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Solid oxide fuel cell (SOFC)–gas turbine (GT) hybrid systems can produce power at high electrical efficiencies while emitting virtually zero criteria pollutants (e.g., ozone, carbon monoxide, oxides of nitrogen and sulfur, and particulate matters). This study presents new insights into renewable hydrogen (RH2)-powered SOFC–GT hybrid systems with respect to their system configuration and techno-economic analysis motivated by the need for clean on-demand power. First, three system configurations are thermodynamically assessed: (I) a reference case with no SOFC off-gas recirculation, (II) a case with cathode off-gas recirculation, and (III) a case with anode off-gas recirculation. While these configurations have been studied in isolation, here we provide a detailed performance comparison. Moreover, a techno-economic analysis is conducted to study the economic competitiveness of RH2-fueled hybrid systems and the economies of scale by offering a comparison to natural gas (NG)-fueled systems. Results show that the case with anode off-gas recirculation, with 68.50%-lower heating value (LHV) at a 10 MW scale, has the highest efficiency among the studied scenarios. When moving from 10 MW to 50 MW, the efficiency increases to 70.22%-LHV. These high efficiency values make SOFC–GT hybrid systems highly attractive in the context of a circular economy as they outcompete most other power generation technologies. The cost-of-electricity (COE) is reduced by about 10% when moving from 10 MW to 50 MW, from USD 1976/kW to USD 1668/kW, respectively. Renewable H2 is expected to be economically competitive with NG by 2030, when the U.S. Department of Energy's target of USD 1/kg RH2 is reached. [ABSTRACT FROM AUTHOR]

Previous study shows that the constant volume sampler incorrectly measures some of the exhaust gas when testing a plug-in hybrid electric vehicle in the cold start condition when comparing the CO2 results from constant volume sampler and fuel flow meter. The main reason is likely associated with the exhaust left in the vehicle tailpipe and constant volume sampler sampling line. Other factors, such as fuel line expansion and water condensation in the exhaust system, are also considered to have contributions. This article evaluates these issues quantitatively by testing a Toyota Prius hybrid electric vehicle on the industry standard constant volume sampler system combined with both a fuel flow meter measurement and an electronic control unit record for fuel consumption. Cold start test cycles and test cycles with a system pre-purge event show that the constant volume sampler has a significant delay in measuring the exhaust, and the estimated exhaust losses for the test car are 15 g CO2. Tests with a purge event at the end of the driving cycle show that there are approximately 7 g of CO2 trapped in the exhaust system and the constant volume sampler sampling line, and the possible reasons for the discrepancy of the above two points (15 and 7 g) are evaluated. The expansion and air bubble influence the fuel flow meter, and the impact of water condensation on CO2 and CO appears to be negligible. [ABSTRACT FROM PUBLISHER]

SUMMARY Quantifying the severity of the intermittencies in solar irradiation is important for (i) understanding the potential impacts of high solar power penetration levels on the electric grid and (ii) evaluating the need for technologies that may be necessary to complement solar power in order to balance the electric grid. This study uses a spectral method to distinguish between cloud-induced and diurnal cycle-induced transients and to quantify the severity of intermittencies occurring over a range of timescales. The method is used to quantify variability between specific sites as well as to evaluate the sensitivity of solar power variability to spatial diversification of the solar farm portfolio. Results indicate that increasing the spatial diversity of the solar farm portfolio reduces the magnitude of the fluctuations in power output as a fraction of the total system capacity. This behavior is associated with two forces: (i) a reduction in the influence of fluctuations occurring at an individual site on the total profile and (ii) should the sites in question be sufficiently spaced apart, the fluctuations in solar irradiation that each site exhibits are uncorrelated and do not generally add up in tandem at short timescales. These effects reduce the degree of uncertainty and variability associated with solar farm output and demonstrate a reduction in the maximum magnitude of solar power fluctuations for a given solar penetration level. The rate of increase of the maximum solar power deviation from the 1-h average associated with increases in desired solar penetration level decreases in an inverse exponential manner with the number of sufficiently spaced sites composing the solar farm portfolio. These results imply that a lower amount of regulation or energy storage capacity is needed to regulate solar intermittency if solar installations and the accommodating transmission infrastructure are designed and operated appropriately. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Proper converter design can allow solid oxide fuel cells operated as distributed generators to mutually benefit both the load and the electric utility during steady-state conditions, but dynamic load variations still present challenges. Unlike standard synchronous generators, fuel cells lack rotating inertia and their output power ramp rate is limited by design. Two strategies are herein investigated to mitigate the impact of a large load perturbation on the electric utility grid: 1) external use of ultracapacitor electrical storage connected through a dc-dc converter and 2) internal reduction of steady-state fuel utilization in the fuel cell to enable faster response to output power perturbations. Both strategies successfully eliminate the impact of a load perturbation on the utility grid. The external ultracapacitor strategy requires more capital investment while the internal fuel utilization strategy re- quires higher fuel use. This success implies that there is substantial flexibility for designing load-following fuel cell systems that are model citizens. [ABSTRACT FROM AUTHOR]

