Volume 2 wind energy 2 22 – special wind power applications

Volume 2 wind energy 2 22 – special wind power applications Volume 2 wind energy 2 22 – special wind power applications Volume 2 wind energy 2 22 – special wind power applications Volume 2 wind energy 2 22 – special wind power applications Volume 2 wind energy 2 22 – special wind power applications Volume 2 wind energy 2 22 – special wind power applications

2.22 Special Wind Power Applications E Kondili, Technological Education Institute of Piraeus, Athens, Greece © 2012 Elsevier Ltd All rights reserved 2.22.1 2.22.2 2.22.2.1 2.22.2.2 2.22.3 2.22.3.1 2.22.3.2 2.22.4 2.22.5 2.22.5.1 2.22.5.2 2.22.5.3 2.22.6 2.22.6.1 2.22.6.2 2.22.6.3 2.22.6.4 2.22.6.5 2.22.6.6 2.22.6.7 2.22.7 2.22.8 2.22.9 2.22.9.1 2.22.9.2 2.22.10 2.22.10.1 2.22.10.2 2.22.10.3 2.22.10.4 2.22.10.5 2.22.11 2.22.12 2.22.12.1 2.22.13 2.22.13.1 2.22.14 2.22.15 2.22.16 References Further Reading Introduction – The Water Demand Problem Desalination Processes and Plants General Considerations Membrane/RO Desalination Processes Energy Requirements of Desalination Processes General Issues Utilizing RESs in Desalination Integrated Systems of RES with Desalination Plants RO–Wind Desalination Basic Characteristics Design Issues Operational Issues – Technical Difficulties Wind–RO Configuration Possibilities Systems with Backup (Diesel/Grid) Systems without Backup Near-Constant Operating Conditions Storage Devices RO Unit Switching Wind Turbine Derating Variable Operating Conditions Implementation of Projects Implementation of Projects with Hybrid Energy Systems Economic Considerations in RES-Based Desalination Introductory Comments Parameters Affecting Economics of Desalination Examples of Wind-Based Desalination Applications – Case Studies General Issues for the Case Studies Analysis Libya Morocco Spain Milos Island, Greece Technological Developments and Future Trends in Hybrid Desalination Systems Telecommunication Stations General Considerations The Wind Power-Based T/C Station Configuration Options Overview Applications of Wind Energy in T/C Stations Wind Water Pumping Systems Water Pumping System Applications Glossary Desalination The process of removing salt from saline water and producing fresh potable water RES based desalination Desalination processes that cover their energy needs from Renewable Energy Sources Comprehensive Renewable Energy, Volume 726 726 726 728 729 729 730 732 732 732 733 734 734 734 734 734 734 734 735 735 735 735 736 736 736 738 738 739 739 739 739 740 740 740 741 742 742 742 744 745 746 Reverse osmosis This process involves the forced passage of water through a membrane against the natural osmotic pressure to separate ions Wind pumping The exploitation of wind power systems to pump water mechanically doi:10.1016/B978-0-08-087872-0.00225-0 725 726 Special Wind Power Applications 2.22.1 Introduction – The Water Demand Problem Wind based desalination is the first of the special applications that are dealt with in this chapter This topic is very crucial as today about billion people around the world have no access to clean drinking water Moreover, about 1.76 billion people live in areas already facing a high degree of water shortage [1] Water shortage is one of the most critical global problems As a result, various solutions for the security of water supply are investigated and desalination is considered as one of the most promising ones [2] To that effect, much attention is being paid in research and technological development fields in desalination issues The specific objectives of this section are to analyze and describe the use of wind energy in desalination processes More specifically, the main directions are • to highlight the critical water shortage problems being faced by various areas of the planet; • to focus on the energy aspects of desalination and emphasize the use of renewable energy sources (RESs) and, more specifically, wind energy in desalination processes and plants; • to identify the critical parameters and provide guidelines for the successful design and operation of a wind-based desalination system; • to provide an insight into the future prospects of wind-based desalination systems As a matter of fact, water is a valuable natural resource and access to freshwater is considered as a basic human right Water shortage is considered as one of the most serious social and environmental problems to be faced in the next years in many areas of the planet Water scarcity implies not only the lack of water in arid regions but also the mismatch between water supply and demand, a problem with very strong spatial and temporal characteristics Even in cases of a positive total water balance, there may be periods of time or specific areas when and where water is not available The water shortage problem is being solved with various methods, depending on the specific case, such as the construction and operation of infrastructure projects like desalination plants, dams, and groundwater reservoirs As almost 97% of the water on earth is seawater, desalination, that is, the removal of salt from the virtually unlimited supply of seawater or brackish water, is considered as a very promising method to meet the water demand and it is today widely applied in areas with limited water resources Wind energy is used for solving the water shortage problem because of the fact that desalination is an energy-intensive process and RES, more specifically wind energy, is a very promising solution for supplying energy to these units 2.22.2 Desalination Processes and Plants 2.22.2.1 General Considerations Desalination is the process of removing salt from saline water and producing fresh potable water Seawater desalination separates saline water into two streams: a freshwater stream containing a low concentration of dissolved salts and a concentrated brine stream A large number of desalination plants have been installed throughout the world, the majority of which can be found in the Middle East and the Caribbean islands, with very good prospects for the coming years in China Desalination is still considered more expensive than other methods, mainly due to its intensive use of energy, but this picture is continuously changing as R&D efforts and technological advancements have reduced the cost of the produced freshwater Today desalination has proved to be more reliable and an economically cheaper solution in various cases, compared with other solutions such as dam construction or transportation of water by marine vessels The new amount added each year to total desalination capacity is shown in Figure Demand in desalination capacity is predicted to grow rapidly and is taking place not only in the Middle East, led by the Gulf Cooperation Council countries, but also in other countries led by Algeria, Australia, and Spain New markets are opening in China, India, and the United States [3] The currently available desalination technologies can be categorized as follows: Phase change processes that involve heating the feed (seawater or brackish water) to ‘boiling point’ at the operating pressure to produce ‘steam’ and condensing the steam in a condenser unit to produce freshwater Applications of this principle include solar distillation (SD), multieffect distillation (MED), multistage flash distillation (MSF), mechanical vapor compression (MVC), and thermal vapor compression (TVC) Nonphase change processes that involve separation of dissolved salts from the feed water by mechanical or chemical/electrical means using a membrane barrier between the feed (seawater or brackish water) and the product (potable water) Applications of this principle include electrodialysis (ED) and reverse osmosis (RO) Hybrid processes that involve a combination of phase change and separation techniques (as in the case of nonphase change processes) in a single unit or in sequential steps to produce pure or potable water Examples include membrane distillation (MD) and RO combined with MSF or MED processes The most common desalination processes being implemented today are distillation and membrane processes (Figure 2), each accounting for about half of the installed global desalination capacity Today, most of the R&D efforts and the technological innovations are oriented toward membrane processes and, more specifically, toward RO processes As in any type of separation, the critical issue in water desalination is the high energy demand Many countries in the world that lack freshwater sources are also deficient in energy sources, making the problem even more difficult to solve With Special Wind Power Applications 727 New desalination capacity 1980−2009 Capacity (million m3/day) 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 Commissioned Contracted Figure New annual desalination capacity [3] Seawater desalination processes Thermal processes (Phase change) Membrane processes (Single phase) Multistage flash evaporation (MSF) Reverse osmosis (RO) Multieffect distillation (MED) Electrodialysis (ED) Vapor compression (VC) mechanical (MVC) and thermal (TVC) Figure Main classification of desalination processes [4] the world’s freshwater demand increasing, much research has been directed at addressing the challenges in using renewable and environmentally friendly energy to meet the power needs for desalination plants Typically, desalination processes are powered by energy derived from combustion of fossil fuels, which contribute to acid rain and climate change by releasing greenhouse gases (GHGs) as well as several other harmful emissions Therefore, the environmental impacts of the energy use in desalination plants are also a very significant problem that needs to be considered Table presents the 728 Table Special Wind Power Applications World population, desalination capacity, oil requirements, and GHG emissions over the past five decades [5] Year World population (billions) World desalination capacity (million m3 day−1) Oil required (million metric tons day−1) GHG emissions (tons CO2 day−1)a 1960 1970 1980 1990 2000 2008 3.1 3.8 4.5 5.3 6.8 0.12 0.72 4.4 13 23 52 0.00 0.02 0.12 0.36 0.63 1.42 0.36 2.16 13.2 39 69 156 a Basis: m3 of water generated from a desalination plant using fossil fuel (oil) contributes to tons CO2 world population growth with