Drivers and implications of alternative routes to fuels decarbonization in net-zero energy systems.

Energy transition scenarios are characterized by increasing electrification and improving efficiency of energy end uses, rapid decarbonization of the electric power sector, and deployment of carbon dioxide removal (CDR) technologies to offset remaining emissions. Although hydrocarbon fuels typically decline in such scenarios, significant volumes remain in many scenarios even at the time of net-zero emissions. While scenarios rely on different approaches for decarbonizing remaining fuels, the underlying drivers for these differences are unclear. Here we develop several illustrative net-zero systems in a simple structural energy model and show that, for a given set of final energy demands, assumptions about the use of biomass and CO2 sequestration drive key differences in how emissions from remaining fuels are mitigated. Limiting one resource may increase reliance on another, implying that decisions about using or restricting resources in pursuit of net-zero objectives could have significant tradeoffs that will need to be evaluated and managed.

A cross-scale framework for evaluating flexibility values of battery and fuel cell electric vehicles.

Flexibility has become increasingly important considering the intermittency of variable renewable energy in low-carbon energy systems. Electrified transportation exhibits great potential to provide flexibility. This article analyzed and compared the flexibility values of battery electric vehicles and fuel cell electric vehicles for planning and operating interdependent electricity and hydrogen supply chains while considering battery degradation costs. A cross-scale framework involving both macro-level and micro-level models was proposed to compute the profits of flexible EV refueling/charging with battery degradation considered. Here we show that the flexibility reduction after considering battery degradation is quantified by at least 4.7% of the minimum system cost and enlarged under fast charging and low-temperature scenarios. Our findings imply that energy policies and relevant management technologies are crucial to shaping the comparative flexibility advantage of the two transportation electrification pathways. The proposed cross-scale methodology has broad implications for the assessment of emerging energy technologies with complex dynamics.

Scenarios of future Indian electricity demand accounting for space cooling and electric vehicle adoption.

India is expected to witness rapid growth in electricity use over the next two decades. Here, we introduce a custom regression model to project electricity consumption in India over the coming decades, which includes a bottom-up estimate of electricity consumption for two major growth drivers, air conditioning, and vehicle electrification. The model projections are available at a customizable level of spatial aggregation at an hourly temporal resolution, which makes them useful as inputs to long-term electricity infrastructure planning studies. The approach is used to develop electricity consumption data sets spanning various technology adoption and growth scenarios up to the year 2050 in five-year increments. The aim of the data is to provide a range of scenarios for India's demand growth given new technology adoption. With long-term hourly demand projections serving as an essential input for electricity infrastructure modeling, this data publication enables further work on energy efficiency, generation, and transmission expansion planning for a fast-growing and increasingly important region from a global climate mitigation perspective.

Environmental and Economic Performance of Hybrid Power-to-Liquid and Biomass-to-Liquid Fuel Production in the United States.

Power-to-liquids are a class of liquid drop-in fuels produced from electricity and carbon dioxide as the primary process inputs, which have the potential to reduce transportation's climate impacts. We quantify the economic and life cycle environmental characteristics of four electrofuel technology pathways that rely on the Fischer-Tropsch synthesis but produce synthesis gas via different schemes: power-to-liquid (PtL) via electrolysis and a reverse water gas shift (RWGS) reaction; PtL via co-electrolysis; gasification of biomass-to-liquid (BtL); and a hybrid power- and biomass-to-liquid (PBtL) pathway. The results indicate that the hybrid PBtL pathway is the most environmentally and economically promising option for electrofuel production, with results highly dependent on input electricity source characteristics such as cost and emissions. The carbon intensities of electricity generation that must not be exceeded for electrofuels to have lower life cycle emissions than conventional diesel are 222, 116, and 143 gCO2e/kWh for PBtL, PtL electrolysis + RWGS, and PtL co-electrolysis, respectively. We characterize the PBtL pathway in more detail by combining spatially resolved data on biomass cultivation, electricity generation, and cost-optimized hydrogen production from renewable electricity in the United States (US). We find that the private emissions abatement cost for PBtL fuels varies between 740 and 2000 $/tCO2e, depending primarily on the location of fuel production.

Life Cycle Greenhouse Gas Impacts of Coal and Imported Gas-Based Power Generation in the Indian Context.

Few studies have evaluated the life cycle greenhouse gas (GHG) impacts associated with India's power sector, despite the expectation that it will dominate new thermal generation capacity additions over the coming decades. Here, we utilize India-specific supply chain data to estimate life cycle GHG emissions associated with power generated by combustion of Indian coal and liquefied natural gas (LNG) imported from the United States. Life cycle impacts of domestic coal power vary widely (80% confidence interval (CI): 951-1231 kg CO2eq/MWh) because of heterogeneity in existing power plant characteristics such as efficiency, age, and capacity. Less variability is observed for LNG sourced from northeast United States and used in the existing Indian combined cycle gas turbine (CCGT) fleet (80% CI: 523-648 kg CO2eq/MWh). On average, life cycle GHG emissions from LNG imported into India are ∼54% lower than those associated with Indian coal. However, the GHG intensity of the Indian coal-power sector may be reduced by 13% by retiring plants with the lowest efficiencies and replacing them with higher-efficiency supercritical plants. Improvement of the CCGT fleet efficiency from its current level (41%) to that of a new plant with an F-class turbine (50%) could reduce life cycle GHG emissions for LNG-sourced power by 19%.

Round-the-clock power supply and a sustainable economy via synergistic integration of solar thermal power and hydrogen processes.

We introduce a paradigm-"hydricity"-that involves the coproduction of hydrogen and electricity from solar thermal energy and their judicious use to enable a sustainable economy. We identify and implement synergistic integrations while improving each of the two individual processes. When the proposed integrated process is operated in a standalone, solely power production mode, the resulting solar water power cycle can generate electricity with unprecedented efficiencies of 40-46%. Similarly, in standalone hydrogen mode, pressurized hydrogen is produced at efficiencies approaching ∼50%. In the coproduction mode, the coproduced hydrogen is stored for uninterrupted solar power production. When sunlight is unavailable, we envision that the stored hydrogen is used in a "turbine"-based hydrogen water power (H2WP) cycle with the calculated hydrogen-to-electricity efficiency of 65-70%, which is comparable to the fuel cell efficiencies. The H2WP cycle uses much of the same equipment as the solar water power cycle, reducing capital outlays. The overall sun-to-electricity efficiency of the hydricity process, averaged over a 24-h cycle, is shown to approach ∼35%, which is nearly the efficiency attained by using the best multijunction photovoltaic cells along with batteries. In comparison, our proposed process has the following advantages: (i) It stores energy thermochemically with a two- to threefold higher density, (ii) coproduced hydrogen has alternate uses in transportation/chemical/petrochemical industries, and (iii) unlike batteries, the stored energy does not discharge over time and the storage medium does not degrade with repeated uses.