T active solar still with effective heating and cover cooling method

Desalination xxx (xxxx) xxx–xxx

Contents lists available at ScienceDirect

Desalination journal homepage: www.elsevier.com/locate/desal

Experimental investigation on hybrid PV/T active solar still with effective heating and cover cooling method ⁎

B. Praveen kumara, D. Prince Winstona, , P. Pounrajb, A. Muthu Manokarc, Ravishankar Sathyamurthyd,e,f, A.E. Kabeelf a

Department of Electrical and Electronics Engineering, Kamaraj College of Engineering and Technology, Virudhunagar 626001, India Department of Electrical and Electronics Engineering, Cheran College of Engineering, Karur, India c Department of Mechanical Engineering, Kamaraj College of Engineering and Technology, Virudhunagar, India d Department of Mechanical Engineering, S.A. Engineering College, Chennai, Tamil Nadu, India e Centre for Excellence in Energy and Nano Technology, S.A. Engineering College, Chennai, Tamil Nadu, India f Mechanical Power Engineering Department, Faculty of Engineering, Tanta University, Tanta, Egypt b

A R T I C L E I N F O

A B S T R A C T

Keywords: Passive solar still Active solar still Hybrid photovoltaic/thermal (PV/T) Thermal efficiency Electrical efficiency

A hybrid photovoltaic/thermal (PV/T) active solar still and a conventional passive solar still with single slope were designed, fabricated and experimented at three different water depths (0.05 m, 0.10 m, and 0.15 m). For the higher production of distillate water, a nickel-chromium (NiCr) heater powered by solar photovoltaic (PV) was incorporated in the proposed hybrid active still. Solar PV module was cooled by the saline water which increases the efficiency of the solar PV as well as the distillate water production. The daily yield from the proposed hybrid active (PV/T) solar still is 6 times more than the conventional passive still. This new system of renewable energy based power and distillate water production is highly self-sustainable in the remote areas. From the experimental study it is clear that, the proposed hybrid active (PV/T) solar still gives an enhanced overall thermal and electrical efficiency, that is nearly 25% higher than the conventional passive one.

1. Introduction Electrical energy and potable water are the essential needs for the life of the human in the present world scenario. The conventional energy resources are degrading day by day which leads to the turning in the use of renewable energy resources. Industrialization in the present world pollutes the nature of the environment, mainly the potable water available below and above the ground level. Over one billion people in the globe, lack access to drinking water. About 80% of all diseases in the developing world happens because people consume unsafe water and without an adequate sanitation [1]. The most effective renewable energy source is the solar photovoltaic (PV). Even though solar PV is effective, the effect of high temperature acts as one of the main challenges to rise above. Increase in temperature of the solar PV causes the decrease in the efficiency. The brackish or saline water (salinity ~10,000 ppm) can be purified by solar still. It may be either active solar still or passive solar still. The passive solar still is a natural slow evaporation process does not need any external source to heat the saline water in the basin. But in the case of active solar still, it uses an external heat source to heat the basin

⁎

saline water to evaporate. The yield of the active solar still (more than 7 L/day) is comparatively high than the passive solar still (around 2 L/ day). A lot of researchers have done many designs in the passive solar still ([2,3,4,5,6,7], multi-basin [8], regenerative [9], inverted trickle [10], multi-effects [11], having reflectors [12], triangular shaped [13], pyramid-shaped [14] and hemispherical [15] type solar still). On the other side, the active solar still also have many ways to heat the basin water but the highly recommended method is the integration of panel with the basin either through the heat exchanger [16,17,18] or directly [6,7]. A. E. Kabeel analysed techniques for quicker evaporation of water by using certain wick materials to absorb the heat other than basin absorption heat [25] and the recent review literature were studied regarding the performance enhancement techniques of the solar still. Integration of solar PV and solar thermal system by various methods were studied in a mini literature [26] and a review of solar collector integration was studied [27]. The heat exchange mechanism [19–24,28], and heat energy storage techniques [29,30] for improving fresh water production were observed. A hybrid active solar still integrated with porous fins [31], acrylic finned [47] and flat plate collector [38] was studied to know the design, fabrication and analysing

Corresponding author. E-mail address: [email protected] (D. Prince Winston).

https://doi.org/10.1016/j.desal.2017.11.007 Received 24 August 2017; Received in revised form 3 November 2017; Accepted 4 November 2017 0011-9164/ © 2017 Elsevier B.V. All rights reserved.

Please cite this article as: Praveen kumar, B., Desalination (2017), http://dx.doi.org/10.1016/j.desal.2017.11.007

Desalination xxx (xxxx) xxx–xxx

B. Praveen kumar et al.

methods of hybrid solar PV/T still. Evaporation [41,42,48] and condensation [43,44,45] processes of the basin saline water can be enhanced by many techniques, which were studied from recent literature. For converting the waste or brackish water into potable water single basin solar still is the simplest and very easy to fabricate with the available materials [32] tested by A. E. Kabeel. From the literature, it is very clear that the active solar still is better in performance than the passive solar still. The yield per day of 1 m2 of the solar still area mainly depends on the rate of evaporation and the rate of condensation of the corresponding surface area. So, to increase the vaporization of water, the saline water from the storage is preheated before fed into the basin by flowing it over the hot solar PV panel in a regulated time interval using solenoid valve. At the same time, condensation of the water vapour is also important so that glass cover cooling is made by the water from the PV panel. Then the maximum power from the solar PV is used to heat the basin saline water by a heating process explained in Section 4. The two main advantages of this process are (i) the saline water is preheated which is easy to evaporate and (ii) the solar PV panel is cooled i.e., the temperature of the PV cell is reduced because of the absorption of heat by saline water which increases the efficiency of the solar PV panel. Since the proposed method uses a battery for power storage, the distilled water can be produced at any time. The aim of this paper is to present high energy efficient active hybrid (PV/T) active solar desalination system in which the efficiency of the solar PV is improved by cooling the PV cell using saline water. Therefore, the intention of the proposed experimental study is to get better performance in the solar still as well as to improve the efficiency of the solar PV panel.

Table 1 Specifications of used solar PV module at STC. Specifications

Maximum power (Pmax) Voltage at Pmax (Vmpp) Current at Pmax (Impp) Short circuit current (Isc) Open circuit voltage (Voc) Module efficiency (μ) Fill factor (FF) Temperature coefficient of Isc Temperature coefficient of Voc Temperature coefficient of Pmax

50 W 17.5 V 2.90A 3.20A 21.8 V 11.1% 0.72 0.105%/°C − 0.360%/°C − 0.45%/°C

Table 2 Temperature coefficient and module efficiency values of different PV cell types. Type of PV cell

Temperature coefficient, Cv (%/oC)

Module efficiency, μ (%)

Reference

a-Si

− 0.26

6.3

CdTe

− 0.20

6.9

CIGS

− 0.45

8.2

m-Si p-Si

− 0.36 − 0.40

11.1 10.6

Yamawaki et al. [35] Nann and Emery [36] Nann and Emery [36] Rüther et al. [37] Nann and Emery [36]

Table 3 Properties and specifications of used NiCr wire.

