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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Techno-Economic Analysis of a Concentrating Solar Power Plant Using Redox-Active Metal Oxides as Heat Transfer Fluid and Storage Media

We present results for a one-dimensional quasi-steady-state thermodynamic model developed for a 111.7 MW e concentrating solar power (CSP) system using a redox-active metal oxide as the heat storage media and heat transfer agent integrated with a combined cycle air Brayton power block. In the energy charging and discharging processes, the metal oxide CaAl 0.2 Mn 0.8 O 2.9-δ (CAM28) undergoes a reversible, high temperature redox cycle including an endothermic oxygen-releasing reaction and exothermic oxygen-incorporation reaction. Concentrated solar radiation heats the redox-active oxide particles under partial vacuum to drive the reduction extent deeper for increased energy density at a fixed temperature, thereby increasing storage capacity while limiting the required on sun temperature. Direct counter-current contact of the reduced particles with compressed air from the Brayton compressor releases stored chemical and sensible energy, heating the air to 1,200°C at the turbine inlet while cooling and reoxidizing the particles. The cool oxidized particles recirculate through the solar receiver subsystem for another cycle of heating and reduction (oxygen release). We applied the techno-economic model to 1) size components, 2) examine intraday operation with varying solar insolation, 3) estimate annual performance characteristics over a simulated year, 4) estimate the levelized cost of electricity (LCOE), and 5) perform sensitivity analyses to evaluate factors that affect performance and cost. Simulations use hourly solar radiation data from Barstow, California to assess the performance of a 111.7 MW e system with solar multiples (SMs) varying from 1.2 to 2.4 and storage capacities of 6–14 h. The baseline system with 6 h storage and SM of 1.8 has a capacity factor of 54.2%, an increase from 32.3% capacity factor with no storage, and an average annual energy efficiency of 20.6%. Calculations show a system with an output of 710 GWh e net electricity per year, 12 h storage, and SM of 2.4 to have an installed cost of $329 million, and an LCOE of 5.98 ¢/kWh e . This value meets the U.S. Department of Energy’s SunShot 2020 target of 6.0 ¢/kWh e ( U. S Department of Energy, 2012 ), but falls just shy of the 5.0 ¢/kWh e 2030 CSP target for dispatchable electricity ( U. S Department of Energy, 2017 ). The cost and performance results are minimally sensitive to most design parameters. However, a one-point change in the weighted annual cost of capital from 8 to 7% (better understood as a 12.5% change) translates directly to an 11% decrease (0.66 ¢/kWhe) in the LCOE.

Gorman, Brandon T.↗
DOE OSTI2025

REDOTHERM: a thermodynamic modeling framework for redox-based thermochemical processes

Two-step thermochemical redox cycles are being developed as a potential pathway for the production of hydrogen and syngas. While there are many possible reactor and system configurations, moving oxide systems are considered promising in terms of the redox thermodynamics, due to the potential implementation of a countercurrent system that can achieve higher performance compared to other configurations. There is a lack of a robust thermodynamic modeling framework in the field, with multiple models incorporating incorrect thermodynamic assumptions that violate the second law of thermodynamics. We present in this work REDOTHERM, an open-source system model for moving oxides that incorporates the correct thermodynamic limits, as well as various options for the system auxiliary units including product separation, heat recovery, and oxygen removal. The model is agnostic to the energy source, and could be used for solar thermal or other configurations. We highlight the uses of this model, presenting some of the tradeoffs and challenges in redox-active material selection and how they affect the entire thermochemical hydrogen production process. This model could be easily adapted and used for material exploration, system/reactor design, and technoeconomic analysis.

08 HYDROGEN↗
NASA NTRS1976

The Redox flow system for solar photovoltaic energy storage

A new method of storage was applied to a solar photovoltaic system. The storage method is a redox flow system which utilizes the oxidation-reduction capability of two soluble electrochemical redox couples for its storage capacity. The particular variant described separates the charging and discharging function of the system such that the electrochemical couples are simultaneously charged and discharged in separate parts of the system. The solar array had 12 solar cells; wired in order to give a range of voltages and currents. The system stored the solar energy so that a load could be run continually day and night. The main advantages of the redox system are that it can accept a charge in the low voltage range and produce a relatively constant output regardless of solar activity.

Odonnell, P.↗
NASA NTRS1976

The Redox Flow System for solar photovoltaic energy storage

The interfacing of a Solar Photovoltaic System and a Redox Flow System for storage was workable. The Redox Flow System, which utilizes the oxidation-reduction capability of two redox couples, in this case iron and titanium, for its storage capacity, gave a relatively constant output regardless of solar activity so that a load could be run continually day and night utilizing the sun's energy. One portion of the system was connected to a bank of solar cells to electrochemically charge the solutions, while a separate part of the system was used to electrochemically discharge the stored energy.

