Showing papers in "International Journal of Energy Technology and Policy in 2007"

Adiabatic compressed air energy storage plants for efficient peak load power supply from wind energy: the European project AA-CAES

Abstract: With the continuing expansion of electricity generation from fluctuating wind power the grid-compatible integration of renewable energy sources is becoming an increasingly important aspect. Adiabatic compressed air energy storage power plants have the potential to make a substantial contribution here. The present article describes activities and first results relating to this technology that are being conducted within the European 'AA-CAES' Project. These interim results indicate not only the demanding design requirements for system components, but also the technical and economic feasibility of the concept.

Combined Heat and Power (CHP) essentials

Abstract: 'CHP essentials' introduces the concept of power and heat 'production possibility sets', starting at the cradle of CHP, i.e., the thermal power generation plant. The latter always occasions 'fatal' heat that is either recovered (the 'merit' of CHP) or wasted (condensing). This split paves the way to defining the production possibility sets of CHP plants, shown for steam turbines, internal combustion engines and gas turbines as main CHP technologies. Three indicators are widely used to monitor CHP performance: the overall conversion efficiency (quantity indicator), the (mostly ill-defined) power to heat ratio (quality indicator), the 'quality norm' advertised by the EU Directive 2004/8/EC. The paper levels the field for discussing the crucial issue of identifying and quantifying CHP activity.

Damping power system oscillations by genetically optimised PSS and TCSC controller

Abstract: This paper presents a procedure for modelling and simultaneous tuning of parameters of Thyristor Controlled Series Compensator (TCSC) controller and Power System Stabiliser (PSS) in a power system to damp power system oscillations. First, a simple transfer function model of TCSC controller is developed and the parameters of TCSC and PSS are simultaneously optimised. Genetic Algorithm (GA) is employed for optimisation of the parameter-constrained non-linear optimisation problem. The results obtained from simulations are presented to validate the effectiveness of the proposed approach. The approach is effective for the tuning of multiple controllers in a power system so that they operate in a coordinated manner. Further, the simulation results show that the proposed TCSC controller is also effective in damping a range of small disturbance conditions in the power system. Further, the TCSC controller is found to be robust and ensures stability of the power system for different operating conditions.

Fuzzy-based Static Synchronous Compensator (STATCOM) for improving transient stability performance

Abstract: The main aim of the paper is to design a fuzzy-based STATCOM for power-system damping. The proposed controllers are designed to coordinate two control inputs - the voltage of the STATCOM location and the capacitor voltage of the STATCOM - to improve the transient stability of a Single-Machine Infinite Bus (SMIB) system and short-scale multi-machine system. The two different STATCOM controllers, namely, (a) conventional PI controller, and (b) fuzzy-based controller, are considered for comparative study. The proposed controllers are tested under two system conditions. The Power Oscillation Damping (POD) control and Power System Stabiliser (PSS) and their coordinated action with proposed controllers are tested. The results indicate that the coordinated POD and PSS action further improves the dynamic performance of the system.

Improved genetic algorithm for voltage security constrained optimal power flow problem

Abstract: Voltage stability has become an important issue in the planning and operation of many power systems. Contingencies such as unexpected line outages in a stressed system may often result in voltage instability which may lead to voltage collapse. This paper presents a Genetic Algorithm (GA) approach for solving the Voltage Security Constrained Optimal Power Flow (VSC-OPF) problem. Base-case generator power output, voltage magnitude of generator buses, transformer tap position and reactive power generation of capacitor banks are taken as the control variables. Maximum L-index of load buses is used to specify the voltage stability level of the system. An improved GA which permits the control variables to be represented in their natural form is proposed to solve this combinatorial optimisation problem. For effective genetic operation, crossover and mutation operators which can directly operate on floating point numbers and integers are used. The proposed approach has been evaluated on the IEEE 30-bus test system. Simulation results show the effectiveness of the proposed approach for improving the voltage security of the system.