2. Characteristics of solar PV (temperature effect) and heating element (nickel chromium) A detailed review of the temperature effects on solar PV and solar still was studied [28,33,46]. The effect of temperature over solar PV is one of the major problems in East Asian countries. The average temperature in the research conducting location is 38 °C (Latitude 9.5680°N, Longitude 77.9624°E) which is 13 °C higher than the Standard Testing Condition (STC) temperature by IEC-61215 and IEC61646. Also, Asia's largest solar PV power plant is located nearer to the location of research conducting place (Latitude 9.34757°N, Longitude 78.39216°E). The change in temperature is directly proportional to the change in voltage output of the PV and vice versa in the case of output current. STC includes the cell temperature of 25 °C, irradiance of 1000 W/m2 and the air mass of 1.5 AM in the solar spectrum. Each degree temperature rise over the STC temperature in the solar cell leads to the decrease of the cell output voltage by 0.3% to 0.5% depending on the type of solar cell material (a-Si, c-Si, CdTe, GaAs, μc-Si, TFSC, m-Si & p-Si). IEC-60904 series of standards provides the details of the performance of the solar PV by considering temperature and irradiance as a function. Temperature coefficient (Cv) and ambient temperature (Ta) decides the actual output of the solar PV panel. The temperature coefficient is a constant which may vary slightly for different cells manufacturers and the ambient temperature is the present atmospheric temperature at the panel. Eq. (1) gives the relation between the ambient temperature and the panel output.

Actual voltage = Vmpp, rated + [Cv × (Ta − 25)]

Electrical parameters

Property

Specification

Electrical resistivity at room temperature Specific heat Thermal conductivity Wire gauge Wire length Resistance at room temperature (32.5 °C Ωm− 1) Increase in resistance with temperature (20–315 °C) Power or heat produced per second w.r.t. panel ratings Weight per meter Cross sectional area

(1.0–1.5) × 10− 6 Ω·m 450 J·kg− 1·K− 1 11.3 W·m− 1·K− 1 14 AWG 0.22 mm 1m 3 Ω·m− 1 0–3.3% 40 W or 40 J·s− 1 0.000276 kg·m− 1 0.0346 mm2

in the cell temperature may cause a loss of about 2 V in this module output. The panel specification of this module is given in Table 1. From Table 2, it is clear that the increase in temperature increases the current to a smaller rate and decreases the voltage to a greater rate and that reduces the efficiency. In the case of irradiance, a decrease in irradiance decreases both the voltage and current. The increase in the irradiance level is possible but not always. So, increase in voltage is done by reducing the temperature of the PV cell i.e., cooling the PV cell using waste or saline water. This improves the overall efficiency of the solar PV panel and the saline gets preheated. This preheated water is used for the solar still and also for cooling glass cover (condensation of water). A.E. Kabeel et al. [32] developed a solar still in which the production of pure water is augmented by a turbulence system powered by solar PV. They used an 18 W solar PV panel that drives a 12 W DC motor for the quick evaporation of basin saline water. This method is cost-effective and produces higher daily yield than the conventional still. From this work, it is seen that the initial saline water fed to the basin is at normal temperature and also the temperature of the solar PV increases gradually depending on the atmospheric condition. To improve the overall (both still and panel) efficiency, the panel is cooled periodically by the saline water (saline water gets preheated) as a part of the proposed work. In another part of the proposed work, DC motor

(1)

For the proposed work, SES-450 J 50 W mono-crystalline type photovoltaic module is used. R. Santbergen et al. [34] found that the mono-crystalline PV cell absorbs more irradiance than other types of PV cells since it is made of pure silicon. Cells which absorb more irradiance can produce more power and also produce more heat. The temperature coefficient of this module is − 0.36%/°C of the open circuit voltage. Various types of solar cell have different temperature coefficients and efficiency which are given in Table 2. Therefore, for the 18 °C increase 2

Desalination xxx (xxxx) xxx–xxx

B. Praveen kumar et al.

Fig. 1. Experimental setup (a) Photographic view of the overall experimental setup. (b) Photograph of the components used and the condensate water formation in stills.

3. Experimental setup and procedure

used in the previous work [32] is replaced by NiChrome (NiCr) wire supplied by solar PV. NiCr is alloys of 80% nickel and 20% chromium which is the form of resistance heating alloy. The main property of the NiCr is the joule heating or resistive (ohmic) heating i.e. when current is passed through it, the NiCr produces heat. The water heating rate of NiCr wire is very high (Table 3) compared to other heating devices like thermoelectric device and the cost of NiCr for the proposed work is too low on comparing with DC motor, because of these purposes NiCr wire is replaced with DC motor. The properties and specifications of the NiCr used are given in Table 3.

3.1. Design and fabrication of the proposed hybrid PV/T still system For validating the proposed work, two stills were designed and fabricated. The conventional solar desalination system with a single basin of area 1 m2 (0.5 m × 2 m) is the first one designed and fabricated with a wall depth of 25 cm on high-side and 10 cm on low-side. To increase the absorption of heat from the sun black paint is coated on the full surface of the basin (bottom and side wall) from inside. Thermocol (polystyrene) sheets of 5 cm thickness are used to insulate the basin from all outer sides (bottom and side wall). This provision of

3

Desalination xxx (xxxx) xxx–xxx

B. Praveen kumar et al.

Fig. 2. Schematic view of the proposed hybrid (PV/T) active solar with NiCr spiral wire heater.

Table 4a Hourly variation of various parameters of conventional (passive) still for 0.05 m water depth on 8th April. (Total yield = 0.134 L/m2/MJ/day.) Time (h)

G (W/m2)

E (MJ/m2/h)

Ta (°C)

Va (m/s)

Tb (°C)

Tgo (°C)

Tgi (°C)

Tapv (°C)

Tbpv (°C)

Pm (W)

ṁew (L/m2/MJ/h)

07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 24:00 01:00 02:00 03:00 04:00 05:00 06:00

260 543 580 630 638 679 708 745 778 680 530 303 0 0 0 0 0 0 0 0 0 0 0 0

0.936 1.954 2.088 2.268 2.296 2.444 2.548 2.682 2.800 2.448 1.908 1.090 0 0 0 0 0 0 0 0 0 0 0 0

23.1 26.1 29.8 32.5 34.3 34.9 36.2 37.1 37.3 36.3 34.3 32.3 28.2 28.2 27.2 27 27 27 26.1 25.2 25.1 25 24.5 23

0.2 0.3 0.3 0.3 0.5 1.4 1.3 1.8 2.4 2.5 2.4 2 1.5 1.3 1.2 0.9 0.6 0.4 0.4 0.4 0.4 0.3 0.2 0.2

25.5 30.2 35.5 40.3 46 52.9 55 56 56.5 54.1 53.8 52 45.8 40 36.2 31.1 30 28.5 26.9 26.6 26 25.6 25 24

24 33.5 38.9 42.1 44.3 45 47.9 53.9 58 54.1 46.9 39 30.2 29.2 28.2 23.6 23 23 22.9 22.8 22.8 22.9 23 23.4

