WIND DIESEL SYSTEM SIMULATION:A SCREENING LEVEL MODEL

This paper describes a screening level simulation model for wind/diesel systems. It is intended for use to give a quick overview of the possible appropriateness of a wind/diesel system and indicate whether more detailed analysis would be of use. The model was developed for use on personal computers and to trade complexity for ease of operation. The wind/diesel system modeled may include: 1) Wind regime, 2) One or more wind turbines, 3) System electrical load 4) One or more diesel generators, 5) Dump load, 6) Short term storage, and 7) System controller. The model does not consider storage explicitly, but does distinguish between the no storage and minimal storage (power smoothing) systems.

This work is based on the more detailed simulation models previously developed at the University of Massachusetts, but uses probabilistic methods rather than time series data inputs. As such it requires only mean and standard deviation of wind speed and load for each month or season. The model functions by assuming that occurrences of wind speed can be modelled by a Weibull distribution and that the lead follows either a Weibull or normal distribution, In addition, both the wind speed and load are assumed to be uncorrelated within each month or season. The paper also includes a comparison of the model with the more detailed UMass model, HYBRID1.     

Exergy-energy analysis of full repowering of a steam power plant

A 320 MW old steam power plant has been chosen for repowering in this paper. Considering the technical conditions and working life of the power plant, the full repowering method has been selected from different repowering methods. The power plant repowering has been analyzed for three different feed water flow rates: a flow rate equal to the flow rate at the condenser exit in the original plant when it works at nominal load, a flow rate at maximum load, and a flow rate when all the extractions are blocked. For each flow rates, two types of gas turbines have been examined: V94.2 and V94.3A. The effect of a duct burner has then been investigated in each of the above six cases. Steam is produced by a double-pressure heat recovery steam generator (HRSG) with reheat which obtains its required heat from the exhaust gases coming from the gas turbines. The results obtained from modeling and analyzing the energy-exergy of the original steam power plant and the repowered power plant indicate that the maximum efficiency of the repowered power plant is 52.04%. This maximum efficiency occurs when utilizing two V94.3A gas turbines without duct burner in the steam flow rate of the nominal load.     

Simulation of forced circulation water heaters; effects of auxiliary energy supply, load type and storage capacity

A hybrid computer was used to simulate forced circulation solar water heater systems using stratified storage. A single month of hourly meteorological data was used to examine the effects of three types of auxiliary heating systems and three different sized tanks. Various time distributions and magnitudes of the load were studied. Results are shown in terms of the ratio of auxiliary energy requirements to total load and indicate best methods for adding auxiliary energy to maximize solar energy gain.     

Generation unit sizing and cost analysis for stand-alone wind,photovoltaic, and hybrid wind/PV systems

This paper presents the results of investigations on the application of wind, photovoltaic (PV), and hybrid wind/PV power generating systems for utilization as stand-alone systems. A simple numerical algorithm has been developed for generation unit sizing. It has been used to determine the optimum generation capacity and storage needed for a stand-alone, wind, PV, and hybrid wind/PV system for an experimental site in a remote area in Montana with a typical residential load. Generation and storage units for each system are properly sized in order to meet the annual load and minimize the total annual cost to the customer. In addition, an economic analysis has been performed for the above three scenarios and is used to justify the use of renewable energy versus constructing a line extension from the nearest existing power line to supply the load with conventional power. Annual average hourly values for load, wind speed, and insolation have been used     

Alternative energy facilities based on site matching and generation unit sizing for remote area power supply

This paper presents the decision support technique and influencing factors in the design of an integrated solar-wind power system for stand-alone applications. Results of investigations on application of alternative energy facility like wind, photovoltaic (PV), and Integration of wind–PV power generating systems for Remote Area Power Supply have been presented. A weather model-based site matching of equipment and a simple numerical algorithm for generation unit sizing have been presented. The program has been used to determine the optimum generation capacity and storage needs for a stand-alone Wind, PV, and integrated wind–PV system for a remote site in India (Sukhalai situated near Suktawa in Hoshangabad district of Madhya Pradesh) that satisfies a typical load. Generation and storage units for each system are properly sized in order to meet the annual load demand for the above three scenarios. Annual average hourly values for load, wind speed, and insolation have been used for analysis. The results are used to justify the use of renewable energy source as a reliable option for remote areas.     

