A comparison of hydrogen storage technologies for solar-powered stand-alone power supplies: A photovoltaic system sizing approach

This paper compares the performance of three different solar based technologies for a stand-alone power supply (SAPS) using different methods to address the seasonal variability of solar insolation—(i) photovoltaic (PV) panels with battery storage; (ii) PV panels with electrolyser and hydrogen (_H2)$({\mathrm{H}}_2)$ storage; and (iii) photoelectrolytic (PE) dissociation of water for _H2${\mathrm{H}}_2$ generation and storage. The system size is determined at three different Australian locations with greatly varying latitudes—Darwin (12^°S${12}^{°}\mathrm{S}$), Melbourne (38^°S${38}^{°}\mathrm{S}$) and Macquarie Island (55^°S${55}^{°}\mathrm{S}$). While the PV/electrolyser system requires fewer PV panels compared to the PV/battery scenario due to the seasonal storage ability of _H2${\mathrm{H}}_2$, the final number of PV modules is only marginally less at the highest latitude due to the lower energy recovery efficiency of _H2${\mathrm{H}}_2$ compared to batteries. For the PE technology, an upper limit on the cost of such a system is obtained if it is to be competitive with the existing PV/battery technology.     

A generalized 3-D dynamic modelling for transverse flux homopolarlinear machines based on statistical saliency-effect superpositionmethod

This paper presents a prototype of a transverse flux homopolar linear machine system, along with a systematic and generalized 3-D approach which is capable of analyzing three kinds of these linear machines: the transverse flux linear induction machine; the homopolar linear synchronous machine; and the transverse flux linear reluctance machine; all in one compact mathematical model. A novel methodology which combines the state-space technique with the statistical saliency effect superposition method is proposed. With such a detailed and generalized modelling approach, the capability of analyzing the saliency effects induced by the distributed windings in practical linear machine systems is enhanced, and the representations of all the related linear machine system equations can be manipulated in compact matrix forms. Experimental verifications confirm that this comprehensive theoretical approach is a convenient and reliable mathematical basis for computer-aided analysis and design studies on linear machine systems     

A model for optimal sizing of solar thermal hydroelectric power plant

This paper presents the model for optimal sizing of a Solar Thermal (ST) power plant with parabolic collectors, which operates with Pump Storage Hydroelectric (PSH), all for the purpose of providing full energy independence of an isolated consumer. The sustainability of such system is based exclusively on solar energy input (without hybridization with any fossil fuel), as a renewable and pure energy resource, and the use of hydro energy, due to the possibility of its continuous production of energy. The feasibility and characteristics of the ST-PSH power plant were tested on power supply of the Island of Vis in Croatia, and the results show that the proposed model describes the operation of the power plant very well. For average solar irradiation of about 1500 kW h/m²/a, precipitation 644 mm/a, evaporation 1444 mm/a, volume of PSH upper reservoir of 20 h m³, electric energy consumption of 18 GV A h/a and reserve in the system for 3-4 months, the obtained power of the ST power plant is 22 MW, which can produce unit value of the annual thermal energy of 459 kW h/m²/a and electric energy of 160 kW h/m²/a, while the total collector aperture in the observed case is about 16 ha. These results show that ST-PSH plants can be successfully applied on locations with relatively low irradiation, wherein the key element that ensures continuous production of energy is precisely the PSH technology that can in the best way, in economic-technical, and especially in ecological sense, balance the relatively large summer surpluses and winter energy shortages.     

A novel optimization sizing model for hybrid solar-wind power generation system

This paper develops the Hybrid Solar-Wind System Optimization Sizing (HSWSO) model, to optimize the capacity sizes of different components of hybrid solar-wind power generation systems employing a battery bank. The HSWSO model consists of three parts: the model of the hybrid system, the model of Loss of Power Supply Probability (LPSP) and the model of the Levelised Cost of Energy (LCE). The flow chart of the HSWSO model is also illustrated. With the incorporated HSWSO model, the sizing optimization of hybrid solar-wind power generation systems can be achieved technically and economically according to the system reliability requirements. A case study is reported to show the importance of the HSWSO model for sizing the capacities of wind turbines, PV panel and battery banks of a hybrid solar-wind renewable energy system.     

