Times Of Low Demand Research Articles

Energy flexible building through smart demand-side management and latent heat storage

One of the greatest challenges for long-term emissions reduction is the decarbonisation of heating and cooling due to the large scale, seasonal variation and distributed nature. Energy flexible buildings with electric heating, smart demand-side management and efficient thermal energy storage are one of the most promising strategies to deploy low-carbon technologies which can benefit the electricity system by reducing the need of reinforcing existing networks and their ability to use electricity in times of low demand and high supply. Combined with spot price contracts, in which the electricity tariff changes every half-hour depending on supply and demand, they can effectively reduce on-peak demand periods, achieve economic profits for end-users and retailers, and reduce the environmental impact of the electricity grid by operating in periods with lower CO2 emissions rate. To achieve these benefits, it is crucial to develop accurate models for energy flexible buildings as well as control strategies to optimise the complex system operation. This paper proposes a novel flexible energy building concept, based on smart control, high density latent heat storage and smart grids, able to predict the best operational strategy according to the environmental conditions, economic rates and expected occupancy patterns. The smart integration model, carried out in TRNSYS for a Scottish case study, solves a multi-criteria assessment based on future energy demand prediction (learning machine model supported by end-user’s predefined occupancy by Internet of Things, present and forecast weather data, and building load monitoring), electricity tariff evolution and building performance. The results show that end-user’s electricity bill savings of 20% are obtained and retailer’s associated electricity cost is reduced by 25%. In addition, despite an increase in final energy consumption of up to 8%, the environmental impact remains constant due to operation at times with lower CO2 emissions rate in electricity generation. The developed tools enable the design of smart energy systems for energy flexible buildings which can have a large positive impact on the building sector decarbonisation.

Comparison of the Location and Rating of Energy Storage for Renewables Integration in Residential Low Voltage Networks with Overvoltage Constraints

Expansion of photovoltaic (PV) generation is increasing the challenge for network operators to keep voltages within operational limits. Voltage rise occurs in low voltage (LV) networks when distributed generators export, particularly at times of low demand. However, there is little work quantifying the scale of voltage issues and subsequently potential solutions across large numbers of real networks. In this paper, a method is presented to analyse a large quantity of geographically and topographically varying distribution networks. The impact of PV on voltages in 9163 real LV distribution networks is then quantified. One potential mitigation measure is increased network demand to reduce voltages. In this work, location algorithms are used to identify where increased demand, through energy storage, has the greatest effect on overvoltage. The study explores the impact on overvoltage of two modes of storage installation reflecting differing routes to adoption: purchase of storage by homeowners and purchase by network operators. These scenarios are compared with traditional re-conductoring in the 9163 networks. It is shown that to avoid violation of absolute voltage limits, storage should be installed at strategically important locations. Storage in homes reduces overvoltage, offering clear benefits to the network operator, but very wide deployment is required to completely remove the need for reinforcement.

Metabolic Flexibility as an Adaptation to Energy Resources and Requirements in Health and Disease.

The ability to efficiently adapt metabolism by substrate sensing, trafficking, storage, and utilization, dependent on availability and requirement, is known as metabolic flexibility. In this review, we discuss the breadth and depth of metabolic flexibility and its impact on health and disease. Metabolic flexibility is essential to maintain energy homeostasis in times of either caloric excess or caloric restriction, and in times of either low or high energy demand, such as during exercise. The liver, adipose tissue, and muscle govern systemic metabolic flexibility and manage nutrient sensing, uptake, transport, storage, and expenditure by communication via endocrine cues. At a molecular level, metabolic flexibility relies on the configuration of metabolic pathways, which are regulated by key metabolic enzymes and transcription factors, many of which interact closely with the mitochondria. Disrupted metabolic flexibility, or metabolic inflexibility, however, is associated with many pathological conditions including metabolic syndrome, type 2 diabetes mellitus, and cancer. Multiple factors such as dietary composition and feeding frequency, exercise training, and use of pharmacological compounds, influence metabolic flexibility and will be discussed here. Last, we outline important advances in metabolic flexibility research and discuss medical horizons and translational aspects.

