Energy Demand Fluctuations Research Articles

PRELIMINARY EVALUATION TOOLS FOR WIND-PUMPED STORAGE ENERGY GENERATION SYSTEM

Energy demand never ceases to increase with larger cities, urbanization and migration to the cities. However, supplying the remaining and important rural areas with electricity remains costly. Exploring the off-grid energy generation is therefore a promising solution. After an exhaustive qualitative evaluation on different energy generation system, this study has chosen the Wind-Pumped Storage Hybrid (WPSH) system to be evaluated. A simulation tool was built to take the wind energy and convert it into pumping power to store water in a reservoir that will supply a hydro-turbine, generating electricity to a domestic area. A preliminary evaluation was done in Kajang for a selected day of July 20 2020. The result shows that the wind fluctuations and energy demand fluctuations affect the WPSH system’s capability to deliver sufficient energy through 24 hours. During the day, the amount of water accumulated in the reservoir is insufficient to meet the energy demand. It is only after 7.00 p.m that the system will be able to meet the demand and reserve a surplus of water in the reservoir.Keywords: renewable energy, wind-pumped storage, hybrid energy generation, wind power, evaluation tools

Drivers behind Residential Electricity Demand Fluctuations Due to COVID-19 Restrictions

The COVID-19 pandemic rapidly reoriented the lives of billions of people across the globe toward working, learning, and subsisting from home. This paper examines the consequences of this disruption of electricity use in Australian households. Using high-frequency electricity monitoring from 491 houses and per-circuit monitoring and in-depth interviews with 17 households, the paper (1) compares changes in energy use before and during COVID-19 lockdown, (2) quantifies the key drivers of changes in energy use experienced by households during lockdown, and (3) tracks households’ interactions with energy use feedback. The findings identify significant increases in certain aspects of household electricity use directly related to COVID-19, including increased cooking and digital device use. Yet despite the government mandate requiring a large proportion of the population to remain at home, overall energy use among the majority of Queensland households monitored actually decreased during lockdown versus prior, driven primarily by a reduction in air conditioner use during lockdown as the weather cooled. Further, despite significant quantified and self-reported changes in energy use, users who had energy use feedback installed accessed their dashboards less during lockdown than they did prior. The paper discusses these results in the context of statistics on COVID-19 related energy demand fluctuations elsewhere, and the implications for the provision of energy use information to residents during significant disruptions such as lockdown.

Hydropeaking Operations of Two Run-of-River Mega-Dams Alter Downstream Hydrology of the Largest Amazon Tributary

© Copyright © 2020 Almeida, Hamilton, Rosi, Barros, Doria, Flecker, Fleischmann, Reisinger and Roland. Large storage dams have widely documented impacts on downstream aquatic environments, but hydroelectric dams with little or no capacity for storage of water inflows (i.e., run-of-river) have received less attention. Two of the world’s largest run-of-river hydropower dams (Jirau and Santo Antonio, Brazil) are located on the Madeira River, the largest tributary to the Amazon River. Here we examine whether the Madeira dams have affected downstream seasonal flood pulses and short-term (daily and sub-daily) flow dynamics. We show that the combined effects of these dams on seasonal flood pulses were modest. However, dam operations significantly increased day-to-day and sub-daily flow variability. The increase in short-term flow variability is largely explained by rapid, short-term variations in river flow caused by fluctuations in energy demand (hydropeaking). Both the magnitude of hydropeaking and the mean absolute day-to-day change in discharge downstream of the dams doubled after dam closure. In addition, the median hourly rate of water level change downstream of the dams was three times higher than upstream. Our findings highlight that even run-of-river dams on very large rivers such as the Madeira—whose average discharge at the dam site is larger than that of the Mississippi River at its mouth—can alter downstream hydrology through hydropeaking. Although little studied in tropical floodplain rivers, hydropeaking by large run-of-river dams may be detrimental to downstream aquatic organisms and human populations that utilize the river for navigation and fisheries.

