Abstract
This study empirically investigated the performance of four configurations of inclined solar water desalination (ISWD) system for parameters such as daily production, efficiency, system cost, and distilled water production cost. The empirical findings show that in terms of daily productivity improved inclined solar water desalination (IISWD) performed best with 6.41 kg/m2/day while improved inclined solar water desalination with wire mesh (IISWDWM) produced the least with 3.0 kg/m2/day. In terms of cost price of the systems, the control system inclined solar water desalination (ISWD) is the cheapest while IISWDWM is the most expensive system. Distilled water cost price ranges from 0.059 TL/kg, for IISWDW, to 0.134 TL/kg, for IISWDWM system. All the systems are economically and technically feasible as a solar desalination system for potable water in northern Cyprus. Potable water from vendors/hawkers ranges from 0.2 to 0.3 TL/kg.
1. Introduction
In many parts of the developed countries, most especially in millennium cities, the supply of potable water to homes is often taken for granted by the people. The assumption that potable water exists in abundance is luxury to those residing in the desert regions of the world. Water as we know it today does not exist as potable in most sources due to contamination (because of industrial and household waste contaminations), heavy metals contents (in some cases), and salinity. In order to use water for human consumption (drinking and/or cooking), it must be treated to get rid of organisms capable of causing all sorts of diseases and minerals and organic substances that could cause harm. Potable water should be colourless (free from colour) and be free from odour, apparent turbidity, and taste. Many developing (and underdeveloped) countries are struggling to make potable water available to their citizens, due to nonavailability of adequate water sources and/or poor management of the available water sources. In most parts of the world, the demand for water outweighs its supply, a situation calling for innovative technologies for new water sources. Cyprus is located on the Mediterranean basin, with very limited potable water sources. The country is surrounded by the Mediterranean Sea; the seawater source is not readily consumable. The northern part of Cyprus is under economic embargo, a situation that exponentially worsens the fresh water availability on that part of the island. The government does not supply potable water to households due to the high cost of treating the high salinity water sources. Seawater intrusion because of over extraction of underground water and consistent drought has led to the high salinity of the water sources [1]. The water supply to houses through different municipalities contains between 1000 and 2500 ppm of salt.
Desalination of seawater is a proven technology and most practical way of producing fresh water where freshwater sources are either not available or limited. Desalination is being considered by many countries as the most viable and economical option for fresh water production. Desalination of brackish or seawater presents an alternative way of getting a new water source. One main drawback to this solution, however, is high-energy consumption and high cost of most of the plants. The huge energy requirement of desalination systems is the driver of renewable energy integration into desalination. The availability of renewable energies in most water scarce areas has allowed the consideration of renewable energy in desalination. The current events in desalination technology are to couple desalination systems with renewable energy technologies. The recent advances in desalination systems make it possible to consider the use of renewable energy instead of the traditional fossil fuel. The use of renewable energy in desalination will guarantee fresh water production in a sustainable and environmentally friendly manner. At present the use of wind and solar energy in desalination is gaining more attention in renewable energy desalination. The use of renewable energy in solar desalination is common with the popular solar still system. A solar still is a simple device that can be used to convert seawater and/or brackish water into potable water. The principle of operation of a typical still uses exactly the same processes that nature uses in generating rainfall. In order to improve the productivity of the solar desalination system a number of authors have tested the system under different climates with different design configurations [2–13]. Today, other solar desalination systems have emerged with better efficiency and daily production capacity. One of such is the inclined solar water desalination systems. Unlike a conventional solar still, the feed in water in the inclined solar water desalination system flows down on the absorber plate that is inclined at an angle. Since it was first designed in 2006 by Aybar [14, 15], a couple of designs have emerged [16] varying some specific parameters in the first design to enhance the performance of the system. Currently four configurations of the system are available as seen in Figures 1, 2, 3, and 4. The inclined solar water desalination (ISWD) system is the first ever design. Agboola and Egelioglu [16] introduce improved inclined solar water desalination (IISWD), improved inclined solar water desalination with wire mesh (IISWDWM), and improved inclined solar water desalination with wick (IISWDW), and these improved designs produce a better system.