A systems approach for sizing a stand-alone residential PEMFC power system

Polymer electrolyte membrane fuel cells (PEMFCs) show great promise in portable, automotive, and stationary applications. They have reached the test and demonstration phase in automotive and power markets today. This paper is focused on a stand-alone residential PEMFC power system that provides the electricity needs of the house. A novel stochastic sizing methodology is developed that considers both fuel cell system dynamics and residential load dynamics in overall system sizing for the stand-alone residential fuel cell power system. Understanding the nature of demand side is critical in stand-alone system sizing. Thus, experimental measurements have been completed to capture the load side dynamics in detail. No such data is found in the current literature. The Threshold Bootstrap method is used to model the residential load demand and to produce many realistic load profiles. Matlab/Simulink is used to run system simulations to determine system sizes based on parameters defined through a designed experiment. Comparison between the proposed sizing method and a possible worst case scenario sizing is given. The new sizing methodology can be used together with sophisticated demand analysis programs to obtain customized sizing for each user as stand-alone power systems become more viable.     

A comparison of two procedures for optimum sizing of a solar heating system

A model for building heat loss that includes hourly variation in solar radiation and windspeed was designed for use in evaluating solar heating system performance. Numerical simulations were run to see if, from an economic standpoint, the two effects were sufficiently large that a different solar collector size would be chosen than that selected using a heat loss model incorporating temperature only. The results show that solar system performance for the two models is significantly different on a daily basis but similar on a long term basis due to compensating factors. Thus, the simple model is adequate for selecting the optimum size of a solar collector.     

Hybrid electric power plant sizing strategy based on ab-initio fuel cell design for weight minimization

This work presents a methodology for the design of a hydrogen fuel cell-based hybrid electric power plant for hybrid electric vehicles (HEV), where a battery bank and ultracapacitors are also considered as components of the hybrid power plant. The methodology considers the design features of an electric vehicle and evaluates its energy and power requirements as to fulfil a driving cycle. The work starts by weight minimizing a fuel cell taking into consideration its physical and electrochemical characteristics. Batteries and ultracapacitors are then sized according to their dynamic response features and considering specifications from commercial candidate cells, to propose an electric configuration and specify the baseline for a hybrid power plant. In order to illustrate the methodology, a crossover utility electric vehicle and a WLTC class I drive cycle are used. This work shows that by reducing the power plant size, power and energy requirements can also be minimized and the overall performance can be increased promoting fuel and costs savings. For comparison and to show the impact of weight minimization on the energy on board and cost, this work presents the energy and power required by different power plant configurations. Results showed that including ultracapacitors to the power plant offers more benefits, such as less stress on batteries, at a marginal initial cost compared to a case without ultracapacitors, where batteries should attend transients with a limited capability for energy recovery from regenerative breaking. The methodology is easily implemented and does not large computational resources providing with a power plant baseline for further design stages, such as particular energy management approaches depending on particular priorities for the developer, such as range, productivity and performance, economy and others.     

Optimization strategy for element sizing in hybrid power systems

This paper presents a procedure to evaluate the optimal element sizing of hybrid power systems. In order to generalize the problem, this work exploits the “energy hub” formulation previously presented in the literature, defining an energy hub as an interface among energy producers, consumers and the transportation infrastructure. The resulting optimization minimizes an objective function which is based on costs and efficiencies of the system elements, while taking into account the hub model, energy and power constraints and estimated operational conditions, such as energy prices, input power flow availability and output energy demand. The resulting optimal architecture also constitutes a framework for further real-time control designs.Moreover, an example of a hybrid storage system is considered. In particular, the architecture of a hybrid plant incorporating a wind generator, batteries and intermediate hydrogen storage is optimized, based on real wind data and averaged residential demands, also taking into account possible estimation errors. The hydrogen system integrates an electrolyzer, a fuel cell stack and hydrogen tanks. The resulting optimal cost of such hybrid power plant is compared with the equivalent hydrogen-only and battery-only systems, showing improvements in investment costs of almost 30% in the worst case.     

An optimal sizing method for stand-alone photovoltaic power systems

The total life-cycle cost of stand-alone photovoltaic (SAPV) power systems is mathematically formulated. A new optimal sizing algorithm for the solar array and battery capacity is developed. The optimum value of a balancing parameter, M, for the optimal sizing of SAPV system components is derived. The proposed optimal sizing algorithm is used in an illustrative example, where a more economical life-cycle cost has been obtained. The question of cost versus reliability is briefly discussed.     

