Potential for economic solar desalination in the Middle East

Fresh water forms only about 1% of the total water available on earth. Technologies for the desalination of seawater have considerably matured in the last decade. However, the energy required for the desalination is usually expensive in arid areas where fresh water is required. Renewable energy provides a clean, free, and low-maintenance source of energy for desalination, limited only by their initial cost, and the variability of the available energy. In this paper the potential use of solar energy for the desalination of seawater in the Middle East is evaluated. Multi-Stage Flash (MSF) desalination requires large amounts of energy, while Reverse Osmosis (RO) desalination is more energy efficient. Solar distillation is a very simple and direct method that may be used, requiring only large flat areas of land, having no running energy costs and being very suitable for remote areas. Photovoltaics is another promising renewable energy source for seawater desalination in the Middle East. It is best suited for the RO and Electrodialysis (ED) methods. The desalination plant doesn't need to run continuously, and therefore no storage batteries are required. Diesel and / or natural gas may be used as a backup energy.     

Hydrostatic pressure plants for desalination via reverse osmosis

Renewable energies (solar and wind energies) associated to reverse osmosis (RO) are gaining renewed interest for brackish and seawater desalination. Another potential source of energy is the hydrostatic pressure at a sufficient operative depth or height to perform the RO process. This article provides a comparison of the energy requirement of various hydrostatic pressure-RO plants. For submarine and underground plants, the required energy is equal to 2.98 and 3.54 kWh, respectively, for 1 m³ of produced fresh water. In case of hydrostatic pressure generated by a column of water due to a head difference between the sea level and an adjacent mountain, the energy required is equal to 1.4 kWh. These energy requirements compare well with the usual energy requirement for desalination, between 3 and 10 kWh for 1 m³ of produced fresh water. However, the main drawback associated with hydrostatic pressure plants relates to their construction and their maintenance, which are expected to be more complicated and costly than for a ground plant.     

Feasibility study of brackish water desalination in the Egyptian deserts and rural regions using PV systems

Fresh water is the most important source for life on the earth. In the Egyptian deserts and rural areas, there is a shortage of fresh water in spite of the presence of large sources of brackish water. Solar energy is abundant in these remote areas of Egypt, where the amount of sunshine hours is around 3500 h/year. This paper introduces a feasibility study of water desalination in these areas using photovoltaic energy as the primary source of energy. The availability of water resources and solar energy in these areas has been investigated. Also, a design of a PV powered small scale reverse osmosis water desalination system is studied and economically estimated. It is found that the cost of producing 1 m³ of fresh water using the small PV powered RO water desalination systems is 3.73$. This cost is based on using a small system that is operating during the daylight only. If the system size and the daily period of operation are increased, the price of producing fresh water will be decreased in these regions. Also, it is important to mention that using renewable energy sources in feeding different systems in these rural areas with their energy demands will maintain their environment clean and healthy for people.     

The potential contribution of geothermal energy to electricity supply in Saudi Arabia

With increase in demand for electricity at 7.5% per year, the major concern of Saudi Arabia is the amount of CO₂ being emitted. The country has the potential of generating 200×10⁶ kWh from hydrothermal sources and 120×10⁶ terawatt hour from Enhanced Geothermal System (EGS) sources. In addition to electricity generation and desalination, the country has substantial source for direct application such as space cooling and heating, a sector that consumes 80% of the electricity generated from fossil fuels. Geothermal energy can offset easily 17 million kWh of electricity that is being used for desalination. At least a part of 181,000 Gg of CO₂ emitted by conventional space cooling units can also be mitigated through ground-source heat pump technology immediately. Future development of EGS sources together with the wet geothermal systems will make the country stronger in terms of oil reserves saved and increase in exports.     

Solar stills for community use—digest of technology

The many factors that influence the productivity of solar stills are discussed in three categories: atmospheric variables, design features and operational techniques. Data on the large solar stills which have been operated are tabulated, and productivity curves are given for several basin-type stills. The economics of solar distillation is also considered, and an equation is presented to calculate the cost of producing fresh water. A primary area for further work is identified, that of proving the durability of improved materials by the successful long-term operation of large solar stills. Solar distillation appears well suited for the supply of potable water to small communities where the natural supply of fresh water is inadequate or of poor quality, and where sunshine is abundant. The capital cost of large permanent-type solar stills can be as low as $1 per ft² of basin area, which is equivalent to $10 to $15 per daily gallon output, depending on the yearly amount of solar radiation and rainfall collection. The corresponding distilled water cost is between $3 and $4 per 1000 gal. These water costs are generally lower than those associated with other types of desalination equipment in plant sizes of up to, perhaps, 50,000 gpd.     