24.5 34.2 39.9 44.3 46 52.8 58 63.9 67.5 66 53.6 48 40.4 36.8 29 26.3 25 24.3 24.3 24.3 24.3 24.3 24 24.2

25 30.2 33.3 42 47.2 56.4 62.8 68.1 70.1 67.8 62 55.3 51.1 40.4 33.3 25.1 20.1 16.8 15 14.8 14.5 14.2 14 19.3

25 29.3 30.8 40 45.9 55.4 62 67.5 68.7 66 60 52.6 48.2 36.8 28 23.5 18.8 16.6 15.1 14.7 14.4 14.2 14 19

13.2 25.5 25.9 26.2 26.3 26.4 27 28.5 29.5 28.2 24.9 12.9 0 0 0 0 0 0 0 0 0 0 0 0

0.06 0.089 0.093 0.12 0.142 0.179 0.188 0.271 0.292 0.262 0.109 0.087 0.075 0.054 0.029 0.029 0.029 0.025 0.02 0.019 0.012 0.011 0.014 0.025

even in the low irradiance time. All the arrangements of the proposed solar still heater with spiral wire (Fig. 2) is shown in the schematic diagram.

insulation reduces the loss of heat from the still to the atmosphere which is supported by packing tape. A glass sheet of 3 mm is used to cover the basin from the top, placed at an angle of 10o horizontally, that is the approximate latitude of Kamaraj College of Engineering and Technology, Virudhunagar, Tamilnadu, India (Research location). Fig. 1(a) shows the photograph of the conventional and proposed solar desalination system. The proposed still (solar PV fed heater still) is the second one which is similar to the conventional still with same dimensions shown in Fig. 1(a). The components used and the top view of the condensate water formation in both conventional and proposed methods are shown in Fig. 1(b). There are two modifications over the conventional still; they are (i) the insertion of the heating filament that touches the saline water inside the solar still basin and (ii) the panel arrangements. The saline water from the storage tank is made to spread over the solar PV by using the spreading pipe and then the preheated water from the panel is collected and fed to the basin and also to the glass cover for cooling (condensation) in a periodic manner by using a solenoid valve. The NiCr wire is placed and sealed inside the basin and the input to the heating element is powered by the solar PV battery controller. The size of the solar PV module is 1 m × 0.65 m. This method uses a battery for storing solar power, so the production of distilled water can be achieved

3.2. Instrumentation Various measuring instruments are used to measure the required parameters for hybrid PV/T still which are as follows. i) Digital thermometer: All the temperatures (saline water, preheated water, basin water, basin, glass cover, panel, ambient) are measured using individual digital thermometer TPM-10. It has a resolution of 0.1 ° C. These sensors are integrated with a controller to read data. ii) Anemometer: Airflow velocity is measured by using Zephyrus Wind meter (anemometer) application which has been installed in a smart mobile phone. iii) Pyranometer: For measuring the solar irradiance LX-101A digital meter is used. iv) Measuring flask: Distillate output water is finally collected and measured using a calibrated flask. v) Voltage and current measurements: Panel's voltage (Voc, VL) and 4

Desalination xxx (xxxx) xxx–xxx

B. Praveen kumar et al.

Table 4b Hourly variation of various parameters of proposed hybrid (PV/T - active) still for 0.05 m water depth on 8th April. (Total yield = 0.335 L/m2/MJ/day.) Time (h)

G (W/m2)

E (MJ/m2/h)

Ta (°C)

Va (m/s)

Tb (°C)

Tgo (°C)

Tgi (°C)

Tsw (°C)

Tapv (°C)

Tbpv (°C)

Twpv (°C)

Tbw (°C)

Pm (W)

ṁew (L/m2/MJ/h)

07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 24:00 01:00 02:00 03:00 04:00 05:00 06:00

260 543 580 630 638 679 708 745 778 680 530 303 0 0 0 0 0 0 0 0 0 0 0 0

0.936 1.954 2.088 2.268 2.296 2.444 2.548 2.682 2.800 2.448 1.908 1.090 0 0 0 0 0 0 0 0 0 0 0 0

23.1 26.1 29.8 32.5 34.3 34.9 36.2 37.1 37.3 36.3 34.3 32.3 28.2 28.2 27.2 27 27 27 26.1 25.2 25.1 25 24.5 23

0.2 0.3 0.3 0.3 0.5 1.4 1.3 1.8 2.4 2.5 2.4 2 1.5 1.3 1.2 0.9 0.6 0.4 0.4 0.4 0.4 0.3 0.2 0.2

25.5 30.2 36 42 47 55 58.6 60.3 66 62.8 53 52 46.5 40 37 32 30 29.5 27 26.6 26 25.6 25.5 25.5

24 26 27.8 30.2 31 34 35 40 42 37 35 35 35 30 28.2 23.6 23 23 22.9 22.8 22.8 22.9 23 23.4

24.5 27 30 32 32.5 34.4 35.6 44 45.7 39.6 35.6 35.6 35.6 31.3 29 24.6 24.3 24.3 24.3 24.3 24.3 24.3 24 24.2

18.5 18.8 20.1 25.6 30.2 40.1 42.5 45.9 48.2 49.1 46.8 44.6 35.2 28.1 28 27 27 26.5 25.1 24.3 23.7 22.1 20.1 19.2

25 30.2 33.3 35 35.2 35.4 36.1 36 36.5 36 35.1 34.8 32 25 24 21.5 17 16.8 15 14.8 14.5 14.2 14 18.3

25 29.3 30.8 32 34.1 34.5 35 36 36.2 35.8 35 34.8 32.1 23.5 23 21 16.8 16.6 15.1 14.7 14.4 14.2 14 17.9

18 18.5 22 28.2 32.2 41 42.5 47 49.8 51 46.9 45 36.1 30 30.2 28 27.6 26.5 25.6 24.3 23 22.4 20 19.1

26 30.7 36.5 42.5 47.5 55.5 59.1 60.8 66.5 63.3 53.5 52.5 47 40.5 37.5 32.5 30.5 30 27.5 27.1 26.5 26.1 26 26

13.2 25.5 25.9 27.5 27.6 27.9 30.6 35.4 37.8 28.2 24.9 12.9 0 0 0 0 0 0 0 0 0 0 0 0

0.08 0.09 0.152 0.353 0.523 0.908 1.111 1.163 1.109 0.921 0.799 0.421 0.2 0.132 0.1 0.092 0.05 0.042 0.041 0.042 0.042 0.045 0.057 0.069

Table 5a Hourly variation of various parameters of conventional (passive) still for 0.10 m water depth on 9th April. (Total yield = 0.083 L/m2/MJ/day.) Time (h)

G (W/m2)

E (MJ/m2/h)

Ta (°C)

Va (m/s)

Tb (°C)

Tgo (°C)

Tgi (°C)

Tapv (°C)

Tbpv (°C)

Pm (W)

ṁew (L/m2/MJ/h)

07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 24:00 01:00 02:00 03:00 04:00 05:00 06:00

