Economic and technical study of a hybrid system (wind–photovoltaic–diesel) for rural electrification in Algeria
Introduction
It is estimated that two billion people in small villages in developing countries currently lack grid-based electricity service. In many cases, grid extension is impractical because of dispersed populations, rugged terrain, or both. Thus, small off-grid stand-alone renewable energy systems represent an important option for narrowing the electricity gap in rural parts of the developing world, where progress in grid extension remains slower than population growth [1], [2]. Even though these small-scale energy systems generate relatively little power, they can significantly contribute to life quality in remote locations in developing countries [3]. Cavello and Grub stress that 1 kWh of electricity provides ten times more electricity services in India than in Indiana. They further state that two small wind generators, which would supply only two homes with electric heating in the United States, could pump water for 4000 people in Morocco [4].
In remote villages, far from the grids of many countries, electric energy is usually supplied by diesel generators or small hydroelectric plants. In most of these cases, the supply with diesel fuel becomes highly expensive while hybrid diesel/photovoltaic/wind generation becomes competitive with diesel-only generation [5]. Photovoltaic/wind/diesel hybrid systems are more reliable in producing electricity than photovoltaic-only/wind-only systems, and often represent the best solution for electrifying remote areas. The diesel generator reduces the photovoltaic/wind component while the photovoltaic/wind systems decrease the operating time of the generator, reducing the running costs of the diesel generator [6]. The addition of battery storage reduces the number of start/stop cycles of diesel generators, thus considerably minimizing fuel consumption [7] and [8].
The utilisation of small-scale off-grid hybrid generation option is not yet in use in Algeria, whose an important proportion of population is in rural areas that are neither grid-connected nor do they have independent generating plants. The main reason for this is the reliance on interconnected generation systems based on large-scale gas and oil plants. Electrical energy produced by these power stations is supplied to urban and some rural areas mainly through grid extension.
To solve the energy crisis specifically in the southern interconnected grid, electricity supplies could be provided through off-grid renewable energy options that are yet to be considered for parts of Algeria where a reasonable solar and/or wind resource is available. However, some research efforts to encourage the use of renewable energy have been conducted but without institutional support and interest. These include the estimation of the solar and wind energy potential of Algeria [9], [10] and the situation of renewable energy in the country [11].
In this work, a combination of three energy sources (solar, wind and diesel) with a continuous electric power production is proposed. A great deal of research related to performance, optimization, and other related parameters [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22] has been carried out on hybrid energy systems. Borowy and Salameh [12] developed an algorithm to optimize a photovoltaic-array with battery bank for a stand-alone hybrid PV/wind system. The proposed model is based on a long-term hourly solar irradiance and peak load demand data relative to the considered site. The number of the PV modules of the hybrid system is calculated by the use of the same algorithm. So, the direct cost of the PV/wind systems is not considered for optimizing the hybrid energy system. Later on, Borowy and Salameh [13] optimized a similar system taking into account both the costs of the PV modules and battery systems. A graphic construction technique to optimize the size of the PV/wind energy system was established and presented by Markvart [14] in which the monthly average solar and wind energy values are considered. On the other hand, unlike the methods based on hourly, daily, and monthly average energy values, a statistical approach for the PV arrays size and the number of batteries of a stand-alone PV/wind hybrid system was presented by Bagul et al. [15]. They proposed a three-event probabilistic approach to overcome the limitations of the conventional two-event approach in matching the actual distribution of the energy generated by hybrid systems. Recently, Celik [16] has made a techno-economical analysis and optimization of a PV/wind hybrid energy system. A comparative study with a stand-alone solar and wind system for the same conditions of load, insulation and wind velocities has also been conducted. On a fundamentally different basis, Morgan et al. [17] have studied the performance of battery units in an autonomous hybrid energy system at various temperatures by considering the state of voltage (SOV) instead of the state of charge (SOC). Their algorithm enabled the prediction of the hybrid energy system performance at various battery temperatures. Yang et al. [18] have proposed an optimization technique following the loss of power supply probability (LPSP) model for a PV/wind hybrid system taking into account the system reliability. They demonstrated the utility of their model through a case study of a hybrid unit for a telecommunication system. Ashok [19] proposes a model based on different system components of a 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.
Photovoltaic solar and wind energy conversion systems have been widely used for electricity supply in isolated locations far from the distribution network. If such systems are designed properly they can provide a reliable service and operate in an unattended manner for extended periods of time. However, they suffer from the fluctuating characteristics of available solar and wind energy sources, which must be considered at design stage. The degree of desired reliability of a solar and wind process so as to meet a particular load can be fulfilled by a combination of properly sized wind turbine, PV panel, storage unit and auxiliary energy. Because the storage unit and auxiliary energy are needed to provide high reliability and avoid gross over-design of the solar and wind system [20], [21], [22] a system comprised of battery storage and auxiliary energy (diesel generator) components is proposed.
Furthermore, this work includes the complete energy modelling and sizing of the various system’s components. For the purpose of illustration, six various Algerian’s climatic zones are considered and an economical study of the hybrid system was elaborated. This will serve as an additional tool that helps choosing the best system (wind or photovoltaic installation) when the two possibilities are technically possible. The choice is based on the determination of the option which corresponds to the least cost and to the best performances.
Fig. 1 shows the synoptic of the system.
Section snippets
Modelling of the wind system
To evaluate the operating performance of an aero generator at a given site, its energy production is first expressed in terms of wind speed. Among the many mathematical models used in wind power studies, the cumulative statistical distribution of Weibull [23] is the most appropriate for describing wind speed variations. Thus, the average power produced by an aero generator is given by [10] and [23], [24], [25] as:where
Vin: wind speed at which electricity production begins
Hybrid system results
Monthly analysis of the measured field data shows that the energy contribution from photovoltaic and wind generators varies greatly from one month to another and from site to site. The obtained results are presented in Fig. 7, Fig. 8, Fig. 9, Fig. 10, Fig. 11, Fig. 12. In these figures, are presented the monthly mean daily household load, photovoltaic energy produced by n modules and m aerogenerators system. From these results, it will be noted that the household load is completely covered by
Conclusion
This paper presents the results of investigations on the application of hybrid PV/wind/diesel power with battery storage generating systems for use in stand-alone systems in Algeria.
The objective of the present work is to estimate the appropriate dimensions of a stand-alone application of hybrid PV/wind/diesel systems with battery storage that guarantee the energy autonomy of a typical remote consumer, to compare the performance and find the optimal sizing of three system configurations for all
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