Multilevel Interactions of Stress and Circadian System: Implications for Traumatic Stress.

The dramatic fluctuations in energy demands by the rhythmic succession of night and day on our planet has prompted a geophysical evolutionary need for biological temporal organization across phylogeny. The intrinsic circadian timing system (CS) represents a highly conserved and sophisticated internal “clock,” adjusted to the 24-h rotation period of the earth, enabling a nyctohemeral coordination of numerous physiologic processes, from gene expression to behavior. The human CS is tightly and bidirectionally interconnected to the stress system (SS). Both systems are fundamental for survival and regulate each other’s activity in order to prepare the organism for the anticipated cyclic challenges. Thereby, the understanding of the temporal relationship between stressors and stress responses is critical for the comprehension of the molecular basis of physiology and pathogenesis of disease. A critical loss of the harmonious timed order at different organizational levels may affect the fundamental properties of neuroendocrine, immune, and autonomic systems, leading to a breakdown of biobehavioral adaptative mechanisms with increased stress sensitivity and vulnerability. In this review, following an overview of the functional components of the SS and CS, we present their multilevel interactions and discuss how traumatic stress can alter the interplay between the two systems. Circadian dysregulation after traumatic stress exposure may represent a core feature of trauma-related disorders mediating enduring neurobiological correlates of trauma through maladaptive stress regulation. Understanding the mechanisms susceptible to circadian dysregulation and their role in stress-related disorders could provide new insights into disease mechanisms, advancing psychochronobiological treatment possibilities and preventive strategies in stress-exposed populations.

Quantification of energy flexibility of residential net-zero-energy buildings involved with dynamic operations of hybrid energy storages and diversified energy conversion strategies

Abstract For immediate response and sufficient reaction to building energy demands by avoiding excessive production, increasing stability of energy networks, and minimising energy congestion, building energy flexibility has potentials to enhance the resilience of hybrid grids to fluctuations in energy demands of multi-energy systems. However, few studies focused on dealing with the complexity of energy flexibility quantification regarding diversified energy conversions and hybrid energy storages. Moreover, few studies focused on the exploitation of energy potential provided by building energy systems itself through flexible energy control strategy. In this study, a generic methodology was proposed to characterise energy flexibility of diversified energy systems. A series of new flexibility indicators are proposed such as flexible power, flexible electricity, on-site flexible electric load fraction, on-site flexible surplus renewable fraction ratio, and flexibility factors. Technical solutions are proposed to improve the energy flexibility using integrated solutions of energy conversion, energy storage, and rule-based control strategies. Case studies with different control strategies (i.e. “battery-to-demand control strategy” and “renewable-to-demand control strategy”) are studied for the technical viability assessment. This study provides a generic methodology to characterise the energy flexibility regarding sophisticated building energy systems, and a rule-based control strategy for the flexibility enhancement, which will be effective in the promotion of energy flexible buildings.

A case study on solar, wind and hydro energy resource potential of Prizren region in Kosovo

Prizren is a city located in the south part of Kosovo with approximately 90,000 inhabitants and land area of 640 km2. The region is covered with distinct geographical features, that favor penetration and deployment of various forms of renewable energy. Particularly, solar, wind and hydro energy potential are considered to be the most available options here. In this study, the potential of these renewable energy sources and their viability for energy production are evaluated using a computational modeling tool. The potential investment opportunities are analyzed based on a 50-year life time project. The results suggest that integrating renewable energy to the existing energy system will enable Prizren region and partly the entire Kosovo for coping with load fluctuations in energy demand. Also, it is expected that the added renewable energy in the existing energy mix will, in a broad perspective, lead to meet the European Union’s target of accelerated renewable energy penetration by the year 2030, and in turn to reduce the greenhouse gas emission to the environment.

