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The goal of the circular economy (CE) is to transition from today's take-make-waste linear pattern of production and consumption to a circular system in which the societal value of products, materials, and resources is maximized over time. Yet circularity in and of itself does not ensure social, economic, and environmental performance (i.e., sustainability). Sustainability of CE strategies needs to be measured against their linear counterparts to identify and avoid strategies that increase circularity yet lead to unintended externalities. The state of the practice in quantitatively comparing sustainability impacts of circular to linear systems is one of experimentation with various extant methods developed in other fields and now applied here. While the proliferation of circularity metrics has received considerable attention, to-date, there is no critical review of the methods and combinations of methods that underlie those metrics and that specifically quantify sustainability impacts of circular strategies. Our critical review herein analyzes identified methods according to six criteria: temporal resolution, scope, data requirements, data granularity, capacity for measuring material efficiency potentials, and sustainability completeness. Results suggest that the industrial ecology and complex systems science fields could prove complementary when assessing the sustainability of the transition to a CE. Both fields include quantitative methods differing primarily with regard to their inclusion of temporal aspects and material efficiency potentials. Moreover, operations research methods such as multiple-criteria decision-making (MCDM) may alleviate the common contradictions which often exist between circularity metrics. This review concludes by suggesting guidelines for selecting quantitative methods most appropriate to a particular research question and making the argument that while there are a variety of existing methods, additional research is needed to combine existing methods and develop a more holistic approach for assessing sustainability impacts of CE strategies.

NREL's Land-based Balance of System Systems Engineering (LandBOSSE) model is a tool for modeling the balance-of-system (BOS) costs of land-based wind plants. BOS costs currently account for approximately 30% of the capital expenditures needed to install a land-based wind plant; they include all costs associated with installing a wind plant, such as permitting, labor, material, and equipment costs associated with site preparation, foundation construction, electrical infrastructure, and tower installation.NREL developed LandBOSSE after identifying a need for a hybrid of a process-based model and an empirically derived model that can provide flexibility for assessing wind plant BOS costs at a system level. Other NREL BOS models have relied on empirical fits of legacy industry data, which limits their predictive ability. LandBOSSE, however, was designed to help users explore tradeoffs between innovative design scenarios while balancing the level of detail and speed required for model execution. The model was developed using a hybrid of process-based and empirically derived methods to create a modular model design that will allow for updates as wind energy technologies evolves. The goal of LandBOSSE is to allow researchers, analysts, wind power developers, government agencies, and the public to explore how BOS costs may vary for different wind plant designs. This report summarizes the approach, methods, and equations used to develop LandBOSSE Version 2.1. Future versions of the model may incorporate additional process-based capabilities or modify calculations within the code. Refer to the GitHub repository at https://github.com/WISDEM/LandBOSSE for the most up-to-date version of the software documentation and code. vi This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Advanced biofuel production facilities (biorefineries), such as those envisioned by the United States (U.S.) Renewable Fuel Standard and U.S. Department of Energy's research and development programs, often lack historical air pollutant emissions data, which can pose challenges for obtaining air emission permits that are required for construction and operation. To help fill this knowledge gap, we perform a thorough regulatory analysis and use engineering process designs to assess the applicability of federal air regulations and quantify air pollutant emissions for two feasibility-level biorefinery designs. We find that without additional emission-control technologies both biorefineries would likely be required to obtain major source permits under the Clean Air Act's New Source Review program. The permitting classification (so-called "major" or "minor") has implications for the time and effort required for permitting and therefore affects the cost of capital and the fuel selling price. Consequently, we explore additional technically feasible emission-control technologies and process modifications that have the potential to reduce emissions to achieve a minor source permitting classification. Our analysis of air pollutant emissions and controls can assist biorefinery developers with the air permitting process and inform regulatory agencies about potential permitting pathways for novel biorefinery designs.

Journal article GHG emissions a) Grey coloring and italicized text highlights studies included in the comparison of life cycle greenhouse gas (GHG) emissions from geothermal electricity performed by . Bold text corresponds to studies reported in the IPCC SRREN (2011). EGS = enhanced geothermal system, and HT = hydrothermal.