Economic assessment of a two-stage solar organic Rankine cycle for reverse osmosis desalination

The current paper presents the economic evaluation of a two-stage Solar Organic Rankine Cycle (SORC) for using the mechanical energy produced during the thermodynamic process to drive a Reverse Osmosis (RO) desalination unit. The developed integrated system is briefly analysed and the specific fresh water cost, as well as the cost of energy is calculated. The economic assessment results are compared with those obtained from a low-temperature SORC-RO and two alternative variants of PhotoVoltaic RO (PV–RO) systems (with and without batteries). It is found that the critical fresh water cost for the system under consideration is 7.48 €/m³ of permeate water and the cost of energy equals to 2.74 €/kWh, when the water cost is slightly higher than the critical one (meaning 8 €/m³). These values are considered satisfactory enough, in comparison to the other autonomous desalination technologies. Additionally, the specific fresh water cost of the developed technology was calculated to be 6.85 €/m³, being very close to the values of the PV–RO systems. The variant of two-stage SORC significantly improves the efficiency and reduces the cost of the already developed prototype system (single-stage low-temperature SORC for RO desalination), because the specific cost is found to be much lower and taking into consideration its reliability, this technology can constitute an alternative desalination method competitive to the PV–RO on the basis of techno-economic feasibility.     

Solar and wind opportunities for water desalination in the Arab regions

Despite the abundance of renewable energy resources in the Arab region, the use of solar thermal, solar photovoltaics, and wind is still in its technological and economic infancy. Great potential exists, but economic constraints have impeded more rapid growth for many applications. These technologies have certainly advanced technically over the last quarter century to the point where they should now be considered clean-energy alternatives to fossil fuels. For the Arab countries and many other regions of the world, potable water is becoming as critical a commodity as electricity. As renewable energy technologies advance and environmental concerns rise, these technologies are becoming more interesting partners for powering water desalination projects. We evaluate the current potential and viability of solar and wind, emphasizing the strict mandate for accurate, reliable site-specific resource data. Water desalination can be achieved through either thermal energy (using phase-change processes) or electricity (driving membrane processes), and these sources are best matched to the particular desalination technology. Desalination using solar thermal can be accomplished by multistage flash distillation, multi-effect distillation, vapor compression, freeze separation, and solar still methods. Concentrating solar power offers the best match to large-scale plants that require both high-temperature fluids and electricity. Solar and wind electricity can be effective energy sources for reverse osmosis, electrodialysis, and ultra- and nano-filtration. All these water desalination processes have special operational and high energy requirements that put additional requisites on the use of solar and wind to power these applications. We summarize the characteristics of the various desalination technologies. The effective match of solar thermal, solar photovoltaics, and wind to each of these is discussed in detail. An economic analysis is provided that incorporates energy consumption, water production levels, and environmental benefits in its model. Finally, the expected evolution of the renewable technologies over the near- to mid-term is discussed with the implications for desalination applications over these timeframes.     

Modeling and optimization of a solar driven membrane distillation desalination system

The desalination technology using membrane distillation driven by solar energy is a feasible solution for reducing the energy cost. A dynamic simulation model for a solar driven membrane distillation desalination system (SMDDS) is developed on the Aspen Custom Modeler^® (ACM) platform for the system performance and optimization study. The rigorous model for the spiral-wound air gap membrane distillation (SP-AGMD) module takes into account the heat and mass transfer resistances associated with each composing layer. The effects of adopting different objective functions, solar radiation conditions, thermal storage tank configurations, as well as the flowrates of the membrane distillation module and the thermal storage tank on the optimized performance are reported. Simple thermal storage tank and lower flowrate of the membrane distillation module are advantageous to higher water production rate. A control system using conventional PI (Proportional/Integral) controllers is proposed and the water production rate can reach about 87% of the optimal result for clear sky operation.     

