Thomas H. Bradley

Microalgae bulk growth model with application to industrial scale systems.

The scalability of microalgae growth systems is a primary research topic in anticipation of the commercialization of microalgae-based biofuels. To date, there is little published data on the productivity of microalgae in growth systems that are scalable to commercially viable footprints. To inform the development of more detailed assessments of industrial-scale microalgae biofuel processes, this paper presents the construction and validation of a model of microalgae biomass and lipid accumulation in an outdoor, industrial-scale photobioreactor. The model incorporates a time-resolved simulation of microalgae growth and lipid accumulation based on solar irradiation, species specific characteristics, and photobioreactor geometry. The model is validated with 9 weeks of growth data from an industrially-scaled outdoor photobioreactor. Discussion focuses on the sensitivity of the model input parameters, a comparison of predicted microalgae productivity to the literature, and an analysis of the implications of this more detailed growth model on microalgae biofuels lifecycle assessment studies.

Nannochloropsis production metrics in a scalable outdoor photobioreactor for commercial applications

Commercial production of renewable energy feedstocks from microalgae will require reliable and scalable growth systems. Two and one half years of biomass and lipid productivity data were obtained with an industrial-scale outdoor photobioreactor operated in Fort Collins, Colorado (USA). The annualized volumetric growth rates for Nannochloropsis oculata (CCMP 525) and Nannochloropsis salina (CCMP 1776) were 0.16 g L(-1) d(-1) (peak=0.37 g L(-1) d(-1)) and 0.15 g L(-1) d(-1) (peak=0.37 g L(-1) d(-1)) respectively. The collective average lipid production was 10.7 m3 ha(-1) yr(-1) with a peak value of 36.3 m3 ha(-1) yr(-1). Results from this study are unique based on publication of biomass and corresponding lipid content combined with demonstration of energy savings realized through analysis of gas delivery requirements, water recycling from successive harvests with no effect on productivity, and culture stability through serial batch lineage data and chemotaxonomic analysis of fatty acid contents.

An Evaluation of State-of-Charge Limitations and Actuation Signal Energy Content on Plug-in Hybrid Electric Vehicle, Vehicle-to-Grid Reliability, and Economics

Researchers have proposed that plug-in hybrid electric vehicles (PHEVs) performing vehicle-to-grid (V2G) ancillary services can accrue significant economic benefits without degrading vehicle performance. However, analyses to date have not evaluated the effect that automatic generator control signal energy content and call rate has on V2G ancillary service reliability and value. This research incorporates a new level of detail into the modeling of V2G ancillary services by incorporating probabilistic vehicle travel models, time-series automatic generation control signals, and time series ancillary services pricing into a non-linear dynamic simulation of the driving and charging behavior of PHEVs. Stochastic results are generated using Monte-Carlo methods. Results show that in order to integrate a V2G system into the existing market and power grid the V2G system will require: 1) an aggregative architecture to meet current industry standard reliability requirements; 2) the construction of low energy automatic generation control signals; 3) a lower percent call for V2G even if the pool of contracted ancillary service resources gets smaller; 4) a consideration of vehicle performance degradation due to the potential loss of electrically driven miles; and 5) a high-power home charging capability.

Quantitative Measurement of Direct Nitrous Oxide Emissions from Microalgae Cultivation

Although numerous lifecycle assessments (LCA) of microalgae-based biofuels have suggested net reductions of greenhouse gas emissions, limited experimental data exist on direct emissions from microalgae cultivation systems. For example, nitrous oxide (N(2)O) is a potent greenhouse gas that has been detected from microalgae cultivation. However, little quantitative experimental data exist on direct N(2)O emissions from microalgae cultivation, which has inhibited LCA performed to date. In this study, microalgae species Nannochloropsis salina was cultivated with diurnal light-dark cycling using a nitrate nitrogen source. Gaseous N(2)O emissions were quantitatively measured using Fourier transform infrared spectrometry. Under a nitrogen headspace (photobioreactor simulation), the reactors exhibited elevated N(2)O emissions during dark periods, and reduced N(2)O emissions during light periods. Under air headspace conditions (open pond simulation), N(2)O emissions were negligible during both light and dark periods. Results show that N(2)O production was induced by anoxic conditions when nitrate was present, suggesting that N(2)O was produced by denitrifying bacteria within the culture. The presence of denitrifying bacteria was verified through PCR-based detection of norB genes and antibiotic treatments, the latter of which substantially reduced N(2)O emissions. Application of these results to LCA and strategies for growth management to reduce N(2)O emissions are discussed.

Microalgae to biofuels: Life cycle impacts of methane production of anaerobically digested lipid extracted algae

This study presents experimental measurements of the biochemical methane production for whole and lipid extracted Nannochloropsis salina. Results show whole microalgae produced 430 cm(3)-CH4 g-volatile solids(-1) (g-VS) (σ=60), 3 times more methane than was produced by the LEA, 140 cm(3)-CH4 g-VS(-1) (σ=30). Results illustrate current anaerobic modeling efforts in microalgae to biofuel assessments are not reflecting the impact of lipid removal. On a systems level, the overestimation of methane production is shown to positively skew the environmental impact of the microalgae to biofuels process. Discussion focuses on a comparison results to those of previous anaerobic digestion studies and quantifies the corresponding change in greenhouse gas emissions of the microalgae to biofuels process based on results from this study.