Estimation of time series urban energy demand and Examination of optimal energy supply system

From the background of the liberalization of electricity and city gas retail market, it is considered that in the future Japan will move to a distributed supply form from each building and household. In order to properly place and operate this decentralized supply facility in the city, knowledge of time-series demand fluctuation in urban scale is necessary, but since there is no data or estimation method corresponding to this, it is necessary to develop one.In this research, we first developed a program to estimate the energy demand fluctuation at five-minute intervals of non-residential buildings in urban scale into four energy applications (electricity, cooling, heating, and hot water supply). First, we acquire the building information (usage, extended floor, and coordinates) of the target city by GIS (Geographic Information System) data. Based on this data, we predict the demand fluctuation by building as a reference. By distributing the value, using probability density based on statistical and measurement data, we reproduced the variation of demand due to the difference of building characteristics which cannot be obtained via GIS data. We estimate the demand fluctuation for a city by integrating the building-specific demand fluctuation estimation values.In this paper, the calculation was carried out using a program for Fukuoka city, Tenjin and Hakata districts, and the estimation result was compared and verified.Based on the data obtained by the urban energy demand estimation program, we will consider optimal placement and operation methods of distributed supply equipment typified by PV panel, cogeneration, and storage battery. By flagging the presence or absence of equipment for each building and calculating it, we compared and examined the amount of energy reduction in each pattern.

Improving the energy sustainability of a Swiss village through building renovation and renewable energy integration

The integration of renewable energy technologies and building renovation are the two main procedures for improving energy sustainability of buildings at neighborhood scale. It is difficult, however, to optimize these procedures simultaneously. This study focuses on improving energy sustainability of Hemberg, a Swiss village with a population of about 900, through optimizing these two procedures. For this purpose a computational platform was developed, combining software CitySim, HOMER Pro, QGIS and Rhinoceros. The energy demand on hourly basis for the buildings in the village was analyzed through comparing the current demand with that after retrofitting according to the Swiss energy labels (i) Minergie and (ii) Minergie-P. Swiss energy maps were used to identify the most promising renewable energy sources while three scenarios were considered for solar PV integration and energy system improvements. The first scenario presents the current condition in the village, while the second scenario explores improvements in electricity generation and the third in both electricity and heat generation. The results show that retrofitting of all buildings according to Minergie reduces the space heating demand by 70–85% and reduces the fluctuations in energy demand, thereby allowing the integration of more renewable energy. According to the simulations, building-integrated solar PV panels can cover the total annual energy demand of the village when considering the Minergie and Minergie-P scenarios. However, the energy system assessment shows that it is difficult to reach beyond 60% when integrating non-dispatchable renewable energy technologies. Finally, and more importantly, integration of wind energy at system level has an important impact in the hub.

The Warburg effect as an adaptation of cancer cells to rapid fluctuations in energy demand.

To maintain optimal fitness, a cell must balance the risk of inadequate energy reserve for response to a potentially fatal perturbation against the long-term cost of maintaining high concentrations of ATP to meet occasional spikes in demand. Here we apply a game theoretic approach to address the dynamics of energy production and expenditure in eukaryotic cells. Conventionally, glucose metabolism is viewed as a function of oxygen concentrations in which the more efficient oxidation of glucose to CO2 and H2O produces all or nearly all ATP except under hypoxic conditions when less efficient (2 ATP/ glucose vs. about 36ATP/glucose) anaerobic metabolism of glucose to lactic acid provides an emergency backup. We propose an alternative in which energy production is governed by the complex temporal and spatial dynamics of intracellular ATP demand. In the short term, a cell must provide energy for constant baseline needs but also maintain capacity to rapidly respond to fluxes in demand particularly due to external perturbations on the cell membrane. Similarly, longer-term dynamics require a trade-off between the cost of maintaining high metabolic capacity to meet uncommon spikes in demand versus the risk of unsuccessfully responding to threats or opportunities. Here we develop a model and computationally explore the cell’s optimal mix of glycolytic and oxidative capacity. We find the Warburg effect, high glycolytic metabolism even under normoxic conditions, is represents a metabolic strategy that allow cancer cells to optimally meet energy demands posed by stochastic or fluctuating tumor environments.

