Design of isolated renewable hybrid power systems

Isolated electrical power generating units can be used as an economically viable alternative to electrify remote villages where grid extension is not feasible. One of the options for building isolated power systems is by hybridizing renewable power sources like wind, solar, micro-hydro, etc. along with appropriate energy storage. A method to optimally size and to evaluate the cost of energy produced by a renewable hybrid system is proposed in this paper. The proposed method, which is based on the design space approach, can be used to determine the conditions for which hybridization of the system is cost effective. The simple and novel methodology, proposed in this paper, is based on the principles of process integration. It finds the minimum battery capacity when the availability and ratings of various renewable resources as well as load demand are known. The battery sizing methodology is used to determine the sizing curve and thereby the feasible design space for the entire system. Chance constrained programming approach is used to account for the stochastic nature of the renewable energy resources and to arrive at the design space. The optimal system configuration in the entire design space is selected based on the lowest cost of energy, subject to a specified reliability criterion. The effects of variation of the specified system reliability and the coefficient of correlation between renewable sources on the design space, as well as the optimum configuration are also studied in this paper. The proposed method is demonstrated by designing an isolated power system for an Indian village utilizing wind-solar photovoltaic-battery system.     

Determination of design space and optimization of solar water heating systems

In this paper, a methodology is proposed to determine the design space for synthesis, analysis, and optimization of solar water heating systems. The proposed methodology incorporates different design constraints to identify all possible designs or a design space on a collector area vs. storage volume diagram. The design space is represented by tracing constant solar fraction lines on a collector area vs. storage volume diagram. It has been observed that there exists a minimum as well as a maximum storage volume for a given solar fraction and collector area. Similarly existence of a minimum and a maximum collector area is also observed for a fixed solar fraction and storage volume. For multi-objective optimization, a Pareto optimal region is also identified. Based on the identified design space, the solar water heating system is optimized by minimizing annual life cycle cost. Due to uncertainty in solar insolation, system parameters and cost data, global optimization may not be utilized to represent a meaningful design. To overcome this, a region of possible design configurations is also identified in this paper.     

Optimum sizing of battery-integrated diesel generator for remote electrification through design-space approach

Battery integrated diesel generation is one of the options for decentralized power production. They are particularly suitable for loads with significant variation in the daily demand. A methodology for the optimum sizing of integrated system involving diesel generator and battery bank for an isolated electrical power generation is proposed in this paper. The proposed methodology is based on the design-space approach involving a time series simulation of the entire system. Based on the proposed approach, for a given load demand, characteristics of the diesel generator and battery bank, a sizing curve is identified on the diesel generator rating vs. storage capacity diagram. The sizing curve helps in identifying all possible feasible system configurations or the design space. Based on the minimum capital cost and the minimum operating cost of the system, the Pareto optimum curve is identified on the system-sizing curve. Optimum system configuration is identified based on the minimum cost of energy through optimal dispatch strategy. Two operating strategies, involving continuous and intermittent operation of the diesel generator are studied and compared. Effect of the load profile on the system sizing is also presented in this paper.     

Optimum sizing of wind-battery systems incorporating resource uncertainty

The inherent uncertainty of the wind is a major impediment for successful implementation of wind based power generation technology. A methodology has been proposed in this paper to incorporate wind speed uncertainty in sizing wind-battery system for isolated applications. The uncertainty associated with the wind speed is incorporated using chance constraint programming approach. For a pre-specified reliability requirement, a deterministic equivalent energy balance equation may be derived from the chance constraint that allows time series simulation of the entire system. This results in a generation of the entire set of feasible design options, satisfying different system level constraints, on a battery capacity vs. generator rating diagram, also known as the design space. The proposed methodology highlights the trade-offs between the wind turbine rating, rotor diameter and the battery size for a given reliability of power supply. The optimum configuration is chosen on the basis of the minimum cost of energy (US$/kWh). It is shown with the help of illustrative examples that the proposed methodology is generic and flexible to incorporate alternate sub-component models.     