Characteristics of modern nonlinear loads and their influence on systems with distributed generation

Abstract: Nonlinear electronic loads may demonstrate unexpected reactions to variations in power system voltage. This effect of the electrical load may be very significant in distributed generation power systems containing relatively small generators. This paper reviews modern nonlinear electronic load current consumption mechanisms and provides typical current waveforms. Based on extensive measurements and field surveys, modified ZIP models have been developed to produce descriptive behaviour for a large class of nonlinear loads that account for cutoff voltages. Finally, an independent PC program was developed to analyse individual load equipment under varying voltage conditions based on the active and reactive powers at the rated voltage. The program also enables the study of combined loads (such as in a single residential or commercial building).

An optimal energy allocation model using fuzzy linear programming for energy planning in India for the year 2020

Abstract: Development of an energy allocation model will help in the proper allocation of the energy sources in meeting the future energy demand in India. In this paper, an attempt has been made to develop a fuzzy-based linear programming optimal energy model that minimises the cost and determines the optimum allocation of different energy sources for the centralised and decentralised power generation in India. The potential, energy demand, efficiency, emission and carbon tax are used as constraints in the model. The model allocates the energy distribution pattern for the year 2020 in India. The results indicate that the energy distribution pattern would be 15 800 GWh (4%) from the coal-based plants, 85 400 GWh (20%) from the nuclear plants, 191 100 GWh (44%) from the hydro plants, 22 400 GWh (5%) from the wind turbine generators, 45 520 GWh (11%) from the biomass gasifier plants, 14 112 GWh (3%) from the biogas plants, 8400 GWh (2%) from the solid waste, 33 600 GWh (8%) from the cogeneration plants and 11 970 GWh (3%) from the mini-hydel plants, for the year 2020. A sensitivity analysis has been done to validate the OEAM model. This study will help in the formation of strategies for the effective utilisation of energy sources in India.

Increasing of the quality of energy from stochastic fluctuating sources using dynamic power conditioning

Abstract: The stochastic fluctuating offer of wind energy limits the capacity of supply in electrical grids for technical and economical reasons. To increase the supply, a concept of dynamic conditioning with the objective of increasing the quality of supply was developed. The concept envisages supporting and managing the electrical grid, respectively by compensating of active and reactive power with static converters ('Electronic Synchronous Machine') and short term storage. Through the four-quadrant operation of the converters, short term fluctuation of the energy sources and changes of the load can be absorbed or smoothed directly on location. By using dynamic storage systems an intermediate storage of the stochastically offered primary energy is achieved. This low order energy can thereby be converted into high order recallable energy, which can even be used to satisfy peak demands. The local compensation of the fluctuation of the energy supply on the one hand and the changes of the demand on the other hand, allows a more steady energy demand from the nation-wide electrical grid.

Energy consumption and firm characteristics in the Hellenic manufacturing sector

Abstract: The main purpose of this paper is to present evidence on the relationship between energy consumption and selected firm characteristics in the Hellenic manufacturing industry. Special effort is made to examine the relation of firm energy consumption with some factors designed to reflect firm-level and industry-level characteristics. It is obvious that the paper proposes a microeconomic approach to the relevant questions. The reason is that, although the effects of the macroeconomic activities have been studied satisfactorily in terms of environmental problems, the study at the microeconomic level lags behind. The analysis uses regression models and is performed on a cross-sectional sample of 4,229 firms, classified by manufacturing sector. The results indicate that firms that are more capital intensive are, also, more energy intensive and that the consumption of energy is less in high technology industries. Large firms have an energy cost advantage in relation to smaller firms only in the low energy consuming industries.

