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In this study, we propose a new experimental setup and methodology that can perform in-situ diagnostic of a solid oxide cell stack without interfering with its normal steady state operation. We establish a floating ground galvanodynamic electrochemical impedance spectroscopy measurement setup connected to a 6-cell short stack. The diagnostic setup is electrically connected in parallel to the electronic load of the stack, so that the respective AC and DC current signals overlap. We demonstrate that this methodology is effective in detecting degradation and assessing the state-of-health of a specific cell or stack without disrupting its operation.

In this work, we apply a machine learning approach to solid oxide fuel cell (SOFC) system diagnostics. Instead of fitting electrochemical impedance spectroscopy (EIS) into a physics based model or equivalent circuit, we train machine learning models to recognize failures from a database of simulated EIS. We use a coarse-grained physics-based model to simulate stack EIS under three different failure modes: fuel maldistribution, delamination, and cathode gas crossover to anode channel. Synthesized machine learning classification models successfully recognize these different degradation mechanisms in simulated data across different operating conditions. We are also able to differentiate these failures from the uniform degradation that tends to occur with SOFC over time. These encouraging results prompt our current effort to implement machine learning diagnostics methods on experimental EIS collected on SOFC short stack.

The integration of a solid-oxide fuel cell (SOFC) and a triple-effect absorption chiller (AC) is proposed to meet the electrical and cooling requirements of a data center. Utilizing waste heat in the exhaust stream of the SOFC, a triple-effect AC system can produce the required cooling. A 200-kW SOFC system is optimized to produce the required electricity at the maximum efficiency, while still producing enough thermal energy to run the 200-kW AC system. Similarly, the AC system is optimized to harness as much thermal energy from the SOFC as possible while meeting the cooling demand of the servers. The optimized system can meet both the electric and cooling demands to produce primary energy savings of 25.8%.

Historically, California has been a world leader in the development and application of environmental regulations. Policies to address air pollution have reduced criteria pollutant emissions, improved regional air quality, and benefited public health. To this end, California has imposed strict regulations on light-duty, medium-duty, and heavy-duty vehicles to reduce ambient concentrations of health-damaging pollutants such as ozone and fine particulate matter (PM2.5). Here, we compare the impact on air quality in California should California not have adopted on-road vehicle regulations (No Regulations Case) with the air quality associated with current regulations (Regulated Case). Simulations of atmospheric chemistry and transport are conducted to evaluate the impact of emissions on ambient levels of ozone and PM2.5, and a health impact assessment tool is used to quantify and monetize societal impairment. Compared with the “Regulated Case,” the “No Regulations Case” results in a maximum peak 8 h ozone level of 162 ppb and 24 h PM2.5of 42.7 μg/m3in summer, and 107 μg/m3and 24 h PM2.5in winter. The associated increases in the daily incidence of human health outcomes are $66 million per day and $116 million per day during peak pollutant formation periods in summer and winter, respectively. Overall, the findings quantitatively establish the role and importance of on-road vehicle regulations in protecting societal well-being.

A method for analyzing the levelized cost of conversion, storage, and return of input energy as an end product net of losses with a zero cost of input energy, termed the levelized cost of returned energy (LCORE), is introduced and applied uniformly to compare the net conversion and storage costs of various renewable electrolysis technologies and hydrogen end-uses with battery and flow-battery energy storage technologies. The LCORE methodology accounts for capital costs, financing costs, operation and maintenance costs, energy efficiency of each step, technology lifetime, and replacement costs. Results show that the most valuable use of the renewable hydrogen is as fuel for fuel cell electric vehicles, although the costs of the hydrogen fueling infrastructure are estimated to be high using the existing paradigm of trucking, compression, and dispensing (adding more than $7/kilogram to the price of hydrogen). Importantly, the analyses show that the range of costs for pathways that produce hydrogen by electrolysis from renewable generation and return it to the electric grid using the natural gas system to transport the hydrogen to an existing combined cycle plant to produce the electricity have costs of $76-$210/MWh. These costs are directly competitive with battery energy storage pathways at $51-$150/MWh while also providing energy storage over durations as long as months, durations that are that are not technically feasible for many battery technologies due to charge leakage.

In this study, the emissions and performance of a commercial Solid Oxide Fuel Cell system with micro-combined heat and power (SOFC mCHP) capabilities are analyzed at various power output levels and with various hydrogen (H2) - natural gas (NG) fuel mixture concentrations. The SOFC mCHP system, although designed to be fueled by pure NG, is intentionally fueled with mixtures between 0 and 30% vol of H2 mixed with NG (balance) and is operated between 0.5 and 1.5 kW. Since these units are used in residential and commercial applications, it is important to ensure that if H2 becomes widely injected into the NG system that the corresponding H2-NG mixtures would not negatively impact the emissions or performance of the system. The performance of the system is characterized by measurement of major exhaust species concentrations (carbon dioxide, carbon monoxide, methane, water, nitric oxide, nitrogen dioxide, etc.). These measurements confirm that NOx emissions are extremely low and that adding hydrogen to the NG system does not increase NOx emissions. In addition, the system's efficiency at part load experienced a small reduction with increasing H2 concentrations in the mixture, compared to pure NG operation.

