In addition, a spatially and temporally resolved video of the temperature gradient versus time and the power produced versus time can be played to get an even better illustration of how the cells in a SOFC stack experience sudden and potentially damaging temperature fluctuations. A snapshot of the spatially and temporally resolved video tool is displayed in Figure 54. The information provided by the video can help understand the severe thermal stresses that the cells undergo during dramatic power demand spikes and provide some preliminary insight to their potential degradation and lifetime characteristics. The far-reaching benefits of the internet are not limited to developed countries. Studies have proven that developing countries can benefit significantly more than developed countries by having access to the internet. With so much of the world’s population currently having little or no internet connectivity, the following question is raised: Can the infrastructure that society now relies on to carry all this digital traffic keep up with the accelerating demand? Recent advances in technology have introduced an alternative to data storage by shifting it from localized on-site physical storage to large-scale out-of-sight centralized storage. This vast, dispersed network of centralized storage systems throughout the world has come to be referred to as the Cloud. Considering a traditional data center connected to the electric grid,equipment for growing weed less than 35% of the energy from the fuel source is delivered to the data center. The most significant inefficiencies result from power plant generation losses and transmission and distribution losses. In addition, within a data center, there are further losses associated with the infrastructure required for daily reliable operation .
The additional power consumed by these resources results in approximately less than 17.5% of the energy from the fuel source being delivered to the servers. It has been demonstrated that further developments for reducing greenhouse gas and criteria pollutant emissions can be made by implementing advanced alternative methods of power production that are proven to be more environmentally friendly and reliable replacements to combustion-based power. Fuel cells are a great alternative to combustion-based power and can convert fossil or renewable fuels into electricity more efficiently and with lower emissions. There are many reasons to consider fuel cells for data center power production, however, a few stand out above the rest. First off, high temperature fuel cells are inherently fuel flexible and as a result, their reliability is heavily influenced by the reliability of the natural gas grid. Estimates show that the reliability of the natural gas grid exhibits greater than five nines reliability, which is much higher than the three nines reliability exhibited by the electric grid. Secondly, the gas distribution network within a data center is much cheaper than the high voltage switch gear, transformers, and copper cables required to connect to the electric grid. If fuel cells are placed closer to the power consumption units , then data centers can easily eliminate the power distribution and backup power generation systems. This would be highly favorable because the electrical infrastructure accounts for over 25% of the capital cost for state-of-the-art data centers. Thirdly, fuel cells are environmentally friendly with near zero pollutant and greenhouse gas emissions. Although initial phases of introducing fuel cells into the data center would require that they operate on natural gas, even with this source of fuel, fuel cell emissions are much cleaner and far more efficient than those from combustion.
Carbon dioxide emissions have the potential to be reduced to 49%, nitrogen oxides by 91%, carbon monoxide by 68%, and volatile organic compounds by 93%. Recognizing the significant energy sink at the power plant level, Microsoft made a commitment to make their operations carbon neutral. Microsoft has envisioned a new concept for their data centers, aptly labelled as the ‘stark’ design. They proposed a direct generation method that places fuel cells at the server rack level, inches from the servers. The close proximity allows for the direct use of DC power without the large capital cost, potential for failures, and efficiency penalties associated with AC-DC inversion equipment. As a result, power distribution units, backup power generation equipment, high voltage transformers, expensive switch gear, and AC-DC power supplies in the servers can be completely removed from the data centers. Although a PEMFC system has demonstrated its dynamic load-following capabilities, its insatiable thirst for hydrogen was a major drawback for immediate implementation. Due to limitations in the burgeoning hydrogen infrastructure, Microsoft decided to opt for a high temperature SOFC system for its fuel-flexible capability, which would allow for quick installment and implementation in any building with an existing natural gas network. An added bonus to operating on natural gas is the highly reliable nature of the natural gas network, which subsequently contributes to the highly reliable nature of fuel cell systems. A relatively inexpensive and commercially tested SOFC system was needed to begin the research work. SolidPower’s Engen-2500 system was selected because it was commercially available and touted as one of the most efficient SOFC systems to date. SolidPower is an experienced developer of SOFC based systems, displaying its newly developed Engen-2500 micro-Combined Heat and Power SOFC appliance for home and industry. This micro-cogeneration system, Engen-2500, is a great solution for projects ranging from 2.5 kW up to 20 kW of electrical power.
