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.
Most European and North American consumers cover their electrification needs by large capacity and robust interconnected electrical networks, supported by nuclear and fossil fuel-fired power stations of considerable size (e.g. 1000 MW). In these cases the free market competition leads to reliable network operation and minimum production cost (Feretic and Tomsic, 2005), achieving unit electricity costs of generation down to 0.03 €/kWh. On the other hand, United Nations estimate (Jensen, 2000) that almost two billion people have no direct access to electrical networks. Hence, their only electrification possibility should be based on autonomous stand-alone systems (Kaldellis, 2002b; Kaldellis et al., 2003). Otherwise one should invest on expensive (Tanrioven, 2005) grid-extensions, whenever possible.
In actual fact, the great majority of rural consumers had no other choice than small diesel-electric generators, while only in limited cases small wind converters, photovoltaic generators or micro-scale hydro-systems contribute in the electricity generation (Beyer et al., 1995; Bhuiyan and Ali Asgar, 2003, U.S. (DOE), 1997; Kaldellis et al., 2005). The utilization of diesel engines presents minimum first installation cost (Hunter and Elliot, 1994) but substantial maintenance and operation (M&O) cost (Fig. 1). On the contrary, wind power installations are capital intensive, presenting however low M&O cost (Kaldellis and Gavras, 2000). As a result, one may find an appropriate combination of a small diesel-electric generator and a micro-wind converter that guarantees the remote consumer electrification at a rational (minimum) initial and long-term cost (Bowen et al., 2001; Elhadidy and Shaahid, 2004; Kaldellis and Vlachos, 2005). Such a system may also use an appropriate battery bank, in order to improve the system reliability. The extreme cases of such a generalized stand-alone solution appear to be either the diesel-only (no wind turbine and/or energy storage) or the stand-alone wind power (zero diesel-oil contribution) configuration. The possibility of biofuel utilization is not included here (Sakkas et al., 2005).
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Fig. 1.
Electricity production cost time-evolution for remote consumers located in small Greek islands.
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In this context, the present study is concentrated on a detailed cost–benefit analysis (Kaldellis and Gavras, 2000; Kaldellis et al., 2005) of an optimum sizing wind–diesel–battery stand-alone system used to meet the electrification requirements of a typical remote consumer, generation capacity up to 15 kW. Accordingly, the corresponding electricity production cost value is predicted using an integrated methodology and is subsequently compared to existing electrical market price. Finally, an extensive sensitivity analysis is carried out in order to improve the proposed analysis reliability.
An integrated energy production cost analysis of typical wind–diesel hybrid systems is presented. In this context, the configuration of the proposed wind–diesel power system is described first, including the lead-acid battery storage system and the necessary electronic devices. Accordingly, an expert-type computational algorithm is presented, in order to estimate the hybrid station dimensions that guarantee the installation energy autonomy for a desired period.
The main part of the analysis is devoted to develop a complete electricity production cost model, considering not only the first installation but also the fixed and variable M&O cost, including diesel-oil consumption cost and battery replacement expenses every 5–7 years. Subsequently, the proposed methodology is applied to four typical wind potential cases, possessing annual mean wind speed values between 6.0 and 10 m/s. For all cases investigated, the predicted electricity production cost is favorably compared with real electricity production cost data, resulting from the operation of existing autonomous diesel-only power stations. Finally, a quite extensive sensitivity analysis is carried out, in order to demonstrate the impact of the main techno-economic parameters on the energy production cost of optimum sized wind–diesel hybrid power stations.
In view of the uncertain future concerning the oil worldwide prices and the continuous air pollution increase, a progressive interest in hybrid power stations is taking place in many regions worldwide. Taking into account the extensive results obtained, hybrid wind–diesel systems may be the best cost-effective electrification solution for numerous isolated consumers, located in regions with fairly good (mean wind speed greater than 6.0 m/s) wind potential. On top of this, subsidy possibilities—granted for example by local authorities or via European Union funds—should greatly increase the economic attractiveness of similar environmental friendly electricity production applications.