increased desalination capacity and the oil requirements to produce freshwater through desalination technologies and associated GHG emissions over the past five decades Therefore, it is necessary to develop alternatives to replace conventional energy sources used in the desalination process with renewable ones and reduce the energy requirements for desalination by developing innovative low-cost, low-energy technologies and processes The driving forces for such an increase are the rising water shortage and the technology-driven cost reductions Although desalination has been considered as a very expensive water supply method, the technological advancements (mainly focused on improved energy utilization) have allowed it to really become a competitive method against other water supply approaches 2.22.2.2 Membrane/RO Desalination Processes Most new desalination plants now use membrane technologies Membrane processes have considerable advantages in desalting water and are now being widely applied in this market More specifically, the most widely applied membrane process, RO, represents more than 88% of membrane processes [6] RO process involves the forced passage of water through a membrane against the natural osmotic pressure to separate water and ions In these high pressures, the water molecules can pass through the membranes and the salts are left behind as a briny concentrate A typical RO system consists of four major subsystems (Figure 3): • • • • pretreatment system, high-pressure pump, membrane modules, and posttreatment system Feed water pretreatment is a critical factor in the operation of an RO system due to membrane sensitivity to fouling Pretreatment commonly includes feed water sterilization, filtration, and addition of chemicals in order to prevent scaling and biofouling The posttreatment system consists of sterilization, stabilization, and mineral enrichment of the produced freshwater The pretreated feed water is forced by a high-pressure pump to flow across the membrane surface Reverse osmosis unit Membranes Pretreatment Seawater supply power High-pressure pump Desalted water Energy recovery Brine rejection Posttreatment Potable water Figure Typical RO unit flow sheet Special Wind Power Applications 729 RO operating pressure varies from 17 to 27 bar for brackish water and from 55 to 82 bar for seawater Part of the feed water passes through the membranes, removing from it the majority of the dissolved solids resulting in the so-called product or permeate water The remaining water together with the rejected salts emerges from the membrane modules at high pressure as a concentrated reject stream (brine) In large plants, the reject brine pressure energy is recovered by a turbine, recovering from 20% up to 40% of the consumed energy In fact this is one of the most significant issues in RO technological development and innovation The energy saving, that is, the percentage of the mechanical energy that can be recovered pressurizing the feed water, and the water recovery ratio – the ratio of the desalinated water output volume to the seawater input volume used to produce it – are the critical parameters in the RO process RO processes have been characterized by a significant reduction in energy consumption Apart from its need for an elaborate pretreatment plant, the RO process has many advantages such as the following: • The modular structure of the process makes it flexible enough to handle different plant capacities • The process is conducted at ambient temperature, which minimizes corrosion hazard • There is an embedded potential of water–power cogeneration and coupling with energy recovery systems • The rate of development in RO technology is high compared with other desalination processes and this fact promises for more cost reduction of desalted water produced by RO in the near future • Desalination by RO results in high salt rejection (up to 99%) and high recovery ratios (up to 40%) • Seawater RO (SWRO) can produce potable water with salt content of about 500 ppm The energy issues of desalination processes and plants are discussed in the following sections of the chapter 2.22.3 Energy Requirements of Desalination Processes 2.22.3.1 General Issues All desalination processes use energy, which is the largest cost component in the operation of a desalination plant and offers the greatest potential for further efficiency improvement and cost reduction In fact, energy consumption is considered as the main reason that desalination has not yet been widely applied The share of energy in overall cost varies with the plant, its operation parameters, and location, as shown in Figures and for thermal and membrane processes, respectively Typical cost structure for a typical thermal desalination of SW Electrical Thermal energy, 9% energy, 50% Capital, 32% Chemicals, 3% Personnel, 6% Figure Typical cost structure of thermal seawater desalination [6] Typical cost structure for SWRO unit Electrical energy, 44% Capital, 37% Consumables, 3% Figure Typical cost structure of SWRO desalination [6] Maintenance and parts, 7% Labor, 4% Membrane replacement, 5% 730 Special Wind Power Applications 4.50% Primary feed pumps 1.80% 6.70% Second-stage feed pumps 2.60% Pretreatment 3.80% Product transfer pumps 80.60% Feed water supply Other Figure Distribution of power usage in an RO plant [7] Therefore, it is necessary to develop alternatives to replace conventional energy sources used in the desalination process with renewable ones and reduce the energy requirements for desalination by developing innovative low-cost, low-energy technologies and processes There are various possible combinations of RESs with well-established desalination technologies with different suitability and cost requirements of such desalination processes for domestic, small-scale, and large-scale applications Furthermore, the distribution of power usage in a two-stage SWRO system is shown in Figure More than 80% of the power is required for the primary feed pumps [7] In any desalination process, the energy consumption depends on a variety of factors, including • • • • • • • seawater salinity, the technology being used, the ability of the system for energy recovery, the temperature of operation for membrane processes, performance ratio, heat losses, and temperature difference for thermal processes In Table the major power requirements of desalination processes are shown [6, 8] The development of RO and more recently the improvements in energy recovery devices have changed that situation With energy consumption on Mediterranean SWRO plants down to kWh m−3, seawater desalination is now feasible for many communities In practice, much higher energy is required by the currently available desalination technologies In countries making significant desalination investments, energy policies and energy investment planning should possibly be revised to provide the right incentives for appropriate desalination processes and to decide whether cogeneration of water and power is a suitable option under particular circumstances This has become more significant for reasons ranging from integration of policies, the demand for water growing at a different rate than the demand for power, and seasonal variations between power and water demands [9, 10] However, thermal processes (MSF, MED) operating with steam supplied by the exhaust and steam bleeding from backpressure or extraction steam turbines are economically attractive and comparable with RO energy cost [11] 2.22.3.2 Utilizing RESs in Desalination The use of RESs for the operation of desalination plants is a feasible and environmentally compatible solution in areas with significant RES potential The main driving forces for applying RES in desalination plants are • the continuous technological advancements in RES systems and their cost reduction; • the seasonal variability in water (and energy) demand, usually occurring in areas with high renewable energy availability, for example, islands; Table Power requirements of various desalination processes [6, 8] Process Gain output ratio Electrical energy consumption (kWh m−3) Thermal energy consumption (kWh m−3) MSF MED MED-TVC MVC BWRO SWRO 8–12 8–12 8–14 N/A N/A N/A 3.25–3.75 2.5–2.9 2.0–2.5 9.5–17 1.0–2.5 4.5–8.5 6.75–9.75 4.5–6.5 6.5–12 N/A N/A N/A N/A, not available Special Wind Power Applications Electricity R E N E W A B L E E N E R G Y SD Geothermal Direct HD Heat Solar collectors Solar thermal Solar pond Solar 731 HD MD MED Pv thermal MSF PV ED Wind Electricity Wave Electricity TVC RO MVC Figure Possible combinations of RESs with desalination processes [5] • • • • the limited availability of a conventional energy supply in remote areas; the technological advancements being achieved in desalination systems; the limitation of environmental impacts of conventional desalination systems; and the relative ease of the plant’s operation and maintenance compared with conventional energy ones To that end, a lot of research and development work has been carried out and the problem of the optimal configuration/ combination of an RES energy source with a desalination plant attracts the interest of many researchers and construction and engineering companies Figure shows potential pathways by which common RESs can be utilized to drive the different desalination processes Each pathway involves different technologies, each with its own yield and efficiency The best coupling of RES to desalination systems is a complicated and interesting problem and its solution is not always obvious and unique In fact, this is a major decision-making issue, part of the wider problem of infrastructure planning Various criteria should be taken into account, including among others • • • • • • the renewable energy availability, the investment and operational cost and the availability of financial resources, the system’s efficiency, the availability of operational personnel, the suitability of the system to the characteristics of the location, and the possibility for future increase of the system capacity Matching renewable energies with desalination units, however, requires a number of important factors to be considered Not all the combinations of RES-driven desalination systems are practicable, as many of these possible combinations may