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223Design and Economics of a Hybrid Desalination System Applied to an Offshore platform*
Dr. Nikitas NIKITAKOS, Professor
Department of Shipping Trade and Transport, University of the Aegean, Greece nnik@aegean.gr
Afrokomi-Afroula STEFANAKOU, Ph.D. Candidate
Department of Shipping Trade and Transport, University of the Aegean, Greece sttm10028@stt.aegean.gr
Abstract. Water scarcity is a major problem that needs to be efficiently solved to ensure water availability for future generations. Desalination is an alternative technology for water production based on salt separation from water. However, the energy requirements for that process are high and can be a problem, mainly in isolated areas. Renewable energy sources are the best way to supply energy needs, because they can be available near the desalination plant, avoiding environmental and availability problems that are associated with fossil fuels. In this paper two forms of renewable energies suited for desalination plant are examined: wind power and wave power. The aim of this study is to present an innovative project which is based on a wind turbine located in a floating platform combined with a wave energy conversion device close to main platform for producing electricity for a desalination plant's energy needs. The whole project can meet the needs of water demand on islands and it has particular characteristics, as it is floating, autonomous and meets its energy needs in an environmental way, utilizing the wave and wind energy. Also, in the paper the cost and benefits analysis on the unit level is presented, as well as the creation of scenarios to come more closely to real world with regard to implementation of such projects. Also, the requirements of installation, the optimal size of the unit and the weather conditions of installation site are examined.
Аннотация. Нехватка воды является важнейшей проблемой, которая должна быть эффективно решена для обеспечения доступной водой будущих поколений. Опреснение - это альтернативная технология производства питьевой воды посредством выделения соли из морской воды. Однако потребности в электроэнергии для этого процесса высоки и могут представлять собой проблему, особенно в удаленных районах. Возобновляемые источники энергии предоставляют наилучший выход для обеспечения энергетических потребностей, так как они могут быть в наличии рядом с опреснительной установкой, и таким образом можно решить проблемы доступности и экологичности, характерные для ископаемого топлива. В этой статье рассматриваются два вида возобновляемых источников энергии, годных для опреснительной установки: энергия ветра и энергия волн. Целью данного исследования является представление инновационного проекта, в основе которого находится установление ветровой турбины, находящейся на плавучей платформе, в сочетании с устройством для преобразования энергии волн поблизости от основной платформы, с целью производства электроэнергии для энергетических потребностей опреснительной установки. Проект может в целом удовлетворить спрос на воду на островах и обладает особыми характеристиками, так как данная установка держится на поверхности воды, автономна, и ее энергетические нужды обеспечиваются в соответствии с требованиями экологии благодаря использованию энергии волн и ветра. Также в документе представлен анализ затрат и выгод на уровне отдельных частей установки, а также разрабатываются сценарии для более полного соответствия практическим требованиям, возникающим при реализации подобных проектов. Также рассматриваются требования к сооружению, оптимальный размер установки и учет погодных условий в месте ее сооружения.
Key words: floating platform, desalination unit, wind and wave energy conversion, desalination costs, full-cost assessment.
* Технико-экономические аспекты проекта гибридной системы опреснения для применения на морской платформе.
INTRODUCTION
Freshwater and energy are two inseparable and essential commodities for sustaining human life on earth. Rapid population growth and industrialization, especially in developing countries in the recent past, have placed pressing demands for both freshwater and energy. Supply of freshwater requires energy and, unfortunately, many countries in the world that lack freshwater sources are also deficient in energy sources. Desalination is an alternative technology for water production based on salt separation from water. However, the energy requirements for that process are high and can be a problem, mainly in isolated areas. Renewable energy sources are the best way to supply energy needs. Although, as desalination technologies are energy-intensive, they would be appropriate in areas where: there is no alternative (islands), cost of other resources are high (transportation costs), low-cost energy is readily available (Middle East oil-reach countries), and high living standards override the cost factor (the case of tourism) (Wade, 2001).
