Design and control strategies of PV-Diesel systems using genetic algorithms

Hybrid photovoltaic systems (PV-hybrid) use photovoltaic energy combined with other sources of energy, like wind or Diesel. If these hybrid systems are optimally designed, they can be more cost effective and reliable than PV-only systems. However, the design of hybrid systems is complex because of the uncertain renewable energy supplies, load demands and the non-linear characteristics of some components, so the design problem cannot be solved easily by classical optimisation methods. When these methods are not capable of solving the problem satisfactorily, the use of heuristic techniques, such as the Genetic Algorithms, can give better results.The authors have developed the HOGA program (Hybrid Optimisation by Genetic Algorithms), a program that uses a Genetic Algorithm (GA) to design a PV-Diesel system (sizing and operation control of a PV-Diesel system). The program has been developed in C++.In this paper a PV-Diesel system optimised by HOGA is compared with a stand-alone PV-only system that has been dimensioned using a classical design method based on the available energy under worst-case conditions. In both cases the demand and the solar irradiation are the same. The computational results show the economical advantages of the PV-hybrid system. HOGA is also compared with a commercial program for optimisation of hybrid systems.Furthermore, we show a number of results and conclusions about hybrid systems optimised by HOGA.     

A novel anti islanding detection method for grid connected fuel cell power generation systems

Renewable energy sources have been developed rapidly all around the world, and one of these green energy sources is hydrogen energy. The fuel cell systems have become prominent in renewable energy sources because of its minimal dimensions and energy conversion method. There have been developed, some applications, especially in domestic and automotive areas, and fuel cell systems are also have been started to use in grid connected systems. Fuel cell systems must have some electrical connection standards while they connected to an electrical grid. One of these electrical conditions and may be the most important one is unplanned islanding condition. Islanding is a very dangerous situation because it can damage to the fuel cell and related electrical systems and also working people have been at risk in islanding situation on the grid. In this study, a novel islanding detection method was introduced for grid connected fuel cell systems. 0.5 kW solid oxide fuel cell (SOFC) system used in developed experimental system and a novel anti islanding detection method was researched by using an effective method. The proposed method was also developed by using Matlab Simulink and its useful tools. The developed islanding detection method is robust, reliable and has a fast response time, according to present methods. The results confirm the suggested conditions, and it can be seen in this method, it can also be adapted easily to the grid connected fuel cell systems.     

A review of materials for solar heating systems for domestic hot water

This paper reviews the fitness-for-purpose of commonly used materials and possible alternative materials for all components of solar heating systems for domestic hot water. Optimum materials are recommended where possible. A conclusion of the survey of materials which has been carried out is that, using current technology, reliable, durable solar heating systems can be built. The cost of such systems is high, due to the use of expensive materials (such as copper and stainless steel) and the systems are unlikely to be cost-effective in the long term. Costs can be reduced by the use of lower cost materials such as the polymerics for many of the components, but as yet there are insufficient materials performance data to ensure long-term reliability.     

Development and validation of a computational model for design analysis of a novel marine turbine

The vast tidal and wave energy resources represent a potential to use marine energy systems to supply part of the global energy demand. However, there are many advances required to develop economic and reliable marine energy systems, which some of these advances can be achieved by using the existing knowledge and experience from offshore and wind energy industry. This research presents a novel marine energy system that integrates the concept of a vertical and horizontal axis wind turbines by combining a Darrieus and Wells type rotor. However, many other different concepts have been proposed, but models that account for hydrodynamic, structure and control are needed to determine their technical and economical feasibility. With the use of the double‐multiple streamtube theory, a hydrodynamic model is developed to predict the performance and the loads on the turbine blades coupled with a finite element model to compute strains and stresses. To validate the model, we used strain data from field measurement of the demo prototype. The validated model was used to compute extreme stresses and calculate the fatigue life. The model gives reliable estimates of stresses and fatigue life. With this result, the design analysis of the turbine blades can be optimized for any site condition and expected life time. Copyright © 2012 John Wiley & Sons, Ltd.     

Incorporation of a new wind turbine generating system model into distribution systems load flow analysis

This paper describes a new model for wind turbine generating systems (WTGSs) that is widely used as distributed generation sources. The model is developed by using the bi‐quadratic equation, which is generally used for the calculation of the line voltages in distribution systems' load flow analysis, and facilitates computation of real and reactive power outputs of the WTGSs for a specified wind speed and terminal voltage. The developed model is validated with an experimental setup composed by an induction generator coupled with an induction motor as a prime mover. In addition to that, measured values are also compared with the calculated values, obtained by using the turbine models found in the literature. The incorporation of the developed model into some well‐known distribution systems' load flow algorithms is detailed. The effect of WTGSs on the power losses, voltage profile of radial distribution systems are evaluated for the sample test systems. Additionally, the performance of the load flow algorithms with the new model are examined and found to be robust and reliable. Copyright © 2008 John Wiley & Sons, Ltd.     

