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Abstract In this paper, an open source tool is introduced to represent urban energy infrastructure in the City of Philadelphia, and different renewable energy scenarios are compared with respect to minimization of the standard deviation of the residual load. Renewable energy sources play a critical role in the world’s ongoing energy transition in response to climate change. Urban Energy Systems may be particularly sensitive to this transition due to the high energy demand density associated with urban environments. Open energy analysis and modeling tools can provide important information that can be used by urban energy planners, policy makers, and other stakeholders during this transition. In the present study, we apply FlexiGIS, an open energy modeling tool developed in a European context, to a case study in the City of Philadelphia. Due to the importance of open access to energy data, we pay particular attention to open energy data sources. Notably, OpenStreetMap was incomplete in its spatial coverage, but alternate open data resources were identified. This work conducts an optimization of the renewable energy mix to minimize the amount of balancing energy required for the residual load. We observe that Philadelphia has an optimal mix of renewables that favors a roughly even share of wind and solar, but that, compared to a previous case study in Oldenburg, Germany, requires more balancing energy at comparable levels of renewable penetration.

With the rapidly growing interest in bifacial photovoltaics (PV), a worldwide map of their potential performance can help assess and accelerate the global deployment of this emerging technology. However, the existing literature only highlights optimized bifacial PV for a few geographic locations or develops worldwide performance maps for very specific configurations, such as the vertical installation. It is still difficult to translate these location- and configuration-specific conclusions to a general optimized performance of this technology. In this paper, we present a global study and optimization of bifacial solar modules using a rigorous and comprehensive modeling framework. Our results demonstrate that with a low albedo of 0.25, the bifacial gain of ground-mounted bifacial modules is less than 10% worldwide. However, increasing the albedo to 0.5 and elevating modules 1 m above the ground can boost the bifacial gain to 30%. Moreover, we derive a set of empirical design rules, which optimize bifacial solar modules across the world, that provide the groundwork for rapid assessment of the location-specific performance. We find that ground-mounted, vertical, east-west-facing bifacial modules will outperform their south-north-facing, optimally tilted counterparts by up to 15% below the latitude of 30 degrees, for an albedo of 0.5. The relative energy output is the reverse of this in latitudes above 30 degrees. A detailed and systematic comparison with experimental data from Asia, Europe, and North America validates the model presented in this paper. An online simulation tool (https://nanohub.org/tools/pub) based on the model developed in this paper is also available for a user to predict and optimize bifacial modules in any arbitrary location across the globe.

Abstract Performance of an improved design for storage-type domestic electrical water-heaters (EWHs) was experimentally investigated for energy conservation. The results were compared with those of conventional design EWHs having the same tank size and power rating. Data were obtained for two tanks with aspect ratios of 1 and 2, two draw-off rates of 5 and 10 l/min, and using three heating elements of different heights. It is found that improved design EWHs provide more hot water at almost constant temperature in the first mean residence time, which is of prime concern for the user. Thus, they exhibit higher discharging efficiencies due to better thermal stratification inside the heater storage tank. Also, thermal performance is enhanced with increasing tank aspect ratio and decreasing draw rate. These characteristics have a direct impact on energy consumption and result in lower electricity bills. The design improvements are simple to adapt as they only require minor modifications to be made to existing EWH models.

Abstract Implementation of carbon nanotubes (CNTs) in various applications can reduce material and energy requirements of products, resulting in energy savings. However, processes for the production of carbon nanotubes (CNTs) are energy-intensive and can require extensive purification. In this study, we investigate the net energy benefits of three CNT-enabled technologies: multi-walled CNT (MWCNT) reinforced cement used as highway construction material, single-walled CNT (SWCNT) flash memory switches used in cell phones and CNT anodes and cathodes used in lithium-ion batteries used in electric vehicles. We explore the avoided or additional energy requirement in the manufacturing and use phases and estimate the life cycle net energy benefits for each application. Additional scenario analysis and Monte Carlo simulation of parameter uncertainties resulted in probability distributions of net energy benefits, indicating that net energy benefits are dependent on the application with confidence intervals straddling the breakeven line in some cases. Analysis of simulation results reveals that SWCNT switch flash memory and MWCNT Li-ion battery cathodes have statistically significant positive net energy benefits ( α = 0.05) and SWCNT Li-ion battery anodes tend to have negative net energy benefits, while positive results for MWCNT-reinforced cement were significant only under an efficient CNT production scenario and a lower confidence level ( α = 0.1).

Abstract This paper proposes the theoretical model and experimental investigations of a broadband piezoelectric based vibration energy harvester with a triple-well potential induced by a magnetic field. The mathematical model is derived from the energy method to describe the response characteristics of nonlinear tristable energy generators. The parameters of the linear energy harvesting system without magnetic force actuation are obtained through intelligent optimization of the minimum error between numerical simulations and experimental responses. The equivalent nonlinear restoring force of the tristable oscillator is experimentally identified as a high order polynomial. Numerical simulations and experiments are performed at different harmonic excitation levels ranging from 1 to 20 Hz. The results verify that the identified electromechanical model can describe the dynamic characteristics of broadband tristable energy harvesters. Furthermore, in comparison to bistable nonlinear energy oscillators with deeper potential well, the tristable arrangement passes easily through potential wells for generating higher energy output over a wider range of frequency.

Abstract The present study is concerned with dynamic simulation of thermal-lag Stirling engines. A dynamic model is built and incorporated with a thermodynamic model to study the engine start process. A prototype engine is designed and simulated by using the dynamic model. In the simulation, different operating modes, including rotating mode, swinging mode, swinging-to-rotate mode, and swinging-to-decay mode, have been observed. The rotating mode is desired and can be achieved if the operating parameters are properly designed. In a poor design, the engine may switch to the swinging or even the swinging-to-decay mode. In addition, it is found that geometric parameters, such as bore size, stroke, and volume of working spaces, also determine the operating mode of the engine. Brake thermal efficiency of the engine is monotonically reduced by increasing engine speed. However, study of the dependence of the shaft power of the engine speed shows that there exists a maximum value of the shaft power at an optimal operating engine speed. The optimal engine speed leading to maximum shaft power is significantly influenced by the geometrical parameters.

Abstract In the United States, natural gas-fired generators gained increasing popularity in recent years due to the low fuel cost and emission, as well as the proven large gas reserves. Consequently, the highly interdependency between the gas and electricity networks is needed to be considered in the system operation. To improve the overall system operation and optimize the energy flow, an interval optimization based coordinated operating strategy for the gas-electricity integrated energy system (IES) is proposed in this paper considering demand response and wind power uncertainty. In the proposed model, the gas and electricity infrastructures are modeled in detail and their operation constraints are fully considered, wherein the nonlinear characteristics are modeled including pipeline gas flow and compressors. Then a demand response program is incorporated into the optimization model and its effects on the IES operation are investigated. Based on interval mathematics, wind power uncertainty is represented as interval numbers instead of probability distributions. A case study is performed on a six-bus electricity network with a seven-node gas network to demonstrate the effectiveness of the proposed method; further, the IEEE 118-bus system coupling with a 14-node natural gas system is used to verify its applicability in practical bulk systems.