The technology offers the ability to combine multiple Engen-2500 appliances in series. The Engen-2500 system is a floor standing unit generating a maximum of 2.5 kWe of net AC power and can run solely on natural gas fuel from the grid at normal supply pressure. Analyzing the Engen-2500 system using the SOFC system model developed for this thesis, spatial resolution is achieved by taking a single cell and dividing it into a grid of smaller elements, which are referred to as nodes. Each node is broken down further into five distinct segments that comprise a single cell: the oxidant separator plate, cathode gas stream, electrolyte , anode gas stream, and fuel separator plate. Spatially resolving each segment of a single cell permits the localized dynamic analysis of the conservation of mass, energy, and momentum equations while also locally evaluating the temperature, species mole fractions, pressure, and other required characteristics. The dynamic analysis of one cell is then scaled to the number of cells in the stack, ultimately representing the dynamic characteristics of the entire stack component. The same discretization method just described is applied to all components of the Engen-2500 SOFC system. The transport phenomena and electrochemical reactions evaluated at each locally resolved temperature, species mole fraction, and pressure, determine the performance of each component in the SOFC system. It is important to note that the results presented in this thesis incorporated educated guesses. Comparing all the model results for the polarization, power, outlet temperatures, and flow rate plots, it is evident that the simulations made in round three provided the best all-around match to the actual experimental data. From the simulations,grow tables 4×8 it is understood that matching the anode outlet temperatures plays a much bigger role in electrochemical theory than matching the cathode outlet temperature when working with high temperature fuel cells. The reason for this is believed to be a result of the electrochemical kinetics primarily occurring at the triple-phase boundary on the anode-electrolyte interface. An interesting trend was noticed when verifying the model outputs to those of the experimental results. The system model consistently predicts anode and cathode outlet temperatures that are very close to one another. This could be due in large part to the difficulty in accurately measuring heat transfer kinetics especially due to limitations in available information provided by SolidPower. The most revealing piece of information that was provided by SolidPower showed the locations of the fuel inlet and outlet thermocouples in the Engen-2500 stack. However, the air inlet and outlet thermocouples were not labelled in the provided confidential diagram. This leads me to question the veracity of the cathode outlet temperature since the location of the thermocouple could give some additional insight to the heat transfer kinetics. Furthermore, the model predicts the anode and cathode outlet temperatures at the immediate exit of the stack. Therefore, it is possible that if an air or fuel thermocouple is placed a distance away from the immediate stack exit, that the temperature measured by the thermocouple would indeed differ from the temperature at the stack exit because of convection and potentially radiation heat transfer kinetics due to such high operating temperatures. A few recommendations can be made to improve the accuracy of the fuel cell model, particularly concerning the operation of the fuel cell stack. The following recommendations would help tremendously with model verification efforts despite the potential for significant increases in computational time and power. The first recommendation would be to divide the PEN further into the anode, electrolyte, and cathode components for additional accuracy in calculating the electrochemical reaction kinetics at the anode-electrolyte interface and cathode-electrolyte interface, specifically concerning species conservation.
Currently, the model divides the cell into 5 distinct components, which are the fuel separator plate, anode gas stream, PEN, cathode gas stream, and oxidant separator plate. Therefore, splitting the PEN into the anode, electrolyte, and cathode could help provide results that are more accurate. Doing so also would also improve the vertical heat transfer that occurs in the direction that crosses all five distinct components. So if the fuel cell stack under consideration is anode-supported or electrolyte-supported, more accurate heat transfer can be modeled hopefully solving the errors encountered in this thesis with either the anode outlet temperature or cathode outlet temperature. The second recommendation would be to separate the activation and concentration over potential calculations to achieve more accurate activation and concentration over potentials when operating the model at very low or high current densities. Through repeated simulations and as is evident in the steady-state results section of this thesis, the lowest and highest current densities were the most inaccurate simulation points. The last recommendation would be to introduce a current-based controller that can replace the power controller for simpler and faster steady-state model verification assessments. A lot of time and care was needed to assess the steady-state model results because the experimental results were based on different current level inputs. Therefore, significant effort was required to repeatedly adjust the electrochemical parameters to achieve appropriate current levels. In 2016, when voters approved Proposition 64, they set the stage for radical change across California’s cannabis landscape. Licensed, regulated cannabis stores would soon throw open their doors. The state’s vast cannabis industry would be gin to emerge from illegality, though unlicensed operations would surely persist. UC researchers immediately understood that cannabis legalization would present California with pressing new questions, along numerous dimensions, that could only be answered through rigorous, broad ranging research. How would legalized cannabis cultivation affect the state’s water, wildlife and forests? How might impaired driving, or interconnections between cannabis and tobacco, influence public health? How would tax and regulatory policy affect the rate at which cannabis cultivators abandoned the illegal market? These questions and many more are now the subject of research around the UC system, and multiple campuses are establishing centers dedicated to cannabis research. This article surveys UC’s emerging architecture for cannabis research in the legalization era — and presents a sampling of notable research projects, both completed and ongoing.The Cannabis Research Center at UC Berkeley is an interdisciplinary program that, bringing together social, physical and natural scientists, evaluates the environmental impacts of cannabis cultivation; investigates the policy-related and regulatory dimensions of cultivation; and directly engages cannabis farmers and cannabis-growing communities. The center, according to Ted Grantham — one of three CRC co-directors and a UC Cooperative Extension assistant specialist affiliated with UC Berkeley’s Department of Environmental Science, Policy, and Management — is “focused on cannabis as an agricultural crop, grown in particular places by particular communities with unique characteristics.” For Grantham and the center’s co-founders, establishing the program was “a chance to develop policy-relevant research at the time of legalization and a time of rapidly shifting cultivation practices.” The center’s co-directors, in addition to Grantham, are Van Butsic — a UCCE assistant specialist affiliated with UC Berkeley’s Department of Environmental Science, Policy, and Management — and Eric Biber, a UC Berkeley professor of law. Other CRC re searchers are associated with entities such as the UC Berkeley Department of Integrative Biology, the UC Berkeley Geography Department, the UC Merced Environmental Engineering program and The Nature Conservancy. The center itself is affiliated with the UC Berkeley Social Science Matrix. The CRC formally launched with a public event in January.