The goal of this study is to evaluate the impacts and capabilities of dynamically dispatching Solid Oxide Steam Electrolysis (SOSE) systems to support high penetration of renewable photovoltaic sources in the UCI microgrid. The UCI microgrid operation has been simulated as a linear programming problem in Matlab(r) considering all of its operational constraints to analyze the microgrid behavior to the additional PV installed capacity. Simulations cases consist of current 4 MW PV installed capacity and future PV installed capacities up to 35 MW. The integration of modular SOSE systems in the University of California, Irvine (UCI) microgrid, to absorb the excess Photovoltaic (PV) generated power is investigated in this study for different PV installed capacity. Also, the possibility of utilizing the available excess steam produced in the Heat Recovery Steam Generator (HRSG) as a portion of the required steam in SOSE systems is evaluated. Microgrid simulation results prove that for cases with PV installed capacity greater than 10 MW, the otherwise curtailed excess electricity would be a great potential to be used in SOSE for hydrogen production. The produced hydrogen in high installed capacities would be enough to feed the gas turbine with a gas mixture containing 15% volumetric hydrogen together with hydrogen used in the UCI hydrogen fuel stations. Consequently, natural gas consumption and carbon dioxide production are decreased substantially.

In this study the integration of a solid oxide fuel cell with liquid desiccant system is considered for powering and cooling a data center at the rack level. The novel idea is that each single fuel cell (~12 kW) is used to power one server rack and the waste heat from the fuel cell is used to regenerate a desiccant to provide dehumidification or cooling. The heat concentrates the liquid desiccant solution that is then stored. When moisture must be removed, the high concentration solution is used to dehumidify the outside air. The objective of this study is to theoretically investigate the capability of the integrated system to provide enough cold and dehumidified air to keep the server rack in the safe range of temperature and humidity. Results show that the SOFC waste heat can produce cold and dehumidified air that is in the safe range for server racks. However, with continuous outside air conditions of 25oC and 70% relative humidity the heat from the current SOFC system is enough to provide only 25% of the air flow demand for each server rack.

While cool coatings have recently received much attention for building applications, their impact on building energy consumption strongly depends upon climatic conditions. Herein we evaluate the energy, cost, carbon, and interior comfort impact of cool coatings applied to a residential multifamily building across 32 climate zones in the United States by applying advanced cool coating properties to established building energy models. The model not only considers promising cool coating properties based upon recent experiments but also an ideal cool coating. Our calculations show that the ideal cool coating can achieve annual cooling energy savings of up to 6.64 kWh/m2(Phoenix, AZ), annual net utility cost savings up to $1.16/m2(Brawley, CA), and net annual carbon emission savings up to 7.7 % (Phoenix, AZ). We also estimate the change in interior temperature for buildings without space cooling systems and show that cool coatings make buildings in the warmest climate zones in the U.S. without space cooling more comfortable by 30 % to 50 % on a cooling degree days basis. Using analysis of variance, we examine the statistical relationships between building performance metrics and climatic parameters. The presented methodology enables evaluation of cool coating application to buildings in various climate zones across the world.

•Modeled clean building energy technologies in a low-income community•Analysis uses building energy and electric infrastructure power flow models•Low-income support programs can reduce community energy costs and emissions by 20%•DHW electrification can reduce community emissions up to 40% but may increase costs•Low-income family energy burden in the community may rise due to electrification

The dynamics of hydrogen energy storage (HES) integrated with large-scale renewable power (119.5 GW) using the capabilities of the existing California natural gas infrastructure were investigated. The dynamics associated with the grid demand, renewable power, pressure, and HES capacity for one week each of November and August were analyzed in detail while a higher level analysis of the entire state for the whole year was simulated in MATLAB/Simulink. It was found that the existing natural gas storage facilities may be converted to hydrogen storage facilities to store otherwise curtailed renewable energy through solid oxide electrolysis (SOE). Moreover, Solid Oxide Fuel Cell (SOFC) systems can also be used to dispatch the hydrogen back to the grid as power. The analysis in this paper shows that the dynamics of California natural gas underground storages associated with pressure and mass flow rate for achieving HES to support 100% renewable gas use are reasonable.

In this study the waste heat from a 2.5 kW solid oxide fuel cell (SOFC) is captured and processed through a 1.5 kW absorption chiller (AC) to provide cooling for a single residence. The integration of an AC with an SOFC could create a highly dispatchable system that can meet the dynamics of measured residential power. A spatially resolved dynamic model was developed in Matlab/Simulink to simulate the dynamic operating characteristics of an SOFC system. A dynamic AC model was developed to study the dynamic characteristics and the performance of the combined co-generation system. Actual dynamic data from a single residential house was used as an input of the SOFC-AC model. For a single week, the SOFC was capable of following the highly dynamic load with an average efficiency of 56%. The AC generated 15.6 kWh of cooling with an average COP and cooling of 1.09 and 0.65 kW, respectively.

