Energy balance analysis of a stand-alone photovoltaic system, including variable system reliability impact

Official statistics estimate that almost two billion people have no direct access to electrical networks, 500,000 of them living in European Union and more than one tenth of them in Greece. An autonomous photovoltaic system is one of the most interesting and environmental friendly technological solutions for the electrification of remote consumers or entire rural areas. The primary objective of this current study is to determine the optimum dimensions of an appropriate stand-alone photovoltaic system, able to guarantee the coverage of remote consumers energy demand located in typical Greek territories using long-term measurements, under the restriction of minimum initial cost. Accordingly, the impact of acceptable reliability level on the stand-alone photovoltaic system energy behaviour and initial cost is also examined. Finally, special emphasis is laid on the detailed energy balance analysis of selected stand-alone photovoltaic system configurations, on an hourly basis at least. According to the results obtained, a properly sized stand-alone photovoltaic system is a motivating prospect for the energy demand problems of numerous existing isolated consumers all around Greece.     

Minimization of the energy storage requirements of a stand‐alone wind power installation by means of photovoltaic panels

Autonomous wind power systems are among the most interesting and environmentally friendly technological solutions for the electrification of remote consumers. In many cases, however, the battery contribution to the initial or the total operational cost is found to be dominant, discouraging further penetration of the available wind resource. This is basically the case for areas possessing a medium–low wind potential. On the other hand, several isolated consumers are located in regions having the regular benefit of an abundant and reliable solar energy supply. In this context the present study investigates the possibility of reducing the battery size of a stand‐alone wind power installation by incorporating a small photovoltaic generator. For this purpose an integrated energy production installation based exclusively on renewable energy resources is hereby proposed. Subsequently a new numerical algorithm is developed that is able to estimate the appropriate dimensions of a similar system. According to the results obtained by long‐term experimental measurements, the introduction of the photovoltaic panels considerably improves the operational and financial behaviour of the complete installation owing to the imposed significant battery capacity diminution. Copyright © 2006 John Wiley & Sons, Ltd.     

Cost–benefit analysis of remote hybrid wind–diesel power stations: Case study Aegean Sea islands

More than one third of world population has no direct access to interconnected electrical networks. Hence, the electrification solution usually considered is based on expensive, though often unreliable, stand-alone systems, mainly small diesel-electric generators. Hybrid wind–diesel power systems are among the most interesting and environmental friendly technological alternatives for the electrification of remote consumers, presenting also increased reliability. More precisely, a hybrid wind–diesel installation, based on an appropriate combination of a small diesel-electric generator and a micro-wind converter, offsets the significant capital cost of the wind turbine and the high operational cost of the diesel-electric generator. In this context, the present study concentrates on a detailed energy production cost analysis in order to estimate the optimum configuration of a wind–diesel-battery stand-alone system used to guarantee the energy autonomy of a typical remote consumer. Accordingly, the influence of the governing parameters—such as wind potential, capital cost, oil price, battery price and first installation cost—on the corresponding electricity production cost is investigated using the developed model. Taking into account the results obtained, hybrid wind–diesel systems may be the most cost-effective electrification solution for numerous isolated consumers located in suitable (average wind speed higher than 6.0 m/s) wind potential regions.     

Optimum autonomous stand-alone photovoltaic system design on the basis of energy pay-back analysis

Stand-alone photovoltaic (PV) systems comprise one of the most promising electrification solutions for covering the demand of remote consumers. However, such systems are strongly questioned due to extreme life-cycle (LC) energy requirements. For similar installations to be considered as environmentally sustainable, their LC energy content must be compensated by the respective useful energy production, i.e. their energy pay-back period (EPBP) should be found less than their service period. In this context, an optimum sizing methodology is currently developed, based on the criterion of minimum embodied energy. Various energy autonomous stand-alone PV-lead-acid battery systems are examined and two different cases are investigated; a high solar potential area and a medium solar potential area. By considering that the PV-battery (PV-Bat) system's useful energy production is equal to the remote consumer's electricity consumption, optimum cadmium telluride (CdTe) based systems yield the minimum EPBP (15 years). If achieving to exploit the net PV energy production however, the EPBP is found less than 20 years for all PV types. Finally, the most interesting finding concerns the fact that in all cases examined the contribution of the battery component exceeds 27% of the system LC energy requirements, reflecting the difference between grid-connected and stand-alone configurations.     

