Modeling and control design of a Vienna rectifier based electrolyzer

Hydrogen production is an interesting alternative of storing energy. Electrolyzers produce hydrogen through water electrolysis; the resulting hydrogen is later used to generate electricity by using fuel cells, that reverse the process. Electrolyzers use rectifiers to convert the grid ac voltage into dc voltage for supplying the electrolyzer cells. Previous research used a rectification process based on conventional rectifiers (diode-or thyristor-based) which draw non-sinusoidal current from the main grid. This requires increased filtering to prevent power quality problems and equipment malfunctioning/failure. In addition, previous literature assumed simplified models for the power electronics converters and lacked a detailed control system. The Vienna rectifier is a non-regenerative converter that produces sinusoidal currents with low losses due to the reduced number of active switches. This manuscript proposes using the Vienna rectifier as an interface to connect electrolyzers to the ac grid. The dc voltage applied to the electrolyzer is regulated by using another DC-DC converter, which is selected to be a synchronous buck converter for simplicity and maximum efficiency. In this paper, the models of the Vienna rectifier, synchronous buck converter, and the electrolyzer are developed along with their respective controls. The control system has the ability to function in two operation modes for the overall reference: hydrogen production and power demand. The first one is adequate for grid-connected operation and the later for off-grid operation. Simulation results are given to show the validity of the proposed procedures

Natural gas fuel and greenhouse gas emissions in trucks and ships

Natural gas is a transport fuel which may help reduce greenhouse gas emissions in shipping and trucks. However, there is some disagreement regarding the potential for natural gas to provide significant improvements relative to current ships and trucks. In 2015, road freight represented ~7% of global energy related CO2 emissions, with international shipping representing ~2.6% of global emissions. These emissions are also expected to grow, with some estimates suggesting road freight emission growing by a third, and shipping emissions growing by between 50% and 250% from 2012 to 2050, making absolute emissions reductions challenging. In addition, reducing emissions in ships and trucks has proved technically difficult given the relatively long distances that ships and trucks travel. This paper documents a systematic review of literature detailing well-to-wheel/wake greenhouse gas emissions and economic costs in moving from diesel and heavy fuel oil to natural gas as a fuel for trucks and ships. The review found a number of important issues for greenhouse gas reduction. First, moderate greenhouse gas reductions of 10% were found when switching to natural gas from heavy fuel oil in shipping when comparing the lowest estimates. Comparing lowest well-to-wheel greenhouse gas emissions estimates for trucks, the benefit of switching to natural gas fuel is approximately a 16% reduction in greenhouse gas emissions. However, these emissions are highly variable, driven particularly by methane emissions in exhaust gas. Given this, in the worst cases natural gas ships and trucks emit more greenhouse gasses than the diesel trucks and heavy fuel oil ships that they would replace. It appears relatively cost effective to switch to natural gas as a transport fuel in ships and trucks. However, the limited emissions reduction potential raises questions for the ongoing role of natural gas to reduce greenhouse gas emissions in line with the challenging greenhouse gas reduction targets emerging in the transport sector

Life beyond 30: Probing the-20 < M (UV) <-17 Luminosity Function at 8 < z < 13 with the NIRCam Parallel Field of the MIRI Deep Survey

We present the ultraviolet luminosity function and an estimate of the cosmic star formation rate density at 8 8 galaxy candidates based on their dropout nature in the F115W and/or F150W filters, a high probability for their photometric redshifts, estimated with three different codes, being at z > 8, good fits based on χ 2 calculations, and predominant solutions compared to z < 8 alternatives. We find mild evolution in the luminosity function from z ∼ 13 to z ∼ 8, i.e., only a small increase in the average number density of ∼0.2 dex, while the faint-end slope and absolute magnitude of the knee remain approximately constant, with values α = − 2.2 ± 0.1, and M * = − 20.8 ± 0.2 mag. Comparing our results with the predictions of state-of-the-art galaxy evolution models, we find two main results: (1) a slower increase with time in the cosmic star formation rate density compared to a steeper rise predicted by models; (2) nearly a factor of 10 higher star formation activity concentrated in scales around 2 kpc in galaxies with stellar masses ∼108 M ⊙ during the first 350 Myr of the universe, z ∼ 12, with models matching better the luminosity density observational estimations ∼150 Myr later, by z ∼ 9

Energy demand and greenhouse gas emissions from urban passenger transportation versus availability of renewable energy in the Canadian Lower Fraser Valley

NRC publication: Ye

Steady State and Transient Water Transport in Liquid- and Vapor-Equilibrated Proton Exchange Membranes

Abstract not Available.</jats:p

Reference Electrodes for Failure Diagnostics in Fuel Cells

NRC publication: Ye

The Economics of High Temperature and Supercritical Water Electrolysis

The growth of green energy in recent decades has resulted in increasing demand for hydrogen production with net-zero carbon emissions. Water electrolysis provides a solution to meet this demand, however it is currently too expensive to be cost competitive with hydrogen production methods of higher carbon intensity. High-temperatures and pressures can be leveraged to increase the energy efficiency of water electrolysis through kinetics and thermodynamic benefits, thereby reducing the overall cost of green hydrogen [1]. Additionally, performing water electrolysis directly at high pressures can help to avoid the added cost associated with gaseous hydrogen compression. Little is known about the electrolysis of supercritical water and what benefits it might offer in terms of hydrogen cost reduction [2,3]. In this work, experimental data was collected for supercritical water electrolysis and used to build an electrochemical model suitable for use under those conditions. The results of this model, combined with components of a previously published technoeconomic model for a high-temperature and pressure water electrolysis plant [4], indicate that while supercritical water electrolysis is achievable it is not the most economically efficient choice for hydrogen production. High-temperature and pressure water electrolysis performed under optimal conditions can be used to achieve higher economic efficiency when compared with contemporary water electrolysis solutions. Finally, a thorough optimization of the model presents a grim picture for achieving the US Department of Energy’s $2 kgH2 -1 target through water electrolysis without government subsidy. References: [1] D. Todd, M. Schwager, W. Mérida, Thermodynamics of high-temperature, high-pressure water electrolysis, J. Power Sources. 269 (2014) 424–429. https://doi.org/10.1016/j.jpowsour.2014.06.144. [2] H. Boll, E.. Franck, H. Weingärtner, Electrolysis of supercritical aqueous solutions at temperatures up to 800K and pressures up to 400MPa, J. Chem. Thermodyn. 35 (2003) 625–637. https://doi.org/10.1016/S0021-9614(02)00236-7. [3] P.C. Ho, D.A. Palmer, Determination of ion association in dilute aqueous potassium chloride and potassium hydroxide solutions to 600°C and 300 MPa by electrical conductance measurements, J. Chem. Eng. Data. 43 (1998) 162–170. https://doi.org/10.1021/je970198b. [4] T. Holm, T. Borsboom-Hanson, O.E. Herrera, W. Mérida, Hydrogen costs from water electrolysis at high temperature and pressure, Energy Convers. Manag. 237 (2021) 114106. https://doi.org/10.1016/j.enconman.2021.114106. Figure 1 <jats:p /

Polybithiophene: A Humidity Sensor

Abstract not Available.</jats:p

New Reference Electrode Approach for Fuel Cell Performance Evaluation

Abstract not Available.</jats:p