Dimensioning of the solar heating system in the zero energy house in Denmark

The paper describes the project for a Zero Energy House constructed at the Technical University of Denmark. The house is designed and constructed in such a way that it can be heated all winter without any “artificial” energy supply, the main source being solar energy. With energy conservation arrangements, such as high-insulated constructions (30–40 cm mineral wool insulation), movable insulation of the windows and heat recovery in the ventilating system, the total heat requirement for space heating is calculated to 2300 kWh per year. For a typical, well insulated, one-storied, one-family house built in Denmark, the corresponding heat requirement is 20,000 kWh. The solar heating system is dimensioned to cover the heat requirements and the hot water supply for the Zero Energy House during the whole year on the basis of the weather data in the “Reference Year”. The solar heating system consists of a 42 m² flat-plate solar collector, a 30 m³ water storage tank (insulated with 60 cm of mineral wool), and a heat distribution system. A total heat balance is set up for the system and solved for each day of the “Reference Year”. Collected and accumulated solar energy in the system is about 7300 kWh per yr; 30 per cent of the collected energy is used for space heating, 30 per cent for hot water supply, and 40 per cent is heat loss from the accumulator tank. For the operation of the solar heating system, the pumps and valves need a conventional electric energy supply of 230 kWh per year (corresponding to 5 per cent of the useful solar energy).     

THE THERMAL CHARACTERISTICS AND ECONOMIC ANALYSIS OF A SOLAR POND COUPLED LOW TEMPERATURE MULTI STAGE DESALINATION PLANT PART I: THERMAL CHARACTERISTICS

Salt Gradient Solar Ponds (SGSP) have the potential of providing low grade energy with the advantage of an annual thermal energy storage cycle. The development of Multi-Stage Flash (MSF) distillation plants operating below 100°C allows SGSP to be considered as the heat source for these systems.

In this paper, two schemes of matching the SGSP with the MSF distillation plant are presented. The first scheme is based on the assumption that the solar pond is to be used as the sole heat source for the distillation plant (i.e. all the plant's thermal energy requirements are provided by the solar pond). The second scheme considers a hybrid system (solar + fuel), where a 20,000 m² solar pond is linked to an otherwise stand alone, fuel driven desalination plant. Both options are simulated with the same daily product water output of 1000m³/day. The thermal simulation of the MSF desalination process was predicted by using a mathematical model based on stage by stage calculations taking into account the variations in fluid properties and flow conditions. The generated simultaneous equations of the mass and energy balances were combined and arranged in a matrix form and then translated into algorithm to predict process variables such as temperature and flash evaporation rates.     

A scheme for large scale desalination of sea water by solar energy

A scheme is proposed to desalinate sea water using solar energy for the Thar Desert of India. The scheme has been using solar energy for the Thar Desert of India. The scheme has been designed to produce about 5.25 × 10⁷ m³/yr (13860 MG/yr) of fresh water with 11.52 km² (4.5 miles²) of collector area. The solar collectors are rectangular concrete tubes, half buried in the ground, through which sea water flows and is heated by solar energy. The heated sea water is then flash evaporated in a multi-stage flash evaporator (MSF) unit to yield fresh water. Pumping of the sea water to the site and through the MSF unit is powered by 415 wind turbines each of 200 kW capacity. Economic analysis of the scheme shows that it compares favorably with the existing fossil fuel fired desalination plants of the equivalent capacity.     

一种新型太阳能、风能联合海水淡化装置

淡水资源短缺已成为一个世界性问题,我国也不例外.为了加大淡水供应,一条现实的途径就是充分利用我国丰富的海水资源,以及西北内陆地区的苦咸水(统称海水)进行淡化.提出了一种海水淡化装置,该装置利用温室效应原理和风能致热原理,可充分利用太阳能与风能进行海水淡化.与现有海水淡化装置相比该装置具有利用清洁能源、对环境无污染、适应性强、性价比高等特点.理论计算结果表明,该装置每小时产水量约为普通盘式太阳能海水淡化装置在晴天工作时的2倍.     

Experimental validation of the distillation module of a desalination station using the SMCEC principle

This paper presents the simulation and the experimental validation of the distillation module of a desalination unit, currently operating in Sfax, Tunisia. The desalination process is based on the Solar Multiple Condensation Evaporation Cycle (SMCEC) principle.The work presented in this paper focuses on modelling the desalination module as it is supplied with either water heated by solar energy or geothermal water. Geothermal water resources are abundant in Tunisia with salinity levels of 1–50 g/l. The simulation of the dynamic behaviour of the desalination module with and without disturbances on the inlet temperature was carried out to predict the variations of key output variables subjected to thermal variations. Such variables include water temperature, air temperature, humidity in the evaporation and condensation chambers and the amount of produced distilled water. To validate the dynamic model of the distillation module, a series of experiments was conducted. Experimental results were compared with the simulation results. It was shown that the developed model is able to predict accurately the trends of the heat and mass characteristics of the evaporation and condensation chambers. As a result, the proposed model can be used to design and test the behaviour of such a type of desalination unit.     

