This study is the first comprehensive life cycle assessment (LCA) of reverse electrodialysis (RED), a technology that converts salinity gradient energy into electricity.Our goal is to identify RED system components of environmental concern and provide insights on potential environmental impacts. We conduct an attributional LCA of two RED scenarios: large-scale energy generation from natural bodies of water and smaller-scale energy generation from industrial processes. A functional unit of 1 MWh of net electricity production enables comparison to existing renewable energy technologies, including wind and solar photovoltaics. Under theoretical, favorable conditions, environmental impacts from RED are found to be comparable to, and often lower than, established renewable energy technologies. Processes associated with membrane manufacture are primary contributors to six of the nine evaluated impact categories. Under baseline assumptions, impacts are an average of 50% higher for the Natural Water scenario compared to the Concentrated Brine scenario because of the increased power density achieved with concentrated brines. This early-stage LCA demonstrates that the expected environmental impacts of RED are comparable to existing renewable technologies and a large improvement over fossil-based generation. However, eutrophication, ecotoxicity, and carcinogenic impacts are larger for RED than other technologies under some assumptions.

Rigorous model-based analysis can help inform state-level energy and climate policy. In this study, we utilize an open-source energy system optimization model and publicly available datasets to examine future electricity generation, CO2 emissions, and CO2 abatement costs for the North Carolina electric power sector through 2050. Model scenarios include uncertainty in future fuel prices, a hypothetical CO2 cap, and an extended renewable portfolio standard. Across the modeled scenarios, solar photovoltaics represent the most cost-effective low-carbon technology, while trade-offs among carbon constrained scenarios largely involve natural gas and renewables. We also develop a new method to calculate break-even costs, which indicate the capital costs at which different technologies become cost-effective within the model. Significant variation in break-even costs are observed across different technologies and scenarios. We illustrate how break-even costs can be used to inform the development of an extended renewable portfolio standard in North Carolina. Utilizing the break-even costs to calibrate a tax credit for onshore wind, we find that the resultant wind deployment displaces other renewables, and thus has a negligible effect on CO2 emissions. Such insights can provide crucial guidance to policymakers weighing different policy options. This study provides an analytical © 2019. https://doi.org/10.1021/acs.est.9b04184 2 framework to conduct similar analyses in other states using an open source model and freely available datasets. INTRODUCTION Many US states have proposed plans to address the climate change threat 1 . North Carolina is the ninth most populous state, the fourteenth largest CO2 emitter (2014) 2 in the United States, and the first state in the Southeast to adopt a Renewable Energy and Energy Efficiency Portfolio Standard (REPS) 3 . The NC REPS requires investor-owned utilities to meet at least 12.5% of their electricity demand through renewable energy resources or energy efficiency measures by 2021 3 . Three carve outs, representing minimum shares of specific fuel types, were also defined: 0.2% solar by 2018, 0.2% swine waste by 2020, and 900,000 MWh of poultry waste by 2016 3 . The deployment of solar PV has far exceeded the solar carve out, with 4.3% of North Carolina's total generation supplied by solar 4 .This high level of solar PV deployment is largely due to the rapid decline in investment costs and favorable contract terms for third party, utility-scale solar under the Public Utilities Regulatory Policies Act (PURPA). However, electric power producers in the state have had difficulty meeting the swine and poultry waste targets, and have repeatedly filed joint petitions to the North Carolina Utilities Commission (NCUC) seeking relief and delay 5 .These outcomes illustrate the challenge that state policymakers face in developing policy that balances environmental performance, affordability, and stakeholder interests. Debates over energyrelated policies and incentives within the state persist, often ...

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