Reliable sealing design of metal-based solid oxide fuel cell stacks for transportation applications

Recently, metal-based solid oxide fuel cells (SOFCs) receive much attention as new power converting systems, and reliable sealing is an essential requirement for the metal-based SOFC stacks. In this study, metal-based SOFC stacks with a reliable sealing method are developed for transportation applications. For successful development, bolt-spring and hydraulic compression methods for stack tightening are discussed in terms of their applicability to vehicles. Then, detailed stack designs are developed to obtain sufficient compressive stress on the surfaces of the sealing gaskets based on the finite element method (FEM). To maintain the compression and heat insulation of the stack, a hot box is designed based on the thermogravimetric properties, shrinkage behaviors, and mechanical properties of sealing gaskets of mica and Thermiculite 866LS, and ceramic fiber insulating board. As a result, a 1-cell stack unit is successfully fabricated and tested based on the designs, and a sealing rate of 100 ± 0.78% is achieved at an operating temperature of 800 °C. This study investigates comprehensive stack and sealing design processes, and it has broad implications for reliable stack development.     

Microprocessor-based fault-tolerant reactor control and informationsystem

The reactor manual control system (RMCS) and the rod position information system (RPIS) applied to boiling water reactor power plants are among the most important systems in controlling the output of nuclear reactor power. A highly reliable RMCS and RPIS employing microprocessors is presented. The developed equipment has been made fault tolerant by adopting the redundancy of each system. The amount of cabling normally required has been reduced by multiplexing transmission via fiber-optic cable. The size of the control panel has been reduced and maintainability improved. The system hardware and software have been standardized into units and modules, which provides the equipment with sufficient flexibility to cope with plants with a varying number of control rods. This system can be applied to the replacement of conventional systems in operating plants as well as initial installation in new plants     

Fuel cells and odorants for hydrogen

Odorants have been proposed as a reliable, inexpensive means to enable leak detection for hydrogen systems and increase public safety. However, traditional odorants cause problems for fuel cell systems. This paper examines the use of odorants for fuel cell systems, including the hydrogen storage. Current odorants and potential odorants have negative impacts on fuel cell performance. Odorants also appear to be problematic for most of the advanced hydrogen storage options. If odorants are used, the odorants will probably need to be removed from the hydrogen prior to the storage medium. Current hydrogen detectors are more reliable than the odorant–human detection system and should provide increased safety.     

Technological aspects of advancement in low-capacity solar thermal desalination units

Drinking water of acceptable quality has become a scarce commodity. The standard high-capacity desalination methods such as multi-stage flash evaporation and multi-effect evaporation, vapour compression and reverse osmosis are reliable in the range of about 100–500,000 m³/day fresh-water productions. However, the wide-scale implementations of these methods face numerous technological, economic and political barriers and these methods are not used in decentralised regions with a poor infrastructure due to their permanent need of qualified maintenance and electricity supply. In this paper, various low-capacity solar thermal desalination systems, with fresh-water output production in the range of 10–150 l/day for the use in rural areas, are reviewed and classified based on five technological aspects such as the development of the technology of the systems, the applicability of high-capacity thermal desalination technologies, the enhancement of solar heat collectors, the hybridisation of thermal desalination technologies and heat recovery processes. Most of the reviewed systems are in the research stage and have not cleared economic feasibility such as the price per cubic metre of water that may stimulate the decision-maker to direct these studies into the actual commercial applications to find a solution to the water scarcity problem in isolated and remote areas. Although many of the developed systems have several novel and valuable features, more efforts are required for further investigating more efficient, economic and applicable solar energy-driven low-capacity desalination systems.     

Mathematical dynamic modeling and thermal-hydraulic analysis of HANARO

This paper describes the development of a dynamic model of HANARO (High-Flux Advanced Neutron Application Reactor), an open tank in pool type research reactor. The reliable dynamic model of the reactor and its cooling systems is developed to perform the thermal-hydraulic analysis for transients. The developed dynamic model is properly implemented in the transient simulation code, H-SIM, which is compiled and executed on a personal computer (PC) using the DESIRE simulation language. The H-SIM is intended for simulating efficiently the operational characteristics and the thermal-hydraulic behavior of HANARO for many transients. The simulation for HANARO transients shows a proper thermal-hydraulic behavior trend for the power step change. Results from the H-SIM with reference calculations are found in general to be very encouraging and the dynamic model is judged to be versatile to fulfill its intended purpose.     