Until now the most part of desalination processes are powered by fossil fuels, contributing to climate change, releasing greenhouse gases and other harmful emissions. Also, apart from the above, the Kyoto Protocol requires global per capita emissions to drop to 0.2-0.7 ton C/cap/year from the current levels of 0.3 in developing countries, 5.5 in USA and 2.5 in Western Europe (Lamei, 2008). Furthermore, the limitation of fossil fuels has necessitated the use of new and alternative energy sources for energy security reasons and future sustainable development. It is worth mentioning that the petroleum reserves are estimated to be depleted in less than 50 years according to present rate of consumption (Demirbas, 2009).
In Table 1 we can see the world population growth with increased desalination capacity and the oil re-
quirements to produce freshwater through desalination technologies and associated greenhouse gas emissions over the past five decades. Until now the world desalination capacity is only 7.5% of world's total minimum freshwater demand, which requires 1.42 million tons of oil/day. And now the most important question, which should be answered, is why we should continue to use conventional source of energy with so much expenses, contributing in greenhouse effect and depleting the natural energy sources, which threaten the human life. In contrast to this, it is considered necessary to develop new alternatives to replace conventional energy sources in desalination process with renewable energy and reduce the energy requirements for desalination by developing new, innovative and low-cost technologies like hybrid models.
This paper presents a possible combination of two renewable energy sources, wave and wind, in a desalination unit placed in a floating platform consisting of a four peripheral cylinders grid with a bigger cylinder at the center. The energy needs of desalination plant are covered by wind and wave devices. The whole project can meet the needs of water demand; it is floating, autonomous and meets its energy needs in an environmental way, utilizing the wave and wind energy. Also, in the paper the cost and benefits analysis on the unit level is presented, as well as the creation of scenarios to come more closely to real world with regard to implementation such projects. Also, the requirements of installation, the optimal unit size and the weather conditions of installation site are examined.
1. STATE OF THE ART
The available desalination technologies until now can be categorized as follows:
(a) Phase change processes that involve heating the feed to boiling point at the operating pressure to
Table 1. World population, desalination capacity, oil requirements & greenhouse gas emissions over past five decades.
Year World Population (billions) World DesalinationCapacity (million m3/day) Oil Required (million metric tons/day) GHG Emissions (Metric tons CO2 / day)
1960 3.1 0.12 0.00 0.36
1970 3.8 0.72 0.02 2.16
1980 4.5 4.4 0.12 13.2
1990 5.3 13 0.36 39
2000 6.0 23 0.63 69
2008 6.8 52 1.42 156
produce steam, and condensing the steam in a condenser unit to produce freshwater. Applications of this category include solar distillation (SD), multi-effect distillation (MED), multi-stage flash distillation (MSF), mechanical vapor compression (MVC) and thermal vapor compression (TVC).
(b) Non-phase change processes that involve separation of dissolved salts from the feed waters by mechanical or chemical/electrical means using a membrane barrier between the feed and product. Applications of this category are electrodialysis (ED) and reverse osmosis (RO).
(c) Hybrid processes involve a combination of phase change and separation techniques in a single unit or in steps to produce pure or potable water. Prime examples of this category are membrane distillation (MD) and reverse osmosis combined with MSF or MED processes (Gude, 2010).
2. RES-BASED DESALINATION pROCESSES
Desalination of water based on renewable energy sources can be a sustainable way to produce clean water. This way of desalination is expected to become economically attractive, as the cost of renewable technologies continues to decline and the price of fossil fuels continues to increase. So, using locally available renewable energy sources for the desalination of water can be a low-cost solution especially for remote areas, with low population and poor infrastructure for fresh water and electricity transmission and distribution. The presence of renewable energy in desalination process corresponds to less than 1% of desalination capacity based on conventional fossil fuels (EU, 2008). This percentage is not considered representative for the advantages which renewable energy technologies offer to us.
Renewable desalination is mostly based on RO process (62%), followed by thermal processes such as MSF and MED. Now, regarding the kind of renewable energy, the dominant energy is considered the solar energy (solar photovoltaic) (PV), which is used in some 43% of the existing applications, followed by solar thermal and wind energy.
The right coupling of a renewable energy source with a desalination plant is considered the key to match power and water demand economically, efficiently and in an environment-friendly way.
So, the right coupling is determined by various criteria such as the system's efficiency, the investment and operational cost, availability of operational personnel, the suitability of the system to the characteristics of the location, the possibility for
future increase of the system capacity etc. (Mathio-ulakis, 2007).
