Small-signal model and dynamic analysis of variable speed induction machine wind farms

A unified, modular, small-signal dynamic model for an induction machine-based wind farm is presented. The proposed model can represent an arbitrary number of fixed-speed, partially variable-speed (doubly fed) and variable-speed induction machine-based wind units in a wind farm. The model represents the dynamics of (i) each wind turbine-generator electromechanical system, (ii) each converter system and the corresponding controls and (iii) the host electrical grid, within the subsynchronous frequency range (0.1?60 Hz). In contrast to the widely used state-space formulation, the proposed approach is based on developing electrical and mechanical transfer-function matrices to formulate the overall system as a multivariable feedback system. Thus, it provides significant flexibility to represent a large number of wind units and their controllers, identical or nonidentical, within a wind farm. Based on the developed model, a frequency response-based method is also introduced, as an alternative to the eigen analysis approach, for small-signal subsynchronous dynamic analysis of the wind farm and its host electrical grid. The proposed method provides a new performance robustness criterion for performance evaluation and also a design tool based on the `size? of the system transfer-function matrix. The concept of induced norm is adopted here as a measure of matrix size. As an example, applications of the model and the analysis approach to a twounit wind farm is presented and the results are validated based on time-domain simulation studies in the PSCAD/ EMTDC environment.     

Wind Energy Analysis for Vadravadra Site in Fiji Islands: A Case Study

Rising fuel costs, increased energy consumption, and growing environmental concerns have led mankind to look for alternate sources of energy apart from conventional fuels. One of the promising renewable energy sources is wind energy. For harnessing wind energy from a wind turbine or wind farm, wind resource assessment (WRA) needs to be carried out. WRA will highlight which site is optimum (in terms of economics and wind characteristics) for wind turbine installation and how much would be the estimated energy output from that particular site. This paper presents the estimate for annual wind energy yield for the Vadravadra site in Gau Island in Fiji. It also presents a method for finding the optimum wind turbine that can be installed at a site and the kind of wind turbine that should be installed at a site, where cyclone may hit the area.      

Energy prices,labour productivity and causality: An empirical examination

This paper is directed at examining the impact of changing energy prices on productivity in the USA. By using a cross correlation test for unidirectional causality, it is clearly demonstrated that for the period 1947–1980, the rate of change of productivity was adversely affected by changing energy prices. Furthermore, there is at least a four to five year lag before the entire impact is exhausted.     

Energy use efficiency in the Indian manufacturing sector: An interstate analysis

This paper approaches the measurement of energy efficiency from a production theoretic framework and uses Data Envelopment Analysis to measure energy efficiency in the Indian manufacturing sector. Using data from the Annual Survey of Industries for the years 1998–99 through 2003–04, the study compares the energy efficiency in manufacturing across states, based on several models. The results show considerable variation in energy efficiency across states. Comparing the results across our models, we find that the relative pricing of energy does not provide the appropriate incentives for energy conservation. A second-stage regression analysis reveals that states with a larger share of manufacturing output in energy-intensive industries have lower energy efficiency. Also, higher quality labor force associates with higher energy efficiency. Finally, the power sector reforms have not yet had any significant impact on achieving energy efficiency.     

Energy efficiency and the slump in labour productivity in the USA

Energy consumption is included in an aggregate Cobb-Douglas production function for the USA. The data suggest that energy conservation has not reduced the growth rate for real GNP by more than 0.3 percentage points and that less than one-fifth of the overall slump in labour productivity since 1973 should be attributed to higher energy prices.     

Energy use efficiency of Indian cement companies: a data envelopment analysis

The present paper aims at measuring energy use efficiency in Indian cement industry and estimating the factors explaining inter-firm variations in energy use efficiency. Within the framework of production theory, data envelopment analysis has been used to measure energy use efficiency. Using firm-level data from electronic PROWESS database for the years 1989–1990 through 2006–2007, the study first estimates energy use efficiency of the firms and then compares the efficiency scores across. Empirical results suggest that there is enough scope for the Indian cement firms to reduce energy uses, though this potential for energy saving varies across firms. A second-stage regression analysis reveals that firms with larger production volume have higher energy efficiency scores and that age of the firms impacts differently on energy use efficiency obtained from two different models. Also, higher quality of labor force associates with higher energy use efficiency.     

Energy use in industry—V: Energy use in a heavy engineering workshop

The paper describes energy use in a particular heavy engineering workshop and investigates the consequences of possible improvements to lighting, to the thermal performance of the building and to the means of distribution of power. Comparisons are made with previous work done on other factories engaged in engineering. A method of describing the economic potential of energy conservation as an element of energy strategy is proposed.     

