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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.

California has ambitious goals for reducing and eliminating greenhouse gas emissions from the State’s electricity system as a cornerstone of efforts to decarbonize the State’s economy more broadly. Electricity decarbonization efforts are codified by Senate Bill (SB) 100 which seeks to have 100% of retail sales of electricity by the year 2045 provided by eligible zero-carbon resources with an interim target of 60% of retail sales of electricity provided by eligible renewable resources by the year 2030. This policy contributes to a broader goal of achieving economy-wide carbon neutrality in the State by 2045, codified by Executive Order B-55-18.Planning studies were undertaken to determine how California should proceed in terms of electricity generation and storage resource rollout to meet these goals, such as the Senate Bill 100 Joint Agency Report [1], which highlights the need for rapid renewable resource and energy storage buildout. Energy storage is typically selected as utility-scale lithium-ion batteries for short-duration storage and pumped hydropower energy storage for long-duration energy storage functions, primarily due to their relatively low cost for the former and technological maturity for the latter. Since the capacity expansion models used for such planning studies focus on minimizing cost, the recommended course from these studies focuses on lithium-ion and pumped hydropower energy storage connected as utility energy storage.In practice, however, energy storage deployment will not be dictated by a central plan. Energy storage is being deployed to serve different priorities. Behind-the-meter energy storage may be deployed by individual residential, commercial, and industrial customers to serve their specific needs, provide electricity savings, and enable higher uptake of local renewable resources. Energy storage may also be installed at wind or solar farms to enable these to act as more dispatchable resources for the electric grid and enable them to provide electricity to the grid when they would otherwise not be generating. Additionally, other energy storage technologies such as flow batteries and hydrogen energy storage are emerging as potential alternatives to lithium-ion batteries and pumped hydropower, each with its own advantages and disadvantages in terms of technical, economic, and practical (i.e. safety, recyclability, etc...) characteristics.Energy storage is a critical enabler of plans for complying with Senate Bill 100 and broader economy-wide decarbonization goals. Therefore, it is critical to understand the effect of alternative configurations for energy storage deployment on the broader electricity system’s ability to rely on zero-carbon electricity for meeting load, how well it can use available renewable electricity generation, and the system-wide cost of electricity.Therefore, the goal of this project is to provide information on the preferred configuration of energy storage technologies for supporting a decarbonized California electric grid by investigating alternative configurations for the buildout of energy storage to meet California’s electricity decarbonization goals and comparing them to the configuration suggested by Senate Bill 100 planning studies.

Batteries are important for promoting renewable energy, but, like most engineered products, they contain multiple hazardous materials. The purpose of this study is to evaluate industrial-scale batteries using GreenScreen® for Safer Chemicals, an established chemical hazard assessment (CHA) framework, and to develop a systematic, transparent methodology to quantify the CHA results, harmonize them, and aggregate them into single-value hazard scores, which can facilitate quantitative comparison and a robust evaluation of data gaps, inconsistencies, and uncertainty through the implementation of carefully selected scenarios and stochastic multicriteria acceptability analysis (SMAA). Using multiple authoritative toxicity data sources, six battery products are evaluated: three lithium-ion batteries (lithium iron phosphate, lithium nickel cobalt manganese hydroxide, and lithium manganese oxide), and three redox flow batteries (vanadium redox, zinc-bromine, and all-iron). The CHA results indicate that many materials in these batteries, including reagents and intermediates, inherently exhibit high hazard; therefore, safer materials should be identified and considered in future designs. The scenario analysis and SMAA, combined, provide a quantitative evaluation framework to support the decision-making needed to compare alternative technologies. Thus, this study highlights specific strategies to reduce the use of hazardous materials in complex engineered products before they are widely used in this rapidly-expanding industry sector.

Air quality associated public health co-benefit may emerge from climate and energy policies aimed at reducing greenhouse gas (GHG) emissions. However, the distribution of these co-benefits has not been carefully studied, despite the opportunity to tailor mitigation efforts so they achieve maximum benefits within socially and economically disadvantaged communities (DACs). Here, we quantify such health co-benefits from different long-term, low-carbon scenarios in California and their distribution in the context of social vulnerability. The magnitude and distribution of health benefits, including within impacted communities, is found to varies among scenarios which reduce economy wide GHG emissions by 80% in 2050 depending on the technology- and fuel-switching decisions in individual end-use sectors. The building electrification focused decarbonization strategy achieves ~15% greater total health benefits than the truck electrification focused strategy which uses renewable fuels to meet building demands. Conversely, the enhanced electrification of the truck sector is shown to benefit DACs more effectively. Such tradeoffs highlight the importance of considering environmental justice implications in the development of climate mitigation planning.

