Assessing renewable energy potential on United States marginal and contaminated sites
Introduction
Recent studies have highlighted irreversible impacts of agriculture as well as direct and indirect land use change related to energy production [1], [2], [3], [4]. Regarding biofuels, and ethanol in particular, Searchinger et al. [5] found that inclusion of land use change in the life-cycle emissions from corn-based ethanol (a first-generation biofuel) results in a 93% increase in total greenhouse gas emissions (GHGs) in comparison to conventional gasoline [5]. The same calculation for switchgrass-based ethanol (a second-generation biofuel) results in a 50% total increase in GHGs compared to gasoline [5]. Microalgal biodiesel (a third-generation biofuel) shows promise for reducing GHGs [6], [7]. However, like many biofuels, microalgal biodiesel can also exhibit positive or negative net energy results depending on cultivation and conversion pathways [8].
All biofuel feedstocks require nutrient inputs, water (often via irrigation), and suitable growing conditions [9]. Some feedstocks, however, are more resilient than others and can grow successfully on marginal lands. Peterson and Galbraith [10] first defined marginal land as “land on the margin of cultivation […] the poorest land that can be remuneratively operated under given price, cost, and other conditions” [10]. Shortall [11] considers three varieties of marginal land to be of particular importance: 1) land unfit for food production, 2) land of ambiguously lower quality, and 3) economically marginal land [11]. Milbrandt et al. [12] describe marginal lands as abandoned, underutilized, and idle [12]. Nearly all definitions refer to poor physical and chemical soil properties and susceptibility to erosion [4], [13], [14], [15]. Furthermore, there is a lack of knowledge regarding feasible and consistent energy crop yields on different types of marginal lands. This study evaluates brownfields, closed landfills, and abandoned mine lands as a subset of marginal lands available for renewable energy production.
Producing renewable energy on marginal lands, when done strategically and with regard to the entire life cycle, could potentially reduce the amount and intensity of inputs required for energy production. Scientific and legislative interest is growing in this area of land-constrained energy production, whether in the case of biofuel crops that can withstand poor soil quality and help meet energy mandates [11], [12], [16], [17], [18], [19] or in the case of building renewable energy facilities on contaminated sites that would otherwise remain unused [12], [20]. The U.S. EPA program: “RE-Powering America׳s Land”, for example, encourages development of renewable energy projects on currently and formerly marginal and contaminated lands and provides resources to communities engaging in such projects [20]. Despite growing interest, previous studies have focused on bioenergy and have largely ignored non-agricultural sources, such as solar or wind [21], [22], [23].
Some studies claim that using marginal lands to produce bioenergy on a global scale is unfeasible for reasons such as the lack of economic incentives, disturbances to food security, and threats to biodiversity and conservation areas [3], [24]. Other studies state that global feasibility estimates vary but marginal production levels become more viable when considered on the regional level [25]. Still others, as in this study, focus on symbiotic relationships between the land, regional characteristics, and the renewable energy potential available [26]. Every geographic and climatic region is different, and therefore spatial analyses are crucial to designing sustainable solutions for land use and for energy infrastructure systems [27]. A variety of energy production technologies can be employed. This study evaluates the energy that can be produced on marginal sites by cultivating soybeans, sunflowers, and algae for biodiesel, and by implementing solar and wind technologies for electricity.
Section snippets
Methods
One of the primary challenges in assessing the amount of marginal land available in an area is deciding what qualifies as “marginal” for the region being evaluated. While diverse definitions exist [10], [14], [17], [28], marginal land is generally classified as land unfit for food-grade agriculture and not otherwise fulfilling conservational purposes or ecosystem services. This study limits consideration of marginal land to three types of marginal sites: brownfields, closed landfills, and
Results and discussion
Brownfields, closed landfills, and AMLs are spread throughout the contiguous United States, however regional clusters do exist. Brownfields appear largely in the Northeastern and Mid-Atlantic states and extend toward the Midwest, with some notable clusters near the West Coast. Abandoned mine lands appear along the Appalachian Mountains in the East, Rocky Mountains in the West, and in other mountainous regions. Closed landfill sites are scattered across the entire United States.
Table 4 lists the
Conclusion
This study constructed and implemented a GIS model to evaluate a range of site-specific energy production potentials on brownfields, closed landfills, and abandoned mine lands. Five energy sources were considered: soybeans, sunflowers, and microalgae for biodiesel, and solar and wind for electricity. When all five resources on all three site types are allocated for optimal performance, energy produced on contaminated lands could help satisfy up to 39% of the total U.S. demand for diesel and
Acknowledgments
This project was supported by NSF IGERT Award no. 0504345 and NSF CBET Awards nos. 0933249/1254559 and 0932606/1241697.
Briana Niblick is a Post-Doctoral Researcher in the Department of Life Cycle Engineering at the Fraunhofer Institute for Building Physics and at the University of Stuttgart in Stuttgart, Germany.
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Briana Niblick is a Post-Doctoral Researcher in the Department of Life Cycle Engineering at the Fraunhofer Institute for Building Physics and at the University of Stuttgart in Stuttgart, Germany.
Amy Landis is an Associate Professor at Arizona State University׳s School of Sustainable Engineering and the Built Environment in Tempe, Arizona.