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online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste iii Executive SummaryAs renewable electricity becomes a larger portion of the electricity generation mix, new strategies will be required to accommodate fluctuations in energy generation from these sources. One of the primary strategies proposed for integrating large amounts of renewable energy is using energy storage to absorb excess electricity-generating capacity during times of low demand and/or high rates of generation by renewable sources and then reconverting this stored energy into electricity during periods of high demand and/or low renewable generation.Various energy storage technologies have been developed or proposed. The goal of this analysis was to develop a cost survey of the most-promising and/or mature energy storage technologies and compare them with several configurations employing hydrogen as the energy carrier. A simple energy arbitrage scenario was developed for a mid-sized energy storage system consisting of a 300-MWh nominal storage capacity that is charged during off-peak hours (18 hours per day on weekdays and all day on weekends) and discharged at a rate of 50 MW for 6 peak hours on weekdays.For all the hydrogen cases, off-peak and/or excess renewable electricity is used to electrolyze water to produce hydrogen, which is stored in compressed gas tanks or underground geologic formations. The hydrogen is reconverted into electricity using a polymer electrolyte membrane (PEM) fuel cell or hydrogen expansion combustion turbine. The hydrogen storage scenarios are compared with the use of several battery systems (nickel cadmium, sodium sulfur, and vanadium redox), pumped hydro, and compressed air energy storage (CAES).All the energy storage systems are evaluated for the same energy arbitrage scenario using consistent financial and operational assumptions. Costs and performance parameters for the technologies were gathered from literature sources and, in the case of the hydrogen expansion combustion turbine, Aspen Plus modeling. Producing excess hydrogen for use in vehicles or backup power is also evaluated. Two production levels are analyzed: 1,400 kg/day (roughly equivalent to the U.S. Department of Energy's standard model for smallscale distributed hydrogen production) and 12,000 kg/day. As for the purely energy arbitrage scenarios, it is assumed that hydrogen would be produced with offpeak/renewable electricity. Cost results for the analysis are presented in terms of the annualized ("levelized" 1 Figure ES -1 ) cost for producing the energy output from the storage system: electricity fed back onto the grid during peak hours ($/kWh) and, in the case of producing excess hydrogen for vehicles, hydrogen ($/kg).summarizes the comparison of levelized cost of delivered electricity for hydrogen (green bars) and competing technologies (blue bars). For each technology, high-cost, mid-range, and low-cost cases were analyzed, and sensitivity analyses were 1 The leve...

The calculation of the per-mile fuel cost for FUTURE TECHNOLOGY HEVs in the first release of this report (Section 9) mistakenly used an older estimate of fuel economy for this vehicle technology. This error also affected the subsequent calculation of the cost of avoided carbon emissions in Section 10 for FUTURE TECHNOLOGY HEVs. The on-road fuel economy for FUTURE TECHNOLOGY HEV used in the first release of this report was 48.2 mi/gge, whereas the fuel economy from Autonomie simulations for this vehicle technology (see Section 6) was 53.5 mi/gge. Using the 53.5 mi/gge fuel economy for FUTURE TECHNOLOGY HEV in the calculation of per-mile fuel cost of FUTURE TECHNOLOGY HEVs resulted in updates to the following figures and tables of the report: Figures ES-3 and ES-5 in the Executive Summary; Figures 23, 25, and 27 in Section 9; Figures 34 and 36, and Tables 55 and 56 in Section 10; and Figures F.2 and F.4 (as well as the repeated Figures 23 and 34) in Appendix F. It is noted that the GHG emissions calculations in the first release of the report correctly used the 53.5 mi/gge for FUTURE TECHNOLOGY HEV. Thus no changes are made to the GHG emissions charts in the report.