275 556 625 680 692 737 795 830 838 778 629 330 0 0 0 0 0 0 0 0 0 0 0 0

0.990 2.001 2.250 2.448 2.491 2.653 2.862 2.988 3.016 2.800 2.264 1.188 0 0 0 0 0 0 0 0 0 0 0 0

22 26.5 30.6 33.2 36.2 36.6 37.8 39 39.9 38.5 37 33 29.5 28.4 27.6 27.3 27.1 27.1 26.6 25.7 25.3 25 24.4 23.1

0.3 0.3 0.4 0.5 0.5 1.6 1.9 2.2 2.9 3 3.2 2.6 2.1 1.7 1.1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.3

23 25.7 28.8 35 37 42.8 48.8 55 56 55.8 53.7 48.3 43.8 38 35.9 30.8 29.9 28.1 26.9 26.3 26 25.6 25.5 24

24.5 34 39.2 43 46.3 46.9 49.3 55.9 60.2 54.7 47.6 39.7 33 31.2 29.2 24.1 23.2 23.2 23 22.9 22.8 22.9 23 23.4

25 34.7 40.2 45.3 48 54.8 59.8 65.8 68.1 66.4 54.6 48.9 42.3 37.3 31 26.9 25.2 24.7 24.5 24.3 24.3 24.1 24 24.5

25 33.5 38.3 44.5 48.2 58.5 65.8 69.4 71.5 69.8 62.2 57.3 52.2 38.4 33.8 25 20 16.8 15.1 14.8 14.4 14.2 14 16.6

25 32.8 37.8 42.8 47.9 57.6 64.6 68.3 70.2 68.6 59.8 53.6 46.2 36.5 29.1 24.7 19.2 16.6 15.1 14.7 14.4 14.2 14 16.5

13.6 25.9 27.3 27.5 27.8 28.4 28.8 30 32.6 29.2 27.9 16.5 0 0 0 0 0 0 0 0 0 0 0 0

0.08 0.08 0.093 0.093 0.102 0.116 0.248 0.321 0.432 0.326 0.3 0.222 0.115 0.094 0.088 0.084 0.099 0.082 0.08 0.079 0.069 0.072 0.07 0.075

3.3. Experimental procedure

current (Isc, IL) are sensed by using a voltage divider and current sensor ACS714 modules which are coupled with a controller for Maximum Power Point Tracking (MPPT). vi) Controller and battery: Arduino MEGA 2560 (15 analog and 53 digital pins) is used as a controller for the converter in solar PV battery (12 V, 4.5 Ah) charging system. vii) Solenoid valve: For the control of water flow in PV panel and glass cover two solenoid valves are used and it is triggered by the controller. viii) DC pump: A 12 V DC pump is used to pump the water in the basin to the solar PV cover for absorbing the heat in the panel.

All the experiments are conducted on the rooftop of D-Block, Kamaraj College of Engineering and Technology, Tamilnadu, India during April 8th, 9th, and 10th of 2017. The readings of the experiments are taken on an hourly basis from 7 AM to 7 AM (next day). Saline water is fed to the basin via the solar panel in a periodic manner using solenoid valve. For validating the proposed technique experimentally, water in the basin is kept for three different depths say 0.05 m, 0.10 m and 0.15 m. Also, two groups of readings are taken (i) conventional still, and (ii) Proposed hybrid active (PV/T) solar still with spiral NiCr wire heater. Straight NiCr wire heater is used for long-term continuous heating. The whole experimentation is carried out only for three continuous days and the readings are taken instantly for each 5

Desalination xxx (xxxx) xxx–xxx

B. Praveen kumar et al.

Table 5b Hourly variation of various parameters of proposed hybrid (PV/T - active) still for 0.10 m water depth on 9th April. (Total yield = 0.228 L/m2/MJ/day.) Time (h)

G (W/m2)

E (MJ/m2/h)

Ta (°C)

Va (m/s)

Tb (°C)

Tgo (°C)

Tgi (°C)

Tsw (°C)

Tapv (°C)

Tbpv (°C)

Twpv (°C)

Tbw (°C)

Pm (W)

ṁew (L/m2/MJ/h)

07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 24:00 01:00 02:00 03:00 04:00 05:00 06:00

275 556 625 680 692 737 795 830 838 778 629 330 0 0 0 0 0 0 0 0 0 0 0 0

0.990 2.001 2.250 2.448 2.491 2.653 2.862 2.988 3.016 2.800 2.264 1.188 0 0 0 0 0 0 0 0 0 0 0 0

22 26.5 30.6 33.2 36.2 36.6 37.8 39 39.9 38.5 37 33 29.5 28.4 27.6 27.3 27.1 27.1 26.6 25.7 25.3 25 24.4 23.1

0.3 0.3 0.4 0.5 0.5 1.6 1.9 2.2 2.9 3 3.2 2.6 2.1 1.7 1.1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.3

23 26.7 29.9 36.7 41.5 47.2 53.4 58.2 62 56.3 49.2 45.1 40.8 36.7 30.8 29.1 28.6 27 26.5 26.1 26 25.8 25 24.3

24.3 26.6 28.2 30.6 31.7 35 36.9 42.5 44.4 37.7 36.2 35.6 34.9 29.4 28.3 24.2 23.6 23.1 23 22.9 22.8 22.7 23.1 23.5

24.6 27.8 31.4 33.8 34.2 35.6 40.4 45.5 47.2 46 40.5 38 37.6 35.3 33 30.1 28.4 25 24.8 24.5 24.7 24.3 24 24.2

19.2 20.1 20.8 26.6 32 41.4 42.9 46.8 49 50.3 47.3 45.1 37.3 30.9 29.4 29 28.2 27.8 26.4 25 23.9 22.1 20.8 20.1

25 32 33.9 36.2 37 37.4 38 38.8 39 38.2 36.2 35.8 33 28.2 26.1 24.5 22.5 18.9 16.2 15.7 15 14.9 15.2 18.3

25 30.8 33 35.7 36.2 36.5 37.4 38.4 38.8 37.5 35.9 35 31.3 25.3 25.1 23.1 20.9 17.5 15.8 15.1 13.9 14.2 14.9 17.9

19 19.7 24 29.6 34.6 44.5 45.2 49.7 49.8 53.2 49.3 46.2 44.1 39.2 35.7 31.5 30.9 28.5 26.5 25.2 24.2 21.1 20.7 19.3

24 27.7 30.9 37.7 42.5 48.2 54.4 59.2 63 57.3 50.2 46.1 41.8 37.7 31.8 30.1 29.6 28 27.5 27.1 27 26.8 26 25.3

13.9 26.2 26.3 28 28.2 28.5 31.4 38 40.2 36.9 30.1 22.6 0 0 0 0 0 0 0 0 0 0 0 0

0.05 0.06 0.089 0.099 0.123 0.208 0.311 0.663 1.009 1.021 0.999 0.621 0.432 0.092 0.099 0.072 0.063 0.045 0.045 0.048 0.048 0.049 0.059 0.071