Zero-emission powertrains, connectivity, and automation are the future of automotive mobility, though their collective impacts on fuel economy is difficult to study. This paper develops a novel methodology to simulate the impacts of cooperative driving automation on battery electric (BEVs) and fuel-cell electric (FCEVs) vehicles. Enabling V2I connectivity for city driving resulted in fuel economy improvement of 6 % to 13 % for BEVs and 9 % to 15 % for FCEVs. Enabling aerodynamic drag reduction in V2V highway driving resulted in fuel economy improvement of 5 % to 32 % for BEVs and 5 % to 26 % for FCEVs. Sensitivity analysis on battery and fuel cell efficiency was conducted to determine how technological improvements could impact connected mobility. Improving powertrain component efficiencies decreased performance gains for V2I city driving while increasing performance gains for V2V highway driving. Fuel-cell efficiency improvements had greater impacts on connectivity gains than battery efficiency improvements. Vehicle testing should verify these results. [ABSTRACT FROM AUTHOR]

With the inexorable depletion of fossil fuel and the increasing need to reduce greenhouse gas emissions, blending renewable fuels like biogas or renewable hydrogen into natural gas is of great interest. Due to various potential sources and low-carbon or even carbon-free properties, biogas and hydrogen are competitive energy carriers and promising gaseous fuels to replace pipeline natural gas in the future. From the perspective of end users and combustion device manufacturers, one of the major concerns is the influence of the renewable content on the combustion device performance. In addition, the upper limit of renewable gas content percentage in pipeline also interests policy makers and gas utility companies. Therefore, the present study is conducted to investigate the influence of renewable gas content on the operating performance of a residential room furnace. Evaluated combustion performance characteristics include ignition performance, blow-off/flashback limits, burner temperature and emissions (NO, NO 2 , N 2 O, CO, UHC, NH 3). The results show that 5% carbon dioxide and 15% (by volume) hydrogen can be added to natural gas separately without significant impacts. Above this amount, the risk of blow-off and flashback is the limiting factor. Generally speaking, carbon dioxide addition helps decrease NO X emission but increases CO emission. However, hydrogen addition up to the amounts studied here in has minimal impact on NO X and CO emissions. Image 1 • Ignition failure and flame blow-off occur when CO 2 addition exceeds 5% and 25%, respectively. • Flashback induced ignition failure occurs when H 2 addition exceeds 15%. • Steady state flashback occurs when H 2 addition exceeds 40% by volume. • CO 2 addition reduces burner material temperature and H 2 addition increases it. • CO 2 addition decreases NO X emission and increases CO emission; however, H 2 addition has minimal impact on either NO X or CO emissions. [ABSTRACT FROM AUTHOR]