I Will Survive. Pricing Strategies of Financially Distressed Firms

We consider a standard result of customer market theory: if firms have stable customer relations and face financial frictions, they may keep prices relatively high in times of low demand and vice versa. Indeed, during recessions, when firms have low cash flow and greater difficulty in raising external funds, they may set higher prices on their locked-in shoppers to maintain short-term profits at the expense of future market shares. We extend this theoretical framework so that the countercyclical behaviour of price margins is strengthened by the expected persistence of the downturn and the procyclicality of competitive pressures. We test these predictions for Italian firms participating in the 2014 Wage Dynamics Network Survey. All things being equal, financially constrained firms charge higher markups when faced with low demand; this behaviour is more evident when demand is perceived as being persistent. Our findings suggest that the severity of financial constraints in Italy was one of the causes of the sustained growth of prices in 2010-2013, notwithstanding the considerable slack in the economy.

On Cloud Resources Consumption Shifting Scheme for Two Different Geographic Areas

With the increasing demands for cloud resources, the task to keep it balanced with supply at all times becomes especially challenging. However, most of existing mechanisms focus on auction-based allocation of cloud resources rather than balancing the demands for cloud resources. In order to deal with this problem, this paper presents the problem of cloud resources consumption shifting between two different time intervals in a formularized manner, and then puts forward a cloud resources consumption shifting scheme with three-tier architecture. Users participating in the scheme, however, are motivated to get extra rewards by shifting certain consumption quantity from high to low demand time intervals. So, taking into account the fact that value ranges of individual shifting costs vary with different geographic areas, this scheme first allocates rewards to agencies in different geographic areas in the way of equilibrium, and then applies a strictly proper rule to reward users according to their contributions. In addition, the paper theoretically proves that the scheme is equipped with economic properties such as equilibrium, individual rationality, budget balance, and truthfulness. Finally, extensive simulation results show that the proposed scheme owns the resources shifting efficiency and computational traceability, and it can generate higher and more stable social rewards than the common scheme with two-tier architecture.

Testing and validation of the ACCESS system

With the increasing penetration of distributed renewable generation, a number of solutions have been developed to avoid network overloads. Several of the schemes already implemented are based on generation curtailment during times of high generation and low demand. The assisting communities to connect to electric sustainable sources (ACCESS) system implements a more sophisticated predictive solution: the generation resource and electrical demand are predicted and the storage heating load is managed accordingly, providing a demand side management instead of a generation curtailment solution. The ACCESS system was installed, tested and demonstrated in the power networks demonstration centre (PNDC), a research facility that enables realistic testing of novel hardware and network operation schemes in a controlled environment, in 2015. Following the testing at the PNDC, the ACCESS system was deployed on the Isle of Mull in 2016. This study reports on the findings from testing of the demand response features of the ACCESS system at the PNDC prior to its deployment on the Isle of Mull. This study reports on the different components of the system; the test regime undertaken at the PNDC; the results of the testing; and the updates to the ACCESS system based on the test results.

Influence of the cross section area reduction in cross wedge rolling on the multi-directional forging of crankshafts

Low energy demand and fast processing time are required in each industrial process for the production of crankshafts. A crankshaft is a part of combustion engines. It has a very complex geometry and is forged with a high percentage of flash compared to other forging parts. Recent research showed the feasibility of a flashless forging of crankshafts. One way to forge a flashless crankshaft within three steps, is to use cross wedge rolling, multi-directional forging and final forging. This paper presents the investigation results of the influence of the cross section area reduction in cross wedge rolling on different parameters at multi-directional forging. First the state of research, the process development and tool design of cross wedge rolling and multi-directional forging will be described. Then the parameter field study will be presented and the influence of the cross section area reduction on flash, billet temperature, forming degree, forming forces and stress will be shown. Generally, flash develops because a rotation-symmetric billet is forced into an asymmetric movement. The least amount of flash develops at high cross section area reductions (>40%).

The Impact of Work Demand and Gender on Occupational and Psychosocial Stress in Hispanic Farmworkers.

Hispanic farmworkers experience hazardous work conditions, language barriers, poverty, and limited healthcare access that increase their risk for health problems. We sought to characterize occupational and lifestyle stressors in farmworker couples and to examine the impact of seasonal work demand and gender on health outcomes. We administered surveys to 31 couples (N = 62) in May (low work demand) and September (high work demand) of 2012. Measures included acculturation, perceived stress, depressive symptoms, quality of life, decision latitude, support (supervisor, co-worker), and work-family conflict. This population did not report significant differences in stress in low and high work demand times. Women reported more work-family conflict (F = 19.06, p 0.0001; F = 11.28, p = 0.0015) and less supervisor support (F = 6.56, p = 0.0135). Women experienced more conflict between work and family and less support at work. This group reported low depressive symptomology and moderate levels of stress; a subset reported elevated levels.