Table 6a Hourly variation of various parameters of conventional (passive) still for 0.15 m water depth on 10th April. (Total yield = 0.065 L/m2/MJ/day.) Time (h)

G (W/m2)

E (MJ/m2/h)

Ta (°C)

Va (m/s)

Tb (°C)

Tgo (°C)

Tgi (°C)

Tapv (°C)

Tbpv (°C)

Pm (W)

ṁew (L/m2/MJ/h)

07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 24:00 01:00 02:00 03:00 04:00 05:00 06:00

270 550 613 675 685 700 744 790 801 730 603 304 0 0 0 0 0 0 0 0 0 0 0 0

0.972 1.980 2.206 2.430 2.466 2.520 2.678 2.844 2.883 2.628 2.170 1.094 0 0 0 0 0 0 0 0 0 0 0 0

22.5 26.3 30 32.7 35.3 36.1 37.2 38 38.9 37.5 36.3 32.5 28.6 28.2 27.3 27.1 27 27.1 26.4 25.1 25.3 25.1 24.4 23.1

0.3 0.3 0.4 0.4 0.5 1.5 1.6 2 2.7 2.8 3 2.3 1.8 1.4 1.1 1 0.9 0.7 0.5 0.5 0.5 0.5 0.3 0.3

21 22.1 26.8 31.1 35.6 40.8 45.8 50.9 55.6 54.4 51.9 47.9 42 39.6 36 31.2 29.5 26 25.9 25.6 25 24.2 23.4 23.1

24.2 33.8 39 42.6 45 46 48.2 54.3 59.7 54.2 47.3 39.3 33.2 31 30.3 25.8 24.5 23.8 23 22.9 22.8 22.9 23 23.4

24.2 34.2 40 45.1 47.1 53.8 59 64.1 66 64.3 54.6 48.4 41.3 37.5 30.3 26.6 25.1 24.5 24.4 24.2 24.2 24.1 24 24.3

21.9 31 35.6 43.4 47.7 57.2 63.5 68.8 70.9 69 61.9 56.3 51.7 38.9 33.5 25.4 19.6 16.9 15.4 14.9 14.4 14.4 14.1 18

20.9 30.2 33.9 41.6 46.9 56.5 63.4 67.9 69.8 67.5 59 53.2 47.2 36.6 28.8 24.2 19 16.7 15.7 14.7 14.4 14.2 14 17.8

13.3 25.6 26.7 26.9 27.5 27.9 28.3 29.6 31.6 30 27.1 17.3 0 0 0 0 0 0 0 0 0 0 0 0

0.03 0.069 0.079 0.098 0.103 0.112 0.148 0.198 0.202 0.232 0.1 0.061 0.05 0.048 0.031 0.029 0.027 0.025 0.02 0.019 0.012 0.014 0.018 0.025

4. Results and discussion

hour. Hence, spiral NiCr wire heater is used alone for this work and the straight wire is also suggested for experimenting in case of long-term. The following are the readings taken hourly for 24 h, solar irradiance (G), solar energy (E), temperature above solar PV (Tapv), temperature below solar PV (Tbpv), storage water temperature (Tsw), preheated water temperature (Twpv), basin water temperature (Tbw), basin temperature (Tb), glass inner temperature (Tgi), glass outer temperature (Tgo), ambient temperature (Ta), airflow velocity (Va), distillate water output (ṁew), maximum PV output power (Pm).

4.1. Hourly variation of solar irradiance, airflow velocity and ambient temperature for experimental days The experiments are carried out in the three typical clear sunny days during the month of April 2017. The experimental readings are taken for various parameters at different depths (0.05 m, 0.10 m and 0.15 m). The water preheating, glass cover cooling and NiCr heater are the three major parts that validate the proposed method. For validating the proposed method, it is compared with the conventional still. Tables 4a–6b gives the hourly observations for the three experimental days at three different depths. The solar intensity varies time to time which is noted periodically 6

Desalination xxx (xxxx) xxx–xxx

B. Praveen kumar et al.

Table 6b Hourly variation of various parameters of proposed hybrid (PV/T - active) still for 0.15 m water depth on 10th April. (Total yield = 0.165 L/m2/MJ/day.) Time (h)

G (W/m2)

E (MJ/m2/h)

Ta (°C)

Va (m/s)

Tb (°C)

Tgo (°C)

Tgi (°C)

Tsw (°C)

Tapv (°C)

Tbpv (°C)

Twpv (°C)

Tbw (°C)

Pm (W)

ṁew (L/m2/MJ/h)

07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 24:00 01:00 02:00 03:00 04:00 05:00 06:00

270 550 613 675 685 700 744 790 801 730 603 304 0 0 0 0 0 0 0 0 0 0 0 0

0.972 1.980 2.206 2.430 2.466 2.520 2.678 2.844 2.883 2.628 2.170 1.094 0 0 0 0 0 0 0 0 0 0 0 0

22.5 26.3 30 32.7 35.3 36.1 37.2 38 38.9 37.5 36.3 32.5 28.6 28.2 27.3 27.1 27 27.1 26.4 25.1 25.3 25.1 24.4 23.1

0.3 0.3 0.4 0.4 0.5 1.5 1.6 2 2.7 2.8 3 2.3 1,8 1.4 1.1 1 0.9 0.7 0.5 0.5 0.5 0.5 0.3 0.3

22.7 25.4 26.9 30.2 33.3 38.5 42.9 46.8 49.9 50 48.8 47.4 40.2 37.4 31.3 28.4 27.1 26.2 25.9 24.9 24.4 23.2 23 23.2

24 25.3 27.3 29.2 30.9 33.1 34.9 38.2 41.6 40.1 35.3 35 34.6 29 28.1 23.8 23.1 22.8 22.4 22 21.5 21.7 22.5 22.9

24.2 25.9 28.2 30.1 32 35.2 36.5 40.2 43.8 41.4 36.9 36.2 33.9 25 25.3 24.7 23.1 21.6 21.1 20.4 20.4 21.1 21.8 22

19.4 20.3 21.1 26.9 32.5 41.9 43.4 47.4 50 50.2 47 45.8 37.6 31 29.6 29.2 28.5 28.1 26.9 25.5 24 22.3 20.9 20.3

24.8 28.3 30.4 33.2 35.4 36.4 37.8 37.9 38.5 38.4 37.5 35.1 32.1 27.1 25.5 24.5 23.5 18.2 15.7 15.1 14.8 14.3 14.9 18.8

24.6 28 30 32.7 35.1 36.1 37 37.2 38 38.1 37 34.2 31.2 26.3 24.9 24 21.1 17.1 14.8 15.1 14.1 14 14.6 17.8

18.4 19.3 23.7 30 34 44.3 44.9 48.9 49.5 52.8 48.5 45.3 43.1 39 35.1 30.7 30 28.1 25.8 24.5 23.9 21.4 20.2 19.1

23 25.7 27.2 30.5 33.6 38.8 43.2 47.1 50.2 50.3 49.1 47.7 40.5 37.7 31.6 28.7 27.4 26.5 26.2 25.2 24.7 23.5 23.3 23.5