Desalination plants based on renewable energy sources can be seen in Cyprus, Greece, Egypt, Jordan, Morocco, Turkey, UAE (Abu Dhabi), Canary Islands etc. (IEA-ETSAP and IRENA, 2012).
3. ECONOMIC ELEMENTS OF A
desalination plant
3.1 factors affecting desalination cost
Cost is a major factor in implementing desalination technologies. In general, cost factor associated with implementing a desalination plant is site-specific and depends on several variables. Details about desalination costs are provided in various documents (Desalting Handbook for Planners, 2003).
So, the most important parameters which affect the desalination cost are the following:
Quality of Feedwater: The quality of feedwater is considered a crucial parameter. Low TDS1 concentration in feedwater requires less energy for treatment compared to high TDS feedwater. Low TDS allows for higher conversion rates and the plant can operate with less dosing of antiscale chemicals. The pre-treatment of surface waters such as tidal waters will be more costly compared to brackish groundwater because of the potential existence of more contaminants in these waters.
Plant Capacity: Plant capacity is also an important parameter. This factor can affect the size of treatment units, pumping, water storage tank, and water distribution system. In general we can say that large capacity plants require high initial capital investment compared to low capacity plants. But due to the economy of scale, the unit production cost for large capacity plants can be lower.
Site characteristics: Site-specific aspects have a significant impact on final costs (IEA-ETSAP and IRENA, 2012). For example, for desalination plants which are placed on land, the availability of land as well as the land conditions can determine the cost. The proximity of land location to water source and concentrate discharge point are other factors. Pumping cost and costs of pipe installation will be substantially reduced if the plant is located near the water source and if the plant concentrate is discharged to a nearby water body. Also, costs associated with water intake, pre-treatment and concentrate disposal can be substantially reduced if the plant is an expansion of an existing water treatment plant, as compared to constructing a new plant.
1 TDS: Total Dissolved Solids
Regulatory Requirements: these costs are associated with meeting local/state permits and regulatory requirements (Younos, 2005).
3.2. DESALINATION IMPLEMENTATION COSTS
Estimation of the capital and production cost of desalination plants is very difficult due to the following reasons: Variable energy, material and labor costs by geographic areas, the type of desalination process/design/size, salinity of feedwater source and financing packages (National Research Council, 2008).
There are three types of costs associated with desalination typically mentioned in the bibliography. These include the capital cost (CAPEX), operating cost (OPEX), and the total water cost (TWC).
The capital cost is often referred as Capital Expenditure or CAPEX, and it describes the capital expenditures required to complete the project. Capital costs for a desalination plant typically are associated with the construction of the over-all infrastructure. The construction cost of plant is 50-80% of the initial investment cost. The remaining percentage, i.e. 20-50%, has to do with costs of design, licensing and loans of investment.
Operating Costs (OPEX), which are requiring costs, typically on annual basis, include, but are not limited to, operating and maintenance labor (O&M), energy consumption, maintenance parts, insurance, laboratory analysis and monitoring etc.
The OPEX is divided into two parameters — the fixed and the variable cost. Fixed costs include insurance and amortization. Usually insurance cost is estimated as 0.5 percent of the total capital cost. Amortization compensates for the annual interest payments for direct and indirect and depends on the interest rate and the lifetime of the plant. Typically, an amortization rate in the range of 5-10% is used. Variable costs include the costs of labor, energy, chemicals and maintenance. Labor costs can be site-specific and also depend on plant ownership or special arrangements such as outsourcing of plant operation. Energy costs depend on availability of inexpensive electricity. Chemical use depends mainly on feedwater quality and degree of pre/post treatment and cleaning process.
The major maintenance cost pertains to the frequency of membrane replacement, which is affected by the feedwater quality. For low TDS brackish water the replacement rate is about 5% per year. For high TDS seawater, the replacement could be as high as 20%. The cost of maintenance and spare parts is typically less than 2% of the total capital cost on annual basis.
Total Water Cost (TWC) is frequently quoted in desalination industry bibliography as a common com-
parison between projects. TWC has been defined as the annual operating cost + the annualized capital cost (or dept. service).