Hydrothermal coordination using modified mixed integer hybrid differential evolution

Abstract: This work presents a novel modified Mixed Integer Hybrid Differential Evolution (MIHDE) algorithm, for solving the unit commitment problem of a hydrothermal power system. Hydrothermal scheduling involves the optimisation of a non-linear objective function with a set of system and hydraulic constraints. Discrete and dynamic constraints such as unit start-up/shutdown and minimum-up/minimum-downtime limits are also included in the hydro unit commitment. The problem of hydrothermal coordination is a mixed integer non-linear optimisation problem, which is well-suited for the use of MIHDE. In this paper, the MIHDE algorithm is modified in order to handle the reservoir end-volume and load balance constraints in the hydrothermal scheduling. The performance of the proposed approach is validated by illustration with standard test systems. The results of the proposed approach are compared with those techniques reported in literature. From the numerical results, it is found that the modified MIHDE-based approach is able to provide better solution at a relatively lesser computational effort.

Energy technologies for rural areas ? decentralised power generation through MARKAL modelling: a case study

Abstract: Due to shortage of power, extremely subsidised tariffs, poor financial recovery, long transmission lines, there exists a very poor demand-supply balance in the rural energy sectors of India. MARKAL bases analysis of a village-group in western India reveals that there is a potential of reducing the electricity demand by about 18% as compared to the business-as-usual case through adopting energy efficiency measures. Results show that in the studied area, renewable energy systems are not likely to penetrate without government subsidy. Sufficient potential was found for making the area independent from grid through decentralised electricity generation. Through decentralised electricity generation, there is a potential of reducing 2200 ton carbon-di-oxide emissions as compared to the business-as-usual case. Electricity generation through bio-gas plants for domestic consumption and through photovoltaic systems for irrigation pumps have been found more attractive as compared to other options.

Fast solution technique for unit commitment by particle swarm optimisation and genetic algorithm

Abstract: In solving the Unit Commitment (UC) problem, two types of decision variables need to be determined: the start/shut down status and the output of power generation. Efficiently calculating the optimal commitment (on/off) and Economic Dispatch (ED) generations of the units at a sequence of times in the scheduling period is known as a challenge issue. In this paper, the proposed integrated PSO/GA approach of UC using Genetic Algorithm (GA) consists of repeating the process of ED employing modified Particle Swarm Optimisation (PSO) and minimising the total objective function for combinatorial units over all scheduled periods. The performance of the integrated PSO/GA approach is compared with results of other algorithms in the literature used to solve the UC problem. The comparison shows that the integrated PSO/GA approach is efficient in terms of computational time while providing good solutions.

Wind energy and system security – the grid connection moratorium in Ireland

Abstract: This examines the interaction between technical challenges and policy choices that are made regarding wind power, and uses the grid connection moratorium in Ireland as a case study. While total installed wind capacity in Ireland is low compared with Germany, Spain and Denmark, wind power penetration is higher in the Irish system than in either the British, UCTE or NORDEL systems. In December 2003 the system operators expressed concerns about high wind power penetration, in particular the challenges of maintaining power system stability, security and reliability, resulting in a moratorium on new grid connection agreements. Significant progress has since been made in grid codes and dynamic models for wind turbines. In March 2006, there remain almost 3000 MW of proposed wind capacity awaiting a grid connection agreement This paper investigates the technical issues underpinning this moratorium, monitors progress made since its introduction and suggests alternative technical solutions to the moratorium.

Hardware-in-the-Loop testing platform for distributed generation systems

Abstract: The rapid validation of the expected performance of distributed generation installations is a critical step in the design process. However, the plethora of distributed generator types and the uniqueness of the load characteristics make the testing quite challenging. This paper introduces an original approach to Hardware-in-the-Loop simulation aimed to evaluate the performance and suitability of distributed generation installations. The approach is based on the Virtual Test Bed real-time simulator and enables rapid evaluation of the capability of a power source to match the power demand and dynamic properties of the local load by testing the actual power source in a synthetic load environment. The same platform can also be used to validate a simulation model of the fuel cell power source. The procedure is illustrated by a specific example of a fuel cell power source.