Energy storage systems are critical for enabling the environmental benefits associated with capturing renewable energy to displace fossil fuel-based generation, yet producing these systems also contributes to environmental impacts through their materials use and manufacturing. As energy storage capacity is scaled up to support increasingly renewable grids, the environmental benefits from their use may scale at different rates than the environmental impacts from their production. This implies the existence of capacity thresholds beyond which installing additional storage capacity may be environmentally detrimental. Identifying such thresholds are important for ensuring that energy storage capacity selection in future grids are consistent with net emissions reduction goals, but such thresholds have not been studied in the present literature. To identify such thresholds, here we combine electric grid dispatch modeling with life cycle analysis to compare how the emissions reductions from deploying three different flow battery energy storage types on a future California grid (>80% wind and solar) compare with emissions contributions from producing such batteries as total battery capacity installed on the grid increases. Depending on the type of battery and environmental impact indicator (greenhouse gas or particulate matter emissions), we find that the marginal environmental benefits of storage begin to diminish at deployed capacities of 38–76% of the mean daily renewable generation (256–512 GWh in our California scenarios) and reach zero at 105–284% of mean daily renewable generation (700–1810 GWh). Such storage capacities are conceivable, but upstream impacts of storage must be assessed in evaluating the environmental benefits of large-scale storage deployment, or they could negate the environmental benefits of regional electricity system decarbonization.

This project assesses the impact of plug-in electric vehicles (PEVs) on the resiliency of the electricity distribution system by: (1) Assessing the use of PEVs as a resiliency resource during grid outages (Mobility Services+), (2) Assessing and simulating the impact of PEVs on the distribution infrastructure during normal operations, and (3) Determining the local environmental impact of clustering PEVs. A previously developed model of a smart grid consisting of two distribution circuits and a distribution substation was modified to enable the use of PEVs in vehicle-to-home (V2H) and vehicle-to-grid (V2G) configurations. Scenarios were simulated in which PEVs were used to serve critical loads in a home or community shelters, and a model was developed to assess the feasibility of using PEVs in grid restoration, which determined the inrush current of the substation transformer to determine the required power and energy for startup. The use of clustered PEVs and scattered PEVs in grid restoration was also considered. During normal operations, the stress on system components from high PEV demand resulted in accelerated aging and possible failure, thereby negatively impacting distribution infrastructure during normal grid operations. Smart charging is required to retain an acceptable level of resiliency. In contrast, during grid outages, this study demonstrated that PEVs can be used as an environmentally friendly resiliency resource to both serve critical loads and facilitate grid restoration with the qualification that implementation requires system upgrades including smart switches, upgraded inverters, energy management systems, and communication links.

While the impact of plug-in electric vehicles (PEVs) on electricity generation and transmission has been studied extensively, the impact of PEVs on the resiliency of the local electricity distribution system has not been addressed in detail. Understanding resiliency impacts is important as the increased use of PEVs, and especially the clustering of PEVs in one area (such as a neighborhood), place additional pressures on already aging power grid infrastructure. As an example, charging a large population of PEVs during normal operations can stress system components (such as transformers) resulting in accelerated aging or even failure, which reduces resiliency of the system. On the other hand, PEVs can also increase system resiliency. When connected to the grid, PEVs are an energy resource that can provide electricity for critical services (such as community shelters) during grid outages and facilitate grid restoration by providing electricity to support the restart of transformers and other utility assets.

In December 2018, the California Air Resources Board (CARB) approved the Innovative Clean Transit regulation, which is designed to transition the state to all-electric bus fleets by 2040. To comply with this first-of its-kind regulation, transit agencies have two alternatives: battery electric buses (BEBs) and hydrogen fuel cell electric buses (FCEBs). These options vary in energy requirements, overall effectiveness in reducing different emission types, associated life cycle costs (including disposal of the bus), and ability to meet operating needs of transit agencies. To support transit agencies and decision makers transition to cleaner bus technologies, researchers at UC Irvine developed a life cycle-based analysis (LCA) tool to estimate the potential costs and benefits of switching to BEBs and FCEBs compared to conventional buses. The LCA tool was tested on the Orange County Transportation Authority (OCTA) to better understand the environmental impacts and cost constraints.