Design and Performance Validation of a Fuel Cell Unmanned Aerial Vehicle

This paper describes methods for design of an unmanned aerial vehicle which uses a proton exchange membrane fuel cell as its primary powerplant. The proposed design methods involve the development of empirical and physics-based contributing analyses to model the performance of the aircraft subsystems. The contributing analyses are collected into a design structure matrix which is used to map aircraft performance metrics as a function of design variables over a defined design space. An exhaustive search within the design space is performed to identify optimal design configurations and to characterize trends within the design space so as to inform lower-level design decisions. The results of the design process are used to construct a demonstration fuel cell-powered aircraft. Test results from the demonstration aircraft and its subsystems are compared to predicted results to validate the contributing analyses and improve their accuracy in further design iterations.

Comparison of Design Methods for Fuel-Cell-Powered Unmanned Aerial Vehicles

This paper presents two comparisons of design methods for fuel-cell-powered unmanned aerial vehicles. Previous design studies of fuel-cell-powered aircraft have used design methods that contain intrinsic assumptions regarding the design of a fuel cell powerplant and regarding the interactions between the powerplant and aircraft application. This study seeks to understand the effects of these design assumptions on the fuel cell powerplant structure and the aircraft performance. A design methods comparison is constructed by first developing a multidisciplinary modeling and design environment that is more general than the design processes proposed in literature. The design processes from previous studies can then be imposed on the more complete design environment to determine the performance costs and morphological changes caused by the design assumptions. In the first design study, results show that designing fuel-cell-powered aircraft using automotive-type fuel cell design rules leads to a low-efficiency powerplant and a low-performance aircraft in long-endurance and long-range unmanned aerial vehicle applications. The second design study shows that designing the aircraft powerplant using powerplant design criteria (such as specific energy) rather than aircraft design criteria (such as range) leads to suboptimal aircraft performance, especially for long-endurance unmanned aerial vehicle applications. The results of these studies show that the application-integrated design of aviation-specific fuel cell powerplants can significantly improve the performance of fuel-cell-powered aircraft for a variety of scales and missions.

Test Results for a Fuel Cell-Powered Demonstration Aircraft

A fuel cell powered airplane has been designed and constructed at the Georgia Insitute of Technology to develop an understanding of the design and implementation challenges of fuel cell-powered unmanned aerial vehicles (UAVs). A custom 448W net output proton exchange membrane fuel cell powerplant has been constructed and tested. A demonstrator aircraft was designed and built to accommodate this powerplant and the fuel cell powered aircraft has performed seven test flights to date. Test data show that the aircraft performance validates the models used for design and optimization and that the fuel cell aircraft is capable of longer endurance, higher performance test flights.

The Efficacy of Electric Vehicle Time-of-Use Rates in Guiding Plug-in Hybrid Electric Vehicle Charging Behavior

This paper presents a series of analyses whose goal is to understand the effectiveness with which time-of-use (TOU) rates can economically incent off-peak charging in plug-in hybrid electric vehicles (PHEV). The total cost of fueling PHEV under modeled and real-world TOU rates is compared to the total cost of fueling PHEV under constant rates. Time-resolved vehicle energy consumption and fueling cost is derived for a variety of PHEV designs from travel survey data and charging behavior models. A decision tree model of PHEV consumer choices is proposed with effectiveness and cost metrics defined at each decision point. Results show that gasoline PHEV that charge off-peak incur higher gasoline costs than PHEV that charge at-will. These additional fueling costs reduce the magnitude of the economic incentives for off-peak charging that TOU rates can provide to PHEV consumers. These results are then used to compare and evaluate the effectiveness of model and real-world TOU rates and to discuss implications for modeling PHEV total fueling cost.

Scale-Up of Flat Plate Photobioreactors Considering Diffuse and Direct Light Characteristics

This study investigates the scaling of photobioreactor productivity based on the growth of Nannochloropsis salina incorporating the effects of direct and diffuse light. The scaling and optimization of photobioreactor geometry was analyzed by determining the growth response of a small‐scale system designed to represent a core sample of a large‐scale photobioreactor. The small‐scale test apparatus was operated at a variety of light intensities on a batch time scale to generate a photosynthetic irradiance (PI) growth dataset, ultimately used to inform a PI growth model. The validation of the scalability of the PI growth model to predict productivity in large‐scale systems was done by comparison with experimental growth data collected from two geometrically different large‐scale photobioreactors operated at a variety of light intensities. For direct comparison, the small‐scale and large‐scale experimental systems presented were operated similarly and in such a way to incorporate cultivation relevant time scales, light intensities, mixing, and nutrient loads. Validation of the scalability of the PI growth model enables the critical evaluation of different photobioreactor geometries and design optimization incorporating growth effects from diffuse and direct light. Discussion focuses on the application of the PI growth model to assess the effect of diffuse light growth compared to direct light growth for the evaluation of photobioreactors followed by the use of the model for photobioreactor geometry optimization on the metric of areal productivity. Biotechnol. Bioeng. 2012; 109:363–370.