Demonstration of reusing electric vehicle battery for solar energy storage and demand side management

This paper demonstrated reusing electric vehicle traction lithium ion batteries for solar energy time shifting and demand side management in a single family house. Batteries retired from electric vehicle usage retain 70% to 80% of their capacity and can be re-purposed as stationary storage system at reduced cost. However, they have mismatched aging conditions and unbalanced state-of-charge levels. Under typical series-parallel connection, the cells in a pack are prone to over charging or discharging due to deviated cycling conditions and misestimated states. The demonstrated battery management system included an extended Kalman filter based states estimator, enhanced current shunting, and protective circuitry to ensure system safety. One novel contribution was the introduction of a worst-difference state-of-charge estimation scheme for the battery pack, which places more computational resources on the battery cell of the worst health. The scheme provided satisfactory overall estimation accuracy and offered a method to optimize computational cost when large number of battery cells was integrated. In addition, a function was proposed to indicate the overall states of the entire energy storage system by aggregating the states of the battery cells within. Therefore, the energy management unit was able to dispatch the battery assembly as a unified pack. Three decision-table-based control strategies were demonstrated with objectives to maximize economic benefits, minimize grid energy consumption, or a balance of both. The data obtained from the demonstrating system located in Davis, CA showed that the battery energy storage system was able to successfully mitigate solar intermittency and energy demand fluctuation by charging from excess solar energy and discharging during the period of peak demand. It reduced daily grid energy consumption by 64%–100% and significantly improved solar penetration.

Generalized Analytical Approach to Assess Reliability of Renewable-Based Energy Hubs

This paper proposes a generalized analytical approach to evaluate the reliability of active distribution networks. The studies are implemented in the context of renewable-based energy hubs. The reliability of energy demands is determined as a function of reliability characteristics of energy hub input resources and converters as well as hub operating strategies. The framework proposed in this paper involves the main attributes of different distributed generation technologies as well as vehicle-to-grid (V2G)-capable vehicles in the reliability studies. Dealing with the uncertainty in energy services provided by the wind turbine output generation and V2G programs, efficient probabilistic methods are presented to attain the reliability models of these energy resources for the studies. The fluctuations in energy demands are also represented through multistate analytical models. Convolving the probabilistic models of energy hub resources by the load profiles’ models, different reliability indices are calculated taking into consideration possible operating strategies of the energy hubs. Effectiveness of the proposed methodology is validated using extensive numerical studies on an energy hub and the obtained results demonstrate its applicability in adequacy studies of active energy networks.

Circadian regulation of cardiovascular and kidney function.

Video slideshow introduction to the symposium by symposium organiser David Pollock can be found here.

Regional energy demand in Japan: dynamic shift-share analysis

To investigate the future trends of energy demand in Japan accurately, it is necessary to clarify the factors that determine the fluctuations in energy demands across regions. Specifically, it is necessary to clarify whether the energy demand fluctuations across regions arise from compositional factors, that is, differences in energy users, or from regionally unique factors. This study analyzes the determinants of energy demand change to clarify the factors that have affected the fluctuations in regional energy demands in Japan, using dynamic shift-share analysis. The results show that the energy demand fluctuations can be explained by compositional effects and regional effects. With regard to the compositional effects, the energy demand growth increased most remarkably in the regions that specialize in residential and commercial activities. However, energy demand did not increase in the regions that specialize in manufacturing activities. With respect to the regional effects, there were constraints on energy demand in big-city regions because of the improved energy intensity achieved through energy conservation. The results imply that having a mixture of industry and civil sector activities in a region potentially flattens out the fluctuations in energy demand changes. This finding suggests that when moderating the change of regional energy demand, it is important to diversify the industrial structure in each region.