Techno‐economic optimization of hybrid power system using genetic algorithm

This paper presents an optimum sizing methodology to optimize the hybrid energy system (HES) configuration based on genetic algorithm. The proposed optimization model has been applied to evaluate the techno‐economic prospective of the HES to meet the load demand of a remote village in the northern part of Saudi Arabia. The optimum configuration is not achieved only by selecting the combination with the lowest cost but also by finding a suitable renewable energy fraction that satisfies load demand requirements with zero rejected loads. Moreover, the economic, technical and environmental characteristics of nine different HES configurations were investigated and weighed against their performance. The simulation results indicated that the optimum wind turbine (WT) selection is not affected only by the WT speed parameters or by the WT rated power but also by the desired renewable energy fraction. It was found that the rated speed of the WT has a significant effect on optimum WT selection, whereas the WT rated power has no consistent effect on optimal WT selection. Moreover, the results clearly indicated that the HES consisting of photovoltaics (PV), WT, battery bank (Batt) and diesel generator (DG) has superiority over all the nine systems studied here in terms of economical and environmental performance. The PV/Batt/DG hybrid system is only feasible when wind resource is very limited and solar energy density is high. On the other hand, the WT/Batt/DG hybrid system is only feasible at high wind speed and low solar energy density. It was also found that the inclusion of batteries reduced the required DG and hence reduced fuel consumption and operating and maintenance cost. Copyright © 2014 John Wiley & Sons, Ltd.     

负载缺电率用于独立光伏系统的最优化设计

在确定光伏方阵最佳倾角时,应综合考虑方阵面上太阳辐射量的连续性、均匀性和极大性。“夏半年”和“冬半年”周期内入射到倾斜面上的平均日辐射量Ｈ１和Ｈ２相等或在盯等之前Ｈ２有极大值,则其对应角度即为最佳倾角。通过改变相应放电深度的简便计算方法,即可得到应于不同负载缺电率的一系列光伏方阵与蓄电池容量组合,从而确定最方阵和蓄电池容量。     

Design of a stand alone system with renewable energy sources usingtrade off methods

The authors present an application of recent theoretical advances in multiobjective planning under uncertainty, in the design of a stand-alone system with renewable energy sources. The system under design consists of a wind energy plant, a solar plant, and an storage battery. Time series data on wind, insolation, and load for the site of interest are assumed to be available. The developed design methodology systematically selects the size of the various components of the system so as to give a robust design, i.e. a design that is a reasonable compromise between the conflicting design objectives under most foreseeable conditions     

Design of solar thermal systems utilizing pressurized hot water storage for industrial applications

A large number of industrial processes demand thermal energy in the temperature range of 80–240 °C. In this temperature range, solar thermal systems have a great scope of application. However, the challenge lies in the integration of a periodic, dilute and variable solar input into a wide variety of industrial processes. Issues in the integration are selection of collectors, working fluid and sizing of components. Application specific configurations are required to be adopted and designed. Analysis presented in this paper lays an emphasis on the component sizing. The same is done by developing a design procedure for a specific configuration. The specific configuration consists of concentrating collectors, pressurized hot water storage and a load heat exchanger. The design procedure follows a methodology called design space approach. In the design space approach a mathematical model is built for generation of the design space. In the generation of the design space, design variables of concern are collector area, storage volume, solar fraction, storage mass flow rate and heat exchanger size. Design space comprises of constant solar fraction curves traced on a collector area versus storage volume diagram. Results of the design variables study demonstrate that a higher maximum storage mass flow rates and a larger heat exchanger size are desired while limiting storage temperature should be as low as possible. An economic optimization is carried out to design the overall system. In economic optimization, total annualized cost of the overall system has been minimized. The proposed methodology is demonstrated through an illustrative example. It has been shown that 23% reduction in the total system cost may be achieved as compared to the existing design. The proposed design tool offers flexibility to the designer in choosing a system configuration on the basis of desired performance and economy.     

Technical and economic assessment of hybrid photovoltaic/wind system with battery storage in Corsica island

The sizing and techno-economical optimization of a stand-alone hybrid photovoltaic/wind system (HPWS) with battery storage is presented in this paper. The main objective of the present study is to find the optimum size of system, able to fulfill the energy requirements of a given load distribution, for three sites located at Corsica island and to analyze the impact of different parameters on the system size. The methodology used provides a useful and simple approach for sizing and analyzing an HPWS. In the proposed stand-alone system, a new concept such as the supply of wind power via a uninterruptible power supply (UPS) is introduced and therefore the energy produced by the wind generator can be sent directly to the load.     