In this study, with measured steady state performance characteristics of a 1.5 kW residential Solid Oxide Fuel Cell (SOFC) system we evaluated the installation of residential SOFC systems for a typical hourly energy use for the entire year through all 16 climate zones in California. We carried out an economic analysis taking into account the dynamic daily and seasonal energy consumption for various climate zones and various current residential time-of-use utility rates. Residential SOFC implementation cases in various climate zones that focus upon 1) reduced energy use, 2) reduced peak demand, 3) utility time-of use rate-structure impacts, and 4) CO2 emission reductions are evaluated. From the customer perspective, this study generates a guideline for the user to make decisions depending upon their electric energy usage profile, utility rate structure and carbon credit, we found that breakeven costs are highly dependent upon the utility rate structures with PG&E structures most favorably encouraging SOFC use.

In this study, we experimentally evaluated electrolysis of water using a short stack of six solid oxide electrochemical cells (SOEC). A model of the SOEC stack was verified and used to evaluate thermal management of the stack operating above and below the thermoneutral voltage, which at these temperatures requires additional heat input into the stack to maintain the system operating temperature. High quality heat was supplied from a molten salt. Heat generated from concentrated solar power (CSP) can reach the required SOEC operation temperature through molten salts and can provide enough heat to sustain sub-thermoneutral voltage operation of an SOEC. The SOEC model is spatially and temporally resolved and was used to evaluate the dynamic performance of a system operating at sub-thermoneutral voltages with dynamic heat input. Dynamic results suggest high efficiency hydrogen generation can occur with external heat input under various conditions including variable power and salt flow.

Nickel metal layers with various morphologies have been investigated as electrical contact, electrocatalyst, and catalyst layers for high temperature hydrogen electro-oxidation and heterogeneous reactions, such as steam methane reforming and water gas shift, in high temperature fuel cells supplied by carbonaceous fuels of various nature. Ni metal alloys, with various dopant concentrations, have been studied to increase metal nickel tolerance to carbon deposition, which is thermodynamically favored in SOFC fed with a steam/methane molar ratio <2.0. The goal of this research is to compare the electrochemical performance, the catalytic activity towards steam methane reforming reaction yield, and the resistance towards the Boudouard reaction for solid carbon formation of a Ni-based SOFC: i) without Ni porous layer; ii) with a 200 μm thick Ni porous mesh; iii) with a 200 μm thick NiSn porous mesh.

Commercialization of solid oxide electrolyzers is restricted by rapid degradation mechanisms of the electrodes, most notably nickel migration and agglomeration which leads to reduced activation sites at the triple-phase boundary. It is desirable to understand the process by which this phenomenon occurs not only to minimize it, but to intentionally induce it in a method which can compare the longevity of various chemistries. The objective of this research is to establish a protocol which mimics long-term electrode degradation. It is hoped that this will lead to a standardized procedure for comparing the projected long-term performance of solid oxide electrolysis cells. To promote degradation, operation at high steam partial pressure (>95% molar concentration) is employed.

The Paris Agreement highlights the need for local climate leadership. The University Of California’s approach to deep decarbonization offers lessons in efficiency, alternative fuels and electrification. Bending the emissions curve globally requires efforts that blend academic insights with practical solutions.

SOFC is a fuel flexible technology suitable for producing clean energy. Understanding of the multi-reaction mechanism that a complex H2-CO fuel presents to the electrochemical kinetics is numerically approached in this work. By using existing fundamental reaction mechanisms and kinetic parameters, elementary reactions involved in an SOFC anode have been assembled, modeled and analyzed. This involves both homogeneous and heterogeneous chemistry, electrochemistry and surface diffusion. The use of the patterned anode approach removes the mass transport complications and allows comparison with pre-existing experimental data. The model provides both polarization curves and surface coverage distribution, among other results, providing a high level of detail and understanding of the physical phenomena involved. In particular, analysis is focused upon understanding how the competitive H2 and CO reactions behave.The presence of CO was found to stabilize OCV response to temperature and while it occupied most of the active sites it did not penalize overall performance except when significant product species were present.

In this study, an islanded microgrid system is proposed that integrates identical stacks of solid oxide fuel cell and electrolyzer to achieve a thermally self-sustained energy storage system. Thermal management of the solid oxide electrolysis cell (SOEC) is achieved by the use of heat from the solid oxide fuel cell (SOFC) with a heat exchanger network and control strategies. The SOFC meets the building electricity demand and the heat generated from its electrochemical reactions is transferred to the SOEC for the endothermic heat and standby demands. Each component is physically modeled in Simulink and ultimately integrated at the system level for dynamic analyses. The current work simulates a system comprised of a wind farm in Palm Springs, CA, coupled with the SOEC (for H2 generation), and an industrial building powered by the SOFC. Results from two weeks of operation using the measured building and wind data showed that despite fluctuating power profiles, average temperature, and local temperature gradients of both the SOEC and SOFC were within desired tolerances. However, for severe conditions of wind power deficit, H2 had to be supplied from previous windy days’ storage or imported.