13.8 26 26.1 27.5 28.1 28.4 31.4 37.9 39.9 36 32 22 0 0 0 0 0 0 0 0 0 0 0 0

0.032 0.039 0.042 0.049 0.053 0.083 0.099 0.154 0.498 0.873 0.999 0.682 0.32 0.086 0.063 0.062 0.042 0.041 0.045 0.039 0.028 0.03 0.032 0.042

for the usage of NiCr heater. During low irradiance period (night time) NiCr heater fed by a solar charged battery is very much useful for heating the saline water to produce the distillate water continuously. The varying intensity of solar, airflow velocity and ambient temperature for three continuous days are shown in Fig. 3(a), (b) and (c) respectively. From Fig. 3, one can see that 9th April have the maximum irradiance (838 W/m2), maximum solar energy (3.016 MJ/m2/h), maximum airflow velocity (2.9 m/s) and maximum ambient temperature (39.9 °C). Similarly, from Fig. 3, it is also found that 8th April have the minimum irradiance (260 W/m2) and minimum solar energy (0.936 MJ/m2/h), and minimum airflow velocity (0.2 m/s) at 07:00 h and minimum ambient temperature (23 °C) at 06:00 h. Comparing the three experimental days, 9th April have the maximum solar energy input followed by 10th and 8th April.

yield. So, during low irradiance, the NiCr heater gets activated by the controller which is fed by the solar charged battery. For the maximum production of the output cover cooling of the glass is also done which increases the condensation of water vapour. The temperature variations in the inner and outer surface of the glass due to cover cooling are shown in Fig. 5 for various water depths. The condensation of the water vapour formed also depends on the temperatures of the glass which can be observed from Fig. 5. From Fig. 5, it is observed that on 9th April (higher ambient temperature, solar irradiance and incident solar energy) the inner and outer surface temperature of the glass cover in conventional solar still is above 60 °C. Due to cover cooling in the proposed hybrid active (PV/T) solar still, it is highly reduced to below 45 °C, which helps in the maximum production of distilled water by condensing the water vapour quickly.

4.2. Hourly variations of basin and glass cover temperature due to effective heating and cover cooling

4.3. Hourly productivity (distillate water and solar PV power) of passive and active solar still

Tables 4a and 4b are the experimental readings taken on 8th April for conventional (passive) still and the proposed hybrid (PV/T – active) still respectively. The total distilled water yield on that day for the conventional still is 3.420 L whereas for the proposed still it is 8.542 L. The variation in the yield claims the proposed technique is far better than the conventional passive one. Also, the proposed method of hybrid (PV/T) solar still produces 1.32 L of yield more than the existing hybrid active solar still integrated with flat plate collector, which is also taken in the same month. The daily yield of the existing hybrid active solar still integrated with flat plate collector with a water depth of 0.05 m is 7.22 L. The thermal stratification in the basin for various water depths is shown in Fig. 4. It is noted that in Fig. 4, the maximum temperature on the conventional still with water depth 0.05 m on 8th April is 56.5 °C, whereas in the proposed hybrid active (PV/T) solar still the maximum temperature on the same day and same depth of water is 66 °C. This increase in temperature of about 10 °C is due to the preheating of water and the activation of NiCr heater in the basin. This is similar to all the other days which are shown in Fig. 4. Increase in water depths decreases the basin temperature and water layer temperature, so the temperature of the basin on 8th April is higher than all other day's basin temperature. From this, it is clear that the solar irradiance is proportional and water depth is inversely proportional to the output

Tables 5a and 5b are the practical observation readings taken on 9th April for the conventional passive solar still and the proposed hybrid active (PV/T) solar still respectively. On this day the water depth of the still was kept at 0.10 m for experimenting. From Fig. 3, it is observed that 9th April have the maximum ambient temperature, solar irradiance and airflow velocity compared with other days. The water yield of the proposed hybrid active (PV/T) solar still (0.228 L/m2/MJ/day) is much higher than the conventional passive solar still (0.083 L/m2/MJ/day) and also higher than the existing hybrid active (PV/T) solar still (0.185 L/m2/MJ/day), also shown in Fig. 6, due to the preheating of saline water, glass cover cooling and NiCr heater. The variation in the distilled water yield per hour can be observed from Fig. 6. From Fig. 6, it is very clear that the production of water is high on 9th April due to high solar energy input but at the same time the depth of water on 9th April is twice the depth on 8th April. The production of fresh water not only depends on the solar input energy but also on the depth of water. Tables 6a and 6b are the readings taken on 10th April for both the conventional and proposed stills respectively. The water depth on this day is maintained at 0.15 m for validating the proposed method with the conventional method. The ambient temperature, solar irradiance and airflow velocity are moderate on 10th April shown in Fig. 3. The thermal stratification, glass inner and outer surface temperatures, and 7

Desalination xxx (xxxx) xxx–xxx

B. Praveen kumar et al.

Fig. 4. Thermal stratification in the basin for various water depths.

Fig. 3. Hourly variation of (a) solar irradiance (b) airflow velocity and (c) ambient temperature for three experimental days.

the water output yield are in Figs. 4, 5 and 6 respectively. The results of the stills with the higher water depths are satisfactory because the production of water output is inversely proportional to the water depth. The performance of the proposed active hybrid PV/T still is with 0.05 m (0.335 L/m2/MJ/day) water depth is better than the still with 0.10 m (0.228 L/m2/MJ/day) and 0.15 m (0.165 L/m2/MJ/day) water depths. This corresponds to an increment of 46.9% production of fresh water than the second level water depth and 103% than the third level water depth. Similar to the enhancement distillate water production, the power output from the solar PV system is highly improved in this technique.

Fig. 5. Temperature variation in the glass (a) inner surface (b) outer surface.

8

Desalination xxx (xxxx) xxx–xxx

B. Praveen kumar et al.

Fig. 6. Distillate water output for three days (a) conventional passive solar still (b) proposed hybrid active (PV/T) solar still.

As mentioned in the characteristics of solar PV, the power output is inversely proportional to the heat and directly proportional to the solar irradiance. So, the heat absorbed by the solar PV system (cell, glass cover, frame and bottom support) will decrease the voltage production and this reduces the overall power production of the PV system. Therefore, to improve the power production as well as to preheat the saline water from the storage tank, cover cooling of the solar PV panel is done. By doing this, the heat in the panel is absorbed by the saline water i.e., it gets preheated. The decrease in heat in the panel will definitely produce more power than the conventional. To validate this, hourly instant power production from a conventional solar PV and the proposed cover cooled proposed PV panel is taken, which is shown in Tables 4a, 4b, 5a, 5b, 6a, and 6b. The instant temperature variations in the solar PV (both above and below) panel is shown in Fig. 7. The power from the solar PV panels is stored in the battery and used efficiently by the NiCr heater for heating. All these actions are controlled by an ARDUINO microcontroller. The power production during the three different days is compared in Fig. 8 for both conventional and proposed system. From Fig. 8, it is clear that the maximum peak power produced at any instant in conventional solar PV is 32.6 W which is 8 W lesser than the proposed PV cover cooling system (40.6 W).