Solar thermal power plants for the Spanish electricity market

Abstract: Solar thermal power plants are at present the cheapest technology for solar electricity production. At good sites Levelised Electricity Costs (LEC) of 11 Ct/kWh have been achieved in commercially operated power plants. Economy of scale and further technical improvements will reduce the LEC for future projects. On the 27th of March 2004 in Spain the existing feed-in-law has been modified in order to support the erection of solar thermal power plants and thus make use of the huge solar potential of Spain. A payment of approx. 21 Ct/kWh, guaranteed for the first 25 years of operation, makes the erection and operation of solar thermal power plants very profitable for possible investors on the Spanish peninsula. This paper will present the present situation in Spain and the planned power plant projects. For one specific project the set-up is presented in more detail.

Pressurised pulverised coal combustion ? a coal-based combined-cycle state of the cooperative project: cleaned flue gas matches specifications for use with gas turbines

Abstract: A high efficiency of 60% in a combined-cycle power plant technology with fuels like gas or light oil is estimated to be achievable. On the other hand existing conventional coal-fired power plants based on steam generation have an efficiency of about 40?45%. A huge potential of improvement in efficiency could be achieved by the implementation of a simple and cost-effective technology: PPCC, a coal-based combined-cycle with combustion of coal at high pressure (up to 20 bar) and temperature (1500?C) with a subsequent efficient ash and alkali removal from the flue gas under pressure at process temperature to use it directly as input for a gas turbine. This process can be considered as the most suitable and straightforward design to utilise hard coal in a combined cycle with an efficiency of ~55% and above. The concept results in a straightforward and robust design at low installation and operating costs. We report the success in removing liquid ash particles to a content of <1 mg/m? s.t.p., particle diameters d <<1 ?m and the progress in alkali-reduction to a content <0.01 mg/m? s.t.p. thus meeting gas turbine specifications. Perspectives and possible spin-offs of the technology are deduced.

Quantifying Combined Heat and Power (CHP) activity

Abstract: The EU 2002 draft and 2004 final CHP Directives propose qualifying CHP activity with the quality norm. This norm benchmarks the energy efficiency of CHP plant outputs on external reference power and heat efficiencies. Because the quality norm amalgamates cogeneration and condensing activity its application entails particular perverse effects for high-quality and adapted scale investment in CHP capacities and for operating available units. Operators get incentives to part-load or shut down their capacities and to avoid condensing activity (lucrative at spiky price conditions in the power market). The formula of the quality norm is only useful when CHP activity (heat recovery, cogenerated electricity, fuel consumption for cogeneration) is first quantified reliably.

Mathematical optimisation techniques applied to power system operation and planning

Abstract: Nowadays, power system operation becomes more complex because of the critical operating conditions resulting from the requirements of a market-driven operation. In this context, efficient methods for optimisation of power system operation and planning become critical to satisfy the operational (technical), financial and economic demands. Therefore, the detailed analysis of modern optimisation techniques as well as their application to the power system problems represent a relevant issue from the scientific and technological points of view. This paper presents a brief overview of the developments on modern mathematical optimisation methods applied to power system operation and planning.

Power electronics for distributed and co-generation

Abstract: Distributed and Co-Generation has great growth potential, as the world is becoming more energy dependent and energy demanding. Distributed and Co-Generation creates alternative solutions to serve the growing energy market. In this paper, a comprehensive review of the different sources of distributed power is discussed including the main sources of the dispersed generation such as solar energy, fuel cell, microturbine, and wind energy, the application of the power electronics in distributed generation and co-generation, and the different kinds of modulation and their applications in AC-DC and DC-AC conversion for distributed generation.