Optimal sizing of stand-alone hybrid systems based on PV/WT/FC by using several methodologies

This paper presents a comparative study of four sizing methods for a stand-alone hybrid generation system integrating renewable energies (photovoltaic panels and wind turbine) and backup and storage system based on battery and hydrogen (fuel cell, electrolyzer and hydrogen storage tank). Two of them perform a technical sizing. In one case, the sizing is based on basic equations, and in the other case, an optimal technical sizing is achieved by using Simulink Design Optimization. The other two methods perform an optimal techno-economical sizing by using the hybrid system optimization software HOMER and HOGA, respectively. These methods have been applied to design a stand-alone hybrid system which supplies the load energy demand during a year. A MATLAB-Simulink model of the hybrid system has been used to simulate the performance of hybrid system designed by each method for the stand-alone application under study in this work. The results are reported and discussed in the paper.     

Measuring the environmental load of household consumption using some methods based on input–output energy analysis: A comparison of methods and a discussion of results

A proper analysis (an evaluation) of the environmental load of consumption is important in the context of sustainable development. Presently, different methods are used to calculate the environmental load of household consumption, mainly in energy and or greenhouse gas emission terms. These methods are all based on input–output energy analysis, but use different data sources and produce different results. In this article, we discern and describe three methods used to calculate the total energy requirements of households, and we discuss the main results produced with these methods. All three methods are applied to the Netherlands in order to compare differences and similarities in the results. We found that the total energy requirement calculated with all three methods was almost the same, with differences less than 4%, however each method provides results at a different level. Basic energy input–output analysis generates total requirements and requirements per consumption category, and is therefore suitable for describing and explaining the effect of household consumption. The hybrid method combining energy input–output analysis with process analysis generates requirements per consumption item and therefore offers opportunities to search for options of change of household consumption patterns to more sustainable consumption.     

Energy-optimal control of a bilinear multizone cooling system with chilled-water storage

The optimal control of multizone fan-coil cooling systems with chilled-water storage is studied. The example system consists of two environmental zones, a fan-coil unit for each zone, a chiller and storage tank, pumps and distribution network. The bilinear model of the system is linearized through the use of state feedback. The method of state-increment dynamic programming, augmented with a label-tracing procedure, is used to identify the periodic but unknown initial/terminal state as well as the associated closed trajectory and control inputs that are optimal for any given periodic 24-h zone cooling load profiles. Practical consideration for the implementation of these methods in a feedback controller for a multizone cooling system are briefly discussed.     

Thermal and economical analysis of a central solar heating system with underground seasonal storage in Turkey

Thermal performance and economic feasibility of two types of central solar heating system with seasonal storage under four climatically different Turkey locations are investigated. The effects of storage volume and collector area on the thermal performance and cost are studied for three load sizes. The simulation model of the system consisting of flat plate solar collectors, a heat pump, under ground storage tank and heating load based on a finite element analysis and finite element code ANSYS™ is chosen as a convenient tool. In this study, the lowest solar fraction value for Trabzon (41°N) and the highest solar fraction value for Adana (37°N) are obtained. Based on the economic analysis, the payback period of system is found to be about 25–35 years for Turkey.     

试论水电站调峰的节煤效益

本文主要论述水电厂调峰节煤的效益。水电节煤与替代电厂─—火电厂的运行特性有关，本文论述了火电机组的运行及煤耗特性，以数字实例说明了水电厂在日负荷曲线上担负不同的工作位置时，替代煤耗率是不同的。还论述水电调峰，还电、抽水蓄能电站的节煤机制。为水电调峰、水电与火电系统联网及抽水蓄能电站效益的正确评价提供了一种论证方法。     

A combined probabilistic/time series model for wind diesel systems simulation

This article describes a new simulation model for wind/diesel systems. It involves a combined time series and statistical approach to estimate the fuel use of diesel generators. In addition to provision for modeling non-identical diesels, the model allows the inclusion of multiple, non-identical wind turbines whose output may or may not be correlated. Three diesel dispatching strategies are provided. One assumes no storage, and when storage is employed, either a peak shaving or cycle charge control option can be used. The storage module uses a flexible battery model specially designed for time series simulation codes. A key assumption for the main analytical model is that, within each time step, the load and wind power are assumed to be normally distributed. The mean net load is the mean load less the mean wind power and its variance is found from the variance of the load and the wind power. A loss of load probability is used to find the maximum and minimum anticipated values of the net load. In addition to summarizing the overall analytical model, this article presents the results of a number of simulations demonstrating the performance prediction (diesel fuel usage) capabilities of the model. For one of these cases (a no storage system), the results show excellent correlation between the model and actual data. Other cases summarized show that the use of the model greatly facilitates the integration of storage into the control scheme, and gives the fuel saving potential for several different wind/diesel system configurations.     