Fig. 7. Temperature variation in the solar PV panel (a) above the cells (b) below the cells.

ηstill =

daily yield × L As × ΣGs (t ) × 3600 + (Ac − Apv ) × ΣGc (t ) × 3600

(2)

where L is the vaporization latent heat and is given as

L = 2.4935 × 106 (1 − 9.4779 × 10−4 Ta + 1.3132 × 10−7 Ta 2 − 4.7974 × 10−9 Ta 3) The electrical efficiency of the solar PV panel is given by;

ηpv =

Pm Apv × Gpv (t )

(3)

where the output power is the product of fill factor (a constant 0.72 given in the datasheet specifications), short circuit current (Isc) and open circuit voltage (Voc) at that instant. Also, the thermal efficiency of the solar PV panel is calculated [40], by using the equation;

ηtpv = 4.4. Daily efficiency of solar (passive and active) still and PV panel

ηpv 0.38

(4)

The overall thermal efficiency of the hybrid active (PV/T) solar still is given as the sum of thermal efficiency of the solar PV and the thermal efficiency of the active still which is given by;

The overall efficiency of the proposed still is calculated by summing the thermal efficiency of the active still and the electrical efficiency of the solar PV. With the reference of Tiwari [39], the overall efficiency is calculated by the following equations. The thermal efficiency of the proposed hybrid active (PV/T) solar still is given by;

ηhybrid = ηtpv + ηstill

(5)

Eqs. (2)–(5) are evaluated to calculate the electrical and thermal efficiency of the proposed hybrid active (PV/T) solar still and the 9

Desalination xxx (xxxx) xxx–xxx

B. Praveen kumar et al.

Table 7 Economic analysis of the solar stills. Particulars

Conventional still (cost in INR)

Proposed still (cost in INR)

Fabrication cost Maintenance cost Operating cost Feed water cost Distilled water cost Cost of water production/day Net profit Payback period

6150 Rs. 5 Rs./day 5 Rs./day 1 Rs./day 15 Rs./L 43.50 Rs./day (2.9 L/day)

9850 Rs. 6 Rs./day 5 Rs./day 2.50 Rs./day 15 Rs./L 108 Rs./day (7.2 L/day)

32.50 Rs./day 6150/32.50 = 190 days

94.50 Rs./day 9850/94.50 = 104 days

efficiency of the conventional solar PV module is shown in Fig. 9. 4.5. Economic analysis of the solar stills Economic analysis of the conventional and proposed solar stills were made and is shown in Table 7. Payback period of the still includes the costs of fabrication, maintenance, feed water cost, operating cost and the cost of distillate water. From Table 7, it is observed that the payback period of the proposed still is 86 days less than the converntional one. It is reasonable because the net production rate of distilled water cost is much higher than the cost of the components (solar PV, valves, storage systems) used in the proposed system. The payback period of the proposed hybrid PV/T still is less than four months (104 days) and this makes the system is more effective in economical aspect. The net profit can be calculated by using the below Eq. (6).

Net profit = water produced cost − feed water cost − operating cost − maintenance cost

(6)

5. Conclusions

Fig. 8. Peak power produced each hour for three days (a) conventional PV system (b) proposed PV system in hybrid active (PV/T) solar still.

The experimental studies of the two different solar still configurations (conventional passive solar still and proposed hybrid active (PV/ T) solar still with NiCr heater) with different water depths on three consecutive days have been presented. Also, a comparative performance of the above-mentioned stills with the existing hybrid active solar still have been presented and the conclusions have been made from the practical study as follows.

conventional passive solar still which is given in Fig. 9. The bar graph in Fig. 9 shows the variation in efficiency. The results in the graph show that the overall efficiency of the proposed hybrid active (PV/T) solar still is much higher than the conventional and the existing solar stills. The variations in water depths as 0.05 m, 0.10 m and 0.15 m create a huge impact in the thermal efficiency. The thermal efficiency of the proposed (24.5%, 21.2% and 20.8%) and existing (20.1%, 18.5% and 17.8%) hybrid active solar still is much lower than the conventional (30.2%, 29.5% and 29%) passive solar still due to heat losses caused by the large operating range in temperature. But when comparing to the overall efficiency the proposed hybrid (62.5%, 48.7% and 46.6%) active (PV/T) solar still is nearly 25% higher than the conventional passive solar still. The electrical efficiency of the proposed solar PV module is 30% higher than the electrical

• The overall average temperature range of the water in the basin for •

the proposed hybrid active (PV/T) solar still is 50% higher than the conventional passive solar still that is due to the absorption of heat from the solar PV panel surface and the heat produced by the NiCr heater during low irradiance. The power output from the proposed solar PV is 30% higher than the conventional one and the power from this modules are used Fig. 9. Comparison of electrial and thermal efficiencies of conventional, existing and proposed solar stills.

10

Desalination xxx (xxxx) xxx–xxx

B. Praveen kumar et al.

• • •

efficiently for heating the basin saline water using NiCr heater. The efficiency of the solar PV is 37.5% enhanced in the proposed system when compared with the conventional system. The yield from the proposed still is about 6 times higher than the passive still during these three experimental days. The overall thermal efficiency of the proposed hybrid active solar still (with solar PV) is about 25% higher than the conventional one and at the same time, the thermal efficiency of the passive still is 15% higher than the proposed still (without PV). Payback period of the proposed hybrid PV/T solar is 86 days (42%) less than the conventional solar still used.