Odonnell, P.↗
NASA NTRS1978

The redox state of planetary basalts

Redox variations of terrestrial and lunar basalts and the redox variations in single cooling units (e.g., lava flows and lava lakes) are reviewed. Estimates for the redox states of inner solar system planetary basalts are presented; these estimates are based on consideration of a number of cosmogenic properties, models for planetary interiors, and the sequence of condensation with heliocentric distance from the protosun. It is suggested that basalts on Mercury and the Moon crystallized below the iron-wustite buffer curve; Venusian basalts are more oxidized than those on Mercury, less oxidized than those on earth, and crystallization within the field of wustite stability is thought likely; basalts on earth are dominantly in the field of magnetite stability; Martian basalts are estimated to crystallize in the upper regions of magnetite stability and well into the hematite field of stability expressed in terms of temperature and oxygen fugacity.

Haggerty, S. E.↗
NASA NTRS1979

Redox flow cell development and demonstration project, calendar year 1977

Research and development on the redox flow cell conducted from January 1, 1977, to December 31, 1977, are described in this report. The major focus of the effort during 1977 was the key technology issues that directly influence the fundamental feasibility of the overall redox concept. These issues were the development of a suitable ion exchange membrane for the system, the screening and study of candidate redox couples to achieve optimum cell performance, and the carrying out of systems analysis and modeling to develop system performance goals and cost estimates.

Source record↗
NASA NTRS1979

Electrochemical cell for rebalancing REDOX flow system

An electrically rechargeable REDOX cell or battery system including one of more rebalancing cells is described. Each rebalancing cell is divided into two chambers by an ion permeable membrane. The first chamber is fed with gaseous hydrogen and a cathode fluid which is circulated through the cathode chamber of the REDOX cell is also passed through the second chamber of the rebalancing cell. Electrochemical reactions take place on the surface of insert electrodes in the first and second chambers to rebalance the electrochemical capacity of the anode and cathode fluids of the REDOX system.

Thaller, L. H.↗
NASA NTRS1981

Pumping power considerations in the designs of NASA-Redox flow cells

Pressure drop data for six different cell geometries of various flow port, manifold, and cavity dimensions are presented. The redox/energy/storage system uses two fully soluble redox couples as anode and cathode fluids. Both fluids are pumped through a redox cell, or stack of cells, where the electrochemical reactions take place at porous carbon felt electrodes. Pressure drop losses are therefore associated with this system due to the continuous flow of reactant solutions. The exact pressure drop within a redox flow cell is directly dependent on the flow rate as well as the various cell dimensions. Pumping power requirements for a specific set of cell operating conditions are found for various cell geometries once the flow rate and pressure drop are determined. These pumping power requirements contribute to the overall system parasitic energy losses which must be minimized, the choice of cell geometry becomes critical.

Hoberecht, M. A.↗
NASA NTRS1981

Design and assembly considerations for Redox cells and stacks

Individual redox flow cells are arranged electrically in series and hydraulically in parallel to form a single assembly called a stack. The hardware currently being tested in the laboratory has an active electrode area of either 310 sq cm or 929 sq cm. Four 310 sq cm stacks, each consisting of 39 active cells, were incorporated into a 1.0 kW preprototype system. The physical design of the stack is very critical to the performance and efficiency of the redox storage sytem. This report will discuss the mechanical aspects of the cell and stack design for the current Redox hardware, with regard to sealing the stack internally as well as externally, minimizing shunt currents and minimizing the electrical resistance of the stack.

Stalnaker, D. K.↗
NASA NTRS1981

Redox storage systems for solar applications

It is noted that the worldwide development of solar photovoltaic and wind turbine systems to meet a range of terrestrial electrical energy requirements has underscored the need for inexpensive and reliable electrical energy storage. The NASA Redox Energy Storage System, based on soluble aqueous iron and chromium chloride redox couples, has exhibited many system-related features which for the most part are unique to this storage system. The technology advances required in the two elements (electrodes and membranes), which are the key to its technological feasibility, have been attained and system development has begun. The design, construction, and testing of a 1-kW system integrated with a solar photovoltaic array is underway to provide early demonstration of the attractive system-related features of the NASA Redox Storage System. Also demonstrated will be its versatility and compatibility with a terrestrial solar photovoltaic electric power system.