Adding renewable hydrogen into natural gas pipeline would bring down the net gas C/H ratio and hence the CO 2 emissions. Also, it can help stabilize electric grids and maximize the renewable output of intermittent energy sources (solar, wind, etc.) via power-to-gas pathway. However, hydrogen differs in its chemical and physical characteristics (flammability range, flame speed, density, adiabatic flame temperature, energy content, etc.) than natural gas. Before transitioning to hydrogen admixing into pipelines, a general agreement on maximum hydrogen tolerance pertaining to end use (residential appliances) operation needs to be established. Focusing on the combustion performance of two representative models of storage water heaters (conventional and low-NO x) in California, this research addresses how much H 2 content in natural gas can be tolerated without loss of critical performance parameters with reliable operation. Characteristics like flashback, ignition delay, flame structure, and emissions (NO x , NO, CO, CO 2 , UHC, and NH 3) at different concentrations of H 2 admixed with natural gas is investigated. The present study shows <10% H 2 can be added to natural gas without any loss of efficiency for both the low-NO x and conventional storage water heater. This work also aims to provide a brief review of burner configuration and emission regulation pertaining to water heating owing to a gap in the literature. Image 1 • Mixtures of hydrogen and natural gas are tested on representative water heaters. • Up to 10% hydrogen added to natural gas has little impact on combustion performance and operability. • Instability (ignition delay/flashback) during re-ignition of the main burner flame to maintain tank temperature is the limiting factor. • The hydrogen injection limit is lower than that proposed in a previous study. • Adding hydrogen up to 30% has minimal impact on emissions. [ABSTRACT FROM AUTHOR]

With the increasing need to reduce greenhouse gas emission and adopt sustainability in combustion systems, injection of renewable gases into the pipeline natural gas is of great interest. Due to high specific energy density and various potential sources, hydrogen is a competitive energy carrier and a promising gaseous fuel to replace natural gas in the future. To test the end use impact of hydrogen injection into the natural gas pipeline infrastructure, the present study has been carried out to evaluate the fuel interchangeability between hydrogen and natural gas in a residential commercial oven burner. Various combustion performance characteristics were evaluated, including flashback limits, ignition performance, flame characteristics, combustion noise, burner temperature and emissions (NO, NO 2 , N 2 O, CO, UHC, NH 3). Primary air entrainment process was also investigated. Several correlations for predicting air entrainment were compared and evaluated for accuracy based on the measured fuel/air concentration results in the burner. The results indicate that 25% (by volume) hydrogen can be added to natural gas without significant impacts. Above this amount, flashback in the burner tube is the limiting factor. Hydrogen addition has minimal impact on NO X emission while expectedly decreasing CO emissions. As the amount of hydrogen increases in the fuel, the ability of the fuel to entrain primary air decreases. Image 1 • Flashback at ignition limits the amount of hydrogen that can be added to natural gas to ~25% by volume. • Hydrogen addition doesn't impact oven burner NO X emissions, but, decreases CO, as expected. • The cyclic operation of the oven leads to complex emissions behavior as a function of time. • Primary air entrainment of the mixtures is successfully predicted using Jones's correlation. [ABSTRACT FROM AUTHOR]

This work presents the atomization characteristics and dynamics of water-in-heptane (W/H) emulsions injected into a gaseous crossflow. W/H mixtures were tested while varying momentum flux ratios and aerodynamic Weber numbers. Different injector orifice diameters and orifice length-to-diameter ratios were used to test the generality of the results. The atomization properties of W/H mixtures were compared with properties of neat water and neat heptane to evaluate the effect of an emulsion on droplet sizing, cross-sectional stability and dispersion, and jet penetration depth. Liquid dynamics were extracted through analyzing instantaneous spray measurements and dynamic mode decomposition (DMD) on high-speed video recordings of the atomization processes. Correlations were proposed to establish preliminary relationships between fundamental spray processes and test conditions. These correlations allowed for emulsion behavior to be compared with neat liquid behavior. The use of emulsions induces greater spray instability than through using neat liquids, likely due to the difficulty in injecting a stable emulsion. Neat liquid correlations were produced and successfully predicted various spray measurements. These correlations, however, indicate that injector geometry has an effect on spray properties, which need to be addressed independently. The emulsions are unable to adhere to the neat liquid correlations suggesting that an increased number of correlation terms are required to adequately predict emulsion behavior. [ABSTRACT FROM AUTHOR]

