We report near-zero crossover for vanadium cross-permeation through single-layer graphene immobilized at the interface of two Nafion?polymer electrolyte membranes.Vanadium ion diffusion and migration,including proton ...We report near-zero crossover for vanadium cross-permeation through single-layer graphene immobilized at the interface of two Nafion?polymer electrolyte membranes.Vanadium ion diffusion and migration,including proton mobility through membrane composites,were studied with and without graphene under diffusion and migration conditions.Single-layer graphene was found to effectively inhibit vanadium ion diffusion and migration under specific conditions.The single-layer graphene composites also enabled remarkable ion transmission selectivity improvements over pure Nafion membranes,with proton transport being four orders of magnitude faster than vanadium ion transport.Resistivity values of 0.02±0.005Ωcm^(2) for proton and 223±4Ωcm^(2) for vanadium ion through single atomic layer graphene are reported.This high selectivity may have significant impact on flow battery applications or for other electrochemical devices where proton conductivity is required,and transport of other species is detrimental.Our results emphasize that crossover may be essentially completely eliminated in some cases,enabling for greatly improved operational viability.展开更多
Accurate measurements of broadband outdoor longwave irradiance are important for renewable energy applications and the study of the atmosphere and climate change. A unique method of pyrgeometer calibration has been de...Accurate measurements of broadband outdoor longwave irradiance are important for renewable energy applications and the study of the atmosphere and climate change. A unique method of pyrgeometer calibration has been developed to improve the measurement uncertainty [1]. The results of this method yielded irradiance values within ±3 W/m<sup>2</sup> of those traceable to the World InfraRed Standard Group (WISG). This article describes a technique for validating this pyrgeometer calibration method using two Absolute Cavity Pyrgeometers (ACPs). The ACPs and pyrgeometer model PIR were deployed outdoors and the irradiance measured by the PIR was compared against the average irradiance measured by the two ACPs. The irradiance measured by the PIR was calculated using two equations, NREL equation and the Physikalisch Meteorologisches Observatorium Davos (PMOD) equation. The uncertainty with 95% confidence level (<em>U</em><sub>95</sub>) of the irradiance measured by the PIR using NREL equation equaled ±3.51 W/m<sup>2</sup> with respect to SI and using PMOD equation <em>U</em><sub>95</sub> equaled ±2.99 W/m<sup>2</sup> with respect to SI. These results suggest that the PIR calibration method might be useful in addressing the international need for a secondary standard pyrgeometer traceable to SI.展开更多
It is becoming clear that Climate Change is getting severe. It was reported that the improved ocean heat measurements have a rate of warming upwards from 4 to 5 Hiroshima bombs liberated heat per second or 388,800 per...It is becoming clear that Climate Change is getting severe. It was reported that the improved ocean heat measurements have a rate of warming upwards from 4 to 5 Hiroshima bombs liberated heat per second or 388,800 per day. It was reported also that our climate has accumulated the equivalent of a total of more than 2.8 billion Hiroshima bombs’ worth of heat since 1998. Despite this global concern about the effect of global change on environment, it is believed that the problem is much more severe and with greater impact on all facets of life. The effect of Climate Change, especially with a 1℃increase in global temperature (from 14℃to 15℃) is equivalent to the heat liberated from explosion of about 300 million Hiroshima of atomic bomb. This is why this CoP 26 becomes more serious and had targeted year 2060 as a year of zero CO<sub>2</sub> emission. This paper discusses the impact of climate change on ten sectors;water, water desalination, energy, renewable energy supply, health, society, agriculture, economy, industry, and built environment.展开更多
Limiting global warming to 1.5°C would be a herculean task to all human beings.To reach this goal,the world would have to curb its carbon emissions by at least 49%of 2017 levels by 2030 and then achieve carbon ne...Limiting global warming to 1.5°C would be a herculean task to all human beings.To reach this goal,the world would have to curb its carbon emissions by at least 49%of 2017 levels by 2030 and then achieve carbon neutrality by 2050.Installing renewable energy systems is a key to achieving the decarbonization goal.However,the intermittent nature of renewable energies is challenging because it can disrupt the daily operation of the electric grid.Energy storage technology is the key to resolve the problems of intermittency,volatility and low energy density in the large-scale utilization of clean and renewable energy.展开更多