This paper analyzes and compares transient and steady-state performance characteristics of different types of single-shaft turbo-machinery for controlling the air through a pressurized solid oxide fuel cell (SOFC) stack that is integrated into a SOFC/GT pressurized hybrid system. Analyses are focused on the bottoming part of the cycle, where the gas turbine (GT) has the role of properly managing airflow to the SOFC stack for various loads and at different ambient conditions. Analyses were accomplished using two disparate computer programs, which each modeled a similar SOFC/GT cycle using identical generic gas turbine performance maps. The models are shown to provide consistent results, and they are used to assess: (1) the influence of SOFC exhaust composition on expander behavior for on-design conditions, (2) the off-design performance of the bypass, bleed, and variable speed controls for various part-load conditions and for different ambient conditions; (3) the features of such controls during abrupt transients such as load trip and bypass/bleed valve failure. The results show that a variable speed microturbine is the best option for off-design operation of a SOFC/GT hybrid system. For safety measures a bleed valve provides adequate control of the system during load trip. General specifications for a radial GT engine for integration with a 550 kW pressurized SOFC stack are identified, which allow operation under a wide range of ambient conditions as well as several different cycle configurations.

This paper analyzes and compares transient and steady-state performance characteristics of different types of single-shaft turbo-machinery for controlling the air through a pressurized solid oxide fuel cell (SOFC) stack that is integrated into a SOFC/GT pressurized hybrid system. Analyses are focused on the bottoming part of the cycle, where the gas turbine (GT) has the role of properly managing airflow to the SOFC stack for various loads and at different ambient conditions. Analyses were accomplished using two disparate computer programs, which each modeled a similar SOFC/GT cycle using identical generic gas turbine performance maps. The models are shown to provide consistent results, and they are used to assess: (1) the influence of SOFC exhaust composition on expander behavior for on-design conditions, (2) the off-design performance of the bypass, bleed, and variable speed controls for various part-load conditions and for different ambient conditions; (3) the features of such controls during abrupt transients such as load trip and bypass/bleed valve failure. The results show that a variable speed microturbine is the best option for off-design operation of a SOFC/GT hybrid system. For safety measures a bleed valve provides adequate control of the system during load trip. General specifications for a radial GT engine for integration with a 550kW pressurized SOFC stack are identified, which allow operation under a wide range of ambient conditions as well as several different cycle configurations.

This paper analyzes and compares transient and steady-state performance characteristics of different types of single-shaft turbo-machinery for controlling the air through a pressurized solid oxide fuel cell (SOFC) stack that is integrated into a SOFC/GT pressurized hybrid system. Analyses are focused on the bottoming part of the cycle, where the gas turbine (GT) has the role of properly managing airflow to the SOFC stack for various loads and at different ambient conditions. Analyses were accomplished using two disparate computer programs, which each modeled a similar SOFC/GT cycle using identical generic gas turbine performance maps. The models are shown to provide consistent results, and they are used to assess: (1) the influence of SOFC exhaust composition on expander behavior for on-design conditions, (2) the off-design performance of the bypass, bleed, and variable speed controls for various part-load conditions and for different ambient conditions; (3) the features of such controls during abrupt transients such as load trip and bypass/bleed valve failure. The results show that a variable speed microturbine is the best option for off-design operation of a SOFC/GT hybrid system. For safety measures a bleed valve provides adequate control of the system during load trip. General specifications for a radial GT engine for integration with a 550kW pressurized SOFC stack are identified, which allow operation under a wide range of ambient conditions as well as several different cycle configurations.

La0.8Sr0.2Ga0.8Mg0.115Co0.085O3-d (LSGMC) has been reported as an optimized composition for LSGM-based electrolytes used in intermediate temperature solid oxide fuel cells (SOFCs). Electrocatalytic properties of the interfaces between LSGMC electrolyte and various cathodes: comprised of Sm0.5Sr0.5CoO3-d (SSC), and La0.7Sr0.3Co0.2Fe0.8O3-d (LSCF) in composite forms (70wt.%) with LSGMC (30wt.%) were investigated under both oxygen reduction and evolution conditions. All the oxides were synthesized using the glycine-nitrate process (GNP) followed by unique powder processing to produce the desired phase purity and particle properties. Symmetrical electrochemical cells were fabricated by a screen-printing technique with precisely controlled alignment. Three-electrode linear dc polarization and ac impedance spectroscopy were used to characterize the kinetics of the interfacial reactions in detail. For the composite SSC-LSGMC cathode/LSGMC interface, the cathodic overpotential under 1 A/cm2 current density was as low as 0.085 V at 973 K, 0.062V at 1023K and 0.051V at 1073K in air. Composite LSCF-LSGMC cathode/LSGMC interfaces were found to have about twice the exchange current density of composite SSC- LSGMC/LSGMC interfaces for the same temperature and overpotential conditions.

This paper presents the electricity and hydrogen co-production concept, a methodology for the study of SOFC hydrogen co-production, and simulation results that address the impact of reformer placement in the cycle on system performance. The methodology is based on detailed thermodynamic and electrochemical analyses of the systems. A comparison is made between six specific cycle configurations, which use fuel cell heat to drive hydrogen production in a reformer using both external and internal reforming options. SOFC plant performance has been evaluated on the basis of methane fuel utilization efficiency and each component of the plant has been evaluated on the basis of second law efficiency. The analyses show that in all cases the exergy losses (irreversibilities) in the combustion chamber are the most significant losses in the cycle. Furthermore, for the same power output, the internal reformation option has the higher electrical efficiency and produces more hydrogen per unit of natural gas supplied. Electrical efficiency of the proposed cycles ranges from 41 to 44%, while overall efficiency (based on combined electricity and hydrogen products) ranges from 45 to 80%. The internal reforming case (steam-to-carbon ratio of 3.0) had the highest overall and electrical efficiency (80 and 45% respectively), but lower second law efficiency (61%), indicating potential for cycle improvements.