To aid in addressing issues of air quality and greenhouse gas (GHG) emissions in the South Coast Air Basin, local transit agencies are considering a shift to battery electric buses (BEBs) and hydrogen fuel cell electric buses (FCEBs). Each of these options vary in their overall effectiveness in reducing different emission types over their life cycle, associated life cycle costs, ability to meet operational needs of transit agencies, and life cycle environmental footprint. This project carried out a life cycle-based analysis and comparison of the GHG emissions, criteria pollutant emissions, and other environmental externalities associated with BEBs and FCEBs, taking into account their ability to meet operational constraints of the Orange County Transportation Authority. From an environmental footprint perspective, this study found the following. First, both FCEBs and long-range BEBs have comparable impacts for global warming potential and particulate matter formation but when the FCEBs were fueled using renewable hydrogen. Second, using electricity from the current California grid mix to drive electrolysis to produce hydrogen for FCEBs produced only marginal benefits compared to current natural-gas fueled vehicles due to the low supply chain efficiency of this pathway. Third, the mining of precious metals is a major contributor to environmental footprint categories for both BEBs and FCEBs. Fourth, both FCEVs and long-range BEBs provide significant reductions in environmental footprint compared to conventional diesel and natural gas buses. From a cost perspective, this study found the following. First, with current-day cost inputs, FCEBs and BEBs have comparable total cost of ownership, but both have slightly higher costs than diesel and natural gas buses. Second, FCEBs have an equivalent total cost of ownership to BEBs when the electricity rate for charging is $0.24/kWh. Higher values render FCEBs as the cheaper option and lower values render BEBs as the cheaper option. Second, the total cost of ownership of these technologies is highly sensitive to electricity costs, and the rapid evolution of the electricity system has strong implications for the economic comparison between BEBs and FCEBs. Overall, this study finds that while both FCEBs and BEBs provide life-cycle environmental benefits, further cost reductions in electricity rates and initial purchase costs are needed to achieve total cost of ownership parity with conventional bus powertrains. With the rapid evolution of the electricity system and falling costs for renewable electricity resources, these cost reductions may occur in the near future.

Climate change and increased electrification of space and water heating in buildings can significantly affect future electricity demand and hourly demand profiles, which has implications for electric grid greenhouse gas emissions and capacity requirements. We use EnergyPlus to quantify building energy demand under historical and under several climate change projections of 32 kinds of building prototypes in 16 different climate zones of California and imposed these impacts on a year 2050 electric grid configuration by simulation in the Holistic Grid Resource Integration and Deployment (HIGRID) model. We find that climate change only prompted modest increases in grid resource capacity and negligible difference in greenhouse gas emissions since the additional electric load generally occurred during times with available renewable generation. Heating electrification, however, prompted a 30-40% reduction in greenhouse gas emissions but required significant grid resource capacity increases, due to the higher magnitude of load increases and lack of readily available renewable generation during the times when electrified heating loads occurred. Overall, this study translates climate change and electrification impacts to system-wide endpoint impacts on future electric grid configurations and highlights the complexities associated with translating building-level impacts to electric system-wide impacts.

The goal of this research is to assess the greenhouse gas (GHG) emissions and air quality (AQ) impacts of transitions to advanced low‐NOx Compressed Natural Gas (CNG) engines in medium-duty vehicle (MDV) and heavy-duty vehicle (HDV) applications in California with a particular emphasis on renewable natural gas (RNG) as a fueling pathway. To evaluate regional AQ impacts in 2035, pollutant emissions from all end-use sectors are projected from current levels and spatially and temporally resolved. Scenarios are constructed beginning with both a conservative (Base Case) and more optimistic (SIP) case regarding advanced vehicle technology and fuels integration to provide spanning of potential impacts. To capture the impact of seasonal dynamics on pollutant formation and fate, two modeling periods are conducted including a winter and summer episode. To estimate the potential GHG impacts of transitions to advanced CNG engines in HDV and MDV, scenarios are evaluated under various assumptions regarding fuel pathways to meet CNG demand from a life cycle perspective. Scenarios are compared to the baseline cases assuming (1) all CNG is provided from conventional fossil natural gas and (2) under a range of possible resource availabilities associated with RNG and renewable synthetic natural gas (RSNG) from in-state resources. Key findings include: i) expanding the deployment of advanced CNG MDV and HDV can reduce summer ground-level ozone concentrations and groundlevel PM2.5 in key regions of California; ii) the largest AQ benefits are associated with reducing emissions from HDV; iii) in-state RNG pathways can meet the CNG demand estimated for both baseline cases; iv) in-state resources are unable to entirely meet CNG demand for the high total CNG demand estimated for the majority of Base alternative cases, and v) advanced CNG HDV and MDV can moderately reduce GHG emissions if fossil natural gas is used (14 to 26%).