• A methodology to assess BEBs as a microgrid resiliency resource. • BEBs offer a compelling microgrid resiliency enhancement. • BEBs offer a flexible portfolio of microgrid Mobility Services+. • A BEB fleet can serve as a blackstart resource for a tripped prime generator. During a grid outage, microgrids can benefit from energy resources that enhance the reliability and resiliency of serving critical loads and overall protection. The present study develops a methodology to assess the efficacy of battery electric buses (BEBs) as a microgrid resiliency attribute during islanded operations, and applies the methodology to an existing 20 MW-class microgrid equipped with a fleet of 20 BEBs. Each BEB comprises 324 kWh of stored energy and can charge/discharge at 80 kW which translates to 1.6 MW and the potential of 6.48 MWh of stored power and energy respectively depending on the state-of-charge of each bus. For the application evaluated, the methodology reveals that a BEB fleet can serve as a viable resiliency and flexible energy resource for an islanded microgrid by enabling Mobility Services +, examples of which include (1) deployment to serve critical loads within the microgrid (e.g., an emergency control center, shelter, clinic), (2) deployment to serve critical loads outside the microgrid (e.g., a hospital, fire station, grocery store), and (3) service as a blackstart resource should the microgrid prime power generator trip. In the present case, the BEB fleet has the ability to support a microgrid emergency center for at least 16 h, and serve as a blackstart resource with a probability of 100% by a combination of parked BEBs and BEBs recalled from on route transit service. [ABSTRACT FROM AUTHOR]

Different configurations of a 100% renewable electricity system are possible, but not all are equally desirable in terms of the scale of material resources required to sustain them. This study compares different approaches for developing a 100% renewable electricity system on the basis of the material mass investment required to sustain their physical components. Electric grid modeling accounting for operational constraints is used to determine the scale of energy technology capacities required to achieve a 100% renewable electricity system using California as a representative example and translating those requirements to material mass requirements. Using a wind/solar/storage approach requires exponentially growing capacities of energy storage to meet operational needs and requires significant material mass investments. Material resource efficiency of the system is shown to be improved by maximizing the use of regional non-variable renewables to the extent possible within local capacity constraints. Alternatively, overbuilding the wind and solar capacity in excess of that needed to meet annual demand is also shown to improve material resource efficiency of the system. Overall, different approaches for meeting a 100% renewable electricity penetration are not equally desirable when material resource usage is considered. This should be taken into account in future energy system planning studies. [ABSTRACT FROM AUTHOR]

The pursuit of future energy systems that can meet electricity demands while supporting the attainment of societal environment goals, including mitigating climate change and reducing pollution in the air, has led to questions regarding the viability of continued use of natural gas. Natural gas use, particularly for electricity generation, has increased in recent years due to enhanced resource availability from non-traditional reserves and pressure to reduce greenhouse gasses (GHG) from higher-emitting sources, including coal generation. While lower than coal emissions, current natural gas power generation strategies primarily utilize combustion with higher emissions of GHG and criteria pollutants than other low-carbon generation options, including renewable resources. Furthermore, emissions from life cycle stages of natural gas production and distribution can have additional detrimental GHG and air quality (AQ) impacts. On the other hand, natural gas power generation can play an important role in supporting renewable resource integration by (1) providing essential load balancing services, and (2) supporting the use of gaseous renewable fuels through the existing infrastructure of the natural gas system. Additionally, advanced technologies and strategies including fuel cells and combined cooling heating and power (CCHP) systems can facilitate natural gas generation with low emissions and high efficiencies. Thus, the role of natural gas generation in the context of GHG mitigation and AQ improvement is complex and multi-faceted, requiring consideration of more than simple quantification of total or net emissions. If appropriately constructed and managed, natural gas generation could support and advance sustainable and renewable energy. In this paper, a review of the literature regarding emissions from natural gas with a focus on power generation is conducted and discussed in the context of GHG and AQ impacts. In addition, a pathway forward is proposed for natural gas generation and infrastructure to maximize environmental benefits and support renewable resources in the attainment of emission reductions. [ABSTRACT FROM AUTHOR]

Substantial changes need to occur in the electricity generation sector in order to address greenhouse gas and urban air quality goals. These goals, combined with increasing energy prices, have led to elevated interest in alternative, low to zero carbon and pollutant emission technologies in this sector. The challenge is to assess the impacts of various technologies, policies, and market practices in order to develop a roadmap to meet energy and environmental goals. To this end, a spatially and temporally resolved resource dispatch model is developed that simulates an electricity market while taking into account physical constraints associated with various components of an electricity grid. Multiple technology simulation modules are developed to provide inputs to the model. The model is used to design a market-based grid, and to develop and evaluate different dispatch strategies. To maintain the system cost at acceptable levels and reduce emissions, the results reveal that the best approach is a combination of economic and environmental dispatch strategies. The methodology and the tools developed provide a means to examine various aspects of future scenarios and their impacts on different sectors, and can be used for both decision making and planning. [ABSTRACT FROM AUTHOR]