This paper presents the electricity and hydrogen co-production concept, a methodology for the study of SOFC hydrogen co-production, and simulation results that address the impact of reformer placement in the cycle on system performance. The methodology is based on detailed thermodynamic and electrochemical analyses of the systems. A comparison is made between six specific cycle configurations, which use fuel cell heat to drive hydrogen production in a reformer using both external and internal reforming options. SOFC plant performance has been evaluated on the basis of methane fuel utilization efficiency and each component of the plant has been evaluated on the basis of second law efficiency. The analyses show that in all cases the exergy losses (irreversibilities) in the combustion chamber are the most significant losses in the cycle. Furthermore, for the same power output, the internal reformation option has the higher electrical efficiency and produces more hydrogen per unit of natural gas supplied. Electrical efficiency of the proposed cycles ranges from 41 to 44&percent;, while overall efficiency (based on combined electricity and hydrogen products) ranges from 45 to 80&percent;. The internal reforming case (steam-to-carbon ratio of 3.0) had the highest overall and electrical efficiency (80 and 45&percent; respectively), but lower second law efficiency (61&percent;), indicating potential for cycle improvements.

This paper presents the electricity and hydrogen co-production concept, a methodology for the study of SOFC hydrogen co-production, and simulation results that address the impact of reformer placement in the cycle on system performance. The methodology is based on detailed thermodynamic and electrochemical analyses of the systems. A comparison is made between six specific cycle configurations, which use fuel cell heat to drive hydrogen production in a reformer using both external and internal reforming options. SOFC plant performance has been evaluated on the basis of methane fuel utilization efficiency and each component of the plant has been evaluated on the basis of second law efficiency. The analyses show that in all cases the exergy losses (irreversibilities) in the combustion chamber are the most significant losses in the cycle. Furthermore, for the same power output, the internal reformation option has the higher electrical efficiency and produces more hydrogen per unit of natural gas supplied. Electrical efficiency of the proposed cycles ranges from 41 to 44%, while overall efficiency (based on combined electricity and hydrogen products) ranges from 45 to 80%. The internal reforming case (steam-to-carbon ratio of 3.0) had the highest overall and electrical efficiency (80 and 45% respectively), but lower second law efficiency (61%), indicating potential for cycle improvements.

Hydrogen will play a critical role in a future comprehensive energy portfolio; hydrogen will be the decarbonizing tie between the different energy production sources and their end uses. Hydrogen acts as a zero-carbon energy carrier to couple energy sources and end uses. This provides the methodology to decarbonize the major energy consumption sectors of (1) the electric grid, (2) transportation and (3) industrial processes. It can provide energy storage supporting intermittent renewable power and cost-effective energy resilience; it enables the massive and seasonal energy storage that is required for a zero-emissions electric grid. It can be used in the transportation sector, especially for heavy-duty transportation where long ranges and fast refueling are critical. Renewable hydrogen is critical to decarbonize industrial processes that have needs for high temperature, chemical reduction and refining and chemical feedstocks. Hydrogen is potentially the only viable method to decarbonize all sectors of the economy simultaneously.

Hydrogen will play a critical role in a future comprehensive energy portfolio; hydrogen will be the decarbonizing tie between the different energy production sources and their end uses. Hydrogen acts as a zero-carbon energy carrier to couple energy sources and end uses. This provides the methodology to decarbonize the major energy consumption sectors of (1) the electric grid, (2) transportation and (3) industrial processes. It can provide energy storage supporting intermittent renewable power and cost-effective energy resilience; it enables the massive and seasonal energy storage that is required for a zero-emissions electric grid. It can be used in the transportation sector, especially for heavy-duty transportation where long ranges and fast refueling are critical. Renewable hydrogen is critical to decarbonize industrial processes that have needs for high temperature, chemical reduction and refining and chemical feedstocks. Hydrogen is potentially the only viable method to decarbonize all sectors of the economy simultaneously.

In this study, the emissions and performance of a commercial Solid Oxide Fuel Cell system with micro-combined heat and power (SOFC mCHP) capabilities are analyzed at various power output levels and with various hydrogen (H2) – natural gas (NG) fuel mixture concentrations. The SOFC mCHP system, although designed to be fueled by pure NG, is intentionally fueled with mixtures between 0 and 30% vol of H2mixed with NG (balance) and is operated between 0.5 and 1.5 kW. Since these units are used in residential and commercial applications, it is important to ensure that if H2becomes widely injected into the NG system that the corresponding H2-NG mixtures would not negatively impact the emissions or performance of the system. The performance of the system is characterized by measurement of major exhaust species concentrations (carbon dioxide, carbon monoxide, methane, water, nitric oxide, nitrogen dioxide, etc.). These measurements confirm that NOx emissions are extremely low and that adding hydrogen to the NG system does not increase NOx emissions. In addition, the system’s efficiency at part load experienced a small reduction with increasing H2concentrations in the mixture, compared to pure NG operation.