3.3. DESALINATION COST ESTIMATIONS
During the last few decades the operating costs of producing desalinated water have steadily decreased due to continuous technological progress. Though still a costly water supply option compared to natural water resources such as ground or surface water, desalination may soon be a competitive alternative even in non-water stressed areas. It is worth mentioning that costs for conventional water sources are expected to increase, while costs for desalting are expected to decrease as technology improves (Reddy & Ghaf-four, 2007).
The international bibliography has shown that the reduction of cost has occurred in three main cost areas: capital, energy, operation and maintenance due to:
• Technological developments;
• Increasing size of plant;
• Lower interest rate and energy costs;
• Changes in managing enterprise performance;
• Intense competition between equipment suppliers worldwide.
Specific improvements that have contributed to cost reduction, among many others, have been optimization of design process and thermodynamic efficiency, use of newer materials with better heat transfer properties, and development of new construction and transportation techniques for MSF, technological improvements of membranes, optimization of pre-treat-ment options, and use of energy recovery devices for RO (Fritzmann et al., 2007; Reddy & Ghaffour, 2007).
It is commonly known that desalination possesses require significant quantities of energy to achieve separation of salts from seawater. Existing MSF and RO plants are powered by conventional energy sources because they still represent the most economical way to satisfy the energy needs of a desalination plant. However, coupling of renewable energy source and desalination plants holds great promise as a feasible solution to water scarcity in remote areas where drinking water and conventional energy infrastructure are currently lacking.
Already several desalination plants driven by solar, wind or geothermal energy have been installed throughout the world, and the majority of them have been successfully in operation for a number of years (Bernat et al., 2010).
However, it is clear that RES are still much more expensive than the conventional sources, although the higher cost of RES is counterbalanced by its en-
Table 2. Comparative costs for common renewable desalination. (Papapetrou, 2010).
Technical Capacity Energy Demand (KWh/m3) Water Cost (uSd/m3)* development Stage
Solar Stills <0.1 m3 /d Solar Passive 1.3-6.5 Application
Solar-Multiple Effect Humidification 1-100 m3 /d Thermal:100 Electrical:1.5 2.6-6.5 R&D Application
Solar-Membrane Distilation 0.15-10 m3 /d Thermal:150-200 10.4-19.5 R&D
Solar/CSp-Multiple Effect distillation >5.000 m3 /d Thermal:60-70 Electrical:1.5-2 2.3-2.9 (possible cost) R&D
photovoltaic-Reverse Osmosis <100 m3 /d Electrical: Brackish Water: Brackish Water: R&D Application
photovoltaic-Electridialysis Reversed <100 m3 /d Electrical: Brackish Water: R&D
Wind-Reverse Osmosis 50-2.000 m3 /d Electrical: Units under 100 m3 /d: R&D Application
Wind-Mechanical vapor Compression <100 m3 /d Electrical: 5.2-7.8 Basic Research
Wind-Electrodialysis - - Brackish Water: -
Geothermal-Multi Effect distillation - - Seawater: -
* Cost calculated at the exchange rate of 1.13 from euro to USD.
Table 3. Investment cost for desalination processes with capacities in range 200-40.000 m3 /day. (Wabgnick, 1989 & Ettouney, 2004).
Desalination process Capacity (m3/day)
200 600 1200 2000 3000 20.000 30.000-40.000
Cost Unit ($/m3) Investment (M$) Cost Unit ($/m3) Investment (M$) Cost Unit ($/m3) Investment (M$) Cost Unit ($/m3) Investment (M$) Cost Unit ($/m3) Investment (M$) Cost Unit ($/m3) Investment (M$) Cost Unit ($/m3) Investment (M$)
mvc 3.8 0.75 2.65 1.7 2.25/3.22 3.2/1/58
RO 3.25 0.5 2.35 1.1 2.15 2 2 3 1.85 4.2
med 1.6 2.3 0.825 3.25 0.65 4.85 1.24 35 1.31/1.08 67 70
med-tvc 3.3 0.5 2.25 1 1.85 1.65 1.8 2.5 1.7 3.3 1.55 35
vironmental benefits. Although due to rapid decrease of renewable energy costs, technical advances and increasing number of installations, renewable desalination is likely to reduce significantly its cost in the near future and become an important source of water supply for areas affected by water scarcity.
Desalination costs of produced water for different desalination processes coupled with renewable energy sources are described in the following table.
