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Abstract A high temperature-proton exchange membrane (HT-PEMFC)-based micro-combined-heat-and-power (CHP) residential system is designed and optimized, using a genetic algorithm (GA) optimization strategy. The proposed system consists of a fuel cell stack, steam methane reformer (SMR) reactor, water gas shift (WGS) reactor, heat exchangers, and other balance-of-plant (BOP) components. The objective function of the single-objective optimization strategy is the net electrical efficiency of the micro-CHP system. The implemented optimization procedure attempts to maximize the objective function by variation of nine decision variables. The value of the objective function for the optimum design configuration is significantly higher than the initial one, with a 20.7% increase.

Major greenhouse gas (GHG) emissions related to plastic waste recycling were evaluated with respect to three management alternatives: recycling of clean, single-type plastic, recycling of mixed/contaminated plastic, and use of plastic waste as fuel in industrial processes. Source-separated plastic waste was received at a material recovery facility (MRF) and processed for granulation and subsequent downstream use. In the three alternatives, plastic was assumed to be substituting virgin plastic in new products, wood in low-strength products (outdoor furniture, fences, etc.), and coal or fuel oil in the case of energy utilization. GHG accounting was organized in terms of indirect upstream emissions (e.g. provision of energy, fuels, and materials), direct emissions at the MRF (e.g. fuel combustion), and indirect downstream emissions (e.g. avoided emissions from production of virgin plastic, wood, or coal/oil). Combined, upstream and direct emissions were estimated to be roughly between 5 and 600 kg CO2-eq. tonne —1 of plastic waste depending on treatment at the MRF and CO2 emissions from electricity production. Potential downstream savings arising from substitution of virgin plastic, wood, and energy fuels were estimated to be around 60— 1600 kg CO2-eq. tonne —1 of plastic waste depending on substitution ratios and CO2 emissions from electricity production. Based on the reviewed data, it was concluded that substitution of virgin plastic should be preferred. If this is not viable due to a mixture of different plastic types and/or contamination, the plastic should be used for energy utilization. Recycling of plastic waste for substitution of other materials such as wood provided no savings with respect to global warming.

Abstract With the increasing access of renewable energy resources and fast ubiquitous connection of everything, the traditional one-way power flow from centralized generation to end consumers will give way to bidirectional-way power flow with multidirectional energy network among central grids and distributed prosumers. To empower the prosumer-centric Energy Internet (EI) and enhance the integration of energy-aware services, digitalization and decentralization are the key enablers to achieve transactive EI. This article presents a systematic overview on how Internet of Things (IoT) drives the digitalization of transactive EI and how blockchain empowers the decentralization of transactive EI. A comprehensive discussion on the key infrastructures is provided for presenting how to implement digitalization and decentralization of transactive EI, including the last mile “Advanced metering infrastructure” (AMI), renewables integrator “smart inverter”, energy flow adjuster “energy router”, and coordinator “Microgrid”. Challenges and future trends are discussed from an extensive point of view, including energy physical space, data cyber space and human social space.

The smart grid is promoted as one of the key elements in a low-carbon transition in many countries. In Denmark, the dominant framing of the smart grid emphasises the challenge of integrating much more wind power into the electricity system and using electricity for heating (heat pumps) and transport (electric cars). In the process of radically transforming the electricity system, strategic system builders need to align many forces, including consumers, who play an important role in the functioning of such large networked systems. System builders need to explore, for instance, whether and how users can be motivated to be flexible in relation to moving electricity consumption over time. This paper reports on one of the first smart-grid-related projects in Denmark in which consumer aspects have been central and where potentials for flexible electricity consumption have been tested. The aim of the paper is to explore what can be learned from such experiments and which roles they play in the construction of the smart grid. In this context, the concept of the ‘aligned user’ is introduced.

Did California's great "deregulation" experiment fail? Was it flawed in the first instance as most economists argue? Or was the deregulation of a public "good" (such as energy) and as such a civic "trust"? What role does public policy play in economic decisions? No matter what the opinions about the causes of the energy crisis, the result is the same the crisis has created a "challenge" for all 34 million Californians. In fact, the challenge is for all US citizens, as it is in other countries as well. The reasons are clear: can energy, like water, waste or the environment, be subject to market forces? Or are these sectors qualitatively different from telecom, transportation, or manufacturing sectors? California has had to confront this basic issue directly since the energy crisis erupted in the summer of 2000. The actual causes of the energy crisis may never be really uncovered even after protracted lawsuits, but three issues became clear in the "challenge": understanding that a "higher" public good, hence a role for government in certain infrastructure sectors such as energy, exists; second, leaving such public good infrastructures to the "free market" is both naive economics and flawed logic - the fact that only a few power generation companies control the flow of energy into California demonstrates the faculty of free markets equals more competition; and finally, California has embarked on a journey with immeasurable consequences. For the first time in modern history, a nation's state must take control of its own destiny. Sustainable development will now be defined over the next few years of the New Millennium. The paper will focus on the economic and business issues surrounding energy with specific recommendations on "sustainable development" drawn from the California challenge.

Many distribution systems nowadays have significant penetration of distributed generation (DG) and thus, islanding operation of these distribution systems is becoming a viable option for economical and technical reasons. The DG should operate optimally during both grid-connected and island conditions, which can be achieved with change in operating strategy. Many islanding detection techniques have been developed but little work has been done to detect grid re-connection. This paper presents strategies to operate DG in grid connected and islanded modes and a new grid re-connection detection algorithm, which uses average rate of change of frequency (Af5) and real power shift (RPS), in the islanded mode. RPS will increase or decrease the power set point of the generator with increasing or decreasing system frequency, respectively. Simulation results show that the proposed method can operate the DG efficiently and is effective in detecting grid-reconnection.

The models currently used in computational fluid dynamics codes to predict solid fuel combustion rely on a spherical shape assumption. Cylinders and disks represent a much better geometrical approximation to the shape of bio-fuels such as straws and woods chips. A sphere gives an extreme in terms of the volume-to-surface-area ratio, which impacts both motion and reaction of a particle. For a nonspherical particle, an additional lift force becomes important, and generally hydrodynamic forces introduce a torque on the particle as the centre of pressure does not coincide with the centre of mass. Therefore, rotation of a nonspherical particle needs to be considered. This paper derives a model for tracking nonspherical particles in a nonuniform flow field, which is validated by a preliminary experimental study: the calculated results agree well with measurements in both translation and rotation aspects. The model allows to take into account shape details of nonspherical particles so that both the motion and the chemical reaction of particles can be modelled more reasonably. The ultimate goal of such a study is to simulate flow and combustion in biomass-fired furnaces using nonspherical particle tracking model instead of traditional sphere assumption, and thus improve the design of biomass-fired boilers.