The goal of this study is to evaluate the impacts and capabilities of dynamically dispatching Solid Oxide Steam Electrolysis (SOSE) systems to support high penetration of renewable photovoltaic sources in the UCI microgrid. The UCI microgrid operation has been simulated as a linear programming problem in Matlab® considering all of its operational constraints to analyze the microgrid behavior to the additional PV installed capacity. Simulations cases consist of current 4 MW PV installed capacity and future PV installed capacities up to 35 MW. The integration of modular SOSE systems in the University of California, Irvine (UCI) microgrid, to absorb the excess Photovoltaic (PV) generated power is investigated in this study for different PV installed capacity. Also, the possibility of utilizing the available excess steam produced in the Heat Recovery Steam Generator (HRSG) as a portion of the required steam in SOSE systems is evaluated. Microgrid simulation results prove that for cases with PV installed capacity greater than 10 MW, the otherwise curtailed excess electricity would be a great potential to be used in SOSE for hydrogen production. The produced hydrogen in high installed capacities would be enough to feed the gas turbine with a gas mixture containing 15% volumetric hydrogen together with hydrogen used in the UCI hydrogen fuel stations. Consequently, natural gas consumption and carbon dioxide production are decreased substantially.

A method for analyzing the levelized cost of conversion, storage, and return of input energy as an end product net of losses with a zero cost of input energy, termed the levelized cost of returned energy (LCORE), is introduced and applied uniformly to compare the net conversion and storage costs of various renewable electrolysis technologies and hydrogen end-uses with battery and flow-battery energy storage technologies. The LCORE methodology accounts for capital costs, financing costs, operation and maintenance costs, energy efficiency of each step, technology lifetime, and replacement costs. Results show that the most valuable use of the renewable hydrogen is as fuel for fuel cell electric vehicles, although the costs of the hydrogen fueling infrastructure are estimated to be high using the existing paradigm of trucking, compression, and dispensing (adding more than $7/kilogram to the price of hydrogen). Importantly, the analyses show that the range of costs for pathways that produce hydrogen by electrolysis from renewable generation and return it to the electric grid using the natural gas system to transport the hydrogen to an existing combined cycle plant to produce the electricity have costs of $76–$210/MWh. These costs are directly competitive with battery energy storage pathways at $51–$150/MWh while also providing energy storage over durations as long as months, durations that are that are not technically feasible for many battery technologies due to charge leakage.

This study investigates the dynamic behavior of a solid oxide steam electrolyzer (SOSE) system without an external heat source that uses transient photovoltaic (PV) generated power as an input to produce compressed (to 3 MPa) renewable hydrogen to be injected directly into the natural gas network. A cathode-supported crossflow planar solid oxide electrolysis (SOE) cell is modeled in a quasi-three-dimensional thermo-electrochemical model that spatially and temporally simulates the performance of a unit cell operating dynamically. The stack is composed of 2500 unit cells that are assumed to be assembled into identically operating stacks, creating a 300 kW electrolyzer stack module. For the designed 300 kW SOSE stack (thermoneutral voltage achieved at design steady-state conditions), powered by the dynamic 0–450 kW output of PV systems, thermal management and balancing of all heat supply and cooling demands is required based upon the operating voltage to enable efficient operation and prevent degradation of the SOSE stacks. Dynamic system simulation results show that the SOSE system is capable of following the dynamic PV generated power for a sunny day (maximum PV generated power) and a cloudy day (highly dynamic PV generated power) while the SOSE stack temperature gradient is always maintained below a maximum set point along the stack for both days. The system efficiency based upon lower heating value of the generated hydrogen is between 0–75% and 0–78% with daily hydrogen production of 94 kg and 55 kg for sunny and cloudy days, respectively.

In this study the integration of a solid oxide fuel cell with liquid desiccant system is considered for powering and cooling a data center at the rack level. The novel idea is that each single fuel cell (~12 kW) is used to power one server rack and the waste heat from the fuel cell is used to regenerate a desiccant to provide dehumidification or cooling. The heat concentrates the liquid desiccant solution that is then stored. When moisture must be removed, the high concentration solution is used to dehumidify the outside air. The objective of this study is to theoretically investigate the capability of the integrated system to provide enough cold and dehumidified air to keep the server rack in the safe range of temperature and humidity. Results show that the SOFC waste heat can produce cold and dehumidified air that is in the safe range for server racks. However, with continuous outside air conditions of 25oC and 70% relative humidity the heat from the current SOFC system is enough to provide only 25% of the air flow demand for each server rack.

The dynamics of hydrogen energy storage (HES) integrated with large-scale renewable power (119.5 GW) using the capabilities of the existing California natural gas infrastructure were investigated. The dynamics associated with the grid demand, renewable power, pressure, and HES capacity for one week each of November and August were analyzed in detail while a higher level analysis of the entire state for the whole year was simulated in MATLAB/Simulink. It was found that the existing natural gas storage facilities may be converted to hydrogen storage facilities to store otherwise curtailed renewable energy through solid oxide electrolysis (SOE). Moreover, Solid Oxide Fuel Cell (SOFC) systems can also be used to dispatch the hydrogen back to the grid as power. The analysis in this paper shows that the dynamics of California natural gas underground storages associated with pressure and mass flow rate for achieving HES to support 100% renewable gas use are reasonable.