I Will Survive. Pricing Strategies of Financially Distressed Firms

We consider a standard result of customer market theory: if firms have stable customer relations and face financial frictions, they may keep prices relatively high in times of low demand and vice versa. Indeed, during recessions, when firms have low cash flow and greater difficulty in raising external funds, they may set higher prices on their locked-in shoppers to maintain short-term profits at the expense of future market shares. We extend this theoretical framework so that the countercyclical behaviour of price margins is strengthened by the expected persistence of the downturn and the procyclicality of competitive pressures. We test these predictions for Italian firms participating in the 2014 Wage Dynamics Network Survey. All things being equal, financially constrained firms charge higher markups when faced with low demand; this behaviour is more evident when demand is perceived as being persistent. Our findings suggest that the severity of financial constraints in Italy was one of the causes of the sustained growth of prices in 2010-2013, notwithstanding the considerable slack in the economy.

On consumption shifting scheme for power

With the rapidly growing demands for power, the task to make users' demand adaptive to power supply is attracting more and more attention. In this paper, we present a novel model of power consumption shifting with continuous market price function instead of the common stepwise piecewise function, and then an applicable shifting scheme with three-tier architecture is designed. In order to get extra rewards, users involved in the scheme are encouraged to shift certain consumption of power from high to low demand time intervals. So, taking into account the fact that value ranges of users' shifting costs and capacities vary because of different geographic areas, grid firstly allocates rewards to power stations in different geographic areas in the way of percentage for shifting cost, and then an appropriate rule is introduced to allocate rewards to contributors according to their bids. We investigate the good economic properties including individual rationality, budget balance and incentive compatibility. At last, to verify the scheme given by this paper, an example is given to illustrate the correctness and effectiveness.

Multi-agent Collaboration for Conflict Management in Residential Demand Response

Balancing electricity supply and consumption improves stability and performance of an electricity Grid. Demand-Response (DR) mechanisms are used to optimize energy consumption patterns by shifting non-critical electrical energy demand to times of low electricity demand (off-peak). Market penetration of electrical loads from Electrical Vehicles (EVs) has significantly increased residential demand, with a direct impact on the grid’s performance and effectiveness. By using multi-agent planning and scheduling algorithms such as Parallel Monte-Carlo Tree Search (P-MCTS) in DR, EVs can coordinate their actions and reschedule their consumption pattern. P-MCTS has been used to decentralize consumption planning, scheduling the optimum consumption pattern for each EV. However, a lack of coordination and collaboration limits its reliability in emergent situations, since agents’ sub-optimal solutions are not guaranteed to aggregate to an optimized overall grid solution.This paper describes Collaborative P-MCTS (CP-MCTS), which enables EVs to actively affect the planning process and resolve their conflicts via negotiation and optimizes the final consumption pattern using collective knowledge obtained during the negotiation. The negotiation algorithm supports agents to actively participate in collaboration, arguing about their stance and making new proposals. The results obtained show a significant load-shifting in peak times, a smoother load curve, and improved charging fairness and flexibility.

Selection of Pumping Configuration for Closed Water Distribution Systems

This paper provides an insight into the selection of the most suitable configuration for closed distribution systems (i.e., systems with no storage capacity). The analysis is developed considering a wide ranges of operational scenarios in terms of flows and required heads. For each scenario, various design configurations are considered and compared. Results show that using more than a minimum of pumps can have lower operational and total costs thanks to the pumps operating closer to their best efficiency point. Small additional benefits in terms of operational and total costs may be obtained as a result of the introduction of the variable speed drive in at least one of the station pumps. Similar costs are obtained in the configuration where large pumps are flanked by a small jockey pump operating at low demand times. The design solution made up of large pumps fitted with a downstream hydropneumatic tank also represents a valid alternative option from the economical viewpoint for small flows.

Batteries as a Service: A New Look at Electricity Peak Demand Management for Houses in the UK

Tesla recently introduced its Powerwall line of batteries, aimed at a sector of housing with solar electricity installed. This paper considers the economics behind mass introduction of batteries in the housing sector in the UK from the perspective of peak demand management. Utilities use differential tariffs (such as the Economy 7 tariff on Southern Electric in the UK) to encourage more homogeneous loads. Given current costs of battery systems, this work considers the rates of return that may be possible by buying electricity from the grid in times of low demand, and reselling at peak demand from the perspective of an average UK household. We consider the regulatory framework that would have to be in place to make this feasible and look at the effect a mass uptake of battery technology would have on peak demand management in the UK scenario. Overall however, it is found to not be economically feasible at current prices without heavy government subsidies.

Electricity in Europe: exiting fossil fuels?