The schematic diagrams of the four configurations of inclined solar water desalination systems are as seen in Figures 1, 2, 3, and 4. Figure 5 shows the pictorial view of the experimental setup for the ISWD. The systems were tested under the climatic weather condition of Famagusta, northern Cyprus. The experiments were performed between 8:00 a.m. and 16:00 p.m. daily. The ISWD system consists of an absorber plate and a glass cover that creates a cavity. The cavity dimension is 1 m2 thickness with height of 0.2 m. Galvanized steel of 0.2 cm is used as the absorber plate which was painted matte black to increase the surface absorptivity (absorptivity of 0.96 and emissivity of 0.08), the cavity was constructed from stainless sheet for better resistance to corrosion, and the inner surface of the cavity was painted matte black. The outer surface was insulated at the sides and at the bottom insulated with specialized foam. The need for the insulation is to prevent heat losses from the stainless sheet material. The system is covered with a 3 mm glass, transmissivity of 0.88. The system was inclined at angle 36° to optimally utilize the 1 m2 surface (solar radiation incidence) of the plate and to allow water flow through the whole length and width of the surface [14]. The feed water is through a longitudinal pipe with multiple holes.
The IISWD, IISWDWM, and IISWDW systems feed water through the jet (nozzles) on the absorber plate intermittently; also, the thickness of the absorber plate in these systems was 0.4 cm.
In the experiments the ISWD was used as a control system. It was tested concurrently with the new improved systems. The daily production of the system is as shown in Figure 6. Figures 7 and 8 show solar radiation versus local time and ambient temperature versus local time of some selected days during the experiment period, respectively. Figure 9 shows the comparison of all the systems in terms of performance indices.
Table 1 shows the average daily production of the systems in comparison with other solar desalination systems. The inclined solar water desalination systems in comparison with other solar desalination systems, as shown in the table, placed the design among the best solar desalination systems. The system is a simple device and cheap to construct as seen in Table 2.
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Table 1: Experimental result of some selected solar desalination systems.
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Table 2: Cost breakdown of different configurations of ISWD system (TL).
NB: 1US$ = 1.9 TL.
On annual bases, taking the average of production in of all collected data between the seasons, the different configurations produced as follows: ISWD (781.10 kg/m2/year), IISWD (1328.6 kg/m2/year), IISWDW (1600 kg/m2/year), and IISWDWM (737.3 kg/m2/year) as seen in Table 3 represented as M.
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Table 3: Cost comparison of the different configurations of ISWD.
The instantaneous efficiency (ηi) of inclined solar water desalination is defined as the ratio of the energy used for water production to the total solar radiation rate given by
| (1) |
where Qev is the evaporative heat transfer (W), Mev is distilled water production rate (kg/m2 h), Ab is the still base area (m2), L is the latent heat of vaporization, and H is the total solar radiation falling upon the ISWS surface (W/m2). ISWD daily efficiency, ηd, is obtained by summing up the hourly condensate production multiplied by the latent heat of vaporization and divided by the daily average solar radiation over the solar cavity area and calculated from the following equation:
| (2) |
where t is the time and A is the area (m2).
2. Economics Analysis
The cost of distilled water produced from an inclined solar water desalination system is influenced by capital and running cost of the system. Costs are influenced by unit size, site location, feed water properties, and product water required quality [17]. The better economic return on the investment depends on the production cost of the distilled water and its applicability. Economic analysis of water desalination unit is given by Kabeel et al. [17], Fath et al. [18], Kumar and Tiwari [19], and Govind and Tiwari [20]. The CRF (capital recovery factor), the FAC (fixed annual cost), the SFF (sinking fund factor), the ASV (annual salvage value), average annual productivity (M), and AC (annual cost) are the main calculation parameters used in the cost analysis of the desalination unit. The AMC (annual maintenance operational cost) of the solar still is required for regular filling of brackish water, collecting the distilled water, cleaning of the glass cover, removal of salt deposited (scaling), and maintenance of the DC pump. As the system life passes on, the maintenance on it also increases. Therefore, 10% of net present cost has been considered as maintenance cost. Finally, the CPL (cost of distilled water per liter) can be calculated by dividing the annual cost of the system AC by annual yield of solar still (M), where S is the salvage value, taken as a fraction of present capital cost. The above mentioned calculation parameters can be expressed as [18]
| (3) |
where P is the present capital cost of desalination system; i is the interest per year, which is assumed as 12%; and n is the number of life years, which is assumed as 10 years in this analysis. The cost price of raw materials is as seen in Table 2. Also, the cost comparison of different conFigurations of inclined solar water desalination is presented in Table 3. Table 4 shows the life cycle analysis of the different configurations of the inclined solar water desalination systems.
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Table 4: The life cycle indicators of different ISWD configurations.
The detailed life cycle analyses of the systems are presented in Table 4. It is assumed that these systems are roof mounted and there will be no need for acquiring land. Large-scale solar plants require huge land space, a factor that contributes to the cost of water. The life cycle indicators show that the entire design configurations are feasible, since none give a negative net present value. NPV approach of assessing projects is viable because it is the algebraic sum of the discounted values of the incremental expected positive and negative net cash flows over a system anticipated lifetime.