This article presents a cradle-to-grave (C2G) assessment of greenhouse gas (GHG) emissions and costs for current (2015) and future (2025-2030) light-duty vehicles. The analysis addressed both fuel cycle and vehicle manufacturing cycle for the following vehicle types: gasoline and diesel internal combustion engine vehicles (ICEVs), flex fuel vehicles, compressed natural gas (CNG) vehicles, hybrid electric vehicles (HEVs), hydrogen fuel cell electric vehicles (FCEVs), battery electric vehicles (BEVs), and plug-in hybrid electric vehicles (PHEVs). Gasoline ICEVs using current technology have C2G emissions of ∼450 gCOe/mi (grams of carbon dioxide equivalents per mile), while C2G emissions from HEVs, PHEVs, H FCEVs, and BEVs range from 300-350 gCOe/mi. Future vehicle efficiency gains are expected to reduce emissions to ∼350 gCO/mi for ICEVs and ∼250 gCO/mi for HEVs, PHEVs, FCEVs, and BEVs. Utilizing low-carbon fuel pathways yields GHG reductions more than double those achieved by vehicle efficiency gains alone. Levelized costs of driving (LCDs) are in the range $0.25-$1.00/mi depending on time frame and vehicle-fuel technology. In all cases, vehicle cost represents the major (60-90%) contribution to LCDs. Currently, HEV and PHEV petroleum-fueled vehicles provide the most attractive cost in terms of avoided carbon emissions, although they offer lower potential GHG reductions. The ranges of LCD and cost of avoided carbon are narrower for the future technology pathways, reflecting the expected economic competitiveness of these alternative vehicles and fuels.

AcknowledgmentsThe authors would like to recognize Rick Farmer, Roxanne Garland, and Jamie Holladay of the U.S. Department of Energy for funding this work. George Sverdrup of the National Renewable Energy Laboratory (NREL) and Vicki McCarl of Xcel Energy were both very helpful in scoping and defining the Wind2H2 project and have provided excellent feedback throughout the project. Brad Hollenbaugh and Curtis Perry of Xcel Energy were instrumental in helping design and configure the Wind2H2 system and in participating in the readiness verification review. The authors would like to acknowledge John Cornish of EPC and Marc Mann of Spectrum Automation for their work installing and programming the Wind2H2 system. The authors would like to thank Connie Komomua for her assistance in editing the work. Finally, the authors would like to thank Robert Remick, Dave Mooney, Ben Kroposki, Mike Stewart, and Genevieve Saur of NREL for their technical assistance throughout the project. and is enjoying success as a demonstration project, producing hydrogen directly from renewable energy sources. This unique research-oriented project uses solar and wind energy to produce and store hydrogen. The stored hydrogen can be used both as a transportation fuel and as an energy storage medium, effectively allowing renewable energy to be stored and converted back to electricity at a later time.The Wind2H2 project is helping researchers understand the hurdles and potential areas for improvement in emerging renewable electrolysis technologies. By allowing engineers to operate and configure an integrated electrolysis facility, this project has enabled the investigation and analysis of hydrogen production, compression, storage, and electricity generation that is providing valuable data that are being used to improve the designs of future renewable electrolysis systems. This first report on the Wind2H2 project provides important guidance to industry and key stakeholders for development of future renewable electrolysis systems.The Wind2H2 project is the only renewable hydrogen production facility in the world that can operate multiple electrolyzers in any of the following configurations: 1. Grid connected 2. Directly connected from the output of a photovoltaic array to the electrolyzer stack 3. Real-time electrolyzer stack current control based on a power signal from a wind turbine 4. Closely coupled photovoltaic (PV) and wind energy sources to the electrolyzer stack with custom designed and built power electronics.NREL and Xcel Energy have undertaken the Wind2H2 project with several key objectives in mind. First and foremost, the Wind2H2 project is being used to demonstrate operation of a renewable electrolysis system, allowing researchers to evaluate actual system performance and costs and to identify areas for cost and efficiency improvements. Additionally, the project provides operational experience with a renewable electrolysis hydrogen production facility, enabling project engineers to investigate operational challenges and to explore system-...