In this study, with measured steady state performance characteristics of a 1.5 kW residential Solid Oxide Fuel Cell (SOFC) system we evaluated the installation of residential SOFC systems for a typical hourly energy use for the entire year through all 16 climate zones in California. We carried out an economic analysis taking into account the dynamic daily and seasonal energy consumption for various climate zones and various current residential time-of-use utility rates. Residential SOFC implementation cases in various climate zones that focus upon 1) reduced energy use, 2) reduced peak demand, 3) utility time-of use rate-structure impacts, and 4) CO2 emission reductions are evaluated. From the customer perspective, this study generates a guideline for the user to make decisions depending upon their electric energy usage profile, utility rate structure and carbon credit, we found that breakeven costs are highly dependent upon the utility rate structures with PG&E structures most favorably encouraging SOFC use.

In this study, we experimentally evaluated electrolysis of water using a short stack of six solid oxide electrochemical cells (SOEC). A model of the SOEC stack was verified and used to evaluate thermal management of the stack operating above and below the thermoneutral voltage, which at these temperatures requires additional heat input into the stack to maintain the system operating temperature. High quality heat was supplied from a molten salt. Heat generated from concentrated solar power (CSP) can reach the required SOEC operation temperature through molten salts and can provide enough heat to sustain sub-thermoneutral voltage operation of an SOEC. The SOEC model is spatially and temporally resolved and was used to evaluate the dynamic performance of a system operating at sub-thermoneutral voltages with dynamic heat input. Dynamic results suggest high efficiency hydrogen generation can occur with external heat input under various conditions including variable power and salt flow.

In this study the waste heat from a 2.5 kW solid oxide fuel cell (SOFC) is captured and processed through a 1.5 kW absorption chiller (AC) to provide cooling for a single residence. The integration of an AC with an SOFC could create a highly dispatchable system that can meet the dynamics of measured residential power. A spatially resolved dynamic model was developed in Matlab/Simulink to simulate the dynamic operating characteristics of an SOFC system. A dynamic AC model was developed to study the dynamic characteristics and the performance of the combined co-generation system. Actual dynamic data from a single residential house was used as an input of the SOFC-AC model. For a single week, the SOFC was capable of following the highly dynamic load with an average efficiency of 56%. The AC generated 15.6 kWh of cooling with an average COP and cooling of 1.09 and 0.65 kW, respectively.

SOFC is a fuel flexible technology suitable for producing clean energy. Understanding of the multi-reaction mechanism that a complex H2-CO fuel presents to the electrochemical kinetics is numerically approached in this work. By using existing fundamental reaction mechanisms and kinetic parameters, elementary reactions involved in an SOFC anode have been assembled, modeled and analyzed. This involves both homogeneous and heterogeneous chemistry, electrochemistry and surface diffusion. The use of the patterned anode approach removes the mass transport complications and allows comparison with pre-existing experimental data. The model provides both polarization curves and surface coverage distribution, among other results, providing a high level of detail and understanding of the physical phenomena involved. In particular, analysis is focused upon understanding how the competitive H2and CO reactions behave.The presence of CO was found to stabilize OCV response to temperature and while it occupied most of the active sites it did not penalize overall performance except when significant product species were present.

The challenges associated with incorporating a large amount of distributed generation (DG), including fuel cells, into a radial distribution feeder are examined using a dynamic MATLAB/SIMULINK™ model. Two generic distribution feeder models are used to investigate possible scenarios where voltage problems may occur. Modern inverter topologies make ancillary services, such as on-demand reactive power generation/consumption economical to include, which expands the design space across which DG can function in the distribution system. The simulation platform enables testing of the following local control goals: DG connected with unity power factor, DG and load connected with unity power factor, DG connected with local voltage regulation (LVR), and DG connected with real power curtailment. Both the LVR and curtailment strategies can regulate the voltage of the simple circuit case, but the circuit utilizing a substation with load drop compensation has no universal solution. Even DG with a penetration level around 10% of rated circuit power can cause overvoltage problems with load drop compensation. The real power curtailment control strategy creates the best overall circuit efficiency, while all other control strategies result in low light load efficiency at high DG penetrations. The lack of a universal solution implies that some degree of communication will be needed to reliably install a large amount of DG on a distribution circuit.

The challenges associated with incorporating a large amount of distributed generation (DG), including fuel cells, into a radial distribution feeder are examined using a dynamic MATLAB/SIMULINK™ model. Two generic distribution feeder models are used to investigate possible scenarios where voltage problems may occur. Modern inverter topologies make ancillary services, such as on-demand reactive power generation/consumption economical to include, which expands the design space across which DG can function in the distribution system. The simulation platform enables testing of the following local control goals: DG connected with unity power factor, DG and load connected with unity power factor, DG connected with local voltage regulation (LVR), and DG connected with real power curtailment. Both the LVR and curtailment strategies can regulate the voltage of the simple circuit case, but the circuit utilizing a substation with load drop compensation has no universal solution. Even DG with a penetration level around 10% of rated circuit power can cause overvoltage problems with load drop compensation. The real power curtailment control strategy creates the best overall circuit efficiency, while all other control strategies result in low light load efficiency at high DG penetrations. The lack of a universal solution implies that some degree of communication will be needed to reliably install a large amount of DG on a distribution circuit.