Sizing a hybrid wind-diesel stand-alone system on the basis of minimum long-term electricity production cost

Hybrid wind-diesel systems are an interesting solution for the electrification of isolated consumers. The proposed system, including a properly sized battery, leads to a significant reduction of the fuel consumption, in comparison with a diesel-only installation, also protecting the diesel generator from excessive wear. On the other hand, a properly designed wind-diesel installation remarkably reduces the required battery capacity, in relation to a wind-only based stand-alone system, especially in medium-low wind potential areas. In this context, a complete sizing model, based on a long-term energy production cost analysis is developed, able to predict the optimum configuration of a hybrid wind-diesel stand-alone system on the basis of minimum long-term cost. According to the application results obtained for representative wind potential cases, the proposed hybrid system guarantees one year’s long energy autonomy of a typical remote consumer, presenting a significant cost advantage in relation either to a diesel-only or to a wind-based stand-alone system.     

Rural photovoltaic electrification program in Jordan

The photovoltaic (PV) technology potential for Jordan is high, based on the fact that many remote and isolated sites are located far away from the national electric grid and cannot be connected to it in the near future. Therefore, a rural PV electrification program—driven by quality-of-life improvement for the users—was launched in Jordan in 2002. An important element of the program is the access of low-income, rural consumers to essential electricity.This paper discusses and analyses the first stage of this program that is the electrification of a remote and small Jordanian village. Nine PV solar home systems (SHS) were installed in this village in order to provide lighting and power for radio and television.Feed back from the users of the installed systems indicates that the PV based electricity has been providing very satisfactory service to the consumers, and that it is an appropriate technology suitable for dissemination in the rural Jordanian areas.     

Energy pay-back period analysis of stand-alone photovoltaic systems

The exploitation of solar energy by autonomous, photovoltaic (PV) based systems offers the opportunity for satisfying the electrification needs of numerous remote consumers worldwide in an environmentally friendly way. On the other hand, the sustainable character of these systems is strongly questioned by the energy intensity of processes involved in the various life cycle (LC) stages of the system components. Although there are several studies concerned with the estimation of the energy pay-back period (EPBP) for grid-connected systems, the same is not valid for stand-alone configurations. In this context, an integrated methodology is currently developed in order to estimate the EPBP of PV-battery (PV-Bat) configurations ensuring 100% energy autonomy. The main scope of the proposed analysis is to determine the optimum size of a corresponding system, comprised of multi-crystalline (mc-Si) PV modules and lead-acid (PbA) batteries, based on the criterion of minimum embodied energy, i.e. minimum EPBP. For this purpose, a representative case study examined considers the electrification needs of a typical remote consumer on the Island of Rhodes, Greece. According to the results obtained, the autonomous energy character of the system is reflected by the comparatively higher EPBP in comparison with the corresponding grid-connected option, nevertheless the PV-Bat configurations analyzed clearly constitute sustainable energy solutions. Finally, in order to increase the reliability of the calculation results, a sensitivity analysis is carried out, based on the variation of the input energy content data.     

Energy balance analysis of wind-based pumped hydro storage systems in remote island electrical networks

The introduction of pumped hydro storage (PHS) systems in isolated electrical grids, such as those found in island regions, appears to be a promising solution that is able to face both the high electricity production cost and the continuously increasing power demand encountered in these areas. In this context, the current work presents a methodology for the sizing of PHS systems that exploit the excess wind energy amounts produced by local wind farms, otherwise rejected due to imposed electrical grid limitations. The methodology is accordingly applied to the Greek island of Lesbos. Initially, a calculation of the wind power penetration ability to the local grid is carried out and the corresponding curtailments of existing and future wind farms are determined. An integrated computational algorithm is then presented which simulates the operation of the system during an entire year and gives in detail the hourly operational status as well as the various energy losses of the system main components. Based on the application results obtained, the ability of the wind energy to remarkably contribute to the electrification of the remote islands becomes evident.     

Renewable-energy integration assessment through a dedicated computer program

This article is intented to present an approach to assess the possibilities of renewable resources through the dynamics of stand-alone and system-integrated renewable-based power plants. Mainly solar and wind energy will be considered leading to the computer program devoted to the simulation of both solar photovoltaic power plants and wind energy converters. Besides, the assessment of the integration of these kinds of intermittent resources into hybrid systems, either pure renewable with hydro-pumped storage units or along with conventional power systems, is the main objective of the program. Finally, the program is aimed at scenario assessment, allowing different energy-mix scenarios to be compared involving both renewable and conventional power plants. Because of the complexity of the problem in a real case, it is useful to stress the rough assessment that will be made in this first version. Examples are provided involving the main topics dealt with.     