Solar-based rural electrification policy design: The Renewable Energy Service Company (RESCO) model in Fiji

Solar photovoltaic technologies have for some time been promoted as a cost effective means of rural electrification in developing countries. However, institutional structures resulting in poor maintenance have adversely affected the sustainability of past solar projects. In Fiji, the Renewable Energy Service Company (RESCO) program is the latest attempt to promote solar-based rural electrification in a fee-for-service model, aiming to remove the high upfront capital costs associated with solar technologies and using a public–private sector partnership for maintenance. This paper assesses the program using survey and interview data. Major flaws are identified, relating to incorrect treatment of principal–agent problems, information asymmetries, motivational problems, and resourcing of government agencies. General lessons for fee-for-service solar home system models emerge, including that incentives for stakeholders must take centre stage in designing and administering such programs, and that active government support and ownership are required to make programs sustainable.     

Energy use in the U.S. service sector: An input-output analysis

The U.S. input-output tables for 1972 and 1977 are used to examine the early adjustment of the service sector to the energy price shock of 1973–1974. IO analysis allows us to look at the indirect as well as direct changes in energy use intensity. We find a substantial decline in both primary and secondary energy intensity between 1972 and 1977 in the service sector. If 1977 energy technology, represented by the 1977 energy IO coefficients, had been used in 1972, the 19 service industry sectors would have required 23% less primary energy and 12% less secondary energy. Electricity use, on the other hand, would have increased by about 9%.     

Energy use and economical analysis of sugar beet production in Tokat province of Turkey

The purposes of this study were to determine energy consumption of input and output used in sugar beet production, and to make a cost analysis in Tokat, Turkey. Data were collected from 146 sugar beet farms in Tokat, Turkey by using a face-to-face questionnaire performed in January and February 2005. Farms were selected based on random sampling method. The results revealed that total energy consumption in sugar beet production was 39 685.51 MJ ha⁻¹, and accounted for 49.33% of fertilizer energy, and 24.16% of diesel energy. The output/input energy ratio was 25.75 and energy productivity was 1.53 kg MJ ha⁻¹. Results further indicated that 82.43% of total energy input was in non-renewable energy form, and only 12.82% was in renewable form. Economic analyses showed that profit–cost ratio of farms was 1.17. The highest energy cost items were labor, land renting, depreciation and fertilizers. Although intensive energy consumption in sugar beet production increased the yield, it also resulted in problems such as global warming, land degradation, nutrient loading and pesticide pollution. Therefore, there is a need to pursue a new policy to force producers to undertake energy-efficient practices to establish sustainable production systems without disrupting the natural resources. In addition, extension activities are needed to improve the efficiency of energy consumption and to sustain the natural resources.     

Energy use analysis of selected palm-kernel oil mills in south western Nigeria

Energy use patterns and utilisation efficiencies in 40 factories producing palm kernel oil (PKO) in southwestern part of Nigeria were studied. The factories were stratified into small, medium and large scale categories based on the mode of operations and production capacities. Questionnaires were administered on the factories to obtain historical data on petrol, diesel and electricity consumption and PKO production outputs for seven years (1998–2004). Energy use efficiency indicators employed include: energy intensity (EI), energy cost per unit product (EC/P), energy ratio (ER), food energy ratio (FER) and percentage oil yield by weight. Results of the study indicated that averagely, 0.58, 0.53 and 0.74 GJ/10³ l of PKO were needed in the small, medium and large PKO factories, respectively. The average food energy ratios in the small, medium and large mills are 2.48, 2.53 and 2.14, respectively. The corresponding values of PKO conversion ratio are 0.43, 0.50 and 0.35. Electrical energy consumption in medium and large mills was lower than thermal energy due to irregularity and decline in electricity supply from the national grid. The results of the study has provided required baseline information needed for budgeting, comparison of yearly energy consumption, forecasting energy requirements and planning expansion in PKO factories.     

Energy from sugarcane bagasse under electricity rationing in Brazil: a computable general equilibrium model

In the midst of the institutional reforms of the Brazilian electric sectors initiated in the 1990s, a serious electricity shortage crisis developed in 2001. As an alternative to blackout, the government instituted an emergency plan aimed at reducing electricity consumption. From June 2001 to February 2002, Brazilians were compelled to curtail electricity use by 20%. Since the late 1990s, but especially after the electricity crisis, energy policy in Brazil has been directed towards increasing thermoelectricity supply and promoting further gains in energy conservation. Two main issues are addressed here. Firstly, we estimate the economic impacts of constraining the supply of electric energy in Brazil. Secondly, we investigate the possible penetration of electricity generated from sugarcane bagasse. A computable general equilibrium (CGE) model is used. The traditional sector of electricity and the remainder of the economy are characterized by a stylized top-down representation as nested CES (constant elasticity of substitution) production functions. The electricity production from sugarcane bagasse is described through a bottom-up activity analysis, with a detailed representation of the required inputs based on engineering studies. The model constructed is used to study the effects of the electricity shortage in the preexisting sector through prices, production and income changes. It is shown that installing capacity to generate electricity surpluses by the sugarcane agroindustrial system could ease the economic impacts of an electric energy shortage crisis on the gross domestic product (GDP).     