In this paper,a coordinated control scheme for wind turbine generator(WTG)and supercapacitor energy storage system(ESS)is proposed for temporary frequency supports.Inertial control is designed by using generator torqu...In this paper,a coordinated control scheme for wind turbine generator(WTG)and supercapacitor energy storage system(ESS)is proposed for temporary frequency supports.Inertial control is designed by using generator torque limit considering the security of WTG system,while ESS releases its energy to compensate the sudden active power deficit during the recovery process of turbine rotor.WTG is modeled using the fatigue,aerodynamic,structure,turbulence(FAST)code,which identifies the mechanical loadings of the turbine and addresses electro-mechanical interactions in the wind energy system.A damping controller is augmented to the inertial control to suppress severe mechanical oscillations in the shaft and tower of the turbine during frequency supports.Furthermore,the result of small-signal stability analysis shows that the WTGESS tends to improve the stability of the whole multi-energy power grid.The major contributions of this paper will be validated by utilizing the proposed control method that combines the grid support capability and maintaining the integrity of structural design of the turbine for normal operations.展开更多
Calculation of eigen-solutions plays an important role in the small signal stability analysis of power systems.In this paper,a novel approach based on matrix perturbation theory is proposed for the calculation of eige...Calculation of eigen-solutions plays an important role in the small signal stability analysis of power systems.In this paper,a novel approach based on matrix perturbation theory is proposed for the calculation of eigen-solutions in a perturbed system.Rigorous theoretical analysis is conducted on the solution of distinct,multiple,and close eigen-solutions,respectively,under perturbations of parameters.The computational flowchart of the unified solution of eigen-solutions is then proposed,aimed toward obtaining eigen-solutions of a perturbed system directly with algebraic formulas without solving an eigenvalue problem repeatedly.Finally,the effectiveness of the matrix perturbation based approach for eigen-solutions’calculation in power systems is verified by numerical examples on a two-area four-machine system.展开更多
Several decades ago,Profs.Sean Meyn and Lei Guo were postdoctoral fellows at ANU,where they shared interest in recursive algorithms.It seems fitting to celebrate Lei Guo’s 60 th birthday with a review of the ODE Meth...Several decades ago,Profs.Sean Meyn and Lei Guo were postdoctoral fellows at ANU,where they shared interest in recursive algorithms.It seems fitting to celebrate Lei Guo’s 60 th birthday with a review of the ODE Method and its recent evolution,with focus on the following themes:The method has been regarded as a technique for algorithm analysis.It is argued that this viewpoint is backwards:The original stochastic approximation method was surely motivated by an ODE,and tools for analysis came much later(based on establishing robustness of Euler approximations).The paper presents a brief survey of recent research in machine learning that shows the power of algorithm design in continuous time,following by careful approximation to obtain a practical recursive algorithm.While these methods are usually presented in a stochastic setting,this is not a prerequisite.In fact,recent theory shows that rates of convergence can be dramatically accelerated by applying techniques inspired by quasi Monte-Carlo.Subject to conditions,the optimal rate of convergence can be obtained by applying the averaging technique of Polyak and Ruppert.The conditions are not universal,but theory suggests alternatives to achieve acceleration.The theory is illustrated with applications to gradient-free optimization,and policy gradient algorithms for reinforcement learning.展开更多
A comprehensive thermo-economic model combining a geothermal heat mining system and a direct supercritical CO_(2) turbine expansion electric power generation system was proposed in this paper.Assisted by this integrat...A comprehensive thermo-economic model combining a geothermal heat mining system and a direct supercritical CO_(2) turbine expansion electric power generation system was proposed in this paper.Assisted by this integrated model,thermo-economic and optimization analyses for the key design parameters of the whole system including the geothermal well pattern and operational conditions were performed to obtain a minimal levelized cost of electricity(LCOE).Specifically,in geothermal heat extraction simulation,an integrated wellbore-reservoir system model(T2Well/ECO_(2)N)was used to generate a database for creating a fast,predictive,and