Analysis of Water Footprint of a Photobioreactor Microalgae Biofuel 1 Production System from Blue, Green and Lifecycle Perspectives

Microalgae are currently being investigated as a feedstock for the commercial production of transportation fuels, due to their potential scalability and sustainability advantages over conventional feedstocks. The water consumption of microalgae has been postulated to be a resource barrier for large-scale production. This study presents an assessment of the water footprint (WF) of a closed photobioreactor-based biofuel production system, where microalgae cultivation is simulated with geographical and temporal resolution. The assessment focuses on the WF as modeled for four different fuel conversion pathways, and in 10 continental US locations corresponding to high productivity yields. The WF is comprehensively assessed using a hybrid approach which combines process and economic input-output lifecycle analysis method, using three metrics: blue, green and lifecycle WF. Results show that the blue WF of microalgae biofuels varies between 23 and 85 m3·GJ-1 depending on process and geographic location. The green WF shows that microalgae cultivation may reduce the required local water withdrawals. Water credits from the co-products vary with allocation methods and end uses, from credits of less than 4 m3·GJ-1 up to credits of 334 m3·GJ- 1. Results for the net lifecycle WF with coproduct credits varies between 80 and -291 m3·GJ-1. Discussion focuses on the sensitivity of microalgae biofuels WF and highlights potential local and national strain of water resources relative to other fuels and biofuels

Achieving Optimal Value of Solar: A Municipal Utility Rate Analysis

Wind and solar renewable energy in the United States is projected to triple by 2050 to nearly 30% of total electric energy generation. The upper Midwest region (Iowa, Minnesota, and North and South Dakota in particular) is considered wind energy country and not historically known for solar energy development. In this work, Value of Solar (VOS) is developed as a photovoltaic (PV) optimization measure and analysis tool using a northwest Iowa municipality as a representative case study. By applying a top-down load duration curve system analysis, VOS is used to optimize PV orientation and compare electric rate structures for increasing levels of total PV energy contribution. VOS of a fixed south-southwest orientation exceeds the levelized annual costs of installation with a larger net benefit than a one-axis-tracking solar system. Production-data modeled VOS is up to 12% higher than Typical Meteorological Year (TMY) predictions, indicating significant correlation between PV generation and peak municipal demand. Compared to alternative time-of-use rates, a demand/energy rate structure better matches VOS economic value and optimal orientation. This VOS methodology is an easy-to-use yet meaningful tool for municipalities and smaller utilities to evaluate strategic installation of and investment in PV for their local community

Net-Zero Energy Districts and the Grid: An Energy-Economic Feasibility Case-Study of the National Western Center in Denver, CO, USA

Given the enormous impact of buildings on energy consumption, it is important to continue the development of net-zero energy districts. Opportunities exist for energy efficiency and renewable energy on a district level that may not be feasible in individual buildings. Due to the intermittent nature of many renewable energy sources, net-zero energy districts are dependent on the energy grid. The novelty of this work is to quantify and optimize the economic cost and grid independence of a net-zero energy district using the National Western Center (NWC) in Denver, CO, USA as a case study. The NWC is a 100+ ha campus undergoing a major redevelopment process with a planned 170,000 m2 of total building space, an emphasis on sustainability, and a net-zero energy goal. Campus plans, building energy models, and renewable energy performance models of on-site solar, biomass, and thermal renewable energy sources are analyzed in multiple energy scenarios to achieve net-zero energy with and without on-site energy storage. Levelized cost of energy (LCOE) is optimized as a function of variables defining the energy and economic relationship with the grid. Discussion herein addresses trade-offs between net-zero energy scenarios in terms of energy load, LCOE, storage, and grid dependence

Feasibility of wireless power transfer for electrification of transportation: Techno-economics and life cycle assessment