Also, capital investment and desalination costs for different desalination processes powered by conventional energy in the capacity range of 200-40.000m3/ day are described in Table 3.
Generally, the desalination cost is considered lower for higher desalination capacities whether they are powered by conventional energy or renewable energy.
The high range of desalination cost is due to the fact that the small-scale applications powered either by renewable energy sources or conventional energy sources require high capital costs (Karagiannis, 2008; Ayoub, 1996; Rheinlander, 2001). The capital cost as well as the operation and maintenance cost can be reduced, if a hybrid energy source comprising both fossil fuel energy and renewable energy is considered (Sagiea, 2001). So, such a hybrid plant can reduce the production cost of desalinated water. Also through
this combination we can have lower emissions of C02 and lower electricity consumption. The combination of desalination processes powered by renewable energy sources worldwide is as follows: reverse osmosis 62%, electrodialysis 5%, MSF 10%, MED 10%, VC 5% and others 4%, out of which 43% of the desalination processes are powered by solar PV energy, 27% by solar thermal, 20% by wind and 10% by hybrid combinations. So, photovoltaic energy and wind energy are more promising source of energy to power desalination processes, but the high cost of photovoltaic modules and the unpredictable nature of wind are the main barriers for their use.
With regard to remote areas the renewable energy applications for very small-scale applications are still viable where the transportation cost to supply fresh water is higher. The value of freshwater increases especially in areas which encounter both water scarcity and energy problems. So, installation of an autonomous renewable energy-driven desalination plant will not only ensure the supply of freshwater but also will bring down the cost of freshwater production. However, the factor of desalination cost can be counterbalanced by the environmental benefits offered by renewable energy sources.
In conclusion, nowadays the renewable energy-powered desalination plants may not compete with conventional systems in terms of direct cost of water produced. Nevertheless, their use is steadily expanding in certain areas and it seems clear that they will become a competitive alternative to conventional energy-powered plants in the future, as fuel prices keep rising and fuel supplies are decreasing (Reddy & Ghaffour, 2007).
4. DESIGN OF HYBRID WAVE & WIND POWERED DESALINATION SYSTEM
4.1. DESIGN ISSUES
System's design and development combine research from several scientific domains. The most important requisites we had to satisfy were that the system is environment-friendly and autonomous.
Environment-friendly means that it does not have any side effects, and autonomous means that the floating platform operates unmanned and that energy comes from renewable source (Lilas, 2007). The solution focused on the development of the required subsystems, their integration on a suitable floating structure and operation under the supervision of intelligent control system.
From an operational point of view potable water is produced from the sea water desalination unit, which requires energy. This energy is provided by the wind
Figure 1. The tubular mesh and cylinders.
generator and wave device which is placed close to main platform.
Also energy management is very important and has three main targets: (a) Ensure system survival in case of prolonged period without significant energy input, (b) Extract as much energy as possible from wind and wave and maximize water production, (c) Reduce maintenance cost.
In addition, the research has focused at the following targets: (a) Optimizing energy efficiency of desalination unit over a wide range of water output according to available power, (b) Environment-friendly operation without any chemical additives (Younos, 2005; Rachel, 2003), (c) Design of the floating structure to be stable and not be affected by waves, and providing safe operation of all components, (d) Design of control and teleoperation system.
4.2. DESIGN ISSUES OF THE FLOATING PLATFORM
The design of the floating structure in order to fulfill some requirements went over the following phases: (a) Survey of studies worldwide for floating wind turbines (Sklavounos, 2008; Skaare, 2006), (b) Design of a feasible solution that can fulfill the requirements, (c) Optimization of design characteristics to improve performance and reduce cost, (d) Final stability study and load analysis of optimized design.
The optimization targets were to minimize movements from waves, improve the operation conditions for the wind turbine and wave device and withstand extreme weather conditions. Concerning our project, the first step was to examine the shape and the dimensions of the structure. Also, it was examined which is the appropriate number of peripheral floaters around the central floating structure. So, four peripheral floaters were selected, because this design provides better stability and it has construction advantages. So, the final design of floating platform consists of four peripheral floating cylinders with total height of 8 meters and diameter 2 meters each,
Windturbine Power KW
Chart 1. Wind turbine power curve.
and a central floating cylinder with diameter of 4 meters and height of 8 meters.