Hagedorn, N. H.↗
NASA NTRS1982

Study to establish cost predictions for the production of Redox chemicals

The chromium and iron chloride chemicals are significant first costs for NASA Redox energy storage systems. This study was performed to determine the lowest cost at which chromium and iron chlorides could be obtained for a complex of redox energy storage systems. In addition, since the solutions gradually become intermixed during the course of operation of Redox units, it was an objective to evaluate schemes for regeneration of the operating solutions. Three processes were evaluated for the production of chromium and iron chlorides. As a basis for the preliminary plant design and economic evaluation, it was assumed that the plant would produce about 25,000 tons of contained chromium as CrCl3 and an equivalent molar quantity of FeCl2. Preliminary plant designs, including materials and energy balances and sizing of major equipment, were prepared, and capital and operating costs were estimated.

Ammann, P. R.↗
NASA NTRS1983

NASA Redox Project status summary

This report is a summary of the results of the Redox Project effort during Cy 1982. It was presented at the Fifth U.S. Department of Energy Battery and Electrochemical Contractors Conference, Arlington, Va., Dec. 7-9, 1982. The major development during 1982 was the shift from Redox system operation at 25 C with unmixed reactants to operation at 65 C with mixed reactants. This change has made possible a two- or three-fold increase in operating current density, to about 65 mA/sq cm, and an increase in reactant utilization from 40% to about 90%. Both of these improvements will lead to significant system cost reductions. Contract studies have indicated that Redox reactant costs also will be moderate. A new catalyst for the chromuim electrode offers all the advantages of the conventional gold-lead catalyst while being easier to apply and more forgiving in use.

Hagedorn, N. H.↗
NASA NTRS1982

Study to establish cost projections for production of Redox chemicals

A cost study of four proposed manufacturing processes for redox chemicals for the NASA REDOX Energy Storage System yielded favorable selling prices in the range $0.99 to $1.91/kg of chromic chloride, anhydrous basis, including ferrous chloride. The prices corresponded to specific energy storage costs from under $9 to $17/kWh. A refined and expanded cost analysis of the most favored process yielded a price estimate corresponding to a storage cost of $11/kWh. The findings supported the potential economic viability of the NASA REDOX system.

Walther, J. F.↗
NASA NTRS1997

Redox Energy and Sulfur Chemistry in Prebiotic Polymer Synthesis and Replication

In the past year we have made significant progress in three research areas: (1) Most importantly, we discovered a new pathway of prebiotic amino acid synthesis in which formaldehyde and glycolaldehyde (substrates of the formose reaction) react with ammonia yielding alanine and homoserine in the presence of thiol catalysts. This thiol-dependent synthesis of amino acids undoubtedly occurs via amino acid thioester intermediates capable of forming peptides. This 'one-pot' reaction system operates under mild aqueous conditions, and like modern amino acid biosynthesis, uses sugar intermediates which are converted to amino acids by energy-yielding redox disproportionation. (2) Finally, in preparation for the analysis of Martian meteorite samples, we upgraded our HPLC system and developed an improved method capable of detecting a I femtomole of amino acid enantiomers. (3) We completed our analysis of the energetics of metabolism that revealed that life depends on biosynthetic processes driven by chemical energy made available by the redox disproportionation of carbon groups of sugars. We established that the favorable energy of redox disproportionation is based on the universal reduction potentials of carbon groups. We concluded that it is hard to imagine any other organic molecule besides sugars (formaldehyde oligomers) having the energy and reactivity needed to drive either modem biosynthesis or the chemical processes behind its origin.

Weber, Arthur L.↗
NASA NTRS2003

In General, the Total Voltammetric Current from a Mixture of Redox-Active Substances will Not be the Sum of the Currents that Each Substance would Produce Independently at the Same Concentration as in the Mixture

At the potential range where both decamethylferrocene (dMeFc) and ferrocene (Fc) are oxidized with rates controlled by linear diffusion, electrogenerated Fc(+) radicals diffusing outwards from the electrode react quantitatively (K23 C=5.8 x 10(exp 8) with dMeFc diffusing towards the electrode and produce Fc and dMeFc. That reaction replaces dMeFc with Fc, whose diffusion coefficient is higher than that of dMeFc(+), and the total mass-transfer limited current from the mixture is increased by approximately 10%. Analogous observations are made when mass-transfer is controlled by convective-diffusion as in RDE voltammetry. Similar results have been obtained with another, and for all practical purposes randomly selected pair of redox-active substances, [Co(bipy)3](2+) and N - methylphenothiazine (MePTZ); reaction of MePTZ(+) with [Co(bipy)3](2+) replaces the latter with MePTZ, which diffuses faster and the current increases by approximately 20%. The experimental voltammograms have been simulated numerically and the role of (a) the rate constant of the homogeneous reaction; (b) the relative concentrations; and, (c) the diffusion coefficients of all species involved have been studied in detail. Importantly, it was also identified that within any given redox system the dependence of the mass-transfer limited current on the bulk concentrations of the redox-active species is expected to be non-linear. These findings are discussed in terms of their electroanalytical implications.