not be viable under certain circumstances The optimum or just simple specific technology combination must be studied in connection with various local parameters such as geographical conditions, topography of the site, capacity and type of energy available at low cost, availability of local infrastructures (including electricity grid), plant size, and feed water salinity More specifically, the factors to be considered for selecting desalination process suitable for a particular application include the following: • the amount of freshwater required in a particular application (i.e., the plant’s capacity) combined with the applicability of the various desalination processes; • the seawater treatment requirements, that is, the feed water’s salinity; • the technical infrastructure of the area (e.g., road access, network) and the local regulations concerning the land use and the land area required, or that could be made available, for the installation of the integrated energy and desalination unit; • the remoteness of the area and the availability of grid electricity; • the suitability and effectiveness of the process with respect to energy consumption; • the capital cost of the equipment; • robustness criteria and simplicity of operation; • low maintenance, compact size, and easy transportation to site; 732 Table Special Wind Power Applications Evaluation of various RESs in desalination applications [12] Criterion Solar thermal energy PV Wind energy Geothermal energy Suitability for powering desalination plants Site requirements and resource availability Continuity of power output Well suited for desalination plants requiring thermal powera Well suited for desalination plants requiring electrical powera Well suited for desalination plants requiring electrical powera Well suited for desalination plants requiring thermal powera Typically good match with need for desalinationa Typically good match with need for desalinationa Resources are location dependentb Resources are limited to certain locationc Output is intermittent (energy storage required)c Output is relatively unpredictableb Output is intermittent (energy storage required)c Output is relatively unpredictableb Output is intermittent (energy storage required)c Output is very stochastic/ fluctuatesc Continuous power outputa Predictability of power output Output is predictablea a Excellent compliance with criterion Good compliance with criterion c Poor compliance with criterion b • acceptance and support by the local community; and • organization at local level with relatively simple training Table evaluates the combinations of desalination and RES according to certain energy-related criteria 2.22.4 Integrated Systems of RES with Desalination Plants Desalination using renewable energy is undergoing a rapid development nowadays The most likely market for coupling renewable energy with desalination is small communities in remote locations where there is no power grid connection or where energy is expensive In the context of the utilization of the more established RESs, that is, the sun (thermal and photovoltaic (PV)) and the wind, stand-alone desalination systems have been widely discussed Even if one focuses on one particular renewable source and a specific desalination method, there may still be many options available in terms of the final system configuration There is very strong research interest in this specific area Many research teams work in specific technical issues or in integration and optimization aspects of the combination between RES and desalination However, as far as implementation is concerned, many small-scale and rather experimental projects have been installed but there is no serious experience from industrial-scale projects The Red-Dead project, aiming at linking the Red Sea with the Dead Sea, might be the first large-scale renewable energy-driven desalination scheme It would have a potential of producing up to 850 million m3 yr−1 of potable water 2.22.5 RO–Wind Desalination 2.22.5.1 Basic Characteristics Desalination systems driven by wind power are the most frequent renewable energy desalination plants (Figure 8) Wind-powered desalination represents one of the most promising renewable energy options for desalination, especially in coastal areas with high availability of wind energy resources In fact, after solar energy, wind energy is the most widely used RES for low-capacity desalination plants The two most common approaches for wind-powered desalination systems include connecting both the wind turbines and the desalination system to the grid and direct coupling of the wind turbines with the desalination system Also a primary concern with the use of wind energy for desalination is that wind speed is very variable Another option is likely to be a stand-alone system at remote locations which have no electricity grid In this case, the desalination system may be affected by power variations and interruptions caused by the wind Hence, the stand-alone wind desalination systems are often hybrid systems combined with another type of RES (e.g., solar) or a backup system such as batteries or diesel generators For stand-alone wind energy-driven desalination units, the reported cost of freshwater produced ranges from 1.5 to 3.5 € m−3 [9] More specifically, wind energy can be used efficiently on condition that the average wind velocity is above m s−1 This makes wind-powered desalination a particularly interesting option for windy islands, both for the solution of their energy supply problem and for the operation of seawater desalination plants The main design variables that affect the design of a wind–RO system are • • • • the water demand and, therefore, the RO plant’s capacity, the location where the wind turbine and the desalination plant will be installed (required siting, altitude, etc.), the feed water salinity, the wind speed distribution, Special Wind Power Applications Wind energy unit 733 Desalination plant Grid Pretreatment Wind Gene­ rator Energy manag ement Pumps Battery bank Sea water RO unit Energy recovery Post treatment Fresh water storage Water Energy Figure Structure of a wind-based RO desalination plant [13] • • • • • • • • • the configuration of the energy system, the water storage capacity, the available power distribution, the feed water source, that is, seawater, brackish water, desalination unit energy consumption, the salt rejection, the forecasted environmental impacts, the operating pressure, and the permeate flux, in terms of both overall product rate and specific rate (per unit membrane area) Desalination plants using membrane technologies are available in a wide range of capacities As far as the recommended RES–desalination combinations are concerned, it is considered that wind desalination is suitable for a wide spectrum of desalina­ tion capacities (50–2000 m3 day−1), resulting in a cost of desalinated water of 1.5–4 € m−3 [14] Recent developments in wind turbine technology imply that wind power can now be regarded as a reliable and cost-effective power source for many areas of the world Wind turbines may be classified depending on their nominal power ‘No’ as very small (No < 10 kW), small (No < 100 kW), medium sized (No < 1.0 MW), and large (No > 1.0 MW) All are based on mature technol­ ogies and they are commercially available except for the very large power systems (> MW), which still require several adjustments 2.22.5.2 Design Issues The basic assumptions for the required calculations concerning the energy efficiency of the wind turbines with or without an energy storage system may be considered as below For a wind turbine with a nominal power of No kW, we expect an energy production ‘E’ in the order of magnitude of ‘E = CF � No � 8760’ kWh yr−1 Note that the installation capacity factor ‘CF’ usually varies between 20% and 30% Depending on the type of desalination plant, the required amount of energy per cubic meter of potable water will also be given Therefore, we may have a series of alternatives concerning the installed power of the wind turbine and the combined capacity of the desalination plant Many other parameters should be taken into account in this design issue, such as the possible losses of an energy storage system and the availability of a water storage system [15] The variable nature of wind power is not a problem as far as water availability is concerned, because water can be stored inexpensively With a plant that is dimensioned according to the local wind conditions, water becomes available any time However, the serious problem of this type of installations is that variable wind power may cause operational problems in the system’s operation and this is one of the most critical issues to be resolved in the design and implementation of an RES–wind-based desalination project One common way of storing the surplus energy is by using batteries [10] or water pumping systems Storage size should be considered in the design stage In addition, capital and maintenance costs should carefully be assessed 734 2.22.5.3 Special Wind Power Applications Operational Issues – Technical Difficulties RESs are characterized by intermittent and variable intensity, whereas desalination processes are designed for continuous steady-state operation One of the problems of utilizing wind power in process applications is the variable nature of the resource While the wind is relatively predictable, it is seldom constant and there will be periods of calm spells The storage of wind energy in the form of electrical power is really practical only when small amounts are involved Storage batteries increase the total investment cost; therefore, running a process of any magnitude on stored electrical energy is not a practical proposition However, if the product of the process can be stored inexpensively, then it may be practical to oversize the process equipment to allow for downtime Water can be stored for long periods of time without deterioration and the storage vessels are relatively cheap Variable power input forces the desalination plant to operate in nonoptimal conditions, which may cause operational problems To avoid the fluctuations inherent in renewable energies, different energy storage systems may be used The only areas that would require some careful