Systematic comprehensive techno-economic assessment of solar cooling technologies using location-specific climate data

A methodology for assessing solar cooling technologies is proposed. The method takes into account location specific boundary conditions such as the cooling demand time series, solar resource availability, climatic conditions, component cost and component performance characteristics. This methodology evaluates the techno-economic performance of the solar collector/chiller system. We demonstrate the method by systematic evaluation of 25 feasible combinations of solar energy collection and cooling technologies. The comparison includes solar thermal and solar electric cooling options and is extended to solar cooling through concentrated solar power plants. Solar cooling technologies are compared on an economic and overall system efficiency perspective. This analysis has implication for the importance of solar load fraction and storage size in the design of solar cooling systems. We also stress the importance of studying the relation between cooling demand and solar resource availability, it was found that overlooking this relation might lead to overestimations of the potential of a solar cooling system in the range of 22% to over 100% of the actual potential.     

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.     

An analytical method to determine the optimal size of a photovoltaic plant

In this paper, a simplified method for the optimal sizing of a photovoltaic system is presented. The results have been obtained for Italian meteorological data, but the methodology can be applied to any geographical area. The system studied is composed of a photovoltaic array, power tracker, battery storage, inverter and load. Computer simulation was used to obtain the performance of this system for many values of field area, battery storage value, solar flux and load by keeping constant the efficiencies. A simple fit was used to achieve a formula relating the system variables to the performance. Finally, the formulae for the optimal values of the field area and the battery storage value are shown.     

Design and optimization of hybrid solar-hydrogen generation system using TRNSYS

Solar thermal systems are an efficient utilization of solar energy for hot water and space heating at domestic level. A Solar Water Heater (SWH) incorporating an Evacuated Glass Tube Collector (EGTC) is simulated using TRNSYS software. Efficiency parameters are pointed, and a parametric optimization method is adopted to design the system with maximum conceivable efficiency. In the first part, the selection of refrigerant for heat transportation in SWH loop is presented. A set of 15 working fluids are chosen, and their chemical properties are computed using NIST standard software (REFPROP). The selected working fluids are tested in the system under study and plots for energy gain and temperature are plotted using TRNSYS. Results showed that ammonia (NH₃) having specific heat 4.6kJ/kg-K and fluid thermal conductivity 2.12 kJ/hr-m supplies peak energy gain of 7500 kJ/h in winter and 8900 kJ/h in summer season along 120 °C temperature rise. On the other hand, R-123 having specific heat 0.65kJ/kg-K and fluid thermal conductivity 0.0293kJ/hr-m showed inferior performance during the simulation. A solar-hydrogen co-generation system is also designed and simulated under low solar insolation and warm climate regions to study annual hydrogen produced by the hybrid system. System comprises main components: a PV array, an electrolyzer, a fuel cell, a battery, a hydrogen storage unit and a controller in the complete loop. Results of Hydrogen cogeneration system provide 7.8% efficiency in the cold climate of Fargo North Dakota state due to lower solar insolation. While hot climate condition of Lahore weather provides efficiency of 11.8% which satisfy the statistics found in literature.     

Application of design space methodology for optimum sizing of wind–battery systems

A methodology for optimum sizing of different components (i.e., rotor diameter, electrical generator rating, and battery capacity) of a standalone wind–battery system is proposed in this paper. On the basis of time series simulation of the system performance along with different design constraints, the entire set of feasible design options, also known as the design space, has been identified on a rotor diameter vs. rated power diagram. The design space of a standalone wind–battery system identifies the entire envelope within which a feasible system may be designed. The optimum configuration of the standalone system is identified on the basis of minimum cost of energy (US$/kWh). It is observed that the cost of energy is sensitive to the magnitude of average demand and the wind regime. Sensitivity of the capital cost on the minimum cost of energy is also studied.     

Sizing of a stand-alone photovoltaic power system at Dhaka

A stand-alone photovoltaic power system is designed to operate residential appliances such as fluorescent lamp, incandescent light and ceiling fan using standard methods. The total load is estimated for four hours of operation per day. The battery is sized considering different factors that affect battery efficiency to reliably operate the estimated loads during a sequence of below average insolation. The minimum battery size is obtained to be 128Ah @ 100 hr, 24V. The PV array is sized to operate the load on a daily basis based on average weather conditions using monthly average daily values of solar radiation data for 11 years. The array is sized to proper values in order to operate the estimated load reliably in the month of minimum insolation taking into account different types of power losses. The minimum array size is obtained as 6×47W_p.     