Assessing Buildings Hourly Energy Needs for Urban Energy Planning in Southern European Context

For decreasing the fossil fuels consumption and reducing air pollution at urban level, current policies encourage a transition to distributed energy generation (DG) and support initiatives towards district heating and cooling networks (DES - district energy systems), promoting the integration of renewable energy sources (RES). Based on these approaches, the assessment of the energy demand fluctuations of the building stock is preliminary for energy planning at district scale, since systems’ operation requires a complex balancing for maximizing the efficiency or minimizing the cost, combining the intermittent nature of RES (except biomasses) with non-RES and/or storage technology. Surveyed literature concerning recent studies aimed at optimizing district energy scenarios revealed that most of the assessment are limited to the seasonal and/or annual based buildings energy needs, while the ones that deal with a proper time scale (i.e. hourly based) refer to specific case studies, which are hardly replicable in other urban contexts. The purpose of the study presented in this paper was to provide reliable reference profiles of buildings thermal energy needs (for both space heating and cooling) with reference to the Italian context. Therefore, a set of building models, representative of typical solutions of different historical periods, was defined for both residential and diffuse tertiary (offices) use. Once elaborated accurate hourly internal loads curves, it was possible to provide, performing detailed simulations with TRNSYS model, profiles of energy need density, referred to cubic meter of building volume, for typical buildings placed in different climatic locations, covering the wide range of Italian context. Based on both the building typologies and the climatic variability considered, assumptions adopted for the study could be extended to other comparable context in southern Europe.

Microclimatic performance of a free-air warming and CO2 enrichment experiment in windy Wyoming, USA.

In order to plan for global changing climate experiments are being conducted in many countries, but few have monitored the effects of the climate change treatments (warming, elevated CO2) on the experimental plot microclimate. During three years of an eight year study with year-round feedback-controlled infra-red heater warming (1.5/3.0°C day/night) and growing season free-air CO2 enrichment (600 ppm) in the mixed-grass prairie of Wyoming, USA, we monitored soil, leaf, canopy-air, above-canopy-air temperatures and relative humidity of control and treated experimental plots and evaluated ecologically important temperature differentials. Leaves were warmed somewhat less than the target settings (1.1 & 1.5°C day/night) but soil was warmed more creating an average that matched the target settings extremely well both during the day and night plus the summer and winter. The site typically has about 50% bare or litter covered soil, therefore soil heat transfer is more critical than in dense canopy ecosystems. The Wyoming site commonly has strong winds (5 ms-1 average) and significant daily and seasonal temperature fluctuations (as much as 30°C daily) but the warming system was nearly always able to maintain the set temperatures regardless of abiotic variation. The within canopy-air was only slightly warmed and above canopy-air was not warmed by the system, therefore convective warming was minor. Elevated CO2 had no direct effect nor interaction with the warming treatment on microclimate. Relative humidity within the plant canopy was only slightly reduced by warming. Soil water content was reduced by warming but increased by elevated CO2. This study demonstrates the importance of monitoring the microclimate in manipulative field global change experiments so that critical physiological and ecological conclusions can be determined. Highly variable energy demand fluctuations showed that passive IR heater warming systems will not maintain desired warming for much of the time.

MULTI-OBJECTIVE OPTIMISATION IN CARBON MONOXIDE GAS MANAGEMENT AT TRONOX KZN SANDS

Carbon monoxide (CO) is a by-product of the ilmenite smelting process from which titania slag and pig iron are produced. Prior to this project, the CO at Tronox KZN Sands in South Africa was burnt to get rid of it, producing carbon dioxide (CO 2 ). At this plant, unprocessed materials are pre-heated using methane gas from an external supplier. The price of methane gas has increased significantly; and so this research considers the possibility of recycling CO gas and using it as an energy source to reduce methane gas demand. It is not possible to eliminate the methane gas consumption completely due to the energy demand fluctuation, and sub-plants have been assigned either CO gas or methane gas over time. Switching the gas supply between CO and methane gas involves production downtime to purge supply lines. Minimising the loss of production time while maximising the use of CO arose as a multi-objective optimisation problem (MOP) with seven decision variables, and computer simulation was used to evaluate scenarios. We applied computer simulation and the multi-objective optimisation cross-entropy method (MOO CEM) to find good solutions while evaluating the minimum number of scenarios. The proposals in this paper, which are in the process of being implemented, could save the company operational expenditure while reducing the carbon footprint of the smelter.