大型燃气发动机起动系统设计与试验研究

在原柴油机基础上研制了6缸燃气发动机,其燃气进气方式为增压前预混,如采用原压缩空气起动方式将无法实现该燃气发动机的可靠起动。对此研究了新型起动系统——三缸起动系统,介绍了其工作原理和设计方案,并针对该系统在试验中暴露的问题进行了改进设计。试验验证表明:改进后的起动系统可保证该燃气发动机的可靠起动。     

Photovoltaic systems for distributed power supply in Nigeria

An adequate and reliable electricity supply system is essential for any developing country. This paper examines the problems in the electricity supply system in Nigeria. Solar photovoltaic (PV) systems are reckoned to be viable alternatives for reliable power supply, particularly for small loads in remote areas and rural communities. The status and potential of photovoltaics in Nigeria are examined, particularly for village electrification and telecommunications. Results of surveys of PV systems installed in the country are presented and policies that would encourage the dissemination of the systems are discussed.     

Heat transfer correlations for vertical mantle heat exchangers

This paper investigates heat transfer in vertical mantle heat exchangers for application in low flow solar domestic hot water systems. Two new heat transfer correlations for vertical mantle heat exchangers with top entry port and bottom exit ports are developed. The correlations are based on computational fluid dynamic modelling of whole vertical mantle tanks. The correlations are combined with a heat storage model in a simulation program that predicts the yearly thermal performance of low flow solar domestic hot water systems based on mantle tanks. The model predictions of energy gains and temperatures are compared with outdoor measurements and the model is found to give reliable results.     

Integrated evaluation of distributed triple-generation systems using improved grey incidence approach

Several distributed triple-generation (DTG) system options to produce cooling, heating and power have been evaluated and compared in a multi-criteria method, such as technical, economic, environmental and social aspects. Due to the fuzzy or uncertain evaluation criteria, this paper presents an improved grey incidence evaluation method for DTG systems. This method adopts the combination of the improved analytic hierarchy process (AHP) and the entropy information method together with the use of linear combination weighting. The optimal weighting method combines both the subjectivity of decision-maker and the objectivity of numerical data to obtain the comprehensive assessment result. As an example, several kinds of DTG systems, whose dynamical sources are respectively Gas Turbine, Gas Engine, Stirling Engine and Fuel Cell, and a separate generation system are compared and evaluated in detail. Based on the different priority to evaluation indexes, the optimal DTG options are established. The results show that this method is simple and practical, and it can provide a reliable evaluation method for DTG systems.     

A grid based multi-objective evolutionary algorithm for the optimization of power plants

There is an increasing need for optimization of energy conversion systems, in particular concerning energy consumption and efficiency to reduce their environmental impact. Usually, optimization is based on designers’ backgrounds, which are able to analyze system performances and modify appropriate operating parameters. However, if these changes aim to optimize simultaneously multiple conflicting objectives, the task becomes quite complex and the use of sophisticated tools is mandatory. This paper presents a multi-objective optimization method that permits solutions that simultaneously satisfy multiple conflicting objectives to be determined. The optimization process is carried out by using an evolutionary algorithm developed around an innovative technique that consists of partitioning the solution search space (i.e., a population of solutions) into parallel corridors. Within these corridors, “header” solutions are trapped to be then involved in a reproduction process of new populations by using genetic operators. The proposed methodology is coupled to specific power plant models that are used to optimize two different power plants: (i) a cogeneration thermal plant and (ii) an advanced steam power station. In both cases the proposed technique has shown to be very powerful, robust and reliable. Further, this methodology can be used as an effective tool to find the set of best solutions and thus providing a realistic support to the decision-making.     

Determination of state-of-charge and state-of-health of batteries by fuzzy logic methodology

A practical method of predicting state-of-charge (SOC) and state-of-health (SOH) of battery systems has been developed and tested for several systems. The method involves the use of fuzzy logic mathematics to analyze data obtained by impedance spectroscopy and/or coulomb counting techniques. Fuzzy logic provides a powerful means of modeling complex, non-linear systems without the need for explicit mathematical models. New detailed impedance date has been obtained on the discharge performance of primary lithium/sulfur dioxide cells. Earlier data, obtained by Rutgers co-workers on nickel/metal hydride and other systems, have been reviewed and re-interpreted using fuzzy logic methodology. Devices are being developed for several systems, which will predict the SOC and SOH of batteries without the need to know their previous discharge and/or cycling history.     