Leventis, Nicholas↗
NASA NTRS1992

Protein sequences and redox titrations indicate that the electron acceptors in reaction centers from heliobacteria are similar to Photosystem I

Photosynthetic reaction centers isolated from Heliobacillus mobilis exhibit a single major protein on SDS-PAGE of 47 000 Mr. Attempts to sequence the reaction center polypeptide indicated that the N-terminus is blocked. After enzymatic and chemical cleavage, four peptide fragments were sequenced from the Heliobacillus mobilis apoprotein. Only one of these sequences showed significant specific similarity to any of the protein and deduced protein sequences in the GenBank data base. This fragment is identical with 56% of the residues, including both cysteines, found in highly conserved region that is proposed to bind iron-sulfur center Fx in the Photosystem I reaction center peptide that is the psaB gene product. The similarity to the psaA gene product in this region is 48%. Redox titrations of laser-flash-induced photobleaching with millisecond decay kinetics on isolated reaction centers from Heliobacterium gestii indicate a midpoint potential of -414 mV with n = 2 titration behavior. In membranes, the behavior is intermediate between n = 1 and n = 2, and the apparent midpoint potential is -444 mV. This is compared to the behavior in Photosystem I, where the intermediate electron acceptor A1, thought to be a phylloquinone molecule, has been proposed to undergo a double reduction at low redox potentials in the presence of viologen redox mediators. These results strongly suggest that the acceptor side electron transfer system in reaction centers from heliobacteria is indeed analogous to that found in Photosystem I. The sequence similarities indicate that the divergence of the heliobacteria from the Photosystem I line occurred before the gene duplication and subsequent divergence that lead to the heterodimeric protein core of the Photosystem I reaction center.

NASA Discipline Number 52-30↗
NASA NTRS1999

Energetics and kinetics of the prebiotic synthesis of simple organic acids and amino acids with the FeS-H2S/FeS2 redox couple as reductant

The thermodynamics of the FeS-H2S/FeS2 redox couple and a select number of reactions critical to the synthesis of simple carboxylic acids and amino acids have been evaluated as a function of temperature. This thermodynamic evaluation shows that the reducing power of the FeS-H2S/FeS2 redox couple decreases drastically with temperature. By contrast the equilibria describing the reduction of CO2 and the formation of simple carboxylic acids and amino acids require an increasingly higher reducing power with temperature. Given these two opposite trends, the thermodynamic driving force for CO2 reduction and amino acid formation with the FeS-H2S/FeS2 redox couple as reductant diminishes with increasing temperature. An evaluation of the mechanism of CO2 reduction by the FeS-H2S/FeS2 couple suggests that the electron transfer from pyrrhotite to CO2 is hindered by a high activation energy, even though the overall reaction is thermodynamically favorable. By comparison the electron transfer from pyrrhotite to either CS2, CO, or HCOOH are far more facile. This theoretical analysis explains the results of experimental work by Keefe et al. (1995), Heinen and Lauwers (1996) and Huber and Wachtershauser (1997). The implication is that a reaction sequence involving the reduction of CO2 with the FeS-H2S/FeS2 couple as reductant is unlikely to initiate a proposed prebiotic carbon fixation cycle (Wachtershauser, 1988b; 1990b, 1990a, 1992, 1993).

Non-NASA Center↗
NASA NTRS2004

Non-Additive Voltametric Currents From a Mixture of Two, Three and Four Redox-Active Compounds and Electroanalytical Implications

We have published recently the effect of dissimilar diffusion coefficients on the size of the voltammetric waves from a mixture of two redox-active compounds. Similarly, at the potential range where three redox-active species, decamethylferrocene (dMeFc), ferrocene (Fc) and N-methylphenothiazine (MePTZ), are oxidized simultaneously with rates controlled by linear diffusion, electrogenerated radicals diffusing outwards from the electrode react with the original species diffusing towards the electrode from the bulk; thus, Fc(+) reacts with dMeFc producing Fc and dMeFc(+), while MePTZ(+) reacts both with dMeFc producing MePTZ and dMeFc(+), and with Fc producing MePTZ and Fc(+). These reactions replace dMeFc with Fc at the second plateau, and both dMeFc and Fc with MePTZ at the third plateau. Since the diffusion coefficients of the three species are not equal, the mass-transfer limited currents of the second and the third oxidation wave plateaus change by approx. 10%. Numerical simulations of the experimental voltamograms support this mechanism. Similar results were also obtained for a mixture of four redoxactive compounds. The implications of this non-additive nature of currents on: (a) the use of internal voltammetric standards for quantitative analysis of a mixture of redox-active compounds; and, (b) the half wave potentials (E1/2) of the 2nd, 3rd and 4th waves for qualitative analysis, will be discussed.

Dass, Amala↗