The optimal selection of on-site CHP systems through integrated sizing and operational strategy

Achievable outcomes of the combined heat and power (CHP) system applications are subject to several factors. In this study the value of integrated system sizing and operational strategy selection has been evaluated. This would facilitate maximum return on investment as well as reducing primary energy resource consumption and environmental impact. The required model improvements are identified and applied, which will encompass the transient characteristics of the CHP system components and their true operational constraints in a more realistic manner. In addition, the proposed methodology is generic enough to cover energy demand fluctuations of any existing manufacturing plant by aggregated data integration to guarantee improved on-site energy generation system outcomes. Finally the proposed methodology is applied to a pharmaceutical manufacturing plant. The results illustrate promising potential improvements in comparison with existing approaches for CHP system configurations.

Multi-objectives, multi-period optimization of district energy systems: II—Daily thermal storage

District heating is an efficient way of providing heat to urban areas. The use of storage tanks integrated with district heating network would permit to increase the annual utilization of base load equipment, avoiding over estimation of the size of backup equipment, and balancing the energy demand fluctuation during day and night.In the present work a multi-objective optimization model for sizing and operation optimization of district heating systems with heat storage tanks is presented. The model includes process design and energy integration techniques for optimizing the temperature intervals, the volume and the operation strategy of thermal storage tanks.The proposed model is demonstrated by means of two test cases. Results show that the efficiency, environmental impacts and total costs of an urban system can be improved after integrating the thermal storage by 4.7%, 5% and 2% respectively.

Fires at storage sites of organic materials, waste fuels and recyclables

During the last decade, the European Union has enforced the diversion of organic wastes and recyclables to waste management companies operating incineration plants, composting plants and recycling units instead of landfills. The temporary storage sites have been established as a buffer against fluctuations in energy demand throughout the year. Materials also need to be stored at temporary storage sites before recovery and recycling. However, regulations governing waste fuel storage and handling have not yet been developed, and, as a result, companies have engaged in risky practices that have resulted in a high number of fire incidents. In this study, a questionnaire survey was distributed to 249 of the 400 members of Avfall Sverige (Swedish Waste Management Association), which represents the waste management of 95% of the Swedish population. Information regarding 122 storage facilities owned by 69 companies was obtained; these facilities were responsible for the storage of 47% of the total treated waste (incineration + digestion + composting) in 2010 in Sweden. To identify factors related to fire frequency, the questionnaire covered the amounts of material handled and burnt per year, financial losses due to fires, storage duration, storage method and types of waste. The results show that 217 fire incidents corresponded to 170 kilotonnes of material burnt and cumulative losses of 49 million SEK (€4.3 million). Fire frequency and amount of material burnt per fire was found to be dependent upon type of management group (waste operator). Moreover, a correlation was found between fire frequency and material recycled during past years. Further investigations of financial aspects and externalities of fire incidents are recommended.

Hourly energy analysis and feasibility study of employing a thermocline TES system for an integrated CHP and DH network

The employment of a TES system to improve the performance of a DH network integrated with a CHP station is investigated. Thermal energy demand fluctuations is the main issue threatening the viability of CHP/DH projects; therefore, TES facility can be coupled with CHP plant by a smart operation strategy to match the production and consumption profiles, and result in better consequences. To evaluate the system performance and energy saving potential, the hourly simulation of a thermocline hot water storage tank coupled with CHP/DH network is carried out, considering annual thermal load of the DH network. Optimal TES size is investigated from energetic, environmental and economical viewpoints. Results depict that by coupling five 1100m3 hot water storage tanks with CHP/DH plant, the annual CHP efficiency increases by 1.12%, and annual fuel consumption rate and CO2 emissions decrease by 2.6%.