Integration of wireless power transfer (WPT) systems in roadways and vehicles represents a promising alternative to traditional internal combustion transportation systems. The economic feasibility and environmental impact of WPT applied to the transportation system is evaluated through the development of engineering system models. For a 20% penetration of the WPT technology in vehicles, results show a 20% reduction in air pollutants, 10% reduction in energy use and CO2 emissions and a societal level payback (defined as total cost of ownership savings compared to a traditional vehicle equal to roadway infrastructure) of 3 years. The modeled system covers 86% of all traffic in the US, impacts 40% of all roadways and shifts $180 billion per year from oil production to jobs in local power generation and development, construction, and maintenance of electrified roadways and new electric vehicles. Results on model sensitivity to energy prices, payback as a function of penetration, and trucking vs light duty use are presented

Quantitative Assessment of Microalgae Biomass and Lipid Stability Post-Cultivation

Processing of microalgal biomass to biofuels and other products requires the removal of the culture from a well-controlled growth system to a containment or preprocessing step at non-ideal growth conditions, such as darkness, minimal gas exchange, and fluctuating temperatures. The conditions and the length of time between harvest and processing will impact microalgal metabolism resulting in biomass and lipid degradation. This study experimentally investigates the impact of time and temperature on Nannochloropsis salina harvested from outdoor plate photobioreactors. The impact of three temperatures, 4°, 40° or 70°C, on biomass and lipid content (as fatty acid methyl esters) of the harvested microalgae was evaluated over a 156 hour time period. Results show that for N. salina, time and temperature are key factors that negatively impact biomass and lipid yields. The temperature of 70°C resulted in the highest degradation with the overall biofuel potential reduced by 30% over 156 hours. Short time periods, 24 hours, and low temperatures are shown to have little effect on the harvested biomass

Geographical Assessment of Microalgae Biofuels Potential Incorporating Resource Availability

Previous assessments of the economic feasibility and large-scale productivity of microalgae biofuels have not considered the impacts of land and carbon dioxide (CO2) availability on the scalability of microalgae-based biofuels production. To accurately assess the near-term productivity potential of large-scale microalgae biofuel in the US, a geographically realized growth model was used to simulate microalgae lipid yields based on meteorological data. The resulting lipid productivity potential of Nannochloropsis under large-scale cultivation is combined with land and CO2 resource availability illustrating current geographically feasible production sites and corresponding productivity in the US. Baseline results show that CO2 transport constraints will limit US microalgae based bio-oil production to 4% of the 2030 Department of Energy (DOE) alternative fuel goal. The discussion focuses on synthesis of this large-scale productivity potential results including a sensitivity analysis to land and CO2 resource assumptions, an evaluation of previous modeling efforts and their assumptions regarding the transportation of CO2, the feasibility of microalgae to meet DOE 2030 alternative fuel goals, and a comparison of the productivity potential in several key regions of the US

Fourier phase and pitch-class sum

Music theorists have proposed two very different geometric models of musical objects, one based on voice leading and the other based on the Fourier transform. On the surface these models are completely different, but they converge in special cases, including many geometries that are of particular analytical interest.Accepted manuscrip

Orbits for the Impatient: A Bayesian Rejection Sampling Method for Quickly Fitting the Orbits of Long-Period Exoplanets

We describe a Bayesian rejection sampling algorithm designed to efficiently compute posterior distributions of orbital elements for data covering short fractions of long-period exoplanet orbits. Our implementation of this method, Orbits for the Impatient (OFTI), converges up to several orders of magnitude faster than two implementations of MCMC in this regime. We illustrate the efficiency of our approach by showing that OFTI calculates accurate posteriors for all existing astrometry of the exoplanet 51 Eri b up to 100 times faster than a Metropolis-Hastings MCMC. We demonstrate the accuracy of OFTI by comparing our results for several orbiting systems with those of various MCMC implementations, finding the output posteriors to be identical within shot noise. We also describe how our algorithm was used to successfully predict the location of 51 Eri b six months in the future based on less than three months of astrometry. Finally, we apply OFTI to ten long-period exoplanets and brown dwarfs, all but one of which have been monitored over less than 3% of their orbits, producing fits to their orbits from astrometric records in the literature.Comment: 32 pages, 28 figures, Accepted to A

Testing the methodological utility of trace element analysis for detetecting dietary differences in fossil fauna from Turkana

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