Detection and classification of power quality events using multiwavelets

Abstract: Wavelet transforms have fundamentally been used to detect the major features of power quality events, as the transforms adapt to dynamic signals and are appropriate for capturing time-localised, short-period phenomena. The multiwavelets technique is proposed here to classify power quality events. This leads to easy extraction of a quality feature set, which is further used for classification and decision making. The proposed classification has three stages. The events detected from the test data are in accordance with the IEEE standards first stage. Two subclassifiers with different confidence levels have been used, along with the Dempster-Shafer classifier, which works as the decision-maker. The two subclassifiers are the chi-square distribution and Heuristic classifier.

Biofuel from algae ? photobiological hydrogen production and CO2-fixation

Abstract: The reduction of CO2-emissions that are damaging our climate is one of the major challenges of contemporary energy management. Nature itself offers us possibilities to produce energy CO2-neutrally with the help of hydrogen producing micro-algae. Under certain conditions the light energy collected by photosynthesis is used to transfer electrons to hydrogen producing proteins called hydrogenases. A new type of hydrogenase that produces molecular hydrogen with high rates was isolated (Happe and Naber, 1993) and characterised on genomic level (Happe and Kaminski, 2002) for the first time in green algae. Processes were recently developed that allow a long-term production of hydrogen by micro-algae (Melis et al., 2000). Under sulphur deprivation the green alga Chlamydomonas reinhardtii adapts its metabolism from oxygen production and CO2-fixation towards hydrogen production. Therefore the biotechnological process is divided into the growth, the hydrogen production and the utilisation and treatment of the available energy in the form of hydrogen and biomass.

Neural-based Tabu Search method for solving unit commitment problem for utility system

Abstract: This paper presents a new approach to solving short-term Unit Commitment Problem (UCP) using Neural-Based Tabu Search (NBTS) for utility system. The objective of this paper is to find the generation scheduling such that the total operating cost can be minimised, when subjected to a variety of constraints. This also means that it is desirable to find the optimal generating unit commitment in the power system for next H hours. A 66-bus utility power system with 12 generating units in India demonstrates the effectiveness of the proposed approach; extensive studies have also been performed for different IEEE test systems consisting of 24, 57 and 175 buses. Numerical results are shown to compare the superiority of the cost solutions obtained using the Tabu Search method, Dynamic Programming and Lagrangian Relaxation methods in reaching the proper unit commitment.

Transient stability improvement by optimally located STATCOMs employing genetic algorithm

Abstract: This paper deals with determining the optimal location of single and multiple Static Synchronous Compensators (STATCOMs) for a long transmission line with predefined direction of real power flow so that maximum improvement in its transient stability performance is achieved. A systematic procedure is proposed to determine the optimal location of a STATCOM employing Genetic Algorithm (GA). The location of STATCOM to minimise the rotor angle difference following a disturbance is formulated as an optimisation problem and the optimal location is searched by means of GA. A two-area test system is used to determine the optimal location of single and multiple STATCOMs to show the effectiveness of the proposed approach. The simulation results are presented to show that optimally located STATCOMs extend the critical clearing time and enhance the power system transient stability.

Control systems for small hydropower plants: a review

Abstract: Hydropower is emerging as a major contributor to world energy requirement. It is inexhaustible, clean and has many other benefits like flood mitigation, water supply, irrigation, etc. However, large-scale hydropower generation suffers from inherent disadvantages, such as massive financial outlays, long gestation periods, geological surprises, environmental factors and rehabilitation of the displaced population. Small power hydrostations, being devoid of these problems have become a viable alternative. Control systems and governors are key components of small hydropower stations as they have to supply stable power while accommodating varying load conditions and erratic water flows. They may also be required to operate in a 'stand-alone' mode i.e., not connected to any grid. This paper examines the role, functioning and design of control systems for small hydropower stations. The characteristics of control systems and traditional and modern designs of governors are discussed. Recent technological advances in the field of governors and control systems are discussed subsequently.