The wind turbine will be placed in the central floating cylinder. Also the connection of all cylinders is made with a tubular mesh. The system has automatic control via GPS for monitoring and remote control. In addition it is worth mentioning that whole construction can operate even in adverse weather conditions.
4.3. DESIGN ISSuES AND ECONOMICS ELEMENTS OF Wind TuRBINE
Almost all countries in the world have the wind energy sources in some areas. Wind conditions in the mountains, coastal areas, in deep sea and in islands are favorable for wind-powered desalination plants. For the operation of a wind-powered desalination plant, it is important to have a suitable process that is insensitive to repeated start-up and shutdown cycles caused by rapidly changing wind conditions.
With regard to position of the wind turbine in the specific project, it is placed at the center of the floating cylinder. The features of this specific wind turbine are the following: (a) It has 30 kW in power, (b) Variable pitch of blades and (c) Variable speed. The role of the wind turbine is to provide energy for the desalination of sea water. So, it becomes understandable that when wind speed is high, the system produces more water, so power consumption increases, whereas when it is low, it decreases. The power supply to the desalination unit is energy that comes from the wind generator and wave device, without using the national supply grid or any kind of diesel generator. In the following chart you can see the power curve of wind turbine.
The economics of a wind-powered desalination plant differ from conventional plant economics since it is almost entirely based on the fixed costs of the systems. Even though there are no fuel costs for the plant, the cost of the wind turbine is considered the main capital expenditure, which replaces the fuel
costs of the system. Therefore, energy efficiency is not the main factor, but rather the economics of the process.
Due to intermittence in the production of wind energy, suitable combinations of other renewable energy sources can be employed to provide smooth operating conditions.
Wind generator and wave energy combination can drive the desalination process to operate all day with the help of the battery bank system (Tzen, 2008), as in intervals in which we have «good wind» we usually have also strong waves. Combining these two renewable energy sources with desalination may have several inherent advantages.
4.4. Design ISSuES AND ECONOMICS ELEMENTS Of WAvE DEviCE
Wave energy is ideal for desalination in coastal areas where both energy and seawater are available. Wave-powered technology to produce electricity has an experimental history of at least 30 years. Six wave energy technologies can potentially power reverse-osmosis and vapor compression, are two main technologies are successful at full scale operation (Davies, 2005).
With regard to our project, a system of wave energy was studied and designed, which was implemented and put into autonomous operation as a trial.
The specific wave device has a wave front of 8 meters, and produces hydraulic power 25 kW, even if the waves have more power. Also, the wave device utilizes 11% of the available wave energy. Waves will generally be available where seawater is desalinated. But the harnessing of wave energy is, as with other forms of renewable energy, expensive in terms of capital plant and the effort needed to develop the technology.
Even though, the capital and investment cost of wave- and wind-powered desalination system are high compared to conventional desalination system, under certain circumstances, for example, in remote areas, where distributed energy generation is
more convenient than centralized energy generation, transmission and distribution, renewable desalination could compete with conventional systems (Pa-papetrou et al., 2010).
4.5. DESIGN ISSUES OF THE DESALINATION PLANT
The most promising potential market for wind/wave powered RO is in present or potential future island touristic developments in places such as Mediterranean islands, Pacific islands etc.
So, for this specific project the method of RO was selected, as the most appropriate desalination method. The desalination unit is installed on the floating platform as well as the control center system for remote operation and the storage tank of potable water. The main issues to be environment-friendly were not to treat brackish water which is also scarce, the use of chemicals to treat water, and the disposal of brine with chemicals. The whole system performed at Elef-sis bay. The reverse osmosis unit operates from 8 kW up to 25 kW. Energy storage is small and therefore water production should follow available power, by varying flow and pressure.