design would be the relative sizes of the wind turbine and the RO plant and the cut-in and cut-out criteria for the RO plant to avoid excessive start-up and shutdown cycles For the operation of a wind-powered desalination plant, it is most important to have a plant that is insensitive to repeated start-up and shutdown cycles caused by sometimes rapidly changing wind conditions RO is, with regard to pretreatment, membrane fouling, after-treatment, and efficiency of the high-pressure pumps, a process that is rather sensitive to a stop and start operation 2.22.6 Wind–RO Configuration Possibilities Different wind-powered RO systems found in the literature have been classified, also taking into account some of the points previously discussed [16]: • the existence of an alternative electrical supply (weak grid or diesel generator); • the matching of the available wind energy to the load; and • the operational characteristics of RO membranes 2.22.6.1 Systems with Backup (Diesel/Grid) In these systems, an additional energy source is provided (a diesel-powered generator or even the local grid) so that the power supplied to the RO is constant The backup generation complements the power production from the wind turbine to match the RO unit power consumption The main benefit of these systems, as in any hybrid wind–diesel configuration, is fuel savings, which may increase the generator availability and reduce overall energy costs On the other hand, problems such as fuel shortages, diesel generator maintenance, and interruptions or power cuts in the supply may lead to unavailability of the RO system as it cannot be powered by the wind turbine alone for a long period of time including calm spells 2.22.6.2 Systems without Backup Systems without an external energy source can be divided into two categories, with emphasis on the RO unit operation: systems which run under approximately constant operating conditions and those that experience variable operational conditions 2.22.6.3 Near-Constant Operating Conditions This first type of operation can be implemented by three different means: on/off switching of the RO units, usage of storage devices, and derating the wind turbine In all three cases, an attempt is made to supply the individual RO modules with approximately constant power 2.22.6.4 Storage Devices In this strategy, storage devices are employed to accumulate energy surplus during periods when the power generated by the wind turbine is greater than the load demand from the desalination unit This surplus would then be used later when the generated power is insufficient to meet the load demand One common way of storing the surplus energy is by using batteries In this case, the relation between operational pressure, storage sizing, and average wind speed should be considered in the design stage In addition, capital and maintenance costs should be carefully assessed A disadvantage of this approach to the system design is the rating of the energy storage system, as this can make it economically unattractive at higher power levels due to the sizing of the battery bank 2.22.6.5 RO Unit Switching This strategy is based on the use of a higher power wind turbine connected with multiple smaller RO units The power control is achieved by switching the units on and off so as to match the demand to the total power generated instantaneously by the turbine There is no limitation concerning the system power rating, and this approach is feasible up to power levels of hundreds of kilowatts Special Wind Power Applications 735 Although frequent cycling of RO units is not usually recommended, this problem can be overcome by implementing different types of configurations Higher power wind turbines operating at near-constant speed connected to many equally smaller RO units switching on/off (load management) may be employed To smooth out the fluctuations, short-term energy storage (a flywheel in this instance) may be used 2.22.6.6 Wind Turbine Derating This approach consists of making use of the flat end of a pitch-controlled wind turbine power curve to operate the RO unit at approximately constant power An implication of this configuration is that, as the turbine rated power is only achieved at high wind speeds, it would have to be derated by changing the settings of the pitching mechanism This will cause the generated power to be flattened at lower wind speeds and consequently to have lower values Therefore, the original rating of the turbine rotor should be considerably higher than the RO unit rated power, making the system more expensive 2.22.6.7 Variable Operating Conditions In contrast to systems that operate under constant conditions, another operational strategy is based on the establishment and imposition of certain operational limits This means that, based on the input power to the RO unit (flow times pressure), a control strategy is determined which imposes a fixed operating point on the system that lies within the allowed region (i.e., the operational window of the RO unit) By doing this, an attempt is made to operate the system autonomously over a wider power range, without the need to use a backup unit or storage device The overall effect is to reduce capital and operating costs One aspect that should be emphasized is that very little is known about the consequences of variable operation of RO membranes It is recognized that mechanical fatigue can occur and that the lifetime of the RO elements may be shortened and performance impaired 2.22.7 Implementation of Projects The practical experience regarding wind-powered RO systems has been with relatively low-capacity systems There have been a number of attempts to combine wind energy with RO A number of plants have actually been operated However, most of them are of small size, mainly for research purposes, as previously mentioned Therefore, not many conclusions have been reached in terms of expertise and know-how It is still difficult to control the usage of wind in a cost-effective way Coupling of a variable energy supply system, as mentioned earlier, to a desalination unit requires either power or demand management, and there is not much experience on it However, the prospects of this combination are high mainly due to the low cost of wind energy The operational experience from early demonstration units is expected to contribute to improved designs, and a large number of commercial systems are expected to be implemented A number of units have been designed and tested; however, most of them are in the demonstration and experimental scale [17–19] As early as 1982, a small system was set at Ile du Planier, France: a kW turbine coupled with a 0.5 m3 h−1 RO desalination unit The system was designed to operate via direct coupling or batteries Another case where wind energy has been combined with RO is that at the Island of Drenec in France, in 1990 The wind turbine in this case was rated at 10 kW and was used to drive an SWRO unit More recently, some R&D projects have been carried out, such as the wind desalination system built at Drepanon on a cement plant, near Patras, Greece The project, including a 35 kW wind turbine, was initiated in 1992 and was completed in 1995 The project called for full design and construction of the wind generator turbine (blades, etc.) plus installation of two RO units with a production capacity of and 22 m3 day−1 Unfortunately, since 1995, operational results have been poor due to the low wind regime A very interesting experiment has been carried out at a test facility in Lastours, France, where a kW wind turbine provides energy to a number of batteries (1500 Ah, 24 V) and via an inverter to an RO unit with a nominal power of 1.8 kW Furthermore, great work on wind RO systems has been carried out by the Instituto Tecnologico de Canarias (ITC) in several projects such as AERODESA, SDAWES, and AEROGEDESA An energy optimization model which simulates hourly power production from RESs has been applied using the wind and solar radiation conditions for Eritrea, East Africa, for the computation of the hourly water production for a two-stage SWRO system with a capacity of 35 m3 day−1 According to the results obtained, specific energy consumption is about 2.33 kWh m−3, which is a lower value than that achieved in most of the previous designs The use of a booster pump, energy recovery turbine, and an appropriate membrane allows the specific energy consumption to be decreased by about 70% compared with less efficient designs without these features The energy recovery turbine results in a reduction in the water cost of about 41% The results show that a wind-powered system is the least expensive and a PV-powered system the most expensive, with water costs of about 0.50 and 1.00 $ m−3, respectively By international standards, for example, in China, these values are considered economically feasible [1] 2.22.8 Implementation of Projects with Hybrid Energy Systems Due to the intermittent production of wind energy, suitable combinations of other RESs can be employed to provide smooth operating conditions Autonomous hybrid systems are independent and incorporate more than one power source 736 Special Wind Power Applications Wind generator/PV energy combination can drive the desalination process round the clock with a battery bank system Diesel generators are mainly used as backup systems; however, fuel transportation to remote areas poses the same difficulties as water transportation RES penetration depends only on the economic feasibility and the proper sizing of the components to avoid oversizing and ensure quality and continuity of supply One important application is the use of PVs and wind generator to drive RO desalination units As has already been mentioned, each desalination system has specific problems when it is connected to a variable power system RO has to deal with the sensitivity of the membranes regarding fouling, scaling, as well as unpredictable phenomena due to start–stop cycles and partial load operation during periods of oscillating power supply Several RO units with intermittent or infrequent operation have to replace their membranes very often On the other hand, units including storage backup system like a battery bank increase the system’s initial cost and, in difficult climatic