Recent commercialization of advanced low-nitrogen oxides (NOx) Compressed Natural Gas (CNG) engines for medium- (MDV) and heavy-duty (HDV) vehicles has garnered significant interest due to the potential air quality benefits. Further, utilizing renewable natural gas (RNG) in advanced CNG engines from sources such as biomass and/ or biogas can achieve reductions in greenhouse gas (GHG) relative to using petroleum fuels and fossil CNG. However, the regional air quality and GHG reduction benefits of large‐scale deployment of advanced CNG trucks are currently unclear. Further, more information is required regarding RNG production potential from California instate biofuel resources, including potential supply volumes and production pathways that provide maximum GHG reductions. The UC Irvine Advanced Power and Energy Program assessed the air quality and GHG implications of transitioning to advanced CNG engines in MDVs and HDVs in California by developing and comparing different future adoption scenarios. The research team also leveraged prior research of biogas and biomass resources in California to consider different options for producing RNG in-state. Key findings from this research are highlighted in the following section.

In this paper, the Spatially and Temporally Resolved Energy and Environment Tool (STREET) is used in conjunction with University of California Irvine - California Institute of Technology (UCI-CIT) atmospheric chemistry and transport model to assess the impact of deploying plug-in electric vehicles and integrating wind energy into the electricity grid on urban air quality. STREET is used to generate emissions profiles associated with transportation and power generation sectors for different future cases. These profiles are then used as inputs to UCI-CIT to assess the impact of each case on urban air quality. The results show an overall improvement in 8-h averaged ozone and 24-h averaged particulate matter concentrations in the South Coast Air Basin (SoCAB) with localized increases in some cases. The most significant reductions occur northeast of the region where baseline concentrations are highest (up to 6 ppb decrease in 8-h-averaged ozone and 6 μg/m3 decrease in 24-h-averaged PM2.5). The results also indicate that, without integration of wind energy into the electricity grid, the temporal vehicle charging profile has very little to no effect on urban air quality. With the addition of wind energy to the grid mix, improvement in air quality is observed while charging at off-peak hours compared to the business as usual scenario.

A study was conducted to compare the technical potential and effectiveness of different water supply options for securing water availability in a large-scale, interconnected water supply system under historical and climate-change augmented inflow and demand conditions. Part 2 of the study focused on determining the greenhouse gas and renewable energy utilization impacts of different pathways to stabilize major surface reservoir levels. Using a detailed electric grid model and taking into account impacts on the operation of the water supply infrastructure, the greenhouse gas emissions and effect on overall grid renewable penetration level was calculated for each water supply option portfolio that successfully secured water availability from Part 1. The effects on the energy signature of water supply infrastructure were found to be just as important as that of the fundamental processes for each option. Under historical (baseline) conditions, many option portfolios were capable of securing surface reservoir levels with a net neutral or negative effect on emissions and a benefit for renewable energy utilization. Under climate change augmented conditions, however, careful selection of the water supply option portfolio was required to prevent imposing major emissions increases for the system. Overall, this analysis provided quantitative insight into the tradeoffs associated with choosing different pathways for securing California's water supply.

The technical potential and effectiveness of different water supply options for securing water availability in a large-scale, interconnected water supply system under historical and climate-change augmented inflow and demand conditions were compared. Part 1 of the study focused on determining the scale of the options required to secure water availability and compared the effectiveness of different options. A spatially and temporally resolved model of California's major surface reservoirs was developed, and its sensitivity to urban water conservation, desalination, and water reuse was examined. Potential capacities of the different options were determined. Under historical (baseline) hydrology conditions, many individual options were found to be capable of securing water availability alone. Under climate change augment conditions, a portfolio approach was necessary. The water savings from many individual options other than desalination were insufficient in the latter, however, relying on seawater desalination alone requires extreme capacity installations which have energy, brine disposal, management, and cost implications. The importance of identifying and utilizing points of leverage in the system for choosing where to deploy different options is also demonstrated.