Preconditioned Solver Performance with Compressed Banded Data Format in Three-Dimensional Convective Heat Transfer Simulations

ABSTRACT

A new data storage format called compressed banded data (CBD) is developed for sparse banded matrices generated by hybrid finite-element/volume methods in numerical heat transfer. The platform of the new CBD structure permits dynamic switching between various solvers. The performance of various Krylov techniques, including GMRES(m) (Generalized Minimal RESidual), Bi-CGSTAB (Bi-Conjugate Gradient STABilized), Bi-CG (Bi-Conjugate Gradient), CG (Conjugate Gradient), and CGS (Conjugate Gradient Squared) with an ILU(0) preconditioner, are compared in three test problems. The performance of each preconditioned iterative solver is compared with a direct solver, particularly in terms of memory storage requirements. It is shown that the new CBD format provides useful benefits with respect to both reduction of storage requirements and CPU runtime.     

When intermittent power production serves transient loads

Renewable power generation exhibits notorious intermittence. The power load varies daily and also seasonally. The topic of renewable generation, storage and grid interfacing is complex in that it brings into one setting many diverse interests and technologies. Our long-term goal is to help define ways to profitably increase renewable generation. In this paper, we focus on normal day for a grid operator, PJM, (Pennsylvania, New Jersey and Maryland). The variability of wind and (and assumed) solar outputs require a certain capability for load following or storage. Using dynamic modelling, we estimate the variability of the wind output and we simulate a projected solar penetration of 3% of new capacity. To save for eventual use every unit of energy thus generated, a storage system must have the capability to levelize the supply of renewable power. The capacity requirements for storage and generation of such a system are mapped out in 1 min intervals, and are used to define the capacities and ramp rates for a hypothetical pumped storage plant. Knowledge of weather patterns may be helpful to plan dispatch and storage of renewable energy. The results of a brief excursion into the difficult topic of weather patterns are recorded here too.     

Residential photovoltaic self-consumption: Identifying representative household groups based on a cluster analysis of hourly smart-meter data

The on-site generation and direct consumption of electricity, so-called self-consumption, with a combined photovoltaic (PV) and battery storage system is becoming increasingly profitable for private households. The profitability of PV self-consumption system largely depends on the match of PV output and the household’s electricity consumption. In energy system modelling, the household’s consumption behaviour is represented by means of a standard load profile. However, the household sector’s heterogeneity is not reflected in one single profile, and the use of only one load profile results in a misjudgement of the profitability of self-consumption. In this study, we present a set of representative household groups that better represent the heterogeneous residential consumption behaviour. The household groups were compiled through the cluster analysis of smart-meter data based on hourly electricity consumption, using household characteristics as explanatory variables. Between the average load profiles of the groups, significant differences were found. Subsequently to the clustering, self-consumption based on a combined PV and battery system was simulated for each household. We found that the achievable level of self-consumption also differs between the groups, which in turn affect the profitability of the PV and battery systems. A statistical analysis revealed that employment and the presence of children are distinguishing factors for the different types of self-consumers. These results suggest that (i) the residential sector is not well represented by a single standard load profile, particularly so in the context of self-consumption modelling. (ii) Different self-consumer types can be identified through socio-demographic characteristics: We found that unemployed households achieve the highest self-sufficiency rates with an average of 40%, the lowest rates with 30% on average occur within households of educated families. (iii) Although the discrepancies are significant, the effect of these differences on profitability is still limited under the current market conditions.     

Performance analysis and cost optimization of a solar-assisted heat pump system

A solar-assisted heat pump system with a conventional backup unit was simulated for a 93 m² (1000 ft²) house in Rhode Island using quasi-dynamic computer models. The performance of the system as a function of collector area and thermal storage volume was evaluated to determine the fraction of the space heating and domestic hot water load that was supplied by the solar-assisted system. This information was used to compute the payback time, based on cumulative costs, for each variation of the system's parameters when compared to a conventional system. The optimal combination of system components which had a payback time less than the mortgage life was determined. For the given initial costs of solar panels and storage reservoir, this optimal combination was found to be insensitive to the variations in mortgage and fuel cost growth rates presented in this report.     