Barriers to fuel cell commercialization are often introduced as general challenges, such as cost and durability, without definition of the terms and usually without prioritizing the degree to which each of these barriers hinder the development of fuel cell technology. This work acts to objectively determine the importance of technology barriers to fuel cell commercialization and to develop a list of appropriate actions to overcome these barriers especially as they relate to the California market. Using previous fuel cell roadmaps and action plans along with feedback from the fuel cell community, benchmarks (i.e., the current technology status), and milestones (i.e., the desired technology status) for fuel cell technology are explored. Understanding the benchmarks and milestones enables the development of a list of fuel cell commercialization barriers. These barriers or gaps represent issues, which if addressed will enhance the market feasibility and acceptance of fuel cell technologies. The research process determined that the best technique to address these barriers, and bridge the gaps between fuel cell benchmarks and milestones, is to develop specific research projects to address individual commercialization barriers or collections of barriers. This technique allows for a high resolution of issues while presenting the material in a form that is conducive to planning for organizations such as industry, regulatory bodies, universities, and government entities that desire to pursue the most promising projects. The current analyses resulted in three distinct research and development areas that are considered most important based on the results. The first and most important research and development area is associated with technologies that address the connection and interaction of fuel cells with the electric grid. This R&D area is followed in importance by the production, use, and availability of opportunity fuels in fuel cell systems. The third most important category concerned the development and infrastructure required for transportation related fuel cell systems. In each of these areas the fuel cell community identified demonstration and deployment projects as the most important types of projects to pursue since they tend to address multiple barriers in many different types of markets for fuel cell technology. Other high priority types of projects are those that addresses environmental and grid-related barriers. The analyses found that cost/value to customer, system integration, and customer requirements were the most important barriers that affect the development and market acceptance of fuel cell technology.

Barriers to fuel cell commercialization are often introduced as general challenges, such as cost and durability, without definition of the terms and usually without prioritizing the degree to which each of these barriers hinder the development of fuel cell technology. This work acts to objectively determine the importance of technology barriers to fuel cell commercialization and to develop a list of appropriate actions to overcome these barriers especially as they relate to the California market. Using previous fuel cell roadmaps and action plans along with feedback from the fuel cell community, benchmarks (i.e., the current technology status), and milestones (i.e., the desired technology status) for fuel cell technology are explored. Understanding the benchmarks and milestones enables the development of a list of fuel cell commercialization barriers. These barriers or gaps represent issues, which if addressed will enhance the market feasibility and acceptance of fuel cell technologies. The research process determined that the best technique to address these barriers, and bridge the gaps between fuel cell benchmarks and milestones, is to develop specific research projects to address individual commercialization barriers or collections of barriers. This technique allows for a high resolution of issues while presenting the material in a form that is conducive to planning for organizations such as industry, regulatory bodies, universities, and government entities that desire to pursue the most promising projects. The current analyses resulted in three distinct research and development areas that are considered most important based on the results. The first and most important research and development area is associated with technologies that address the connection and interaction of fuel cells with the electric grid. This R&D area is followed in importance by the production, use, and availability of opportunity fuels in fuel cell systems. The third most important category concerned the development and infrastructure required for transportation related fuel cell systems. In each of these areas the fuel cell community identified demonstration and deployment projects as the most important types of projects to pursue since they tend to address multiple barriers in many different types of markets for fuel cell technology. Other high priority types of projects are those that addresses environmental and grid-related barriers. The analyses found that cost/value to customer, system integration, and customer requirements were the most important barriers that affect the development and market acceptance of fuel cell technology.

La0.8Sr0.2Ga0.8Mg0.115Co0.085O3-d (LSGMC) has been reported as an optimized composition for LSGM-based electrolytes used in intermediate temperature solid oxide fuel cells (SOFCs). Electrocatalytic properties of the interfaces between LSGMC electrolyte and various cathodes: comprised of Sm0.5Sr0.5CoO3-d (SSC), and La0.7Sr0.3Co0.2Fe0.8O3-d (LSCF) in composite forms (70wt.%) with LSGMC (30wt.%) were investigated under both oxygen reduction and evolution conditions. All the oxides were synthesized using the glycine-nitrate process (GNP) followed by unique powder processing to produce the desired phase purity and particle properties. Symmetrical electrochemical cells were fabricated by a screen-printing technique with precisely controlled alignment. Three-electrode linear dc polarization and ac impedance spectroscopy were used to characterize the kinetics of the interfacial reactions in detail. For the composite SSC-LSGMC cathode/LSGMC interface, the cathodic overpotential under 1 A/cm2 current density was as low as 0.085 V at 973 K, 0.062V at 1023K and 0.051V at 1073K in air. Composite LSCF-LSGMC cathode/LSGMC interfaces were found to have about twice the exchange current density of composite SSC- LSGMC/LSGMC interfaces for the same temperature and overpotential conditions.