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More than half of U.S. states have renewable portfolio standards (RPS) in place and have collectively deployed approximately 46,000 MW of new renewable energy capacity through year-end 2012. Most of these policies have five or more years of implementation experience, enabling an assessment of their costs and benefits. Understanding RPS benefits and costs is essential for policymakers evaluating existing RPS policies, assessing the need for modifications, and considering new policies.This report surveys and summarizes existing state-level RPS cost and benefit estimates and examines the various methods used to calculate such estimates. The report relies largely upon data or results reported directly by electric utilities and state regulators. As such, the estimated costs and benefits itemized in this document do not result from the application of a standardized approach or the use of a consistent set of underlying assumptions. Because the reported values may differ from those derived through a more consistent analytical treatment, we do not provide an aggregate national estimate of RPS costs and benefits, nor do we attempt to quantify net RPS benefits at national or state levels. The report summarizes state-level RPS costs to date and considers how those costs may evolve going forward given scheduled increases in RPS targets and cost containment mechanisms incorporated into existing policies. The report also summarizes RPS benefits estimates, based on published studies for individual states, and discusses key methodological considerations. These estimates, for example, of the social value of carbon emissions reduction and the human health impacts of reduced air emissions, are based on a variety of methodologies and assumptions. In comparison to the summary of estimated RPS costs, the summary of RPS benefits is more limited, as relatively few states have undertaken detailed benefits estimates. Further, for those states that have estimated RPS benefits, most assess only a limited number of impact types; as a consequence, some types of benefits are not reflected in this report. RPS CostsOur analysis focuses specifically on the incremental cost of meeting RPS targets, i.e., the cost above and beyond what would have been incurred absent the RPS, over the 2010-2012 period. For states with restructured markets, we derive RPS compliance costs based on the cost of renewable energy certificates (RECs) and alternative compliance payments (ACPs). For traditionally regulated states, we instead rely upon RPS cost estimates reported directly by utilities or regulators within annual compliance reports or other regulatory filings (not prospective studies), and translate those estimates into a set of common metrics for comparison. The methods used by utilities and regulators to estimate incremental compliance costs vary considerably from state to state, in some cases reflecting statutory or regulatory requirements, and a number of states are currently engaged in processes to refine and standardize their approaches to RPS cost calcu...

Patterns of bat activity and mortalities at wind energy facilities suggest that bats are attracted to wind turbines based on bat behavioral responses to wind turbines. For example, current monitoring efforts suggest that bat activity increases post-wind turbine construction, with bats making multiple passes near wind turbines. We separated the attraction hypothesis into five previously proposed explanations of bat interactions at or near wind turbines, including attraction based on noise, roost sites, foraging and water, mating behavior, and lights, and one new hypothesis regarding olfaction, and provide a state of the knowledge in 2022. Our review indicates that future research should prioritize attraction based on social behaviors, such as mating and scent-marking, as this aspect of the attraction hypothesis has many postulates and remains the most unclear. Relatively more data regarding attraction to wind turbines based on lighting and noise emission exist, and these data indicate that these are unlikely attractants. Analyzing attraction at the species-level should be prioritized because of differences in foraging, flight, and social behavior among bat species. Lastly, research assessing bat attraction at various scales, such as the turbine or facility scale, is lacking, which could provide important insights for both wind turbine siting decisions and bat mortality minimization strategies. Identifying the causes of bat interactions with wind turbines is critical for developing effective impact minimization strategies.

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Bats are killed at wind energy facilities worldwide and we must improve our understanding of why this is happening and implement effective strategies to minimize impacts. To this end, we need accurate assessments of which individuals from which bat species are being killed at individual wind projects and at regional and range-wide scales. Traditional fatality searches have relied on physical characteristics to ascertain species and sex of bat carcasses collected at wind turbines; however, the resulting data can be incomplete and inaccurate. In contrast, the use of readily available and low-cost molecular methods improves both the quality and quantity of available data. We applied such methods to a bat fatality dataset (n = 439 bats) from far-south Texas, USA. Using DNA barcoding, we increased accurate species identification from 83% to 97%, and discovered the presence of 2 bat species outside of their known geographic ranges. Using a PCR-based approach to determine sex, the number of carcasses with correct sex assignment increased from 35% to 94%, and we documented a female-biased sex ratio for all species combined and for Dasypterus ega. We recommend that molecular methods be used during future survey efforts to accurately assess the impacts of wind energy on bats.