Reliability Of Energy Systems Research Articles

Energy Conservation through Ongoing Commissioning

ABSTRACT Building systems and their controls have become very complex. A modern building automation system (BAS) can have thousands of data points, a network of controllers, and software with programming logic that is often inaccessible by the building personnel. If not regularly calibrated, maintained, and monitored, the complexity of the system can become more a liability than an asset. This article is based on observations and lessons learned through field experience, as opposed to an in-depth discussion of controls theory or operations and maintenance methodologies. Based on experience from a multitude of retrocommissioning and energy efficiency projects, a pattern has emerged: existing buildings have a significant number of BAS defects which cause excessive energy consumption, reliability problems, and occupant comfort issues. Through case studies, this article illustrates the importance of implementing a process for uncovering control system defects and will discuss ongoing commissioning as a potential method for identifying and resolving BAS defects and achieving optimum building energy efficiency and system reliability.

Shared recovery for energy efficiency and reliability enhancements in real-time applications with precedence constraints

While Dynamic Voltage Scaling (DVS) remains as a popular energy management technique for modern computing systems, recent research has identified significant and negative impacts of voltage scaling on system reliability. To preserve system reliability under DVS settings, a number of reliability-aware power management (RA-PM) schemes have been recently studied. However, the existing RA-PM schemes normally schedule a separate recovery for each task whose execution is scaled down and are rather conservative. To overcome such conservativeness, we study in this article novel RA-PM schemes based on the shared recovery (SHR) technique. Specifically, we consider a set of frame-based real-time tasks with individual deadlines and a common period where the precedence constraints are represented by a directed acyclic graph (DAG). We first show that the earliest deadline first (EDF) algorithm can always yield a schedule where all timing and precedence constraints are met by considering the effective deadlines of tasks derived from as late as possible (ALAP) policy, provided that the task set is feasible. Then, we propose a shared recovery based frequency assignment technique (namely SHR-DAG) and prove its optimality to minimize energy consumption while preserving the system reliability. To exploit additional slack that arises from early completion of tasks, we also study a dynamic extension for SHR-DAG to improve energy efficiency and system reliability at runtime. The results from our extensive simulations show that, compared to the existing RA-PM schemes, SHR-DAG can achieve up to 35% energy savings, which is very close to the maximum achievable energy savings. More interestingly, our extensive evaluation also indicates that the new schemes offer non-trivial improvements on system reliability over the existing RA-PM schemes as well.

Investigations of the state-of-the-art methods for electromagnetic NDT and electrical condition monitoring

This paper reviews the research and development of eddy current NDT testing, electrical condition monitoring and the associated instruments, with which the author has been closely involved over the past decade. The first part of the paper presents eddy current testing and imaging methods designed for use in the electrical property measurement of porous metals and liquid metal flow profile imaging during continuous casting. The second part of the paper addresses condition monitoring techniques from fundamental aspects in the high-voltage insulation diagnosis through applications in large-scale generators in conventional power plants to the latest applications in distributed generation systems with wind turbines. Finally, the challenges we will face in these areas are discussed. The research achievements have shown that the reliability and availability of future industrial processes and advanced energy systems can be increased by the application of improved eddy current sensing and condition monitoring techniques.

A hybrid intelligent approach for the prediction of electricity consumption

Power load forecasting is an essential tool for energy management systems. Accurate load forecasting supports power companies to make unit commitment decisions and schedule maintenance plans appropriately. In addition to minimizing the power generation costs, it is also important for the reliability of energy systems. This research study presents the implementation of a novel fuzzy wavelet neural network model on an hourly basis, and validates its performance on the prediction of electricity consumption of the power system of the Greek Island of Crete. In the proposed framework, a multiplication wavelet neural network has replaced the classic linear model, which usually appears in the consequent part of a neurofuzzy scheme, while subtractive clustering with the aid of the Expectation–Maximization algorithm is being utilized in the definition of fuzzy rules. The results related to the minimum and maximum load using metered data obtained from the power system of the Greek Island of Crete indicate that the proposed forecasting model provides significantly better forecasts, compared to conventional neural networks models applied on the same dataset.

Development of approach for reliability assessment of pipeline network systems

The aim of the work presented in this paper is to develop a common scientific methodology for the assessment of reliability of the pipeline network energy systems. The developed methodology is applicable for district heating, gas and oil supply networks. The reliability of all these systems depends on the degradation mechanisms and structural integrity of pipes. Structural integrity is influenced by loadings, defined by thermal–hydraulic processes. The reliability of energy network systems also depends on reliability of the installed equipment and the supply source. The reliability of pipeline networks is treated as a complex task. Consequently, the developed methodology includes three types of analyses: probabilistic mathematical, deterministic thermal–hydraulic and deterministic-probabilistic structural integrity analyses. As a pilot study, the application of the developed methodology for the analysis of Kaunas (Lithuania) district heating system was performed. The main results of this pilot study are presented in the paper. Although the original intention is to apply the developed methodology for the assessment of the reliability of the Lithuanian energy systems, in general, the methodology is applicable for any pipeline network system in any country.

