Low carbon hydrogen can be produced using a range of technologies. Green hydrogen is produced using electrolysis and renewable electricity, while blue hydrogen is produced using steam methane reforming (SMR) with carbon capture and storage (CCS). Recent studies and strategies have compared these technologies but have not assessed the effects of lower-than-perfect CCS capture rates on long term cost competitiveness. This paper computes the amount of emissions that would occur under different carbon dioxide capture rates, and the relative costs of blue and green hydrogen under different scenarios for carbon costs and for lifetimes of production facilities. Our analysis gives insights into the cost competitiveness of blue versus green hydrogen under strengthening climate policy over time. Our assessment takes into account expected hydrogen production opportunities and costs in Australia, and parameters in the Japanese Hydrogen Strategy. We find that while blue hydrogen (from fossil fuels, with CCS) is generally cheaper to produce now, green hydrogen is likely to improve its cost competitiveness over time. Tightening carbon constraints will raise the possibility that blue hydrogen production assets could become stranded.
The future of passenger transportation lies in electrification. Freight transportation however has size and weight limitations that make electrification challenging, such that the continued emission of carbon dioxide from the combustion exhaust of heavy-duty vehicles is likely. A carbon capture strategy to intercept CO2 from mobile emission sources, analogous to stationary capture systems for power plants, is therefore attractive to reduce CO2 emissions from freight shipping. The economic and environmental implications of a conceptual technology, utilizing a porous adsorbent bed to selectively remove CO2 from tailpipe exhaust, are examined herein. In the economic evaluation, the hypothetical abatement cost for mobile carbon capture is found to be competitive with stationary capture and with vehicle electrification at about $100 per ton of avoided CO2 emissions. Based on the market potential of land freight shipping, 0.12 to 0.15 °C of avoided warming through the end of the century is achievable by the implementation of mobile carbon capture for long-haul freight vehicles. Collectively, carbon capture from heavy-duty vehicles could provide a practical, cost-competitive, and sustainable contribution to mitigating global greenhouse gas emissions.
Thermal energy storage (TES) can alleviate peak demand on the electricity grid by offsetting building thermal loads, increasing the grid’s reliability and resilience. However, low energy density and poor energy performance of existing TES technologies limit their applications. Sorption-based thermal battery (STB) system is thus developed using three-phase sorption technology to harvest low-temperature heat, store it with a much higher energy density than common TES systems and dehumidify air or provide space cooling in buildings. Although STB has been experimentally proved to be feasible, influencing factors on its performance are still unknown by far. Therefore, this paper conducted a parametric analysis on crystallization and crystal dissolution performance of a developed STB test rig. The crystallization results showed that the energy density of the STB increased with reducing the solution flow rate and the cooling water temperature. The dissolution results showed that a higher discharge rate of the STB can be achieved with increasing the flow rate and temperature of inlet diluted solution. The work in this study is helpful to the optimal design and operation of the STB system.
The emergence of increasingly affordable variable speed drive technology has changed the approach for how chilled water systems equipped with variable speed drives should be controlled. The purpose of this research was to estimate the potential energy savings that can be achieved through optimization of a single chiller system equipped with Variable Frequency Drives (VFDs) on all pieces of equipment in the condenser water system. Data for a case study was collected from a local museum’s chilled water system. To accomplish the objective, physical component models of the centrifugal chiller, cooling tower and condenser water pump were established with the goal of incorporating the system’s condenser water flow rate and cooling tower fan speeds as optimization variables. Furthermore, a cooling load prediction algorithm was developed using a multiple non-linear regression model to approximate the buildings cooling load subject to a range of environmental conditions. The inputs and outputs of the individual component models were linked to estimate how adjusting the cooling tower fan and condenser water pump speed would influence the system’s overall performance. The overall system model was then optimized using a generalized reduced gradient optimization algorithm to determine the potential energy savings through speed control with VFDs and ascertain a simple control logic strategy for the building automation system to operate the system. The saving potential of the optimized system was found to be 12-15%.
Approaches to reducing energy consumption in multi-family residential buildings can benefit from being more intentionally integrated with non-energy urban planning efforts. Despite the large volume of energy data available, some of the data that would be useful to plan more sustainable urban development or retrofit existing building stocks are incomplete or not integrated with data that is being used for decision-making. This article identifies data issues that limit the effectiveness of energy efficiency planning efforts and proposes solutions to surmount these challenges. Further, the role of an Energy Urban Planner (EUP) is proposed to resolve the identified gaps with consideration for more thoughtful and integrated planning approach. Lastly, the article discusses the potential implications of an EUP role for both urban planning more broadly and specific approaches to reduce energy consumption. The methodology combines qualitative research with key energy efficiency decision-makers in three municipalities and a data quality and spatial analysis case study of Chicago Energy Benchmarking data. The qualitative research consisted of interviews that were conducted to explore how municipalities and NGOs plan efforts to reduce energy consumption in multi-unit residential buildings. In the case study, 2017 energy benchmarking data (reported in 2018) are analyzed for data quality issues and patterns that emerge from geographic and urban form variables. The qualitative findings are combined with the results from the Chicago case study to identify the need for more integrated urban planning. The objective is to highlight data that can be intentionally integrated to bolster energy efficiency efforts across professions.