Research on optimal confguration of hybrid energy storage capacity for wind-solar generation system

储能系统可以有效解决微电网中分布式可再生能源特别是风光互补发电的间歇性、波动性以及“源”与“荷”错位的问题。不同储能技术在响应时间、容量规模、技术成熟度及成本等方面各有特点,两种或多种储能技术耦合将可以更有效地满足用电系统的技术性和经济性的要求。针对电力用户对分布式可再生能源的利用情况,本文提出一种由压缩空气储能、锂电池和超级电容器组成的混合储能系统,建立了三种储能的数学模型,针对其不同的特性,提出了基于二次移动平均滤波的储能系统功率分配方法和基于连续性运行的容量优化配置方法。基于某个实际的用户负荷进行了案例分析,得到了混合储能系统的功率和容量配置结果,并分析了其运行特性。研究表明,在分布式可再生能源微电网中,多种储能技术耦合既能充分发挥每种储能的优势,又可以通过相互配合弥补各自的劣势,这对于可再生能源的充分利用和满足用电负荷的严苛需求具有重要的作用和意义,在分布式能源利用领域具有较好的工程应用前景。     

Modelling an off-grid integrated renewable energy system for rural electrification in India using photovoltaics and anaerobic digestion

This work describes the design optimisation and techno-economic analysis of an off-grid Integrated Renewable Energy System (IRES) designed to meet the electrical demand of a rural village location in West Bengal – India with an overall electrical requirement equivalent to 22 MWh year⁻¹. The investigation involved the modelling of seven scenarios, each containing a different combination of electricity generation (anaerobic digestion with biogas combined heat and power (CHP) and photovoltaics) and storage elements (Vanadium redox batteries, water electrolyser and hydrogen storage with fuel cell). Micro-grid modelling software HOMER, was combined with additional modelling of anaerobic digestion, to scale each component in each scenario considering the systems' ability to give a good quality electricity supply to a rural community. The integrated system which contained all of the possible elements – except hydrogen production and storage presented the lowest capital ($US 71 k) and energy cost ($US 0.289 kWh⁻¹) compared to the scenarios with a single energy source. The biogas CHP was able to meet the electrical load peaks and variations and produced 61% of the total electricity in the optimised system, while the photovoltaics met the daytime load and allowed the charging of the battery which was subsequently used to meet base load at night.     

Simplified design of independent hydropower-PV-storage micro-grid system

含可再生能源的独立微电网为解决无电地区用电提供了一种因地制宜的可持续的电力解决方案,但目前微电网由于理论性强、可操作性差,市场推广困难。为了解决目前微电网项目开展的壁垒,提出了一种关于独立水光储微电网系统的简化设计。根据项目所在地的微电源与负荷特性,计算系统的需电量,得出光伏及水电等电源所需的配置容量。为合理地协调各个时段微电网系统内各电源的出力来满足各时段负荷的需求,确保微电网内各电源模块出力与负荷需求的实时功率平衡,最大程度保障系统供电可靠性,本文提出了系统的两个重点考核指标——系统缺电率及能量溢出比,根据这两个指标,确定微电网系统的电池储能系统的配置容量。本文总结了一套合理的关于微电网的通用初步设计方法,为从事微电网的工程设计人员提供了便利。     

A method of economical load dispatch for steam turbine unit of thermal power plant

In this paper, by combining the equality differential increment theory (EDIT) with the equivalent polyhedron body (EPB) searching extremum strategy, a method of economical load dispatch for the steam turbine unit of the thermal power plant has been presented. Simultaneously, a method for the order of load shedding and the related optimal economic operational modes of each turbine unit in decreasing its load are ascertained. According to the methods, the results of the optimal economical dispatch of the peak loads, the order of load shedding and the related optimal economic operational modes of each turbine unit while decreasing the load of a certain thermal power plant have been obtained. These results are applied in the thermal unit, and its economic benefits are shown to be obviously higher than that of applying the relative efficiency of each turbine unit. The methods can be used as a reference for obtaining the optimum economical load dispatch for similar thermal power turbine units. Copyright © 2007 John Wiley & Sons, Ltd.     

Maximizing the value of customer-sited PV systems using storage and controls

This paper determines how the value of customer-sited PV can be increased with battery storage by enhancing the load management and outage protection attributes of PV. Case studies in San Jose, CA and Long Island, NY for residential and commercial PV applications are used for a quantitative illustration of storage value enhancement. Results indicate that: (1) a small amount of storage for local load control and a larger amount of storage for emergency load protection significantly increases the value of distributed PV to the customer; (2) the value of PV combined with emergency storage exceeds the sum of the value of these options implemented separately; and (3) there is a potential opportunity to use dispersed PV + storage to enhance grid security (capturing this value, however, will require regulatory and policy changes).