A new model of saturated synchronous machines for power systemtransient stability simulations

This paper presents a new method to express the main flux saturation in synchronous machines. In the new method, the saturation is expressed by auxiliary currents and unsaturated magnetizing inductances instead of the saturated inductances. The new model using the currents contains only constant coefficients defined in terms of the unsaturated magnetizing inductances     

A numerical approach to the flux density integral for reflected sunlight

A computer model of the central receiver system must evaluate the flux density on the receiver due to sunlight reflected by the heliostats in the collector field. Several approaches are available but each has its limitations. The Monte-Carlo approach represents all of the heliostat behavior but is relatively slow in terms of CPU time and is not suitable for optimization purposes. FLASH is an analytically exact approach for flat polygonal heliostats but is slow and not applicable to dished heliostats or aureole effects. Cone optics programs evaluate the flux density by a direct numerical integration of the double integral, but this method is very slow if accuracy is required. HCOEF is a two dimensional Hermite polynomial method which is relatively fast and can be extended to include canting, focusing, solar limb, and guidance error effects. However, the polynomial approximation breaks down for near heliostats, small guidance errors, and aureole effects. The new image generators based on KGEN overcome this limitation, but running times compare to FLASH and are 3 or 4 slower than HCOEF.The new approach proposed in this study assumes isotropic gaussian guidance errors. Hence, the flux density integral reduces to several iterated single integrals which can be precalculated and stored in a table for interpolation as needed. The LBL solar telescope data are fed into a convolution integral which represents the guidance errors. Aureole effects can be switched on or off at this point. A vector of convoluted solar data is input to another integration which gives the table of normalized flux contributions. The tabular values depend on the position of the flux point with respect to an edge of the heliostat as seen in the image plane. The image map of the heliostat is linear unless ripples or irregularities occur; hence, effects due to canting and dishing can be included by a ray trace of the heliostat vertices.The use of tabular interpolation is not as fast as expected because of the time required to calculate the distance between the flux point and the image of the vertices. The accuracy of this method is limited by interpolation errors, and better results can be obtained with the same CPU time if more core is used for a larger table. It is possible to eliminate the table by introducing a Romberg type of integrator which bisects the interval until sufficient accuracy is achieved; however, this approach is inefficient unless the images are relatively small compared to the receiver.The convolution process in KGEN is fast and can be used to calculate moments for HCOEF and coefficients for FLASH which utilize the LBL data.     

燃气轮机中冷循环功率和功率密度优化比较

计入高低温侧换热器和中冷器的热阻损失、压气机和涡轮机中的不可逆压缩和膨胀损失及管路中压力损失,用有限时间热力学方法导出了变温热源条件下不可逆闭式燃气轮机中冷循环功率和功率密度（功率与循环中最大比容之比）的解析式;分别以功率和功率密度为目标,优化了中间压比、高低温侧换热器及中冷器热导率分配,并对结果进行了比较.     

Direct control of air-gap flux in permanent-magnet machines

A new field weakening and adjustment technology for PM machines by direct control of air-gap fluxes is introduced. This new technology requires no current decomposition by the inverter eliminating the need for a position sensor. Demagnetization, which normally occurs during field weakening, does not occur with this new method. The field-weakening ratio can reach 10:1 or higher. This technology is robust and particularly useful for, but not limited to, electric vehicle drives and PM generators     

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.     

Performance comparison of an irreversible closed Brayton cycle under maximum power density and maximum power conditions

In this paper, the power density, defined as the ratio of power output to the maximum specific volume in the cycle, is taken as objective for performance analysis of an irreversible closed Brayton cycle coupled to constant-temperature heat reservoirs in the viewpoint of finite time thermodynamics (FTT) or entropy generation minimization (EGM). The analytical formulas about the relations between power density and pressure ratio are derived with the heat resistance losses in the hot- and cold-side heat exchangers and the irreversible compression and expansion losses in the compressor and turbine. The obtained results are compared with those results obtained by using the maximum power criterion. The influences of some design parameters on the maximum power density are provided by numerical examples, and the advantages and disadvantages of maximum power density design are analyzed. The power plant design with maximum power density leads to a higher efficiency and smaller size. However, the maximum power density design requires a higher pressure ratio than maximum power design. When the heat transfer is carried out ideally, the results of this paper become those obtained in recent literature.     