There are many options for generating electricity with low carbon emissions, and the elec- trification of heat and transport can decarbonize energy use across the economy. This places the power sector at the forefront of any move away from fossil fuels, even though fossil-fuelled generators are more dependable and flexible than nuclear reactors or intermittent renewables, and vital for the second- by-second balancing of supply and demand. Renewables tend to supplement, rather than replace, fos- sil capacity, although output from fossil-fuelled stations will fall and some will have to retire to avoid depressing wholesale power prices. At times of low demand and high renewable output prices can turn negative, but electricity storage, long-distance interconnection, and flexible demand may develop to absorb any excess generation. Simulations for Great Britain show that while coal may be eliminated from the mix within a decade, natural gas has a long-term role in stations with or without carbon cap- ture and storage, depending on its cost and the price of carbon.

水道送水システムにおける電力デマンドレスポンスのためのポンプ運転スケジューリング方式

Environmental concern has recently led to saving of electric power for water transmission and distribution systems in water utilities. To cope with the problem, effective water supply operation and appropriate management of water pressure have been researched. Moreover, after a large earthquake in eastern Japan, the problem of electricity shortage has been evident. To address the problem, the water saving which results in the electricity saving has been encouraged and the driving of waterworks facilities has been shifted from a peak demand time zone to a low demand time zone in order to achieve power peak cut. We propose a transmission pump operation scheduling method that minimizes the maximum value of power consumption in a time zone of demand response request. The optimal operational plan of pumps is made by mathematical programming so that the power consumption is minimized under constraints that the each reservoir keeps water level to enable 12-hour consecutive water supply and the water level does not go under lower limit during and after a time period of demand response. Simulation tests showed that the proposed method reduced power consumption by more than 65% compared with the current pump operation.

Assessing greenhouse gas emissions from electric vehicle operation in Australia using temporal vehicle charging and electricity emission characteristics

ABSTRACTSignificant interest exists in the potential for electric vehicles (EVs) to be a source of greenhouse gas (GHG) abatement. In order to establish the extent to which EVs will deliver abatement, however, a realistic understanding of the electricity and transport sector GHG emissions impacts arising from different approaches to integrating EVs into the power system is required. A key issue in this regard is the extent to which GHG emissions are a function of where and when EV charging will be enabled (or disabled) by the provision of recharging infrastructure and implementation of charging management strategies by the electricity industry. This article presents an investigation of the GHG emissions arising from electricity and gasoline consumption by plug-in hybrid EVs under a range of standard EV-power system integration scenarios. An assessment framework is presented, and GHG emissions from EV use are assessed for the New South Wales (NSW) and South Australian (SA) pools of the Australian National Electricity Market (NEM) using retrospective electricity system generation data for 2011. Results highlight that there is a range of possible outcomes depending on the integration scenario and emissions accounting approach used. This range illustrates value of a temporally explicit assessment approach in capturing the temporal alignment of electricity sector emission intensity and EV charging. Results also show the importance of a clean electricity generation mix in order for EVs to provide a GHG abatement benefit beyond what would be achieved by a hybrid (but non-plug-in) vehicle. The extent to which overnight charging in NSW is observed to produce higher emissions relative to unmanaged charging also illustrates a possible trade-off between GHG emissions and benefits for electricity industry from EV charging at times of low demand.