compatible geothermal heat mining model by employing a response surface methodology.A parametric study was conducted to demonstrate the impact of turbine discharge pressure,injection and production well distance,CO_(2) injection flowrate,CO_(2) injection temperature,and monitored production well bottom pressure on LCOE,system thermal efficiency,and capital cost.It was found that for a 100 MWe power plant,a minimal LCOE of$0.177/kWh was achieved for a 20-year steady operation without considering CO_(2) sequestration credit.In addition,when CO_(2) sequestration credit is$1.00/t,an LCOE breakeven point compared to a conventional geothermal power plant is achieved and a breakpoint for generating electric power generation at no cost was achieved for a sequestration credit of $2.05/t.展开更多
文摘We report near-zero crossover for vanadium cross-permeation through single-layer graphene immobilized at the interface of two Nafion?polymer electrolyte membranes.Vanadium ion diffusion and migration,including proton mobility through membrane composites,were studied with and without graphene under diffusion and migration conditions.Single-layer graphene was found to effectively inhibit vanadium ion diffusion and migration under specific conditions.The single-layer graphene composites also enabled remarkable ion transmission selectivity improvements over pure Nafion membranes,with proton transport being four orders of magnitude faster than vanadium ion transport.Resistivity values of 0.02±0.005Ωcm^(2) for proton and 223±4Ωcm^(2) for vanadium ion through single atomic layer graphene are reported.This high selectivity may have significant impact on flow battery applications or for other electrochemical devices where proton conductivity is required,and transport of other species is detrimental.Our results emphasize that crossover may be essentially completely eliminated in some cases,enabling for greatly improved operational viability.
文摘Accurate measurements of broadband outdoor longwave irradiance are important for renewable energy applications and the study of the atmosphere and climate change. A unique method of pyrgeometer calibration has been developed to improve the measurement uncertainty [1]. The results of this method yielded irradiance values within ±3 W/m<sup>2</sup> of those traceable to the World InfraRed Standard Group (WISG). This article describes a technique for validating this pyrgeometer calibration method using two Absolute Cavity Pyrgeometers (ACPs). The ACPs and pyrgeometer model PIR were deployed outdoors and the irradiance measured by the PIR was compared against the average irradiance measured by the two ACPs. The irradiance measured by the PIR was calculated using two equations, NREL equation and the Physikalisch Meteorologisches Observatorium Davos (PMOD) equation. The uncertainty with 95% confidence level (<em>U</em><sub>95</sub>) of the irradiance measured by the PIR using NREL equation equaled ±3.51 W/m<sup>2</sup> with respect to SI and using PMOD equation <em>U</em><sub>95</sub> equaled ±2.99 W/m<sup>2</sup> with respect to SI. These results suggest that the PIR calibration method might be useful in addressing the international need for a secondary standard pyrgeometer traceable to SI.
文摘It is becoming clear that Climate Change is getting severe. It was reported that the improved ocean heat measurements have a rate of warming upwards from 4 to 5 Hiroshima bombs liberated heat per second or 388,800 per day. It was reported also that our climate has accumulated the equivalent of a total of more than 2.8 billion Hiroshima bombs’ worth of heat since 1998. Despite this global concern about the effect of global change on environment, it is believed that the problem is much more severe and with greater impact on all facets of life. The effect of Climate Change, especially with a 1℃increase in global temperature (from 14℃to 15℃) is equivalent to the heat liberated from explosion of about 300 million Hiroshima of atomic bomb. This is why this CoP 26 becomes more serious and had targeted year 2060 as a year of zero CO<sub>2</sub> emission. This paper discusses the impact of climate change on ten sectors;water, water desalination, energy, renewable energy supply, health, society, agriculture, economy, industry, and built environment.
文摘Limiting global warming to 1.5°C would be a herculean task to all human beings.To reach this goal,the world would have to curb its carbon emissions by at least 49%of 2017 levels by 2030 and then achieve carbon neutrality by 2050.Installing renewable energy systems is a key to achieving the decarbonization goal.However,the intermittent nature of renewable energies is challenging because it can disrupt the daily operation of the electric grid.Energy storage technology is the key to resolve the problems of intermittency,volatility and low energy density in the large-scale utilization of clean and renewable energy.