Effects of Load Sector Demand Side Management Applications in Generating Capacity Adequacy Assessment

Electric power utilities are facing increasing infrastructure investment and awareness of environmental issues. Demand side management (DSM) can play an important role in meeting some of the challenges faced by electric power utilities in that it can be used to improve energy efficiency, system reliability, and security, reduce costs for both customers and utilities, and mitigate environmental damage. This paper applies load shifting on seven different customer load sectors and illustrates the effects of the various DSM measures on the load shapes and on the system reliability indices used in generating capacity adequacy assessment.

An Empirical Study of Knowledge Discovery on Daily Electrical Peak Load Using Decision Tree

Load forecasting plays an important role in effective energy management and system reliability. However, difficulty in load forecasting arises due to its nonlinear and irregular variation. This paper presents a case study in which the effect of weather elements on public utility system peak demand is first studied to find the most decisive weather index. The average temperature and previous load demand data are then selected as input variables to predict next-day peak load. The empirical results indicate that the forecasting performance can be improved by applying support vector regression machines.

Systems-based modeling of generation variability under alternate geographic configurations of photovoltaic (PV) installations in Virginia

With increased focus on renewable energy in our modern era, it is increasingly important to understand the impact of policies on the performance and reliability of regional energy systems. This research develops a model to understand how geographic dispersion of PV installations impacts the reliability of electricity generated from the total PV network, measured by the variance of the distribution of generated electricity. Using NREL data, beta probability distributions of sunlight (kWh/m 2/day) in various regions of Virginia are estimated using a fitting method that minimizes the Kolmogorov–Smirnov test statistic. A Monte Carlo simulation model is developed to measure PV electricity generation from multiple centralized and dispersed configurations over 100,000 days of probabilistic sunlight. There is a calculable tradeoff between average generation and generation variability, and increased geographic dispersion of PV installations can decrease this variability. Controlling variable generation through policies that promote efficient PV siting can help provide reliable power, minimizing the need for load-balancing peaking power infrastructure and costly electricity purchases from the grid. Using a tradeoff framework of generation and costs, this paper shows that geographically dispersed generation can mitigate the risk of unreliable solar generation that can significantly impact the end-user costs and make PV infrastructure unattractive.

Tribo-corrosion of Ag and Ag-alloy ITO multilayers used in solar energy applications

The efficiency and long term reliability of multilayered films of Ag/Ag-alloy based indium tin oxide (ITO) used in solar energy applications depend on the surface integrity of the film. Surface integrity can be breached due to exposure to a harsh outdoor environment and mishandling. It is therefore important to study the tribo-corrosion properties of such film systems. Reciprocating polytetrafluoroethylene (PTFE) ball-on-film tests are conducted in a NaCl solution under moderate loading conditions and increasing number of cycles. Ag, Ag–Pd and Ag–Au alloy based ITO multilayers, deposited on a polymer substrate, are used and the tribo-corrosion resistance is investigated. Electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy are used, after testing, in order to characterize and determine the corrosion and wear mechanisms. The effect of the reciprocating cycles on the multilayer failure initiation and propagation is studied. The resulting tribo-corrosion mechanisms are observed using scanning electron and optical microscopy. Understanding the tribo-corrosion properties of such model multilayers can lead to increasing the efficiency and long term reliability of various solar energy and energy-efficient systems.

Switching on the Future: Midwestern Models for a Clean Energy Transition

A clean energy future is both plausible and in the best interests of the country. The Upper Midwest, acting in concert with appropriate policy changes at the national level, could play a pivotal role in helping the nation move in that direction. As the past century’s embrace of centralized power is beginning to weaken, a variety of policy drivers, including concerns about energy system capacity and reliability, the improvement of public health by reducing pollution, the enhancement of national security by decreased reliance on nuclear power, and the need to curtail greenhouse gas emissions, are beginning to make clear the outlines of this energy transition. The proposals offered by the Environmental Lawand Policy Center and Minnesotans for an Energy-Efficient Economy rely on proven, economical, and environmentally sustainable technology options. An aggressive development plan featuring efficiency, wind, and other renewable resources will be a significant first step in solving the climate change problem.