Investigation of the Soret effect in binary,ternary and quaternary hydrocarbon mixtures: New expressions for thermodiffusion factors in quaternary mixtures

Thermodiffusion or the Soret effect in binary, ternary and quaternary hydrocarbon mixtures is studied. Using the linear non-equilibrium thermodynamic (LNET) approach, expressions are derived for the estimation of the thermodiffusion coefficients or factors in quaternary mixtures using different approaches. New series of experimental data for binary, ternary and quaternary mixtures are used to evaluate the performance of the Firoozabadi, Kempers (Haase) and our two developed expressions based on the LNET approach. Results show that the model expressions are generally more effective for binary mixtures. In binary mixtures, the Firoozabadi model is preferred, whereas in ternary and quaternary mixtures, our developed expressions based on the LNET and the LNET–Kempers combined approach are superior. Overall, we may conclude that the LNET approach, extended by the authors to ternary and quaternary mixtures, is a reliable model for less-complex systems, such as the linear hydrocarbon mixtures. The LNET approach is also flexible in that provided the required modifications are made, it may be applicable to more complex systems, such as associating mixtures, as well. It is also argued that a thermodiffusion model should be independent of the mass transfer frame of reference, as thermodiffusion coefficients are calculated at the steady state condition, where all fluxes are zero.     

Benefits of partial-state-of-charge operation in remote-area power-supply systems

Many people throughout the world are remote from electricity networks and do not have access to reliable power. Remote-area power-supply (RAPS) systems offer a reliable and cost-effective alternative to grid connection. Achieving adequate performance from such systems requires appropriate componentry and well-designed control systems/strategies. A relatively new operating methodology—known as partial-state-of-charge (PSoC) operation—is now finding application in the field. The strategy, which can give a three-fold increase in the lifetime energy-delivery of gelled-electrolyte batteries compared with that obtained using traditional charging procedures, is to be employed in RAPS systems in Peru. The PSoC algorithms will be formulated and trailed in the laboratory, and then installed in the Peru facilities where they will be monitored and controlled remotely via a satellite link-up. This approach allows the algorithms to be fine-tuned in situ, and will ensure that system efficiency and battery lifetime are maximised. Use of the PSoC concept is expected to provide a battery lifetime of 8 years.     

Modeling and simulation of grid-connected photovoltaic energy conversion systems

Solar power generation using PV (photovoltaic) technology is a key but still evolving technology with the fastest growing renewable-based market worldwide in the last decade. In this sector with tremendous potential for energy security and economic development, grid-connected PV systems are becoming today the most important application of solar PV generation. Based on this trend, PV system designers require an accurate and reliable tool in order to predict the dynamic performance of grid-tied PV systems at any operating conditions. This will allow evaluating the impact of PV generation on the electricity grids. This paper presents a detailed characterization of the performance and dynamic behavior of a grid-connected PV energy conversion system. To this aim, a flexible and accurate PV simulation and evaluation tool (called PVSET 1.0) is developed. The PV system is modeled, simulated and validated under the MATLAB/Simulink environment. The accuracy of simulation results has been verified using a 250 Wp PV experimental set-up.     

Experimental evaluation of solar thermosyphons with heat exchangers

The advantages of solar thermosyphons in terms of simplicity, reliability and cost have long been recognized. Recent studies have also shown their thermal performance to be comparable with that of equivalent active systems. When pump power is considered, the energy savings of domestic hot water thermosyphons can be significantly superior to active systems. In spite of these advantages, use of solar thermosyphons in the United States is almost negligible compared to their widespread use in other countries. A major limitation to the use of thermosyphons in the United States is lack of effective, reliable freeze protection. One technique for reliable, passive freeze protection is to use a heat exchanger in the storage tank and a nonfreezing fluid in the collector. Previous analytical work indicates that the performance penalty for these systems with practical-sized heat exchangers may be small enough to make these systems economically feasible. A full-scale, residential-size test facility has been constructed for testing this concept and validating the theoretical models. This paper describes results of testing comparing the performance of a horizontal tank with and without heat exchanger to a baseline case of a vertical tank without heat exchanger. An analytical expression for a “heat exchanger penalty factor” for these systems is derived and compared with the experimental results.