基金supported by the U.S.National science foundation(No.1711951)
文摘In this paper,a coordinated control scheme for wind turbine generator(WTG)and supercapacitor energy storage system(ESS)is proposed for temporary frequency supports.Inertial control is designed by using generator torque limit considering the security of WTG system,while ESS releases its energy to compensate the sudden active power deficit during the recovery process of turbine rotor.WTG is modeled using the fatigue,aerodynamic,structure,turbulence(FAST)code,which identifies the mechanical loadings of the turbine and addresses electro-mechanical interactions in the wind energy system.A damping controller is augmented to the inertial control to suppress severe mechanical oscillations in the shaft and tower of the turbine during frequency supports.Furthermore,the result of small-signal stability analysis shows that the WTGESS tends to improve the stability of the whole multi-energy power grid.The major contributions of this paper will be validated by utilizing the proposed control method that combines the grid support capability and maintaining the integrity of structural design of the turbine for normal operations.
基金supported in part by the National Science Foundation of United States(NSF)(Grant No.0844707)in part by the International S&T Cooperation Program of China(ISTCP)(Grant No.2013DFA60930)
文摘Calculation of eigen-solutions plays an important role in the small signal stability analysis of power systems.In this paper,a novel approach based on matrix perturbation theory is proposed for the calculation of eigen-solutions in a perturbed system.Rigorous theoretical analysis is conducted on the solution of distinct,multiple,and close eigen-solutions,respectively,under perturbations of parameters.The computational flowchart of the unified solution of eigen-solutions is then proposed,aimed toward obtaining eigen-solutions of a perturbed system directly with algebraic formulas without solving an eigenvalue problem repeatedly.Finally,the effectiveness of the matrix perturbation based approach for eigen-solutions’calculation in power systems is verified by numerical examples on a two-area four-machine system.
基金ARO W911NF1810334NSF under EPCN 1935389the National Renewable Energy Laboratory(NREL)。
文摘Several decades ago,Profs.Sean Meyn and Lei Guo were postdoctoral fellows at ANU,where they shared interest in recursive algorithms.It seems fitting to celebrate Lei Guo’s 60 th birthday with a review of the ODE Method and its recent evolution,with focus on the following themes:The method has been regarded as a technique for algorithm analysis.It is argued that this viewpoint is backwards:The original stochastic approximation method was surely motivated by an ODE,and tools for analysis came much later(based on establishing robustness of Euler approximations).The paper presents a brief survey of recent research in machine learning that shows the power of algorithm design in continuous time,following by careful approximation to obtain a practical recursive algorithm.While these methods are usually presented in a stochastic setting,this is not a prerequisite.In fact,recent theory shows that rates of convergence can be dramatically accelerated by applying techniques inspired by quasi Monte-Carlo.Subject to conditions,the optimal rate of convergence can be obtained by applying the averaging technique of Polyak and Ruppert.The conditions are not universal,but theory suggests alternatives to achieve acceleration.The theory is illustrated with applications to gradient-free optimization,and policy gradient algorithms for reinforcement learning.
基金funded by the Mexican National Council of Science and Technology(CONACYT in Spanish),under the Sectorial Fund for Energy Sustainability,CONACYT-Secretaiy of Energy(No.S0019-2012-04).
文摘A comprehensive thermo-economic model combining a geothermal heat mining system and a direct supercritical CO_(2) turbine expansion electric power generation system was proposed in this paper.Assisted by this integrated model,thermo-economic and optimization analyses for the key design parameters of the whole system including the geothermal well pattern and operational conditions were performed to obtain a minimal levelized cost of electricity(LCOE).Specifically,in geothermal heat extraction simulation,an integrated wellbore-reservoir system model(T2Well/ECO_(2)N)was used to generate a database for creating a fast,predictive,and compatible geothermal heat mining model by employing a response surface methodology.A parametric study was conducted to demonstrate the impact of turbine discharge pressure,injection and production well distance,CO_(2) injection flowrate,CO_(2) injection temperature,and monitored production well bottom pressure on LCOE,system thermal efficiency,and capital cost.It was found that for a 100 MWe power plant,a minimal LCOE of$0.177/kWh was achieved for a 20-year steady operation without considering CO_(2) sequestration credit.In addition,when CO_(2) sequestration credit is$1.00/t,an LCOE breakeven point compared to a conventional geothermal power plant is achieved and a breakpoint for generating electric power generation at no cost was achieved for a sequestration credit of $2.05/t.