Highlights: [•] Advanced technologies and their integrations for H2 coproducing IGCCs are identified. [•] HHV and moisture% of feedstock have significant effects on plant performance. [•] Net equivalent power efficiencies of coproducing IGCCs range from 35% to 38%. [•] Thermal performance of identified H2 coproducing IGCCs are competitive with SMR H2 plants. [•] Cost of produced H2 ranges from $1.42/kg to $2.77/kg depending on feedstock. [ABSTRACT FROM AUTHOR]

• Wildfires contribute 92 % of Naphthalene, 82 % of PM_PAH emissions in study period. • Model performance improved for PM2.5 and PAHs prediction with proposed method. • PM_PAH impacts broader areas, while naphthalene's effect is localized to fire zones. • In fire season, 32 % (particles) and 10 % (gas) of PAH exposure linked to wildfires. In recent years, wildfires in California have increased in frequency and intensity due to climate change and prolonged drought. The air pollutants released by wildfires cause significant health consequences, among which polycyclic aromatic hydrocarbons (PAHs) are particularly toxic. Estimating PAH emissions from wildfires is challenging due to variability in vegetation types. In this study, we estimate PAH emission rates across California at a high resolution, based on laboratory-measured PAH emission rates from 22 different vegetation types and detailed vegetation mapping. By combining these estimates with biomass burning data from the NCAR Fire Inventory, the Community Multiscale Air Quality Modeling System simulates PAH concentrations for the 2017 fire season. The modeling results compare favorably to measurements from three PAH monitoring sites in California. The peak PAH emissions from wildfire events are up to be 80 times higher in the gas phase and 32 times higher in the particle phase compared to a case without fire emissions. The population-weighted PAH concentrations from the fire case (0.053 µg/m3) are 47 % higher compared to a non-fire case (0.036 µg/m3) in the particle phase and 11 % higher in the gas phase (9.82 ppt compared to 8.83 ppt) during the study period. While highly depended on the meteorological condition, the simulated spatial distribution indicates that gas-phase PAHs are less likely to travel long distances from the fire source and are prone to aging into the particle phase during transport. Consequently, populations are more likely to be exposed to particle-phase PAHs during wildfire events. This finding has important implications for understanding the health impacts of wildfire-induced PAH concentrations, as particle-phase PAHs may have different toxicological effects compared to gas-phase PAHs. [ABSTRACT FROM AUTHOR]

Abstract: This work builds upon previous high temperature fuel cell (HT-FC) modeling studies, capturing both steady state performance and transient behavior of HT-FC stacks by merging simplified dimensional aspects of a planar fuel cell stack with first principles physical modeling. Dynamic simulations are developed that spatially resolve fluctuations in temperature, pressure and concentration distributions during transient operation. A significant portion of the heat transfer occurs prior to and after the air passes over the electrochemically active portions of the cell, justifying additional heat transfer pathways from the stack to the air in order to accurately characterize the thermal transients and temperature distributions in the HT-FC stack. The highly configurable MatLab-Simulink® model developed can simulate both solid oxide and molten carbonate fuel cells utilizing either direct or indirect internal reforming. The perturbation response characteristics of the dynamic model to load, fuel flow, air flow and composition perturbations are discussed, and control strategies are introduced that minimize temperature fluctuations. Analysis indicates air flow and inlet temperature controls are sufficient to control average temperature and average internal temperature gradients. Internal heat transfer dynamics substantially change the spatial temperature distribution and local temperature gradients during typical operating conditions and perturbations. [Copyright &y& Elsevier]

Autoignition delay times of mixtures of a/kanes and natural gas were studied experimen- tally in a high pressure and intermediate temperature turbulent flow reactor Measure- ments were made at pressures between 7 atm and 15 atm and temperatures from 785 K to 935 K. The blends include binary and ternary mixtures of methane, ethane, and propane along with various natural gas blends. Based on these data, the effect of higher hydro- carbons on the ignition delay time of natural gas type fuels at actual gas turbine engine conditions has been quanti~fied. While the addition of higher hydrocarbons in quantities of up to 30% was found to reduce the ignition delay by up to a factor of 4, the delay times were still found to be greater than 60 ms in all cases, which is well above the residence times of most engine premixers. The data were used to develop simple Arrhenius type correlations as a function of temperature, pressure, and fuel composition for design use. [DOl: 10.1115/1.4001981] [ABSTRACT FROM AUTHOR]