Multi-objective optimization of batteries and hydrogen storage technologies for remote photovoltaic systems

Stand-alone photovoltaic (PV) systems comprise one of the promising electrification solutions to cover the demand of remote consumers, especially when it is coupled with a storage solution that would both increase the productivity of power plants and reduce the areas dedicated to energy production.     

Optimised model for community-based hybrid energy system

Hybrid energy system is an excellent solution for electrification of remote rural areas where the grid extension is difficult and not economical. Such system incorporates a combination of one or several renewable energy sources such as solar photovoltaic, wind energy, micro-hydro and may be conventional generators for backup. This paper discusses different system components of hybrid energy system and develops a general model to find an optimal combination of energy components for a typical rural community minimizing the life cycle cost.The developed model will help in sizing hybrid energy system hardware and in selecting the operating options. Micro-hydro-wind systems are found to be the optimal combination for the electrification of the rural villages in Western Ghats (Kerala) India, based on the case study. The optimal operation shows a unit cost of Rs. 6.5/kW h with the selected hybrid energy system with 100% renewable energy contribution eliminating the need for conventional diesel generator.     

Simulation of a combined wind and solar power plant

The combined generation of electricity by wind and solar energy is a very attractive solution for isolated regions with high levels of yearly wind energy and insolation. A computer model is developed for the simulation of the electricity system of a Mediterranean island, including a wind power plant, a photovoltaic power plant and a storage system. In order to obtain an overall view of the system performance and economic aspects, the model also incorporates a number of diesel generators. Daily simulations for the Greek island Kythnos show that such a combined system of moderate size can provide a large fraction of the electrical energy requirements. Various parameters calculated in the simulation can be used to improve the configuration of the system and to estimate the cost of the electrical energy unit.     

Analytical model for predicting the performance of photovoltaic array coupled with a wind turbine in a stand-alone renewable energy system based on hydrogen

We present the results of an analysis of the performance of a photovoltaic array that complement the power output of a wind turbine generator in a stand-alone renewable energy system based on hydrogen production for long-term energy storage. The procedure for estimating hourly solar radiation, for a clear sunny day, from the daily average solar insolation is also given. The photovoltaic array power output and its effective contribution to the load as well as to the energy storage have been determined by using the solar radiation usability concept. The excess and deficit of electrical energy produced from the renewable energy sources, with respect to the load, govern the effective energy management of the system and dictate the operation of an electrolyser and a fuel cell generator. This performance analysis is necessary to determine the effective contribution from the photovoltaic array and the wind turbine generator and their contribution to the load as well as for energy storage.     

Experimental performance assessment of an online energy management strategy for varying renewable power production suppression

Lately, interest in renewable sources, especially wind and solar energy, has shown a significant increase in all over the world that mostly depends on climate-threatening conventional fossil fuels. Besides, hybrid use of these power sources with suitable back-up units provides many advantages compared to sole use of these sources. In this regard, a hybrid system consisting of a wind turbine for utilizing the wind energy, photovoltaic panels for solar energy, fuel cell for providing back-up power and a battery unit for storing the possible excess energy production and supplying the transient load is considered in this study. Experimental assessment of this system in different case studies including the real time measured dynamic power demand of an office block is realized. The collaborative actions of the proposed hybrid system with a fuzzy logic based energy management strategy during fluctuations of renewable-based power production are investigated. Thus, results of this study may be valuable for evaluating the feasibility of stand-alone hybrid renewable energy units for future power systems.     

An Integrated Feasibility Analysis of a Stand‐alone Wind Power System,including No‐energy Fulfillment Cost

Autonomous wind power systems are among the most interesting and environmentally friendly technological solutions for the electrification of remote consumers. However, the expected system operational cost is quite high, especially if the no‐load rejection restriction is applied. This article describes an integrated feasibility analysis of a stand‐alone wind power system, considering, beyond the total long‐term operational cost of the system, the no‐energy fulfilment (or the alternative energy coverage) cost of the installation. Therefore the impact of desired system reliability on the stand‐alone system configuration is included. Accordingly, a detailed parametric investigation is carried out concerning the influence of the hourly no‐energy fulfilment cost on the system dimensions and operational cost. Thus, by using the proposed method, one has the capability–in all practical cases–to determine the optimum wind power system configuration that minimizes the long‐term total cost of the installation, considering also the influence of the local economy basic parameters. Copyright © 2003 John Wiley & Sons, Ltd.     

