoxyl radical additives.

Basel, Tek↗

DOE OSTI2021

Lead-Free Organic–Perovskite Hybrid Quantum Wells for Highly Stable Light-Emitting Diodes

Two-dimensional perovskites that could be regarded as natural organic-inorganic hybrid quantum wells (HQWs) are promising for light-emitting diode (LED) applications. High photoluminescence quantum efficiencies (approaching 80%) and extremely narrow emission bandwidth (less than 20 nm) have been demonstrated in their single crystals; however, a reliable electrically driven LED device has not been realized owing to inefficient charge injection and extremely poor stability. Furthermore, the use of toxic lead raises concerns. Here, we report Sn(II)-based organic-perovskite HQWs employing molecularly tailored organic semiconducting barrier layers for efficient and stable LEDs. Utilizing femtosecond transient absorption spectroscopy, we demonstrate the energy transfer from organic barrier to inorganic perovskite emitter occurs faster than the intramolecular charge transfer in the organic layer. Consequently, this process allows efficient conversion of lower-energy emission associated with the organic layer into higher-energy emission from the perovskite layer. Thus, this greatly broadened the candidate pool for the organic layer. Incorporating a bulky small bandgap organic barrier in the HQW, charge transport is enhanced and ion migration is greatly suppressed. We demonstrate a HQW-LED device with pure red emission, a maximum luminance of 3466 cd m -2 , a peak external quantum efficiency up to 3.33%, and an operational stability of over 150 h, which are significantly better than previously reported lead-free perovskite LEDs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2016

Spin-current-driven thermoelectric generation based on interfacial spin-orbit coupling

The longitudinal spin Seebeck effect (SSE) in Bi{sub 2}O{sub 3}/Cu/yttrium-iron-garnet (YIG) devices has been investigated. When an out-of-plane temperature gradient is applied to the Bi{sub 2}O{sub 3}/Cu/YIG device, a spin current is generated across the Cu/YIG interface via the SSE and then converted into electric voltage due to the spin–orbit coupling at the Bi{sub 2}O{sub 3}/Cu interface. The sign of the SSE voltage in the Bi{sub 2}O{sub 3}/Cu/YIG devices is opposite to that induced by the conventional inverse spin Hall effect in Pt/YIG devices. The SSE voltage in the Bi{sub 2}O{sub 3}/Cu/YIG devices disappears in the absence of the Bi{sub 2}O{sub 3} layer and its thermoelectric conversion efficiency is independent of the Cu thickness, indicating the important role of the Bi{sub 2}O{sub 3}/Cu interface. This result demonstrates that not only the bulk inverse spin Hall effect but also the spin–orbit coupling near the interface can be used for SSE-based thermoelectric generation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