Abstract

Whole energy system modelling is a valuable tool to support the development of policy to decarbonise energy systems, and has been used extensively in the UK for this purpose. However, quantitative insights produced by such models methods necessarily omit potentially important features of physical and engineering reality. The authors argue that important socio-technical insights can be gained by studying critical events such as the loss of 2.1 GW generation from the electricity system of Great Britain in August, 2019. The present paper uses this event as a starting point for a discussion of the need for additional tools, drawn from the System Architecture literature, to support the design and realisation of future fully decarbonised systems with high penetrations of renewable energy, capable of providing high levels of resilience and flexibility.

Abstract

Photovoltaic (PV) distributed generation (PVDG) has grown significantly in the recent years due to the rapid development of power electronic technologies. The PVDG is usually integrated to distribution systems. The integration of PVDG can alleviate energy demand effectively while reduce air pollution and greenhouse gas emissions. However, with the increasing integration, the PVDG systems inevitably lead to significant challenges on operation of power systems, including protection of distribution systems. In the existing literature, only a few papers discussed the impact of the integration of PVDG on the protection of distribution systems, and the corresponding technical challenges are not fully clarified. To fill the gap, this paper develops a generic distribution system with the integration of a PVDG system to analyze the impact of integration of PVDG on the overcurrent protection of the distribution system. It is found that the control of PV inverters can limit the fault current significantly during a short-circuit (SC) fault. This makes the SC current of the faulted feeder too low to trigger the circuit breaker, leading to a protection failure (should operate but does not). To verify this conclusion, a comparison case with the connection of a traditional synchronous generator is provided in this paper.

Abstract

This paper presents a roadmap for the build-out and deployment of renewable hydrogen (RH2) production facilities in California. The purpose is to provide a fact-base to support policy decisions and inform stakeholders. The analysis includes demand projections, forecasts of technology progress, supply chain costs and temporal and spatial facility siting scenarios. The work places specific focus on lessons from early project activity and projection through 2030 with higher level forecasts through 2050. The work concludes with research needs and policy recommendations to successfully launch and scale the California renewable hydrogen sector. The overall conclusion is that, with appropriate policy support, the renewable hydrogen sector can reach self-sustainability (price point at parity with conventional fuel on a fuel-economy adjusted basis) by the mid to late 2020s.

Abstract

Currently, prediction of trip-based electricity consumption of electric buses (EBs) has become an important prerequisite for the deployment of large-scale electric bus fleets and the location of the charging infrastructures. Previous state-of-the-art approaches to estimate the electricity consumption focus on making rough electricity consumption assumptions or building physics-based electricity consumption model. This paper constructed a neural network model to predict the trip-based electricity consumption of EBs and six influencing factors were taken as input variables. Further, sensitivity analyses were performed to investigate how these factors influence the consumption results. This model was implemented and validated on real-world electric bus data from a five-month consecutive collection in Shenzhen, China, comprising 1024 EBs. The experiment demonstrated the predictive effectiveness of this model and the results from sensitivity analyses show that trip length is the key factor to determine the consumption, but other factors average travel speed, the number of bus stops and traffic lights, direction, time parameters also have different level of impacts on the results.

Abstract

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.

Abstract

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.

Abstract

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.

Abstract

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.

Abstract

Liquid fossil fuels (1) enable transportation and (2) provide energy for mobile work platforms and (3) supply dispatchable energy to highly variable demand (seasonal heating and peak electricity). We describe a system to replace liquid fossil fuels with drop-in biofuels including gasoline, diesel and jet fuel. Because growing biomass removes carbon dioxide from the air, there is no net addition of carbon dioxide to the atmosphere from burning biofuels. In addition, with proper management, biofuel systems can sequester large quantities of carbon as soil organic matter, improving soil fertility and providing other environmental services. In the United States liquid biofuels can potentially replace all liquid fossil fuels. The required system has two key features. First, the heat and hydrogen for conversion of biomass into high-quality liquid fuels is provided by external low-carbon energy sources–nuclear energy or fossil fuels with carbon capture and sequestration. The potential quantities of liquid biofuels are much smaller if biomass is used as (1) the carbon feedstock and (2) the source of energy for the conversion process. Using external energy inputs can almost double the energy content of the liquid fuel per unit of biomass feedstock by fully converting the carbon in biomass into a hydrocarbon fuel. Second, competing effectively with fossil fuels requires very large biorefineries—the equivalent of a 250,000 barrel per day oil refinery. This requires commercializing methods for converting local biomass into high-density storable feedstocks that can be economically shipped to large-scale biorefineries. Large-scale biorefineries also enable efficient coupling of nuclear reactors to the biorefinery.

Abstract

For the past five years, the Department of Energy’s Co-Optima program has explored biomass-derived blendstocks with fuel properties that boost the efficiency of engines, seeking to enable technology for fuel-engine co-optimization. Past analysis quantified benefits of introducing co-optimized fuels and engines for light-duty vehicles with the core assumption that efficiency gains would be the same for vehicles with and without hybridized power trains. Vehicles with hybridized powertrains, however, could experience a different energy efficiency change than conventional vehicles, which could be a decrease, if the blended fuel is not tailored for their operation, or an increase, if the hybrid engine’s operational conditions take better advantage of the blended fuel. Therefore, this study examines opportunities to reduce the environmental effects of light-duty transportation when fuel properties are tailored to the unique needs of hybrid electric and plug-in hybrid electric (HEV, PHEV) vehicles to improve their engine efficiency. The analysis tracks greenhouse gas emissions reductions on a well-to-wheels basis when co-designed fuels and engines for vehicles with hybridized power trains are introduced into the market. Engine efficiency gains and incremental vehicle cost are key parameters in the analysis as we seek fuel-engine technology that will significantly boost overall vehicle efficiency at a price point that is commercially viable. Twelve co-deployment scenarios were generated based on 3 different levels of engine efficiency improvement (8% ,10% and 12%) and 4 level incremental costs ($100, $250, $500 and $1000) and the corresponding environmental effects are tracked as the technologies gain market adoption. The preliminary results show that the effect of incremental cost and efficiency gain on vehicle sales indicates that adoption of co-optimized HEV, and PHEVs are relatively insensitive to incremental vehicle purchase costs up to $250. In addition, the results indicate higher adoption of co-optimized HEVs at $100 and $250 price increase and 12% efficiency gain while the adoption of HEVs and PHEVs across other scenarios remain consistent. From the best-case scenario ($100, vehicle price increase and 12% engine efficiency increase), the result shows that using biofuels with tailored properties and advanced engines to achieve an increase hybridized engine efficiency could translate to 17.5% reduction in greenhouse gas emissions from the light duty vehicle fleet including non-hybridized vehicles in 2050.