The net present value (NPV) helps to measure the changes in wealth created by the system. A positive NPV means the project is viable and when comparing different systems the one with the highest NPV value is the best. In this work we have used NPV, internal rate of return (IRR), savings to investment ratio, and simple payback (years) to evaluate the economic feasibility of the system. The simple payback approach evaluates economic viability of a system with the shortest payback period. This approach is biased because it did not put into consideration the discounted benefit of the systems. The simple payback is still considered as okay for assessing a system if the life span of the system is not more than 10 years. The internal rate of return ranks mutual systems. The system with highest internal rate of return is judged the best or the most economically viable.
According to Table 4 the NPV, IRR, savings to investment ratio, and simple payback period for ISWD with wick and 2 spray jets are the most economically viable. It is interesting to note that of all the economic approaches used the ISWD with wick and 2 spray jets was the best. The NPV approach is taken as the most reliable economic evaluation of the approach. According to the NPV evaluation the ISWD with wire mesh is the system with the weakest economic benefit. In the economic consideration the system life (year) was taken as 10 years and interest rate on the capital as 12%.
The NPV and IRR are calculated using the following equations:
| (4) |
3. Conclusion
This work presents the findings of four different configurations of inclined solar water desalination system in terms of performances and economic viabilities. The improved designs were tested with bare absorber plate, wick on absorber plate, and wire mesh on absorber plate. Also the different spray jets arrangement was tested on the designs for optimum performance. The effect of spray jets on inclined solar water desalination was investigated while running the Aybar designs as the control system. The results obtained show that solar radiation, wick material, and the jets variation are the main factors that influence the system.
The ISWD is the simplest of the design and fabrication, which was model after the design of Aybar et al. [14]. The cost of the system is 305 TL making it the lowest in terms of cost of production. The daily production of the ISWD system is given as 3.25 kg/m2/day and with daily efficiency of 40.1%. The IISWD design cost 485 TL to fabricate but with the daily production of 5.46 kg/m2/day with daily efficiency of 48.3%. The IISWD was tested with variation (2, 4, and 6 jets) in the number of spray jets for optimum production. The system performed the best of all the configurations with 6.41 kg/m2 day and 50.3% efficiency. The IISWDWM performed the worst with 3.03 kg/m2 day and 32.6% efficiency with the highest cost of fabrication of 501 TL. The use of porous media in IISWDWM system did not work as expected. The distilled water cost price analysis also shows that IISWDW with 2 spray jet is the most economically viable among all the systems while the IISWDW with 6 spray jets was the most expensive. Life cycle analysis of the systems also shows that IISWDW with 2 spray jets has the highest NPV value of 1348.20 TL for interest rate of 12% and 10 years life span. In addition, the IISWDW with 2 spray jets has the least payback period of 1.5 years. The pump used in the IISWDS, IISWDW, and IISWDWM for powering the spray jets is a 33 W pump, and the pump works for 4 minutes in one hour. The electricity consumption in this system is negligible compared to the effect on the system performance. The findings presented show that all the systems are feasible for potable water production in household but the IISWD give the optimum performance.
| ISWD: | Inclined solar water desalination |
| IISWD: | Improved inclined solar water desalination |
| IISWDW: | Improved inclined solar water desalination with wick |
| IISWDWM: | Improved inclined solar water desalination with wire mesh |
| NPV: | Net present value (TL) |
| PV: | Present value (TL) |
| IRR: | Internal rate of return |
| SIR: | Savings to investment ratio (%) |
| SP: | Simple payback (year) |
| CRF: | Capital recovery factor |
| FAC: | Fixed annual cost (TL) |
| SFF: | Sinking fund factor |
| S: | Salvage value (TL) |
| ASV: | Annual salvage value (TL) |
| P: | Present capital cost (TL) |
| TL: | Turkish lira. |
| i: | Interest rate (%) |
| n: | Number of life years |
| ηi: | Instantaneous efficiency |
| ηd: | Daily efficiency |
| Qev: | Evaporative heat transfer (W) |
| H: | Total solar radiation (W/m2) |
| Ab: | Base area (m2) |
| L: | Latent heat of vaporization |
| Mev: | Distilled water production rate (kg/m2 h) |
| t: | Time (hr) |
| A: | Area (m2). |
Acknowledgment
The authors extend their appreciation to the Deanship of Scientific Research at King Saud University for funding the work through the research group Project no. RGP-VPP-091.
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