Generation unit sizing and cost analysis for stand-alone wind,photovoltaic, and hybrid wind/PV systems

This paper presents the results of investigations on the application of wind, photovoltaic (PV), and hybrid wind/PV power generating systems for utilization as stand-alone systems. A simple numerical algorithm has been developed for generation unit sizing. It has been used to determine the optimum generation capacity and storage needed for a stand-alone, wind, PV, and hybrid wind/PV system for an experimental site in a remote area in Montana with a typical residential load. Generation and storage units for each system are properly sized in order to meet the annual load and minimize the total annual cost to the customer. In addition, an economic analysis has been performed for the above three scenarios and is used to justify the use of renewable energy versus constructing a line extension from the nearest existing power line to supply the load with conventional power. Annual average hourly values for load, wind speed, and insolation have been used     

Enhancement of a stand-alone photovoltaic system’s performance: Reduction of soft and hard shading

A stand-alone photovoltaic (PV) system is the most promising solution to supply electric power to meet energy demand in isolated locations. This technology can offer an interesting alternative to other currently existing sources of energy. Due to space constraint in the remote offshore oil and gas industry, a stand-alone system is used for cathodic protection, telemetry and valve control. However in such an environment, dust accumulation and bird droppings have been critical issues to the operation of off-grid solar devices. These factors do not only reduce the available power of the modules but also makes the cost of solar devices ineffective since cleaning, especially on well-head towers, is very expensive due to the location. Hence this paper presents two technical solutions that have shown promising results in reducing the impact of these factors.     

Alternatives to grid extension for rural electrification: Decentralized renewable energy technologies in Vietnam

This paper examines the economic viability of stand-alone, household-sized renewable energy technologies, namely wind generator and solar PV for application in remote and rural areas of Vietnam. Three reference technologies are chosen. These are two solar PV systems of 130 and 100 Wp for solar conditions in the North and the South, respectively, and one 150 W wind turbine. It is found for all regions that levelized costs of PV energy are lower than the cost of energy from gasoline gen-set, and are cost-competitive with grid extension, especially for areas with low load density and low number of households to be electrified. Regarding wind energy, the viability is dependent on the location due to the wide variation of wind resource to topography. However, in locations with proper resources, wind energy is even more cost-competitive than solar PV. Thus, the use of either wind generator or solar PV is economically feasible in rural villages and remote areas of Vietnam. Policy recommendations for promoting the market development of renewable energy technologies are discussed in the final section of the paper.     

A current and future state of art development of hybrid energy system using wind and PV-solar: A review

The wind and solar energy are omnipresent, freely available, and environmental friendly. The wind energy systems may not be technically viable at all sites because of low wind speeds and being more unpredictable than solar energy. The combined utilization of these renewable energy sources are therefore becoming increasingly attractive and are being widely used as alternative of oil-produced energy. Economic aspects of these renewable energy technologies are sufficiently promising to include them for rising power generation capability in developing countries. A renewable hybrid energy system consists of two or more energy sources, a power conditioning equipment, a controller and an optional energy storage system. These hybrid energy systems are becoming popular in remote area power generation applications due to advancements in renewable energy technologies and substantial rise in prices of petroleum products. Research and development efforts in solar, wind, and other renewable energy technologies are required to continue for, improving their performance, establishing techniques for accurately predicting their output and reliably integrating them with other conventional generating sources. The aim of this paper is to review the current state of the design, operation and control requirement of the stand-alone PV solar–wind hybrid energy systems with conventional backup source i.e. diesel or grid. This Paper also highlights the future developments, which have the potential to increase the economic attractiveness of such systems and their acceptance by the user.     

Dynamic modeling and sizing optimization of stand-alone photovoltaic power systems using hybrid energy storage technology

Economic and environmental concerns over fossil fuels encourage the development of photovoltaic (PV) energy systems. Due to the intermittent nature of solar energy, energy storage is needed in a stand-alone PV system for the purpose of ensuring continuous power flow. Three stand-alone photovoltaic power systems using different energy storage technologies are studied in this paper. Key components including PV modules, fuel cells, electrolyzers, compressors, hydrogen tanks and batteries are modeled in a clear way so as to facilitate the evaluation of the power systems. Based on energy storage technology, a method of ascertaining minimal system configuration is designed to perform the sizing optimization and reveal the correlations between the system cost and the system efficiency. The three hybrid power systems, i.e., photovoltaic/battery (PV/Battery) system, photovoltaic/fuel cell (PV/FC) system, and photovoltaic/fuel cell/battery (PV/FC/Battery) system, are optimized, analyzed and compared. The obtained results indicate that maximizing the system efficiency while minimizing system cost is a multi-objective optimization problem. As a trade-off solution to the problem, the proposed PV/FC/Battery hybrid system is found to be the configuration with lower cost, higher efficiency and less PV modules as compared with either single storage system.