Large Active Area PEM Electrolysis Stack Test Bed - Design, Data and Development

In a growing number of regions around the world, solar and wind generated electricity is a large percentage of the overall supply. In times of low demand and high renewable electricity production energy storage can be deployed to shift the environmentally preferred energy to times of the day/week/month when it is needed most. Additionally, energy storage enables even higher penetrations of naturally varying renewable electricity sources to provide the increasing demand of the planet. Historically, polymer electrolyte membrane (PEM) electrolysis systems have been limited to small active areas, current density in the range of 1500 mA/cm2 and stack power levels in the 10's of kilowatts. Today, PEM stack active area and current density are both increasing to enable smaller footprints than their alkaline counterparts. Both of these changes are helping to decrease the cost of PEM electrolyzer systems.The National Renewable Energy Laboratory (NREL) has shown that both PEM and alkaline electrolyzer systems can ramp power up and down very quickly to accommodate the needs of grids with high penetration of renewable electricity installed. In addition, their ability to ramp quickly enables these electrolyzer systems to participate in grid ancillary services aimed at assuring a safe and reliability electrical grid. The 99.99+% purity levels of the hydrogen product from these electrolyzer systems can be used in a number of industries including; fuel cell electric vehicle refueling, stored for use in stationary fuel cell applications, material handling refueling (e.g., forklifts) and can be reacted with carbon dioxide to produce renewable hydrocarbon chains (e.g., methane), which can then take advantage of existing infrastructure. In a project with DOE, NREL has designed, built and now operates a large active area stack test bed (STB) to support water electrolyzer industry partners. The STB provides a flexible and open platform to allow the quick exchange and testing of stacks, sub-systems and components. The goal of the modular system design is to provide industry a place to develop and validate hardware, process software and sub-system control algorithms to improve electrolyzer system efficiency, response, safety and capital costs. The electrolyzer stack test bed was commissioned at NREL's Energy Systems Integration Facility (Golden, CO) in third quarter 2014 and then immediately provided factory acceptance testing of three 150 kW PEM electrolyzer stacks built by Giner, Inc. in November. The STB is providing a testing platform for a novel hydrogen drying technique, developed at NREL, to reduce the amount of hydrogen product wasted when the stack is being powered with variable power. In 2015 and 2016, research, development and demonstration work conducted with the STB will focus on improving system efficiency by optimizing balance of plant power requirements, power conversion optimization, grid integration and providing gas for hydrogen infrastructure component validation and 700 bar refueling demand.

Technique for Low Amperage Potline Operation for Electricity Grid Storage

Following a critical review and analysis of steady-state energy balance windows for large modern cell technologies [Taylor et al., Met. Mat. Transactions E, 9th Sept. 2014], the issue of a substantial reduction in energy input and heat output to a specific cell technology is addressed in this paper. To investigate the feasibility of such a reduction, the dynamic response to substantial changes in cell amperage and energy input must be quantified. If large amperage reductions can be shown to be feasible and to have no major detrimental affects, a flexible amperage operating philosophy would allow the use of smelting cells as an energy reservoir in the following way: in times of high electricity demand the cells would operate at reduced amperage, releasing electricity to the grid, while in times of low demand or an over-supply of electricity on the grid, the cells would store the surplus electricity in the form of additional aluminum metal. However, to take the above concept out of the realms of the theoretical, it will first be necessary to demonstrate an ability to predict and control the response of the cell to such changes in energy input through regulating the heat losses from the cell. The process of regulation of cell heat loss is quite foreign to operators of aluminum smelters, because the technology to regulate heat loss from smelting cells has not existed previously. This technology does now exist in the form of patented heat exchangers [Taylor et al., US Patent 7,901,617 B2, Mar. 8, 2011], but its impact on smelter cell walls must be examined in a dynamic analysis to determine the effect on the molten bath temperature and liquid mass within the cell. The objective of this paper therefore is to perform a first-order analysis of this problem, and to identify the key scientific issues in regulating cell heat loss and in the operating philosophy of heat loss regulation.

Minimal Thermal Generation in Power Systems - Inferring Private Cost Parameters from Observed Firm Behavior

Most production processes can be turned off easily during times of low demand; this is not true for the generation of electricity. For a number of technical reasons, a certain number of conventional (thermal) power stations needs to keep producing electricity at all times, despite negative margins. Empirically, this is evidenced by the fact that even during times of low or negative prices, some power stations keep generating electricity. This paper estimates empirically the quantity of such minimal or “must run” generation levels in a large integrated power system, using observed price and production data. The level of must-run generation is not only an interesting aspect of power systems in itself, it is also an important parameter for power market and energy system modelling. It is particularly important in times of low demand for electricity from conventional plants, such as moments of high wind or solar in-feed, hence this parameter is an important input for high-renewables scenarios. Using German data, we find aggregated must-run generation to be on average 34 GW, about 60% of average thermal generation. However, the variation in this parameter is significant, with observed must-run levels between 20 GW and 49 GW. Regression analysis suggests that the must-run constraint is 2-3 GW higher in winter than in summer and 5-7 GW higher during the day than at night. While we expected technological learning and increased awareness among market participants to reduce minimal generation over time, the data shows an increase since 2012.

Measurements and Analysis of Cavitation in a Pressure Reducing Valve During Operation – a Case Study

Abstract This paper proposes a methodology and presents its practical application for evaluating whether a pressure reducing valve (PRV) is under cavitation during its operation in a water distribution system. The approach is based on collecting measurements over a 24-hour period such that high demand and low demand times are included. The collected measurements allow evaluation of four indicators related to cavitation, namely the hydraulic cavitation index, noise generated by the valve, acoustic cavitation index and the spectra of the noise. These four indicators provide sufficient information for diagnosis of cavitation with high certainty.