A unified approach to main flux saturation modelling in D-Q axismodels of induction machines

Main flux saturation is most frequently modelled by selecting either stator and rotor d-q axis currents or stator and rotor d-q axis flux linkages as state-space variables. This paper attempts to unify main flux saturation modelling in d-q axis models of induction machines by presenting a general method of saturation modelling. Selection of state-space variables in the saturated machine model is arbitrary and appropriate models in terms of different state-space variables result by application of the method. A couple of models, obtainable with different selection of state-space variables, are presented. The cross-saturation effect is explicitly present in all the models, except for the one with stator and rotor flux linkage d-q axis components as state-space variables. The models are verified by simulation and experimental investigation of induction generator self-excitation     

A new approach for sizing stand alone photovoltaic systems based in neural networks

Several methods for sizing stand alone photovoltaic (pv) systems has been developed. The more simplistic are called intuitive methods. They are a useful tool for a first approach in sizing stand alone photovoltaic systems. Nevertheless they are very inaccurate. Analytical methods use equations to describe the pv system size as a function of reliability. These ones are more accurate than the previous ones but they are also not accurate enough for sizing of high reliability. In a third group there are methods which use system simulations. These ones are called numerical methods.Many of the analytical methods employ the concept of reliability of the system or the complementary term: loss of load probability (LOLP). In this paper an improvement for obtaining LOLP curves based on the neural network called Multilayer Perceptron (MLP) is presented. A unique MLP for many locations of Spain has been trained and after the training, the MLP is able to generate LOLP curves for any value and location.     

Optimal sizing of projects in a hydro-based power system

The author considers the problem of obtaining the optimal design of hydroelectric power systems with respect to determining each project's optimal size or capacity. The problem of sizing projects is analyzed from a theoretical and economical standpoint, and a mathematical model is presented to examine project sizing in the general framework of expanding a purely hydroelectric system. The interaction between sizing and sequencing decisions is also discussed. The results give design rules for choosing the optimal size and marginal cost for individual projects, and show the interdependence of scaling and sequencing decisions. According to these rules, it is optimal to make the current marginal cost of each new project equal to the discounted weighted average of the long-term marginal unit cost for all future projects     

Unit sizing and control of hybrid wind-solar power systems

The aim of this paper is to provide the core of a CAD/CAA tool that can help designers determine the optimal design of a hybrid wind-solar power system for either autonomous or grid-linked applications. The proposed analysis employs linear programming techniques to minimize the average production cost of electricity while meeting the load requirements in a reliable manner, and takes environmental factors into consideration both in the design and operation phases. While in autonomous systems, the environmental credit gained as compared to diesel alternatives can be obtained through direct optimization, in grid-linked systems emission is another variable to be minimized such that the use of renewable energy can be justified. A controller that monitors the operation of the autonomous/grid-linked systems is designed. Such a controller determines the energy available from each of the system components and the environmental credit of the system. It then gives details related to cost, unmet and spilled energies, and battery charge and discharge losses     

Application of artificial neural network to estimate power generation and efficiency of a new axial flux permanent magnet synchronous generator

An estimation study on the output power and the efficiency of a new-designed axial flux permanent magnet synchronous generator (AFPMSG) is performed. For the estimation algorithm, a multi-layer feedforward artificial neural network (ANN) is developed. Various experimental results from the generator have been used for the training purpose in the cases of different electrical loads and rotational speeds. Some experimental data is kept out of the training process for testing the network and the errors have been evaluated after the formation of the network. According to the findings, a network with three layers has been adequate to achieve very good error percentage between the ANN and laboratory studies. The maximal testing error percentages are found to be nearly 3% and 4% for the output power and efficiency estimations, respectively. According to that finding, the developed ANN has a good property that it can be used in place of the designed generator, especially when the generator mathematical model is required. In addition, since power and efficiency are important for present applications, the present tool can be used to estimate the data for those characteristics of the machines and even it can be beneficial for the applications, where a nonlinear relationship among the power generation, generator efficiency, speed and load is required.