Global Surface Solar Energy Anomalies Including El Nin˜o and La Nin˜a Years*

Weather anomalies that increase clouds influence the reliability of both renewable energy and building environmental-control systems. Non-grid solar power systems may run out of capacity for such items as communications electronics, flood-warning stream gages, refrigerators, and small village power systems. This paper provides 1×1-degree resolution global maps that identify those regions which experienced large abnormal solar energy during a 10-year period. A source is identified where specific values for maximum year-to-year variability can be obtained in regions where ground-site measurements do not exist. The information may aid in the selection of safety factors for solar power systems.

Demonstrating remote area power supply systems on the World Wide Web

One of the primary advantages of the internet is its ability to enable flexible, 24-h access to up-to-date information, irrespective of the geographic location of the user. It is thus rapidly becoming an important tool for the dissemination of information on a global scale. In order to take advantage of the increased accessibility available through the internet, the Murdoch University Energy Research Institute has developed an internet-based version of its physical renewable energy remote area power supply (RAPS) demonstration system. In this way, the physical site, which aims to inform the community about the cost, performance and reliability of renewable energy systems by enabling them to visit a practical operating RAPS system, is available to a much larger audience. The internet-based site, WebRAPS, contains a number of features including case studies of the three RAPS systems at the physical site, specifications of the components used in the systems and general information about the renewable energy system technologies. It also displays historical and real-time data from a monitoring system integrated with the largest of the physical RAPS systems. Visitors to the internet site are able to see how the RAPS system is operating, almost as well as if they were present at the physical site itself. This paper demonstrates the features of the WebRAPS site and discusses how it was developed.

An optimal renewable energy model for various end-uses

Renewable energy sources are likely to play a significant role in meeting the future energy requirement of a developing country like India. The effect of introducing renewable energy sources on the commercial energy scene may have to be analyzed carefully. In this paper, we present an Optimal Renewable Energy Model that minimizes the cost/efficiency ratio and determines the optimum allocation of different renewable energy sources for various end-uses. The potential of renewable energy sources, energy demand, reliability of renewable energy systems and their acceptance level will determine the pattern of renewable energy distribution and are used as constraints in the model. The model allocates the renewable energy distribution pattern for the year 2020–21 in India, which would be helpful for policy makers in commercializing the renewable energy sources to the greatest extent. The results indicate that solar energy systems can be utilized for lighting, pumping, heating and cooling to an extent of 6%, 16%, 2%, and 12% of total renewable energy demand in India, respectively. Similarly, the bio-energy systems can be utilized 9% of lighting, 18% of cooking, 1% of pumping, 17% of heating, and 14% of transportation of total renewable energy demand. It is also observed that wind energy can be utilized for pumping end-use to an extent of 4% of total renewable energy demand. The scenario for different potential limits is presented in this paper. A sensitivity analysis has been also carried out to validate the model.

Hand Calculation of Safe Separation Distances between Natural-Gas Pipelines and Boilers and Nuclear Facilities in the Hanford Site 300 Area

The U.S. Department of Energy has undertaken a project to reduce energy expenditures and improve energy system reliability in the 300 Area of the Hanford Site near Richland, Washington. This project replaced the centralized heating system with heating units for individual buildings or groups of buildings, constructed a new natural-gas distribution system to provide a fuel source for many of these units, and constructed a central control building to operate and maintain the system. The individual heating units include steam boilers that are housed in individual annex buildings located in the vicinity of a number of nuclear facilities operated by the Pacific Northwest National Laboratory (PNNL).The described analysis develops the basis for siting the package boilers and natural-gas distribution system used to supply steam to PNNL’s 300 Area nuclear facilities. Minimum separation distances that would eliminate or reduce the risks of accidental dispersal of radioactive and hazardous materials in nearby nuclear facilities were calculated based on the effects of four potential fire and explosion (detonation) scenarios involving the boiler and natural-gas distribution system. These minimum separation distances were used to support siting decisions for the boilers and natural-gas pipelines.

Effect of wind energy system performance on optimal renewable energy model—an analysis

The Optimal Renewable Energy Model (OREM) has been developed to determine the optimum level of renewable energy sources utilisation in India for the year 2020–21. The model aims at minimising cost⧹efficiency ratio and determines the optimum allocation of different renewable energy sources for various end-uses. The extent of social acceptance level, potential limit, demand and reliability will decide the renewable energy distribution pattern and are hence used as constraints in the model. In this paper, the performance and reliability of wind energy system and its effects on OREM model has been analysed. The demonstration windfarm (4 MW) which is situated in Muppandal, a village in the southern part of India, has been selected for the study. The windfarm has 20 wind turbine machines of 200 KW capacity. The average technical availability, real availability and capacity factor have been analysed from 1991 to 1995 and they are found to be 94.1%, 76.4% and 25.5% respectively. The reliability factor of wind energy system is found to be 0.5 at 10,000 hours. The OREM model is analysed considering the above said factors for wind energy system, solar energy system and biomass energy systems. The model selects wind energy for pumping end-use to an extent of 0.3153×10 15 KJ.