Energy use efficiency and economical analysis of almond production: a case study in Chaharmahal-Va-Bakhtiari province,Iran

The aim of this study was to analyse input–output energy and economical assessment of almond production in three age groups of orchards (group I 6–10, group II 11–15 and group III 16–20 years old) in Chahrmahal-Va-Bakhtiari province, Iran. Data for almond production were collected by administering questionnaire in face-to-face interviews from the orchards selected based on random sampling method during a 3-year period. The results showed that 57,027.13, 60,341.14 and 61,640.43 MJ ha^?1 energy was consumed by group I, group II and group III, respectively. The most energy input was consumed by electricity, followed by chemical fertilizer. Energy indices were calculated, and the results revealed that energy efficiency was 0.62, 1.12 and 0.81 in the triple groups of orchards, respectively. Economical assessment showed that total production cost of almond in group I, II and III was $4547.54, $5799.26 and $5687.05 ha^?1, respectively. In all orchard groups, the shares of variable and fixed production costs found to be same nearly. Net return for almond production was $14,516.22, $30,735.19 and $21,395.57ha^?1, respectively. According to the research results, it was concluded that although almond production in the study region was not an efficient process in terms of energy consumption, it was a profitable agricultural operation.     

The potential and economic viability of hydrogen production from the use of hydroelectric and wind farms surplus energy in Brazil: A national and pioneering analysis

Energy security is an issue at stake in governments all over the world, and also in Brazil. Although the country's energetic matrix is largely based on hydropower sources, the need for diversification is increasingly needed. The possibility of hybrids between hydropower and wind power for hydrogen production emerges as a clean alternative source for energy security. In high-throughput seasons, excess energy could be used to produce hydrogen, which could supply shortages of energy. This study shows the potential for producing hydrogen in Brazil, using excess energy from hydroelectric and wind farms. Taking into account one hour per day of surplus energy production, it would be possible to generate 6.50E+09 Nm³.y⁻¹ of H₂. On the other hand, considering two and three hours, the H₂ generation would be equal to 1.30E+10 Nm³.y⁻¹ and 2.00E+10 Nm³.y⁻¹, respectively. This study calculated the economic viability for hydrogen production, at a cost of 0.303 USD.kWh⁻¹, a higher cost if compared to that of the wind and hydroelectric plants.     

Energy use,energy savings and emission analysis in the Malaysian rubber producing industries

In this paper an analysis of energy use and energy conservation in the Malaysian rubber producing industries is presented. It has been found that rubber industries consume a substantial amount of energy. Excessive use of energy is usually associated with many industrial plants worldwide, and rubber plants are no exception. This study is based on the realization that enormous potential exists for cost-effective improvements in the existing energy-using equipment. Through the method of a walkthrough energy audit, power rating, operation time of energy-consuming equipment/machineries and power factor were collected. The data were then analyzed to investigate the breakdown of end-use equipment/machineries energy use. The results of the energy audit in the Malaysian rubber and rubber producing industries showed that the electric motor accounts for a major fraction of total energy consumption followed by pumps, heaters, cooling systems and lighting. Since the electric motor takes up a substantial amount of the total energy used in rubber industries, energy-savings strategies such as the use of high efficient motors, and variable speed drive (VSD) have been used to reduce energy consumption of motors used in rubber industries. Energy-savings strategies for compressed-air systems, boilers, and chillers have also been applied to estimate energy and cost savings. It has been found that significant amount of energy and; utility bills can be saved along with the reduction of emission by applying the foretold strategies for energy using machineries in the rubber industries.     

Generation management using batteries in wind farms: Economical and technical analysis for Spain

This paper presents an hourly management method for energy generated in grid-connected wind farms using battery storage (Wind–Batteries systems). The method proposed is analysed technically and economically.     

Energy use and appliance ownership in Ireland

This paper examines household energy use and appliance ownership in Ireland. Logit regression analyses on a large micro-dataset reveal how household characteristics can help explain the ownership of energy using appliances. Using OLS regression models, we explore the factors affecting residential energy demand conditional on appliance ownership. Results suggest that the methods of space and water heating employed by a household are even more important than electrical appliances in explaining domestic energy usage. However, the stock of appliances must be included in such models so that results will not be biased. The methods employed in this paper can be easily adopted for studies of household energy use in other countries where household expenditure survey data are available.     

考虑电转气与冷热负荷惯性的综合能源系统优化调度

风电、光伏等清洁能源发电具有反调峰特性和不确定性,容易造成弃风、弃光。为应对清洁能源消纳这一挑战,提出考虑电转气与冷热负荷惯性的综合能源系统优化调度模型。搭建电转气和冷热负荷惯性模型,并分析碳交易机制下电转气设备的工作特性以及冷热负荷惯性对其需求的影响,从而建立冷热负荷供需不等式约束条件;进一步建立考虑电转气与冷热负荷惯性的综合能源系统运行成本最小目标函数,以及相应的各机组与系统功率约束。通过YALMIP和GUROBI工具箱建立并求解最优调度模型,结果表明：所提方法能够提高清洁能源消纳能力,降低综合能源系统运行成本。