5. ECONOMIC EVALUATION OF INSTALLATION FLOATING DESALINATION UNIT POWERED BY WIND AND WAVE
5.1. THE EXISTING SITUATION
Greece is one of seven countries of EE which face water scarcity problems together with Malta, Spain, Cyprus, Belgium, Portugal and Italy. In our country, the problem is becoming more intense in the islands, due to their ground morphology and the minimum water sources, which usually are not drinkable but brackish. The situation reaches its peak in the summer due to high temperatures, drought as well as the increase in consumption due to tourism in these areas. The situation is not the same in every island. The problems are more intense in the waterless islands of Cyclades and Dodecanese. Also the problem of scarcity is encountered more in small islands and in islands with low touristic development. This fact is expected, as these islands do not have the necessary resources for expensive solutions to be financed, and also because in these islands there is drinking water scarcity, something that rightly leads to the name «deserted islands». As a temporary solution to the problem, the state has chosen to transfer the water to the islands by ships. However, the amount which is spent on this practice is increasing, as the problem is still unsolved. It is worth mentioning that between 1997 and 2007
Table 4. Characteristics of installation point.
Installation Area Iraklia Island
Island Complex Cyclades
Area 18.078 km2
Population 151 residents
Mean Wind Speed 6m/sec
Mean Significant Wave Height 0.8 m
Mean Wave Period 4.8 s
Mean Wave Slope 1.8 p
Depth of installation point 30 m
Distance from the cost of desalination unit 4 km
Table 5. Mean annual coverage of water supply needs of iraklia island.
Desalination (%) -
Transported Quantities (%) 91,99
Quantities transported water m3/year 16.818
Reservoir of Water (%) -
Groundwaters (%) 4.35
Coverage of Water Supply Needs (%) 96.35
Population (2001) 151
Total Requirements in water (m3) Current Situation 55
Total Deficit (%) Current Situation 5.9
Total Requirements in water (m3) Foreseeable Situation in 2020 67
Total Deficit (%) Foreseeable Situation in 2020 64.3
Source: Aquatic Consortium System of the Aegean, behalf on Ministry of Development
the transfer cost has grown tenfold from 1.244.881€ to 11.206.409€ with increasing trend of about 10% for the next years (Group ITA, 2006). In 2007 the Ministry of the Aegean and Islands Policy paid 4,91€/m3 for transportable water for Dodecanese and 8,32€/m3 for transportable water for the Cyclades.
Also, in many cases the transferred water is not enough to meet the summer needs of some islands, with constant interruptions and many problems in economic and social activities of residents. Also, it is worth mentioning that the quantities of transferred water do not meet the standards of potable water due to insufficient hygiene conditions in transfer vessels. Also, the isolated areas and the islands have difficult
access, resulting in difficulties with electricity supply. These areas are not interconnected with the mainland grid of Greece or are interconnected with weak and low capacity local grids, which are fed from diesel generators. Consequently, the cover of energy needs of desalination methods by conventional source of energy is often not possible, as the local electrical grids are low-power and unable to meet other loads. Even when there is the possibility of energy supply, this solution is not considered cost-effective and economically advantageous, as the available energy sources are considered costly, like diesel in contrast to cheap but polluting lignite.
So, the combination of desalination units powered by RES is considered the most appropriate method for production of potable water in waterless and isolated areas.
5.2. THE CASE STuDY
So, taking everything into consideration, it was decided that an installation of desalination unit in specific areas in Greece would be feasible.
According to data from a study, which was made by the Consortium of Aquatic Systems of Aegean Sea, on behalf of Ministry of Development, it was found that the current needs of Aegean islands are 170.942.219 m 3 per annum and the total deficit is 19.049.212 m3. In 2020 the total needs are forecasted to reach at 224.157.511 m3 and the total deficit to reach 24.462.470 m3. These predictions were based on a number of parameters such as expected growth of population and tourism activity, reduction of consumption of agriculture and livestock as well as the hydrological characteristics of each island.
So, according to these data and taking into account the morphological characteristics, the wind and the wave potential, the bathometric characteristics, as well as the non-existence of natura areas, it was decided that a desalination unit could be installed in Iraklia island.
5.3. SuSTAINABILITY OF DESALINATION pLANT
Calculation of future results, Internal Rate of Return (IRR), Net Present Value (NPV) and Profitability Index (PI): To analyze the viability of this desalination unit in specific installation area, the techno-economic data of the unit should be taken into account.
The assumptions are the followings:
Size Unit: 70m3/day
Type: Reverse Osmosis (RO) with wind turbine and wave device
Mean Wind Speed: 6m/sec
Table 6. Economic Evaluation of Investment.