conditions, the maintenance requirements As stated earlier, most of the plants constructed to date have been either as research or demonstration projects With the end of the project, most of the systems stop their operation due to limited budget and staff unavailability General Electricity Company of Libya (GECOL) and a consulting consortium of experts are managing the implementation of an experimental research facility for SWRO desalination powered from RESs (SWRO-RES) in the Mediterranean Sea off the coast of Libya The nominal production of the plant will be 300 m3 day−1 for the supply of a village with potable water Both wind energy conversion (WEC) and PV power generation will be integrated into a grid-connected power supply for an RO desalination plant with power recovery by pressure exchange The facility design is flexible for the integration of diesel generator and electrochemical storage as power supply alternatives as well as brackish water reverse osmosis (BWRO) The wide range of feasible plant configurations will allow for extension of the scope of research to off-grid stand-alone performance analysis of such hybrid systems While the expected nominal power load for the operation of the RO desalination system is 70 kW (net power after recovery), the solar PV system is designed for 50 kWp and the WEC for 200 kW nominal output The design aims at a reduction of the annual nonrenewable energy consumption to about 40% The economic analysis of the integrated renewable energy systems predicts levelized water cost (LWC) of the integration of grid and wind energy with RO 1.8 € m−3 and for grid and PVs with RO 1.9 € m−3 compared with 1.3 € m−3 for operation of the plant only from the grid [20, 21] 2.22.9 Economic Considerations in RES-Based Desalination 2.22.9.1 Introductory Comments Various efforts have been made to develop tools for the design, economic evaluation, and the determination of the main parameters for RES-based desalination plants Estimating the capital and production costs of desalination systems is very difficult due to many reasons such as the following: • the varying energy, material, and labor costs per geographic area; • the type of the desalination process (design, size, etc.); and • the salinity of the feed water There are many references [21–31] and research and development works analyzing design and financial issues of these units and reaching various conclusions concerning the optimal decision under specific circumstances As a general rule, an SWRO unit has low capital cost and significant maintenance cost due to the high cost of the membrane replacement The cost of the energy used to drive the plant is also significant As described in the previous sections of this chapter, a number of parameters affect decision making on the design of such a plant This also applies in the financial evaluation of the units; that is, a number of parameters and their complex interactions affect the produced freshwater cost A conclusion of all the efforts being made on this issue is that there is no specific and generally applicable tool for determining the cost of such units All the parameters, being technical, environmental, and social, are very site specific In this context, the contribution of this chapter to those that need to develop and evaluate an RES-based desalination plant and to the researchers of the field could be seen in two directions: • to enumerate (exhaustively) the parameters and factors that should definitely be taken into account in such a work; • to provide examples of real case studies with specific design and cost 2.22.9.2 Parameters Affecting Economics of Desalination The economics of a wind-powered desalination system differ from conventional plant economics as it is almost entirely based on the fixed costs of the system Certainly there are no fuel costs as they are replaced by the wind turbine In fact it should be mentioned at this point that a detailed financial analysis leading to the estimation of precise financial indices should be carried out in case private investments are attempted It is expected that this type of project implementa­ tion will prevail in many countries in the next years, and in some places (e.g., Cyprus) significant experience on that has already been built Special Wind Power Applications 737 In this case, the investor will possibly undertake the capital and – for some years at least – the operational cost of the project expecting to benefit from the selling of water, either in the free market or in the municipality it belongs to (e.g., the case of a Greek island desalination plant [13]) It is expected that many such private investments will take place in the next years, especially in areas with water shortage and financial activities in the field of tourism Desalination costs per unit of produced water for different desalination processes with RESs and different feed sources are shown in Tables and Table makes a synthesis of the most critical parameters and choices that affect the feasibility and financial attractiveness of an RES-based desalination project (e.g., wind-based desalination plant) More specifically, for the case of wind–RO desalination, the factors that are taken into account in water production cost are shown in Table Table Desalination water costs for various combinations of desalination processes with RES [5] Water type Water cost ( m–3) Desalination system powered by RES Brackish water Conventional energy + RO, ED Brackish water Photovoltaic energy + RO Brackish water Photovoltaic energy + ED Brackish water Wind + RO Brackish water Wind + ED Brackish water Geothermal + MED Seawater Conv energy + RO, ED, MSF, MED, VC Seawater Photovoltaic energy + RO Seawater Wind + RO Seawater Wind + VC Seawater Solar thermal + MED Seawater Geothermal + MED Table Investment and operation costs for desalination processes with capacities in the range 200–40 000 m3 day−1 [5] Desalination processes Capacity (m3 day−1) 200 600 1200 2000 3000 20 000 30 000–40 000 Costs MVC RO Cost/unit ($ m−3) Investment (M$) Cost/unit ($ m−3) Investment (M$) Cost/unit ($ m−3) Investment (M$) Cost/unit ($ m−3) Investment (M$) Cost/unit ($ m−3) Investment (M$) Cost/unit ($ m−3) Investment (M$) Cost/unit ($ m−3) Investment (M$) 3.8 0.75 2.65 1.7 2.25 3.2 3.25 0.5 2.35 1.1 2.15 2 1.85 4.2 MED 1.6 2.3 0.825 3.25 0.65 4.85 1.24 35 1.31 67 MED–TVC 3.3 0.5 2.25 1.85 1.65 1.8 2.5 1.7 3.3 1.55 35 738 Special Wind Power Applications Table Parameters affecting economics of wind-based desalination plants Parameters affecting economics of RES-based desalination plants Comments The desalination technology (thermal, RO) Plant’s capacity The climatic conditions and the characteristics of wind turbines The energy requirement of the desalination plant The feed water salinity The location where the wind turbine and the desalination plant will be installed The configuration of the energy system The water storage capacity The available power distribution (e.g., the wind speed distribution) Table In general, RO units have lower investment cost but high operation and maintenance costs Large capacity units are more expensive but the water unit cost is lower They define the size of the wind farm required for a given annual production of freshwater This is determined by the water supply salt concentration and the coupling of the energy and the desalination system BWRO is generally cheaper than SWRO Required siting, altitude, infrastructure preparation costs Main design decision determining the operation and the cost of the unit Design parameter determining the operation of the unit It affects the size, the configuration, and, therefore, the investment cost Cost items of a wind-based desalination plant Investment cost Cost of land Cost of wind turbine Cost of energy storage systems Cost of the RO plant components Annual operating cost Manpower cost Chemicals cost Electricity cost Maintenance and spares cost Membrane replacement 2.22.10 Examples of Wind-Based Desalination Applications – Case Studies 2.22.10.1 General Issues for the Case Studies Analysis The experience from the design and operation of a number of selected desalination systems powered by wind energy that have been installed and operating in various locations around the world is described in review research works [32, 33] It is interesting to mention that cost analysis of a wind-assisted RO system for desalinating brackish groundwater in Jordan has been conducted and the authors stated that it would cost less to desalinate brackish water with a wind-assisted RO system than with a conventional diesel-powered system [34] Forstmeier et al [35] demonstrated that the costs of a wind-powered RO desalination system are in line with what is expected for a conventional desalination system, proving to be particularly cost-competitive in areas with good wind resources and that have high costs of energy In all these studies, results obtained were theoretical and not verified by experimental data At the same time, the implementa­ tion of several wind-powered RO desalination system prototypes has been reported A prototype wind-powered RO desalination system was later constructed and tested on Coconut Island off the northern coast of Oahu, Hawaii, for brackish water desalination [32] The system has four major subsystems: a multivaned windmill/pump, a flow/ pressure stabilizer, an RO module, and a control mechanism The authors showed that at an average wind speed of m s−1, brackish feed water at a total dissolved solids concentration of 3000 mg l−1 and at a flow rate of 13 l min−1 could be processed The average rejection rate and recovery ratio were 97% and 20%, respectively Energy efficiency equal to 35% was shown to be comparable to the typical energy efficiency of well-operated multivaned windmills Miranda and Infield [15] developed a system with a 2.2 kW wind turbine generator powering a variable-flow RO desalination unit Operation at variable flow allows the uncertainty and variability of the wind to be accommodated without the need for energy storage Batteries, which are common in stand-alone systems, are avoided and water production is dependent on the instantaneous wind speed A prototype of a fully autonomous wind-powered desalination system has been installed on the island