In 2018, nuclear energy generated 55% of United States’ and one third of the world’s carbon free electricity. Nuclear energy can be a key tool in current efforts to mitigate climate change before 2050. However, nuclear construction costs escalated dramatically in recent years: from $3,000/kW in the 1990’s to over $7,000 today, and this has severely limited its potential for impact. Nuclear plants are construction megaprojects that require thousands of workers and a decade of construction. The capital costs and construction timelines were double the original estimates for the last five nuclear plants completed or under construction in western nations. Moreover, the current nuclear technology can only provide heat at low temperatures (300°C), which limits its use as a decarbonization tool to the electricity grid. Heat for industrial processes accounts for 10% of carbon emissions. High temperature gas reactors (HTGRs) can meet this need with carbon free nuclear heat. Unfortunately, the estimated cost of advanced reactor alternatives such as HTGRs are even higher than current Light Water Reactors (LWRs). In this paper, we built a simple model to estimate the capital cost of existing nuclear plants and apply it to HTGR designs. We propose a structures-first design framework to minimize cost and apply it to the HTGR, resulting in a horizontal, integrated HTGR. The reactor core and steam generator are mounted on rails and in-line with one another. The rail-mounted horizontal orientation simplifies installation and eliminates the overhead crane. The proposed concept reduced the reactor building size by more than 50%/kW relative to other HTGR designs, putting the building power density on par with LWR designs but with the inherent safety and high temperature capability of an HTGR. Finally, we estimate a >30% cost reduction from the new design and the potential impact on carbon emissions.
The electric vehicles can be charged through plug-in chargers but there are challenges such as heavy battery packs (e.g. electric buses with large batteries), and high battery costs. An alternative charging method of wireless charging where wireless power transfer technology is applied may overcome the problem with plug-in charging. Due to limited operational ranges of battery-electric buses, two range remedy methods are available: (a) regular plug-in battery charging with backup vehicles; (b) en-route wireless charging during service where wireless charging takes place while a bus is loading and un-loading passengers. Thus, costly backup vehicles could be eliminated and battery packs can be downsized as well. This paper compares two charging scenarios plug-in charging and stationary wireless charging for all-electric bus systems and compare them to conventional diesel buses, with respect to costs, battery downsizing potential and energy consumption rates. A model is developed to evaluate plug-in and wireless charging electric bus systems and conventional diesel bus systems. A city’s transit bus system is selected for a case study on the plug-in charging and stationary wireless charging systems, together with diesel buses. The plug-in charging and stationary wireless charging systems are modelled through the case study. The wirelessly charged battery for electric buses can be downsized by 46% of the plug-in charged battery, thus significantly decreasing the cost and weight of battery packs for electric buses. Energy consumption rates for wirelessly charged buses also decrease, resulting from reduced bus weight. Simulation results showed that if 10% vehicle mass reduction is achieved by implementing wireless charging, energy consumption of electric buses can be reduced by 5.5%. In addition, wireless charging systems have the advantages of increased safety and city aesthetics, and the potential to make road transportation more intelligent.
Building space heating consumes approximately a third of all global natural gas end use, contributing significantly to global warming. Higher efficiency (aka, condensing) furnaces hold only about 25% of the furnace market in US buildings. One reason for this is that the condensing heat exchanger must use highly expensive, needs corrosion-resistant materials due to acidic components in the furnace flue gas stream. Increasing the market share of high efficiency furnace is beneficial to reducing greenhouse gas emissions. This study developed and tested a benchtop prototype of a novel membrane-based condensing (heat recovery) heat exchanger for high efficiency furnace to achieve non-acidic condensation via nano-porous membranes. Test results show that both sensible and latent heat are recovered with a fraction of latent heat recovery varies from 39% to 73%. The amount of water condensed through the membrane heat exchanger increases with the increase of flue gas flow rate while it decreases by increasing coolant temperature. The fraction of latent heat recovery decreases with the increase of flue gas flow rate and coolant temperature. The pH value of condensed water was only mildly acidic, varying from 5.0 to 6.3 without any additional treatment. It achieves significant improvement when compared with the conventional condensing furnace. Therefore, feasibility of the membrane-based condensing heat exchanger has been experimentally verified, and it has potential to enable wider market penetration of highly energy-efficient condensing furnaces by reducing costs for dealing with the acid condensation.
Climate change, population growth, and increasing peak electricity demand highlight the importance of the sustainable use of energy in our communities. Residential and commercial buildings account for almost 40% of the total energy use in the United States, putting building energy efficiency among the main objectives for energy planning and policy. To reinforce their sustainable energy plans, many cities across the United States have adopted energy transparency ordinances in recent years. The data released under these energy benchmarking laws enable researchers to investigate the performance of residential and commercial buildings. Using these data sources, many studies have been performed, notably to help municipalities meet their energy efficiency and carbon emission reduction goals. The main goal of this work is to present a comprehensive review of the energy benchmarking policies across the United States to pool together the lessons that were learnt. In particular, the work reviews the characteristics and implementation of the building energy benchmarking laws, it identifies the benefits of adopting energy transparency laws, and it assesses the potential challenges that can hinder their effective use.
It is widely recognized that cellulose accessibility is closely connected to sugar yield which determines economic viability of biorefining. However, existing kinetic models are not able to capture the evolution of the microscopic properties of biomass (e.g., cellulose accessibility) during pretreatment. Motivated by the limitation, we developed a multiscale model that is capable of describing the dynamic evolution of cellulose accessible area by integrating a macroscopic kinetic model with a microscopic kinetic Monte Carlo model. Then, a model reduction technique is employed to lower the computational complexity of the multiscale model, and employed to a model-based feedback controller to enhance the cellulose accessibility while minimizing the heat during alkaline pretreatment. The implementation of the control framework improved the glucose yield by 19.9% compared to a conventional constant-temperature pretreatment method.