Estimating the performance of a photovoltaic pumping system

A simple algorithm for estimating the long-term performance of a photovoltaic pumping system without battery storage is presented. This methodology uses the standard solar utilizability correlation equation to calculate the flow rate of a system with an insolation threshold and a pumping rate that has a nonlinear dependence on insolation. The algorithm's estimates of total monthly pumped volume compare well with those of an hourly simulation using Typical Meteorological Year data for four U.S. locations.     

A novel parameter extraction method for the one-diode solar cell model

With the increase in the capacity of photovoltaic generation systems, studies are being actively conducted to improve system efficiency. To develop precise solar cell simulators or design a high-performance photovoltaic generation system, it is important to accurately understand the physical properties of solar cells. However, solar cell models have a non-linear form with numerous parameters. To obtain accurate parameter values, assumptions that differ from real operating conditions must be made to avoid computational complexity. In this paper, a new method for extracting parameter values is proposed. The proposed method deduces the characteristic curve of an ideal solar cell without resistance using the I-V characteristic curve measured and reported by solar cell manufacturers and calculates the difference between the deduced and actual measured curves. In addition, the precision of the proposed method is demonstrated by calculating the correlation between the I-V characteristic curve based on modeling parameters and the I-V curve actually measured employing the least-squares method.     

Photovoltaic diesel-generator hybrid power system sizing

This research aims to minimize the cost of the PV system according to minimization of the PV array area and storage battery. In this paper, a new method is used to calculate the minimum number of storage days and the minimum PV array area. The pre-operating time of the diesel-generator is also incorporated in our system design. A system sizing program using FORTRAN language is developed. The program is used to size our experimental system which consists of a PV system, storage subsystem and diesel-generator. The proposed sizing program can be used to size any system. A comparison between stand-alone and hybrid system sizing is presented in this paper.     

SIZING AND TECHNO-ECONOMICAL OPTIMIZATION FOR HYBRID SOLAR PHOTOVOLTAIC/WIND POWER SYSTEMS WITH BATTERY STORAGE

A general methodology is presented for the sizing and optimization of renewable power supply systems, including hybrids such as those with solar photovoltaic and wind power components. The technical and economic optimum configurations are found by reference to periods over which the average resource (e.g. wind/solar) is least or the average load demand is greatest. For stand-alone systems, the annual autonomy is an important further design factor. This is the fraction of time for which the specified load can be met. The optimization seeks the least expensive system configuration which achieves the required autonomy level. It is the autonomy level which largely determines the size of battery storage capacity required. A system performance simulation procedure, with an hourly time-step, is used to obtain the autonomy levels of potentially optimum arrangements as the battery size is varied. Illustrative examples of the use of the method employ annual and monthly averaging periods, although any other period may be used. Data refer to the particular location and load pattern for an existing hybrid system, but the method is quite generally applicable. © 1997 by John Wiley & Sons, Ltd.     

Improving photovoltaic system sizing by using electrolyte circulation in the lead-acid batteries

Lead-acid batteries are, between all types of batteries, the most used today as storage systems for photovoltaic applications. The sizing of the lead-acid batteries is based on some external parameters, solar irradiation and load consumption, and some battery characteristics, charge capacity and efficiency, depth of discharge, operating voltage, and ageing effects. The improvement of any of these parameters will result in an improvement of the sizing of the lead-acid battery and, consequently, of the sizing of the photovoltaic array. We have studied in this paper the influence of the improved capacity of lead-acid batteries with electrolyte circulation onto the sizing of the lead-acid battery and the PV array. The experimental results have shown that the lead-acid battery capacity can be improved as much as 20% if electrolyte circulation is used. The improvement results in a reduction of up to 30% in the size of the battery if combined with the improvement in the reduction of the battery capacity due to annual cycling and ageing, another beneficial effect of the electrolyte circulation. The reduction of size is extended to the PV array which is affected not only by the above mentioned effects, but also by the higher charge efficiency of the electrolyte circulation battery. The reduction in sizing the PV array can be as much as 41% for the most exigent operating conditions, deep depth of discharge and high discharge rate. The use of an electrolyte circulation system is especially useful in lead-acid batteries for PV systems which must operate at very deep cycling and require a minimum size of the battery block.