In recent literature, prospective application of life cycle assessment (LCA) at low technology readiness levels (TRL) has gained immense interest for its potential to enable development of emerging technologies with improved environmental performances. However, limited data, uncertain functionality, scale up issues and uncertainties make it very challenging for the standard LCA guidelines to evaluate emerging technologies and requires methodological advances in the current LCA framework. In this paper, we review published literature to identify major methodological challenges and key research efforts to resolve these issues with a focus on recent developments in five major areas: cross-study comparability, data availability and quality, scale-up issues, uncertainty and uncertainty communication, and assessment time. We also provide a number of recommendations for future research to support the evaluation of emerging technologies at low technology readiness levels: (a) the development of a consistent framework and reporting methods for LCA of emerging technologies; (b) the integration of other tools with LCA, such as multicriteria decision analysis, risk analysis, technoeconomic analysis; and (c) the development of a data repository for emerging materials, processes, and technologies. K E Y W O R D S emerging technology, ex ante LCA, industrial ecology, life cycle assessment (LCA), technoeconomic analysis (TEA), technology readiness level (TRL)

Carbon capture and storage (CCS) for fossil fuel power plants is perceived as a critical technology for climate mitigation. Nevertheless, limited installed capacity to date raises concerns about CCS ability to scale sufficiently. Conversely, scalable renewable electricity installations-solar and wind-are already deployed at scale and have demonstrated a rapid expansion potential. Here we show that power sector CO 2 emission reductions accomplished by investing in renewable technologies generally provide a better energetic return than CCS. We estimate the electrical Energy-Return-on-Energy-Invested ratio of CCS projects accounting for their operational and infrastructural energy penalties to range between 6.6:1 and 21.3:1 for 90% capture ratio and 85% capacity factor. These values compare unfavorably to dispatchable scalable renewable electricity with storage, which ranges from 9:1 to 30+:1 under realistic configurations. Therefore, renewables plus storage provide a more energetically effective approach to climate mitigation than constructing CCS fossil power stations.

Life cycle assessment (LCA) analysts are increasingly being asked to conduct life cycle-based systems level analysis at the earliest stages of technology development. While early assessments provide the greatest opportunity to influence design and ultimately environmental performance, it is the stage with the least available data, greatest uncertainty, and a paucity of analytic tools for addressing these challenges. While the fundamental approach to conducting an LCA of emerging technologies is akin to that of LCA of existing technologies, emerging technologies pose additional challenges. In this paper, we present a broad set of market and technology characteristics that typically influence an LCA of emerging technologies and identify questions that researchers must address to account for the most important aspects of the systems they are studying. The paper presents: (a) guidance to identify the specific technology characteristics and dynamic market context that are most relevant and unique to a particular study, (b) an overview of the challenges faced by early stage assessments that are unique because of these conditions, (c) questions that researchers should ask themselves for such a study to be conducted, and (d) illustrative examples from the transportation sector to demonstrate the factors to consider when conducting LCAs of emerging technologies. The paper is intended to be used as an organizing platform to synthesize existing methods, procedures and insights and guide researchers, analysts and technology developer to better recognize key study design elements and to manage expectations of study outcomes. K E Y W O R D Searly stage technology assessment, environmental impacts, industrial ecology, life cycle assessment (LCA), research and development (R&D), unintended consequences

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Global wind power and photovoltaic (PV) installed capacities are growing at very high rates (20% per year and 60% per year, respectively). These technologies require large, 'up-front' energetic investments. Conceptually, as these industries grow, some proportion of their electrical output is 're-invested' to support manufacture and deployment of new generation capacity. As variable and intermittent, renewable generation capacity increases grid penetration, electrical energy storage will become an ever more important load-balancing technology. These storage technologies are currently expensive and energy intensive to deploy. We explore the impact on net energy production when wind and PV must 'pay' the energetic cost of storage deployment. We present the net energy trajectory of these two industries (wind and PV), disaggregated into eight distinct technologies-wind: onshore and offshore ; PV: single-crystal (sc-), multi-crystalline (mc-), amorphous (a-) and ribbon silicon (Si), cadmium telluride (CdTe), and copper indium gallium (di)selenide (CIGS). The results show that both onshore and offshore wind can support the deployment of a very large amount of storage, over 300 hours of geologic storage in the case of onshore wind. On the other hand, solar PV, which is already energetically expensive compared to wind power, can only 'afford' about 24 hours of storage before the industry operates at an energy deficit. The analysis highlights the societal benefits of electricity generationstorage combinations with low energetic costs. Broader context Rapid deployment of power generation technologies harnessing wind and solar resources has the potential to reduce the carbon intensity of the power grid. But as these technologies comprise a larger fraction of power supply, their variable nature poses challenges to power grid operation. Storage technologies are an obvious solution to provide grid exibility to balance power supply with power demand. In this study we ask the question, 'if the wind and PV industries had to 'pay' the energetic cost of deploying storage, would these industries be providing a net energy surplus to society?' We employ a dynamic net energy analysis to compare the annual electricity production by the wind and solar photovoltaic (PV) industries with the annual energy consumption in order to manufacture and deploy new capacity additions by these industries when they must also 'pay' the additional energetic cost of also deploying storage. We nd that the answer depends very much on the type of generation and storage technologies. Wind can be combined with over 80 days of geologic storage backup and still produce an energy surplus. The dominant PV technology multi-crystalline silicon can 'afford' around 6.5 days of geologic storage backup but only around 1.3 days of battery storage. Other PV technologies cannot 'afford' any storage while still supplying an energy surplus to society. This analysis clearly emphasizes the benets of combining low energy intensity generation and storage technologies. Our goal...