of Gran Canaria in the Canarian Archipelago [36] The system consists of a wind farm, made up of two wind turbines and a flywheel, which supplies the energy needs of a group of eight RO modules throughout the complete desalination process (from the pumping of seawater to the storage of the product water), as well as the energy requirements of the control subsystems The authors concluded that this Special Wind Power Applications 739 system can be applied to seawater desalination, both on a small and large scale, in coastal regions with scarcity of water for domestic and/or agricultural use but with adequate resources In the following section, some case studies from real plants are presented They are all different types of plants installed in different areas, with each having its own technical characteristics 2.22.10.2 Libya A demonstration plant has been designed in Libya (Integrated Power and Water Point) that will supply up to 300 m3 day−1 of water and 240 kW electricity to a village [20, 25] For the 60 kW RO power demand, a 275 kW wind turbine is integrated with a 300 kW diesel plant The process simulation for desalination of seawater with 4.3% salinity under nominal operating conditions yields 57% recovery rate at a specific energy consumption of 4.8 kWh m−3 (pumping included) The power demand at nominal output of 300 m3 day−1 is 60 kW, based on the calculation of 300.0 m3 day−1 � 4.8 kWh m−3/24 h day−1 = 60 kW The resulting cost of water is 2.24 € m−3 In the specific plant, detailed measurements have been taken in order to make reliable calculations of the costs 2.22.10.3 Morocco Morocco is characterized by a semiarid climate [28] The obligation to use other nonconventional water resources such as desalinated water or wastewater reuse becomes a necessity In addition, Morocco has a large potential of wind energy sources that could be used in seawater desalination In the following, the cost of desalinated water is calculated for three towns in the south of Morocco, using the method of LWC The cost was estimated for two seawater desalination processes: RO and MVC powered by wind turbines Electric connection to the grid is available, so that the grid can be used to power the plant when RESs are not available This alternative is then compared with the baseline which consists of the grid-only configuration The desalination processes studied in this chapter were designed to produce 1200 m3 day−1 of water, the daily consumption of almost 10 000 inhabitant-equivalent Depending on the wind potential of a given region, the installed power of wind turbines will be chosen in order to deliver an annual energy production equivalent to the annual energy consumption of the desalination system The baseline water cost per cubic meter was evaluated at €0.91 for the RO It is interesting to notice the cost breakdown structure for a wind-based desalination unit, as has been given for the plant in Morocco In these two cases being referred, this breakdown for an RO unit is as follows: • • • • 37.5% desalination investment cost, 31.6% wind turbine cost, 24.2% operation and maintenance of desalination unit cost, and 6.7% operation and maintenance of wind turbine cost The sum adds up to an LWC of almost 0.85 € m−3 2.22.10.4 Spain For a given wind farm capacity (with a particular type of wind turbine) and a given wind regime, there exists, from an economical point of view, an optimum nominal production capacity for each plant that needs to be specified in each case under consideration [36, 37] In this context, a wind farm with a nominal power of 460 kW and a wind regime (in the area of Pozo Izquierdo, proposed for its installation in Gran Canaria) with an annual average speed of 7.9 m s−1 and 10 m above ground level would give rise to an optimum number of RO plants of 11, each with a capacity of 100 m3 day−1 However, for technical and economical reasons, the decision was made to use eight RO plants, each with a capacity of 25 m3 day−1 The water cost of a wind BWRO unit (large system, about 250 m3 day−1) is of the order of € m−3 The implemented project in Tenerife, Spain, included a 200 kW wind turbine, which would operate on an average wind velocity of 7.5 m s−1, with an expected yearly energy yield around 600 MWh This amount of energy is capable of producing over 200 m3 day−1 of water 2.22.10.5 Milos Island, Greece A wind-based desalination unit has recently been installed in a Greek island called Milos belonging to the Cyclades complex [13] The plant (Figure 9) has been in operation since summer 2007 and has a capacity of 3000 m3 day−1 At the moment, it produces 2000 m3 day−1 of potable water This is a private investment that has been subsidized by the state The water is sold to the municipality of Milos, in a continuous effort to solve the water shortage problem, especially during the summer months The contract that has been signed between the private company and Milos municipality refers to a selling price of almost 1.8 € m−3 The entire plant includes • the desalination unit, • a wind turbine of 600 kW, 740 Special Wind Power Applications Figure Milos wind-based desalination plant • the storage tanks (capacity 3000 m3), and • the remote control system Before the installation of the unit, water was transported from Athens at a very high cost and rather poor quality [13] The implementation of this novel project has improved the quality of life of the island in many respects The siting of the unit in a very touristic island such as Milos could be a major problem, mainly because of the visual and noise disturbance Therefore, the unit has been located on a hill that is not visible from most island villages 2.22.11 Technological Developments and Future Trends in Hybrid Desalination Systems Although present desalination technologies and various forms of RESs are well developed, there is scope for improvements in efficiency, reliability, simplicity, and investment costs in each one of these technologies Therefore, a lot of research efforts should be directed toward improving and enhancing the presently utilized technologies It is also important that new technologies be investigated There is definitely a wide scope for research and development in the coupling between desalination and RES Serious progress in the field will take place in case industrial-scale projects are implemented, something that has not happened yet The following examples indicate the trends in R&D activities: • Energy consumption in all desalination processes is much higher than the thermodynamic minimum requirement Energy cost is the major component of the operating cost of a desalination plant Research under this topic is focused on reduction in energy consumption and the use of alternative energy sources • Development of high-flux membranes and introduction of energy recovery devices have greatly reduced overall energy consump­ tion, resulting in a currently possible energy consumption of even below kWh m−3 • Coupling of desalination processes with RESs A significant contribution in the design and operation of these systems would be twofold: • The development of a tool for the selection and design of the appropriate energy and desalination system, including its configura­ tion The parameters that should be taken into account in this decision include the desalination plant capacity, energy availability, infrastructure available, investment and operational costs, and operation and maintenance capabilities in this specific site • The development of a tool for the optimal operational planning of the coupled desalination–energy system mainly determining optimal size, the storage capacity, and the detailed operation of the system, that is, which hours per day the system will operate to produce water for the consumption, or to be stored, and which hours the energy system will operate to supply energy to the consumption, to the storage, or to the desalination unit [38, 39] In addition to all the references already cited, many other contributions are mentioned at the end of this document in order to facilitate further reading 2.22.12 Telecommunication Stations 2.22.12.1 General Considerations The telecommunication (T/C) sector has experienced a rapid growth over the past years in the developed world As the need for connectivity continues to grow extensively, more T/C equipments such as cellular base stations and satellite communication devices Special Wind Power Applications 741 need to be installed in urban as well as in remote locations The majority of T/C stations cover their electrification needs by large and robust electrical networks supported by fossil fuel-fired power stations However, there are several cases wherein T/C stations are located far away from the electrical grid Furthermore, in many developing countries and remote areas, there is no grid connection This insufficient infrastructure has hindered the up-to-now establishment of T/C networks in these regions Certainly, cost-effective operation of the T/C equipment (i.e., remote T/C stations) becomes critical in order to satisfy local demand The use of electrification alternatives such as diesel power generation, comprising a common power supply option for the existing remote T/C stations, entails considerable life cycle costs and aggravation of the local environment In this context, the use of RES may replace costly and heavily polluting diesel engines [40] Among the alternatives of electricity generation for T/C stations, T/C providers themselves [41] identify wind energy as an energy solution of minimum operating expenses and negligible environmental footprint, suitable for coastal locations or hilly areas with appreciable wind potential Small-sized wind turbines may even be adjusted on the relay mast (Figure 10) as a supplementary to the diesel option energy solution, while wind-based stand-alone systems occupy comparatively larger wind turbines These are installed near the mast area and are able to minimize the fuel consumption of diesel generators used for backup supply only In any given case, however, a battery bank of the appropriate capacity is also necessary; while depending on the local area characteristics, reduction of the battery bank size may be achieved through the incorporation of a PV array Introducing PV power to the