Some aspects of solar distillation for water purification

In recent experimental work a solar still design which produces 5 to 7 liters of purified water per day has been developed using aluminum components and polyethylene film as the basin liner. A number of such units already have been set up to supply distilled water for laboratory work. There is a need for a supply of fresh drinking water in many salt works. A new design suitable for easy installation in salt works is being tested.

An appraisal of solar distillation under present conditions in certain parts of India has been reported earlier. The development work, including experience gained during the installation and operation of a pilot plant constructed by CSMCRI, Bhavnagar, forms the basis for this assessment of solar distillation. The importance of a combined method for solar distillation and rainwater collection is obvious. In the various regions of India there are vast differences in rainfall. They range from an average of less than 20 cm to more than 1000 cm per year. In most of the regions rainfall is spread over a period of several months. The possibility of having rainfall collection and solar distillation combined at certain locations is examined following methods outlined in the literature.     

Techno-economic performance analysis of solar cooling systems

Vapour absorption cooling systems, powered by solar thermal energy, are now commercially manufactured in sizes ranging from 1.5 to over 20 RT (one refrigeration ton = 3.51 kW of cooling). The needed thermal energy at appropriate temperature potential can either be provided by solar thermal collectors or else from a solar pond. The paper gives the assessment criteria and results for technical and economic evaluation of the performance of absorption chiller using a solar pond. These results, based on Kuwait's environmental data and costs, have been compared with three alternate cooling systems, namely:

• 1 Solar thermal collector absorption cooling system.
• 2 Solar photovoltaic cooling system.
• 3 Standard vapour compression cooling system.

The criteria, used for performance evaluation of the solar cooling systems on a technical basis, consists of assessing the extent to which such systems can make a positive contribution in a conserving fossil fuel. This is done by first estimating the total electrical energy needed by the standard system (defined in para. 3 above) to produce one unit of cooling output. Solar cooling systems are then analysed and compared with a standard system to establish their electrical energy saving or generation capability, after accounting for the parasitic electrical energy used in pump/fan motors and equivalent energy needed for the production of soft water (used-up in the cooling tower) from seawater desalination. The economic analysis considers the cost and life of subsystems and that of the electrical and water desalination plants to arrive at the unit cooling cost. The unit cooling is defined as the ratio of amortized capital investments plus operation and maintenance costs over the year and the total yearly cooling production by the system. The results show that the solar pond absorption cooling system is the closest competitor to the conventional cooling system.     

Sustainably integrating desalination with solar power to overcome future freshwater scarcity in China

Freshwater resources and energy are the two material foundations of human survival and the two challenges for human sustainable development. China’s huge population needs a large amount of freshwater for basic necessities. Desalination is an intelligent and promising technology for increasing water resources to realize a sustainable supply of freshwater. However, high levels of energy consumption and greenhouse gas emissions have restricted the development of desalination. Solar energy has the unique advantage that it can be harnessed in different forms. This paper discusses the water resources and solar energy utilization status in China and presents a comprehensive review on a possible solution: coupling desalination technologies with sustainable energy. China’s desalination market is reviewed, and the energy consumption for several desalination processes is summarized to present a brief outlook of desalination techniques in China. Potential coupled methods for solar-powered desalination are compared. This study will facilitate understanding of the latent water crisis in China and help China’s desalination market transition from conventional energy sources to choose an appropriate solar-powered desalination process.     