To increase reliability, resiliency, and overall efficiency, distributed generators are being deployed at sites including hotels, hospitals, and data centers. This study provides a novel evaluation of the operational and economic performance of a megawatt-class high-temperature fuel cell (HTFC) cogeneration plant coupled to a 200RT absorption chiller. With unique access to high-resolution data, comprehensive analyses are conducted to assess both the plant operational and, combined with electric utility data, economic performance including identifying the operational parameters that most affect economic performance. The analyses reveal the challenges in achieving viable operational and economic performance of distributed generators, the difficulty of acquiring detailed operational data, and the complex and varying array of electric utility rates and demand charges. The fluctuation in electric and natural gas utility rates represent the largest impact on the economic performance. While the fuel cell can reduce the monthly demand charge that would otherwise be applied, a trip of the fuel cell can result in a monthly demand charge and compromise the financial viability of the plant. In the present case, the first four years of operation resulted in a net loss rather than the savings expected. Strategies to yield a net gain are presented. [Display omitted] • Multi year operational and economic performance of a commercial 1.4 MW HTFC/Chiller. • Detailed sensitivity analysis of factors affecting operational performance. • Projection of future economic performance with measures for improvement. • Results that inform the design and commercial deployment of HTFC/Chiller systems. [ABSTRACT FROM AUTHOR]

The thermodynamic performance of a solid oxide fuel cell (SOFC)-gas turbine (GT) hybrid system has been investigated at steady state operating conditions considering overall cell temperature differences and local thermal gradients inside the SOFC. The obtained simulation results served as input for the thermo-economic evaluation of the SOFC-GT hybrid. The system has been studied at two different operating voltages, various operating pressures, and fuel utilization factors. The results show that operating the system at higher fuel utilization factors and higher pressure ratios results in a substantially increased air flow requirement to maintain acceptable temperature differences and thermal gradients. The highest efficiency is obtained at the higher operating voltage of the two studied scenarios, a moderate pressure ratio of 5 bar and a moderate fuel utilization of 87.6%. However, the lowest cost of electricity is obtained at the lower operating voltage, the same pressure ratio and a lower fuel utilization compared to the highest efficiency case. • Using only GT exhaust gas recuperation achieves highest efficiency. • Pressure ratios around 5 bar achieve highest efficiencies. • Pressure ratios around 5 bar achieve lowest cost of electricity. • Fuel utilization around 85% achieves lowest cost of electricity. [ABSTRACT FROM AUTHOR]

Facilities such as ports that are associated with goods movement face challenges in managing energy requirements including growing demands, maintaining economic competitiveness, increasing efficiencies of operation, and improving the resiliency, reliability, and security of the energy supply. Furthermore, ports face pressure to meet environmental goals including reducing the emissions of both pollutants and greenhouse gases and increasing the levels of renewable sources. Within this framework, many port operators are pursuing the development of microgrids supported by self-generation including fuel cell systems. Given the breadth of energy requirements of ports, the range of fuel cell applications is an attractive resource for stationary power generation, motive power and fuel generation, and backup/auxiliary power in concert with base load power. This work involves a review of the literature, from a technical perspective, to assess microgrids and fuel cell systems at ports including comparison with combustion-based power distributed generation sources. Additionally, novel simulations are presented to provide insight into economic and emission considerations associated with fuel cell deployment in critical facilities. Important distinctions of fuel cells for ports include flexibility of size and fuel, low to negligible emissions, capability to operate in grid-forming mode, and high electric-only efficiencies. While combined cooling, heating, and power improves performance and should be pursued, the mismatch in port electrical and thermal loads is a potential barrier and increases the importance of high electric-only efficiencies of fuel cells. Tri-generation systems have the potential to maximize benefits with the production of hydrogen along with electricity and, if needed, heat. • Fuel cell systems can support microgrids at ports. • A critical facility is modeled and use of fuel cells in islanding is simulated. • Microgrids can provide necessary reliability and resiliency for ports operations. [ABSTRACT FROM AUTHOR]