system may complement wind energy generation while also eliminating oversizing of storage and further reducing oil fuel consumption, especially during the summer months, that is, when the air-conditioning needs of the station increase [43] 2.22.13 The Wind Power-Based T/C Station Small wind turbines can be used cost-effectively to power such T/C sites Wind power, coupled with an appropriately designed energy system, can secure constant power supply, which is crucial for telecom services, and reduce the need for ongoing maintenance such as fuel and equipment transportation Reliable energy supply and significant cost savings increase wind power competitiveness and turn it into the best energy choice for telecom and network operators The main benefits from the exploitation of RES in general and wind energy – more specifically – in T/C stations are the following: • • • • The very small need for maintenance This is very important as the T/C stations are in remote regions The easy and simple installation The high-energy output thus implying a cost-effective operation In some cases, there is no need for a tower as the wind turbines may be attached to the existing T/C towers Nowadays, many engineering and manufacturing companies have been active in the area of design, manufacturing, and installation of wind turbines for T/C applications, suggesting that various types of wind turbines are providing a range of alternative solutions to specific implementation projects suitable for these types of applications [42, 44, 45] In fact, the suggested wind turbines exhibit properties that make them very attractive for these applications, such as Figure 10 Wind turbine in a T/C station [42] 742 • • • • Special Wind Power Applications variable pitch blades, aluminum alloy castings, upgraded electronic systems and wiring for improved reliability over standard models, and externally regulated controller designed for rugged environments The critical point of such an application is the very high reliability that is required, a feature that must be taken into account very seriously in the design of the system Various configurations are implemented for stand-alone or grid-connected systems and they are summarized below The configuration to be chosen depends on the application characteristics and requirements and the infrastructure available 2.22.13.1 Configuration Options Overview In the stand-alone systems (off-grid), there is the option of connection to the battery bank using a charge controller In this case, connection is suitable in sites that include a large battery bank and where a diesel generator charges batteries every few hours (noncontinuous diesel generator operation) The power generated by the turbines charges the batteries and reduces diesel generator costs There is the option for wind turbine only or hybrid wind and PV The hybrid system benefits from complementary energy cycles from each technology (day/night, summer/winter, etc.) Again, there is the option of connecting the hybrid system to the battery bank using charge controllers There is also the option of connecting the wind turbine directly to the consumption using an inverter In this case, connection is suitable in sites that include a diesel generator working on a continuous basis and small back up battery bank The power generated by the turbine/s reduces the required diesel generator output level and thus reduces generator costs In this context, various researchers have been investigating different interesting issues in this area, such as the design and the feasibility of specific RES and hybrid energy sources in T/C stations [40, 43, 46] The problems under consideration usually are the modules to be included, that is, the system configuration itself and the determination of the optimum size of each system component, in order to satisfy a selected optimization criterion, for example, the minimum cost Usually, the results obtained indicate that properly sized hybrid power stations appear to be one of the most attractive energy solutions for the support of remote T/C stations, providing increased levels of reliability and presenting low maintenance needs 2.22.14 Applications of Wind Energy in T/C Stations Energy efficiency programs run by T/C companies, for example, in Portugal, use wind micro-generating systems countrywide, reducing fuel consumption and emissions by a considerable 15–20%, while in other cases the employment of higher power output wind turbines minimizes oil use and its impacts For example, three very remote base stations were installed in Kenya in 2005, based on pilot wind–diesel hybrid energy systems The systems consisted of a 7.5 kW turbine on a 24 m tower, sealed batteries, and an inverter, with the results obtained showing excellent reliability and diesel fuel savings of 70–95% Other examples include the similar but comparatively larger wind-diesel installation located at Osmussaar, Estonia, comprising a 30 kW wind turbine, two ordinary diesel generator sets of 32 kW each, and a battery bank of 250 Ah, while another two wind–PV systems may be found in Turkey, with the system incorporating two wind turbines of kW each, PV panels of kWp, and an appropriate battery bank system [43] The majority of the mobile T/C cell stations in the developing world rely on diesel generators for their power However, wind power could soon be challenging the diesel generators and power the cell stations with renewable green energy Over 99% of cell sites worldwide are deployed with diesel generators as a backup or as the primary source of electrical power But the operating expense involved in keeping the diesel fuel flowing can be prohibitive, especially in light of increasingly remote base station sites and rising theft of diesel fuel and generators As diesel generators are favored for their low capital cost, the price of diesel has risen and the cost of solar panels and wind turbines has dropped Economists estimate that the return on investment (ROI) will flip in favor of renewable green energy by 2014 By 2015, an installed base of 1.9 million mobile telecom sites will be candidates for green power upgrades or retrofits, with a compelling ROI driving operators to choose solar and wind power [47] 2.22.15 Wind Water Pumping Systems Wind energy is used very frequently for pumping of water Wind water pumping embraces a number of potential applications [43], including domestic water supply, community water supply, cattle watering, and irrigation Wind water pumping systems may belong to the following categories as far as the exploitation of wind energy is concerned: • to use wind energy to supply shaft power that is used in a direct manner to pump water or • to use wind energy to generate electricity to drive an electrical pump Special Wind Power Applications 743 The former shows higher efficiency at low wind velocities, whereas electric wind systems show better efficiency at high wind velocities The electro-wind pumping systems present greater annual efficiency concerning the water pumped Efficiencies about 10–15% are achieved in the electro-wind pumping compared with efficiencies of 5% or 6% from a mechanical water pumping system of the same rotor diameter [48] In fact, there are two types of wind power systems to pump water mechanically, namely • the piston pump system that converts rotary wind power to vertical motion using a piston pump to lift water and • the airlift pump system that uses wind power to charge a compressor that pumps air to lift water The design of the system to be chosen depends on the specific energy needs and various other parameters, such as the type of application, the battery storage system, and the wind available on the site [49] In electrical water pumping, a wind turbine, generally a fast running one, drives an electric generator which feeds an electric motor connected to a pump This solution is valuable when aquifers are deep under the soil surface and when the wind mean speed is higher than or m s−1 [50] Erecting a wind-driven generator away from the water source, at an elevated place where the wind rate is higher, can increase the power output by 30% or more To achieve good results in water delivery, it is preferable to have a battery for storage of electricity The battery stores energy when the wind speed is higher and gives it back when the wind has low velocity In that case the generator is an alternator and the current must be rectified In practice, the pumps used are chosen in such a manner that their manometric heads are equal to 1.5 or times the height of elevation [50] In the general case, the electrical systems have the added advantage that the turbine can be located on a site with a better wind profile and not necessarily on the site where the water is pumped Wind electrical systems for water pumping are more expensive because, generally speaking, they require five components to convert the wind energy into electrical energy (wind generator, rectifier, charge controller, batteries, and inverter) A less expensive system can be obtained by connecting the electric pump to the generator with a controlled converter, which provides safe operating conditions for both the wind generator and the electric pump [48] This method reduces the number of components and allows the power storage in the battery bank to be replaced by a water storage tank A storage tank is most feasible where the morphology of the land allows locating the tank at a convenient height that permits distribution of the water gravitationally Low-power wind turbines generally operate in isolated systems and frequently the energy is stored in battery banks One of the most crucial issues of these systems is that they need to be very efficient, that is, they need to maximize the quantity of pumped water per unit of electricity or work being produced This consideration affects the design of the pumps employed Many researchers have investigated various aspects of wind-based water pumping and have dealt with the analysis, design, and control of these systems Several wind water pumping installations may be encountered in remote areas (e.g., in isolated farms, see Figure 11), where infrastructure is poor and water supply is used to cover additional needs, on top of domestic ones Actually, the