Total Initial Cost 800.000
Percentage of State Subsidy 40%
Payback Period 5 th-6 th year
Net Present Value 712.342.88€.
Profitability Index 1.49
Internal Rate of Return 21.8
Table 7. Economic Evaluation for Various Operation Scenarios.
Internal Rate of Return (IRR), Net Present Value (NPV) & Profitability Index (PI) for various operation scenarios of desalination unit
Scenario #1 Scenario # 2
Water production. Probability (20%) higher production from mean production according to wind & wave conditions of location Water production. Probability (20%) lower production from mean production according to wind & wave conditions of location
Net Present 1.038.142,22 € 532.518,96 €
Value
Payback Period 3rd-4th year 6th-7 th
Internal Rate 27.6 17.6
of Return
Profitability Index 1.89 1.26
Total Annual 28.046,016 m3 18.697,34 m3
Production of
the Unit (m3)
Mean Significant Wave Height: 0.8 m Maintenance etc: 0,3 €/m3
Total Annual Production (Sales) of the Unit:
23.506 m3
Availability of Unit: 92% due to maintenance, cleaning of membranes, filters, etc
Total Investment Cost: 800.000€ (including the floating platform, wind turbine, wave device, piping, studies, licensing)
Scheme of Investment Financing: 40% state subsidy (according to Law 3299/2004, as in force after its amendment with the Article 37 of Law 3522/2006), 30% equity, 30% bank loans
Operating Conditions: The investment cost is undertaken by individuals (30% equity, 30% bank loans), with operating duration 15 years. After this period the facility will be given to municipality. When the
unit will be given in municipality it should be in good condition and fully operational. The municipality undertakes the costs of connection to the network as well as the cost of storage (water tanks) Also, the municipality is committed to buy the guaranteed quantity of drinking water for 15 years, at a price that exceeds the production cost, to ensure the viability of the unit.
Inflation: 1.5%
Interest Rate: 5%
Cost of Water Transportation by Ship: 8-10€/m3 (Karagiannis, 2010)
Selling Price of Water: 5 €/m3
The results of economic analysis of the desalination unit are the following:
The total net annual cash flows of the project for 15 years are around 1.192.342,88 €. So, the NPV of the investment, subtracting from the amount of 1.192.342.88€ the initial investment cost (not including the subsidy), we conclude that the NPV amounts to 712.342.88€.
The results of the model for the cost-effectiveness of the desalination unit, from both the main case study and two scenarios show that such an investment can become especially attractive for private investors with good payback period, NPV, IRR and profitability index for all cases. Also, as we can observe from data of the table, the annual water production from both main case study and two scenarios are sufficient to cover the annual needs of Iraklia island (16.818 m3), even in case of minimum water production (Scenario 2).
conclusions
The effects of climate change, the depletion of groundwater resources, as well as the demographic and other changes (population growth, tourism etc) cause serious problems of water shortage in the islands and in some coastal areas, especially during the summer season. The mismanagement of water resources is considered one of the most important factors, which cause water scarcity. This fact is caused by overexploitation of ground and surface water, the lack of project management, poor infrastructure, as well as temporary or ineffective efforts made in the past. In many cases the alternative solutions, which were implemented, were not effective or economically viable, and despite the high costs they did not succeed to solve the problem of water scarcity.
The severity of current problems, the lack of alternatives and mainly the predicted growing needs for the next 10 years, require the desalination as the
most reliable and appropriate solution. Already several countries of Mediterranean and Middle East, such as Israel, Cyprus, Malta, Spain and many others, cover the greater part of their water needs by using desalination systems.
In a first phase, the desalination should be considered as the only viable solution that would replace the water transportation to waterless islands, as it could provide high quality water and reduce the cost compared to cost of water transportation. In the second phase, desalination could be extended to coastal areas with serious degradation problems of ground-water, for which the water transfer is unprofitable or difficult.
Based on current technology and production costs, the sustainability of desalination plants, which will be created by municipalities or private investors, can be ensured, with relatively low price levels compared to those in islands.
Apart from the radical solution of water scarcity, the use of available comparative benefits which our country has for the technology development of floating desalination plants, it could contribute to economic growth through the creation of an extremely promising industrial activity, (offshore floating wind parks, exports of floating desalination units to other island countries or developing regions which encounter serious problems of potable water quality).
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