Experimental study of a solar desalination pond as second stage in proposed zero discharge desalination process

This work represents the efficiency of a solar desalination pond as a second stage of proposed zero discharge desalination processes to reach fresh water and also concentrated brine from the effluent wastewater of the desalination unit of Mobin petrochemical complex. So a solar desalination pond is constructed after a pretreatment unit to concentrate the softened wastewater to about 20 wt%. The concentrated wastewater is as a suited feed for a forced circulation crystallizer. During one year, the effects of major parameters such as ambient temperature and solar insolation rate are investigated, experimentally. specific gravity in each layer of concentrated brine wastewater is evaluated. Also, evaporation rates are calculated theoretically and are verified by experimental data. Theoretical values predict evaporation rate accurately. Results show good agreement with experimental data. According to results, maximum evaporation rate is 5 l/m² day when the insolation rate is about 24,602 kJ/m² day Solar energy absorption factor on June is max. Also, experimental results show the best proposed time to gain highest thermal energy is on spring therefore performance efficiency of solar desalination pond promote on spring comparing with the other months. Extracted data for specific gravity prove the bottom of solar desalination pond, layer 1, is best zone for energy saving and energy utilization.Also, theoretical values of evaporation rate are calculated according to measured temperatures and related mass conservation equation. Comparison between theoretical and experimental values shows dusty weather, humidity and wind velocity affects on heat transfer coefficients approximately. So, deviations between theoretical data and measured values can be explained. Results show good agreements with experimental data.     

Feasibilty study of renewable energy powered seawater desalination technology using natural vacuum technique

With an ever-increasing population and rapid growth of industrialization, there is great demand for fresh water. Desalination has been a key proponent to meet the future challenges due to decreasing availability of fresh water. However, desalination uses significant amount of energy, today mostly from fossil fuels. It is, therefore, reasonable to rely on renewable energy sources such as solar energy, wind energy, ocean thermal energy, waste heat from the industry and other renewable sources. The present study deals with the energy-efficient seawater desalination system utilizing renewable energy sources and natural vacuum technique. A new desalination technology named Natural Vacuum Desalination is proposed. The novel desalination technique achieve remarkable energy efficiency through the evaporation of seawater under vacuum and will be described in sufficient detail to demonstrate that it requires much less electric energy compared to any conventional desalination plant of fresh water production of similar capacity. The discussion will highlight the main operative and maintenance features of the proposed natural vacuum seawater desalination technology which seems to have promising techno-economic potential providing also advantageous coupling with renewable energy sources.     

A review of renewable energy technologies integrated with desalination systems

Energy is an essential ingredient of socio-economic development and economic growth. Renewable energy provides a variable and environmental friendly option and national energy security at a time when decreasing global reserves of fossil fuels threatens the long-term sustainability of global economy. The integration of renewable resources in desalination and water purification is becoming increasingly attractive. This is justified by the fact that areas of fresh water shortages have plenty of solar energy and these technologies have low operating and maintenance costs. In this paper an attempt has been made to present a review, in brief, work of the highlights that have been achieved during the recent years worldwide and the state-of-the-art for most important efforts in the field of desalination by renewable energies, with emphasis on technologies and economics. The review also includes water sources, demand, availability of potable water and purification methods. The classification of distillation units has been done on the basis of literature survey till today. A comparative study between different renewable energy technologies powered desalination systems as well as economics have been done. The real problem in these technologies is the optimum economic design and evaluation of the combined plants in order to be economically viable for remote or arid regions. Wind energy technology is cheaper than the conventional ones, and used extensively around the world. The slow implementation of renewable energy projects especially in the developing countries are mostly due to the governments subsides of conventional fuels products and electricity. The economic analyses carried out so far have not been able to provide a strong basis for comparing economic viability of each desalination technology. The economic performances expressed in terms of cost of water production have been based on different system capacity, system energy source, system component, and water source. These differences make it difficult, if not impossible, to assess the economic performance of a particular technology and compare it with others. Reverse osmosis is becoming the technology of choice with continued advances being made to reduce the total energy consumption and lower the cost of water produced.     

Application of geothermal energy for heating and fresh water production in a brackish water greenhouse desalination unit: A case study from Algeria

The aim of this paper was to outline a proposed a new brackish water greenhouse desalination unit powered by geothermal energy for the development of arid and relatively cold regions, using Algeria as a case study. Countries which have abundant sea/brackish water resources and good geothermal conditions are ideal candidates for producing fresh water from sea/brackish water. The establishment of human habitats in these arid areas strongly depends on availability of fresh water. The main advantage of using geothermal energy to power brackish water greenhouse desalination units is that this renewable energy source can provide power 24 h a day. This resource is generally invariant with less intermittence problems compared to other renewable resources such as solar or wind energy. Geothermal resources can both be used to heat the greenhouses and to provide fresh water needed for irrigation of the crops cultivated inside the greenhouses. A review of the geothermal potential in the case study country is also outlined.