importance of serving the water needs of remote communities is well illustrated by the fact that even though there is increasing water consumption in both the domestic and the industrial sector, agriculture – especially in the developing countries – is still the dominant water user, absorbing almost three-quarters of the global water resources More specifically, the use of freshwater is distributed as follows [51] • 70% for irrigation, • 22% for industry, and • 8% for domestic use Figure 11 Wind water pumping system in a remote area 744 Special Wind Power Applications In this context, the use of wind pumps throughout the developing world remains very valuable and has led to the development of small-scale markets for multibladed and low-rated speed wind turbines For successful wind pumping, the availability of adequate wind and water resources is essential On the other hand, grounded on the complementarity between increased water needs and high solar potential available during the summer months, a shift is noted during the recent years to the PV pumping concept, encouraged also by the gradual cost reduction of contemporary PV modules Nevertheless, the possibility of wind-based hybrid energy systems incorporating PV power as well is also an option A similar pilot hybrid energy system is operated by the Soft Energy Applications & Environmental Protection Laboratory in Greece (Figure 12), where a kW wind turbine along with 610 Wp of PV power and an appropriate lead acid battery bank are able to elevate water quantity of 23 m3 day−1 from a ground depth of 30 m [52] Wind pumping is economically feasible at very moderate average wind speeds of m s−1 and above In some conditions, average wind speeds of 2.5 m s−1 are sufficient for cattle watering and domestic water supply applications Such wind speeds can be found in so many regions of developing countries that solely on the basis of wind resources the potential for wind pumping is enormous, probably tens of millions of wind pumps Water resources could be the bottleneck; wind pumps, however, are especially suited for pumping water from wells with low recharge rates 2.22.16 Water Pumping System Applications Wind pumping systems are used for a variety of applications: for community or domestic water supply, animal husbandry, irrigation and drainage, fish ponds, and salt pans Pumping heads vary from very low (< m), to low (< 10 m), to medium (10–30 m), to deep (30–100 m), and in exceptional cases up to 200 m Pumping requirements may vary from a few cubic meters per day for private domestic water supply to a few hundred cubic meters per day for drainage Solar collector PV panels Wind turbine Lamps Data logger stylitis-41 Charge controller Control panel Water pump PC Water reservoir Battery bank 24 V DC circuit Data circuit Water circuit Figure 12 Experimental hybrid wind-based stand-alone unit in the Soft Energy Applications & Environmental Protection Laboratory [52] Special Wind Power Applications 745 These requirements are mainly met by mechanical wind pumps, having a pure mechanical transmission It should be noted that other transmissions are also used In Northern Brazil, wind pumps are manufactured with a pneumatic transmission, using compressed air These machines are installed in very remote sites Mechanical wind pumps can be subdivided into three types The majority of these machines have diameters between and m and seldom exceed m Classical multibladed wind pumps driving piston pump with the main manufacturers in Australia, South Africa, the United States, and Argentina This design was developed from before the turn of the century up to the 1930s These machines are quite heavy, include a reduction gearbox, are complicated to install, and are quite costly On the other hand, their reliability is high, they have a long lifetime, and maintenance is reasonably simple, provided spare parts are available It is estimated that between half a million and a million are still operational, especially in Argentina for cattle watering This classical multiblade is also referred to as the first-generation wind pump and has also been more or less copied by a number of manufacturers in developing countries, in general without attaining the high quality of production of the traditional manufacturers Second-generation machines Most of these machines were developed after 1975, for example, by ITDG (UK), Gaviotas (Colombia), CAAMS (China), CWD (The Netherlands), BHEL (Kenya), and Oasis (France) Most of these machines were developed for local production These modern light-weight wind pumps (also driving piston pumps) are characterized by the use of standard materials (angle iron, ball bearings, pipes, steel plates, etc.) and the absence of castings and reduction gear boxes Usually their rotors have fewer blades than the classical wind pump and so rotate faster As a gearbox is also omitted, the pump speeds are higher, which can lead to detrimental pump loads and shorter lifetimes if the machine has not been designed adequately Low-cost wind pumps This type has an investment cost which is a fraction of that for a comparable first- or second-generation wind pump Low cost is attained by the simplicity of the product, the low manufacturing cost, and the use of cheap local materials For example, a lathe is not necessary for production Maintenance can be considerable, but it can all be carried out locally The application is usually restricted to low heads (salt pans in Cape Verde and Thailand, low-head irrigation in Peru) Various research projects have been carried out in order to determine the optimal design and operating conditions of such systems [53, 54] References [1] Gilau AM and Small MJ (2008) Designing cost-effective seawater reverse osmosis system under optimal energy options Renewable Energy 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Stand-Alone and Hybrid Wind Energy Systems: Technology, Energy Storage and Applications, ch 1.5 Woodhead Publishing, ISBN 1-84569-527-5, ISBN-13: 978-1-84569-527-9 [44] Telecommunications, http://www.globalwindgroup.com/services/telecommunication-solutions (accessed March 2011) [45] Telecommunication stations, http://www.china-windturbine.com/telecommunication-stations.htm (accessed March 2011) [46] Kaldellis JK (2010) Optimum hybrid photovoltaic-based solution for remote telecommunication stations Renewable Energy 35(10): 2307–2315 [47] Wind and solar could power telecommunications in developing world, http://www.tomorrowisgreener.com/wind-and-solar-could-power-telecommunications-in-developing­ world/ (accessed March 2011) [48] Lara DD, Merino GG, Pavez BJ, and Tapia JA (2011) Efficiency assessment of a wind pumping system Energy Conversion and Management 52: 795–803 [49] Jaramillo OA, Rodriguez-Hernandez O, and Fuentes-Toledo A (2010) Hybrid wind hydropower systems In: Kaldellis JK (ed.) Stand-Alone and Hybrid Wind Energy Systems: Technology, Energy Storage and Applications, ch Woodhead Publishing, ISBN 1-84569-527-5, ISBN-13: 978-1-84569-527-9 [50] Gourieres D Wind Power Plants, Theory and Design Pergamon Press, ISBN 0-08-029966 [51] World Water Assessment Programme for development, capacity building and the environment http://www.unesco.org/water/wwap (accessed March 2011) [52] Kaldellis JK, Spyropoulos GC, Kavadias KA, and Koronaki IP (2009) Experimental validation of autonomous PV-based water pumping system optimum sizing Renewable Energy Journal 34: 1106–1113 [53] Ramos JS and Ramos HM (2009) Sustainable application of renewable sources in water pumping systems: Optimized energy system configuration Energy Policy 37: 633–643 [54] Smulders Paul T and Jan de Jongh I (1994) Wind water pumping: Status, prospects and barriers Renewable Energy 5(Pt I): 587–594 Further Reading ALTENER Programme (2002) Renewable energy driven desalination systems – REDDES Technical analysis of existing RES desalination schemes Stylianos Loupasis http://www.nad gr/readsa/files/TechnodatabaseREDDES.PDF (accessed March 2011) Ekren BY and Ekren O (2009) Simulation based size optimization of a PV/wind hybrid energy conversion system with battery storage under various load and auxiliary energy conditions Applied Energy 86(9): 1387–1394 Fritzmann C, Löwenberg J, Wintgens T, and Melin T (2007) State-of-the-art of reverse osmosis desalination Desalination 216(1–3): 1–76 Garcia-Rodriguez L, Romero-Ternero V, and Gomez-Camacho C (2001) Economic analysis of wind-powered desalination Desalination 137: 259–265 Hamed OA (2005) Overview of hybrid desalination systems – Current status and future prospects Desalination 186(1–3): 207–214 Kamal I (2008) Myth and reality of the hybrid desalination process Desalination 230(1–3): 269–280 Kim YM, Kim SJ, Kim YS, et al (2009) Overview of systems engineering approaches for a large-scale seawater desalination plant with a reverse osmosis network Desalination 238 (1–3): 312–332 NREL, Wind Energy/Desalination System (2005) wwww.nrel.gov/wind/pdfs/39485.pdf (accessed February 2011) Schiffier M (2004) Perspectives and challenges for desalination in the 21st century Desalination 165: 1–9 Tzen E, Theofilloyianakos D, and Kologios Z (2008) Autonomous reverse osmosis units driven by RE sources, experiences and lessons learned Desalination 221(1–3): 29–36 Continuous and unlimited operation of telecom sites, http://www.tswind.com/index.php/telecom.html (accessed March 2011) Kondili E (2010) Design and performance optimization of stand-alone and hybrid wind energy systems In: Kaldellis JK (ed.) Stand-Alone and Hybrid Wind Energy Systems: Technology, Energy Storage and Applications, ch Woodhead Publishing, UK, ISBN 84569 527 5, ISBN-13: 978 84569 527  ... Electrical energy consumption (kWh m−3) Thermal energy consumption (kWh m−3) MSF MED MED-TVC MVC BWRO SWRO 8– 12 8– 12 8–1 4 N/A N/A N/A 3 .25 –3 .75 2. 5 2. 9 2. 0 2. 5 9. 5–1 7 1.0 2. 5 4. 5–8 .5 6.7 5–9 .75 4. 5–6 .5... 3.8 0.75 2. 65 1.7 2. 25 3 .2 3 .25 0.5 2. 35 1.1 2. 15 2 1.85 4 .2 MED 1.6 2. 3 0. 825 3 .25 0.65 4.85 1 .24 35 1.31 67 MED–TVC 3.3 0.5 2. 25 1.85 1.65 1.8 2. 5 1.7 3.3 1.55 35 738 Special Wind Power Applications. .. of a solar powered water desalination plant Energy Conversion and Management 44: 22 17 22 40 [25 ] Rheinländer J (20 07) De-central water and power supply integrating renewable energy – Technical