CRITICAL ANALYSIS OF WIND FARMS FOR SUSTAINABLE GENERATION

A critical analysis on wind farms has been carried out to improve the performance and reliability of wind energy system. The effect of its improvement has been studied with the Optimal Renewable Energy Mathematical (OREM) model which is developed for sustainable generation in India. The performance and reliability of the wind turbine generators have been evaluated in a demonstration windfarm (6 MW) in India. The windfarm is situated in Kayathar, a village in the south of Tamil Nadu State. The average technical availability, real availability and capacity factor have been analysed from 1991 to 1995 and they are found to be 92%, 54% and 19% respectively. Fault analysis for grid failures has been done using pareto analysis. The analysis indicates that when grid drop failures are reduced by 50%, the overall reduction in the frequency of faults would be 35.2%, which is significant. The reliability analysis has also been done for the wind turbine generator. The failure rate is high to an extent of 6.7×10 −5 h −1 in the case of a yaw control defect and the factor of reliability is found to be 0.5 at 10 000 h. The OREM model developed reveals that when the reliability factor of wind energy system is improved from 0.5 to 0.9 then the utilisation of wind energy would be increased by 82%.

On the development of a reliability based optimal renewable energy model for the sustainable energy scene in India

SYNOPSIS Sustainable Energy Development Planning has been the thrust area in developing countries like India. An Optimal Renewable Energy Model (OREM) with Reliability constraint which minimises the cost/efficiency ratio has been developed. The other constraints included in the model are social acceptance, resource limitation, demand and reliability factors. Thirty eight different renewable energy options are considered in the model. The OREM gives the allocation of renewable energy sources for lighting, cooking, pumping, heating, cooling and transportation end-uses for the year 2020–21 in India. For sustainable energy, the reliability of renewable energy systems have to be considered. In this paper, a detailed study has been made to analyse the reliability of a 15 kW solar photovoltaic system, which will be used in one of the constraint equations of the model. Reliability analysis reveals that there were no technical failures in the photovoltaic devices. But the power conversion accessories, such as the inverter and output contactor experienced failure rates of 1.48 × 10−4/hour and 1.67 × 10−4/hour respectively, resulting in poor reliability of the system. The reliability factor of the photovoltaic system is found to be 0.2 at 5000 hours. The fault analysis by Pareto diagram reveals that by eliminating the system component failures, the reliability factor can be improved to the factor of 0.67. As far as the solar PV is concerned, the model (OREM) selects solar PV for lighting to an extent of 0.5198 × 1015 kJ and for pumping 1.2084 × 1015 kJ.

Evaluation of energy conservation potential by exhaust air recirculation for a commercial-type heated-air batch hay dryer

Energy conservation in drying and processing operations is essential in order to improve the reliability of low and moderate temperature renewable energy systems, and to reduce operating costs and energy consumption in systems using high-energy content fossil fuels in farms and processing plants especially in industrialized economies. An experimental evaluation of energy conservation potential by recirculating exhaust air in a commercial heated-air batch hay dryer is presented. The design of the exhaust recirculation unit is such that only about 30% of the total exhaust air is recirculated through the heater inlet. Experimental tests were conducted on the dryer with and without exhaust air recirculation. Maximum energy savings of 27% and 17% were achieved with exhaust air recirculation during fall and summer dryer operation, respectively.

Prediction and evaluation of the performance of wind-diesel energy systems

A Monte Carlo based method for predicting the economic performance and reliability of autonomous energy systems consisting of diesel generators and wind energy converters (WECs), is proposed. Several technical constraints are applied, among them the most significant are the limitation of wind power penetration due to both the load demand and a minimum permissible power of the diesel generators. Start up-shutdown costs, two-fuel diesel units and reliability are considered. The proposed method divides the total simulation period into time intervals and for every time interval uses dynamic programming techniques to determine the diesel unit commitment. Results are presented for two Greek islands. It is shown that proper central control of WECs in a system increases significantly the wind energy penetration, which is strongly affected by the way commitment is made.

96/00645 The true cost of renewables

In marked contrast to a coal industry-funded study, the National Renewable Energy Laboratory analysts find that renewable energy technologies are economic, environmentally beneficial generation options. The topics covered in this article, which reviews both analyses, are the following: the true cost of renewables; energy subsidies; environmental impacts; the reliability of renewable energy systems;the impact of electricity competition. A short inset entitled `another perspective` offers a more optimistic perspective on the cost of renewables is included.