Power conditioning of an uncontrolled micro-hydroturbine-driven induction generator for distributed generation using a battery energy storage system

Abstract: Distributed Generation (DG) and its interconnection to the AC power grid is a relatively new concept. DG employs small generators, which are distributed throughout the power system. The electricity is usually generated by renewable energy sources such as wind, hydro and tidal, which are intermittent in nature. These generators connected to the AC grid may lead to severe power quality problems. The issues are the voltage dip while connecting/disconnecting the generator, and unbalanced and distorted power supply. In this paper, the power conditioning of a micro-hydro-driven induction generator connected to the grid using a Battery Energy Storage System (BESS) is simulated for voltage regulation, load balancing, load levelling, harmonics reduction and voltage dip mitigation during motor start-up.

The 700?C steam turbine power plant ? status of development and outlook

Abstract: This paper appraises the current development status of the 700?C steam power plant under consideration of process optimisation as well as design aspects of the steam turbine and steam generator. The results for a compact arrangement of the steam turbine and steam generator are also presented. Based on a cycle analysis, a net efficiency between 49.3% and 51.4% can be achieved with the 700?C steam power plant ? depending on the implementation and based on an inland plant site. No competing development activities for the 700?C steam power plant are known from the USA or Japan.

Online condition monitoring of electrical power system imbalance

Abstract: Symmetrical components are of great importance in many applications in electrical power systems, such as power protection and condition monitoring. This paper presents a computer-based algorithm for online symmetrical components estimation. The proposed algorithm uses the samples of the phase variables (currents or voltages) to estimate the magnitude and phase angle of each phase phasor at each sampling instant, and then these estimated phase phasors are used to formulate the symmetrical components as phasors and time-domain functions as well. Then the identified symmetrical components are used for condition monitoring of the electrical power system. Test examples of different power-system unbalanced conditions are computed to validate the developed algorithm.

The impact of the protection scheme of converter-connected distributed generation on power system transient stability

Abstract: In this paper the impact of the protection scheme of converter connected (power electronic interfaced) distributed generation (DG) on power system transient stability is investigated. Two simulation setups are used for this purpose. In the first setup, a small/simple test system is used and the converter connected DG is modelled as a practical three-phase full-bridge Voltage Source Converter (VSC). In the latter, a medium size power system is considered and the converter connected DG is represented as simple PQ-source. In both setups, two possible protection schemes of converter connected DG are studied. The first one disconnects the DG from the power network during a fault while the second one keeps the DG connected.

Optimum distribution of heat exchanger inventory and optimum thermal capacitance rate matching for power optimisation of a regenerated closed Brayton cycle

Abstract: The power output of the cycle is taken as objective for performance analysis and optimisation of an irreversible regenerated closed Brayton cycle coupled to variable-temperature heat reservoirs. The analytical formulae about the relations between power output and pressure ratio are derived with the heat resistance losses in three heat exchangers, the irreversible losses in the compressor and turbine, the pressure drop losses in the piping and system, and the effect of the finite thermal capacity rate of the heat reservoirs. The power output optimisation is performed by searching the optimum heat conductance distribution among the three heat exchangers for the fixed total heat exchanger inventory, and by searching the optimum thermal capacitance rate matching between the working fluid and the heat reservoir.

Combined cycles for CO2-capture with high efficiency

Abstract: The presented paper gives an overview on combined cycles for CO2-capture with high efficiency focussed on processes using a Solid Oxide Fuel Cell (SOFC), because of the air separating ability of the SOFC-membrane. The SOFC-membrane is only permeable for oxygen ions, so the cathode exhaust gas is oxygen depleted air, which should be discharged to the atmosphere after recycling or using the heat via a heat exchanger. Using fuels consisting of hydrocarbons like gasified fossil fuels and biomass or reformed (bio)gas, the anode exhaust gas consists of CO2, water vapour and not used gaseous fuel. If the not used gaseous fuel is separated and recycled instead of being burnt by mixing with the cathode exhaust gas as usual today, CO2 is left as only anode exhaust gas by simply condensing the water vapour. Similar results can be achieved by a mixed conducting membrane and chemical (metal?metal oxide) looping.