distillation, Desalination 169 (2004) 121–127. [5] M.A.S. Malik, G.N. Tiwari, A. Kumar, M.S. Sodha, Solar Distillation: A Practical Study of a Wide Range of Stills and Optimum Design, Construction and Performance, Pergamon Press, New York, 1982. [6] A.K. Tiwari, G.N. Tiwari, Annual performance analysis and thermal modeling of passive solar still for different inclination of condensing cover, Int. J. Energy Res. 31 (14) (2007) 1358–1382. [7] G.N. Tiwari, A.K. Tiwari, Solar Distillation Practice in Water Desalination Systems, Anamaya Pub. Ltd., New Delhi (India), 2007. [8] G.N. Tiwari, S.K. Singh, V.P. Bhatnagar, Analytical thermal modeling of multi-basin solar still, Energy Convers. Manag. 34 (12) (1993) 1261–1266. [9] M. Abu-Arabi, Y. Zurigat, Year-round comparative study of three types of solar distillation units, Desalination 172 (2005) 137–143. [10] A.A. Badran, Inverted trickle solar still: effect of heat recovery, Desalination 133 (2001) 167–173. [11] Y. Yuichi, S. Haruki, Development of Small-scale Multi-effect Solar Still, International Solar Energy Conference, (2003), pp. 167–173. [12] H. Tanaka, Y. Nakatake, Theoretical analysis of a basin type solar still with internal and external reflectors, Desalination 197 (2006) 205–216. [13] E. Rubio-Cerda, M.A. Porta-Gándara, J.L. Fernández-Zayas, Thermal performance of the condensing covers in a triangular solar still, Renew. Energy 27 (2002) 301–318. [14] A.E. Kabeel, Water production from air using multi-shelves solar glass pyramid system, Renew. Energy 32 (2007) 157–172. [15] B.I. Ismail, Design and performance of a transportable hemispherical solar still, Renew. Energy 34 (2009) 145–150. [16] M. Arslan, Experimental investigation of still performance for different active solar still designs under closed cycle mode, Desalination 307 (2012) 9–19. [17] M.A. Eltawil, Z.M. Omara, Enhancing the solar still performance solar photovoltaic, flat plate collector and hot air, Desalination 349 (2014) 1–9. [18] H. Taghvaei, M.R. KhosrowJafarpur, M. KarimiEstahbanati, A. MansoorFeilizadeh, A. Seddigh, A thorough investigation of the effects of water depth on the performance of active solar stills, Desalination 347 (2014) 77–85. [19] Z.S. Abdel-Rehim, A. Lasheen, Experimental and theoretical study of a solar desalination system located in Cairo, Egypt, Desalination 217 (2007) 52–64. [20] A.A. Badran, A.A. Al-Hallaq, I.A. Eyal Salman, M.Z. Odat, A solar still augmented with a flat-plate collector, Desalination 172 (2005) 227–234. [21] O.O. Badran, H.A. Al-Tahaineh, The effect of coupling flat plate collector on the solar still productivity, Desalination 183 (2004) 137–142. [22] V.K. Dwivedi, G.N. Tiwari, Annual energy and exergy analysis of single and double slope solar stills, Trends Appl. Sci. Res. 3 (3) (2008) 225–241. [23] R. Tripathi, G.N. Tiwari, Effect of water depth on internal heat and mass transfer for active solar distillation, Desalination 173 (2005) 187–200. [24] Y.P. Yadav, S.K. Yadav, Parametric studies on the transient performance of a high temperature solar distillation system, Desalination 170 (2004) 251–262. [25] A.E. Kabeel, Performance of solar still with a concave wick evaporation surface, Energy 34 (2009) 1504–1509. [26] A. Muthu Manokar, D. Prince Winston, A.E. Kabeel, S.A. El-Agouz, Ravishankar Sathyamurthy, T. Arunkumar, B. Madhu, Amimul Ahsan, Integrated PV/T solar still-a mini-review, Desalination, https://doi.org/10.1016/j.desal.2017.04.022 (Available online 3 May 2017, In Press). [27] R. Sathyamurthy, S.A. El-Agouz, P.K. Nagarajan, J. Subramani, T. Arunkumar, D. Mageshbabu, B. Madhu, R. Bharathwaaj, N. Prakash, A review of integrating solar collectors to solar still, Renew. Sust. Energ. Rev. 77 (2017) 1069–1097. [28] A.E. Kabeel, T. Aerunkumar, D.C. Denkenberger, Ravishankar Sathyamurthy, Performance enhancement of solar still through efficient heat exchange mechanism – a review, Appl. Therm. Eng. 114 (2017) 815–836, http://dx.doi.org/10.1016/j. applthermaleng.2016.12.044. [29] Ravishankar Sathyamurthy, P.K. Nagarajan, M. Edwin, B. Madhu, S.A. El-Agouz, A. Ahsan, D. Mageshbabu, Experimental investigations on conventional solar still with sand heat energy storage, Int. J. Heat Technol. 34 (4) (2016) 597–603, http:// dx.doi.org/10.18280/ijht.340407. [30] D.G. Harris Samuel, P.K. Nagarajan, Ravishankar Sathyamurthy, S.A. El-Agouz, E. Kannan, Improving the yield of fresh water in conventional solar still using low cost energy storage material, Energy Convers. Manag. 112 (2016) 125–134, http:// dx.doi.org/10.1016/j.enconman.2015.12.074. [31] Hitesh Panchal, Ravishankar Sathyamurthi, Experimental analysis of single-basin solar still with porous fins, Int. J. Ambient Energy (2017) 1–7, http://dx.doi.org/10. 1080/01430750.2017.1360206. [32] A.E. Kabeel, Mofreh H. Hamed, Z.M. Omara, Augmentation of the basin type solar still using photovoltaic powered turbulence system, Desalin. Water Treat. 48 (1–3) (2012) 182–190, http://dx.doi.org/10.1080/19443994.2012.698811. [33] Swapnil Dubey, Jatin Narotam Sarvaiya, Bharath Seshadri, Temperature dependent photovoltaic (PV) efficiency and its effect on PV production in the world – a review, Energy Procedia 33 (2013) 311–321. [34] R. Santbergen, R.J.C. van Zolingen, The absorption factor of crystalline silicon PV cells: a numerical and experimental study, Sol. Energy Mater. Sol. Cells (2007), http://dx.doi.org/10.1016/j.solmat.2007.10.005. [35] T. Yamawaki, S. Mizukami, T. Masui, H. Takahashi, Experimental investigation on generated power of amorphous PV module for roof azimuth, Sol. Energy Mater. Sol. Cells 67 (2001) 369–377, http://dx.doi.org/10.1016/S0927-0248(00)00305-6. [36] S. Nann, K. Emery, Spectral effects on PV-device rating, Sol. Energy Mater. Sol. Cells 27 (1992) 189–216, http://dx.doi.org/10.1016/0927-0248(92)90083-2. [37] R. Rüther, H.G. Beyer, A.A. Montenegro, M.M. Dacoregio, I.T. Salamoni, P. Knob, Performance results of the first grid-connected, thin-film PV installation in Brazil: temperature behaviour and performance ratios over six years of continuous

Nomenclatures NiCr Cv Vmpp,rated Pmax Vmpp Impp Isc Voc IL VL FF Apv As Ac Tapv Tbpv Tsw Twpv Tbw Tb Tgi Tgo Ta Va ṁew Pm G E Gs(t) Gc(t) Gpv(t) L

nickel-chromium temperature coefficient, %/°C rated voltage at maximum power point, V maximum power from solar PV, W voltage at maximum power point, V current at maximum power point, A short circuit current, A open circuit voltage, V load current, A load voltage, V fill factor area of solar PV module, m2 area of solar still, m2 area of collector, m2 temperature above solar PV surface, °C temperature below solar PVsurface,°C storage water temperature, °C preheated water temperature from PV, °C basin water temperature, °C basin temperature, °C glass inner surface temperature, °C glass outer surface temperature, °C ambient temperature, °C airflow velocity, m/s distillate water output (L/m2/MJ/h) maximum PV output power, W solar irradiance, W/m2 solar energy, MJ/m2/h solar irradiance on soalr still, W/m2 solar irradiance on collector, W/m2 solar irradiance on solar PV, W/m2 latent heat vapourization, J/kg

Greek symbols μ hstill hpv htpv hhybrid

module efficiency,% thermal efficiency of proposed hybrid (PV/T) solar still, % electrical efficiency of PV module in proposed hybrid (PV/T) solar still, % thermal efficiency of PV module in proposed hybrid (PV/T) solar still, % overall thermal efficiency of proposed hybrid (PV/T) solar still, %

References [1] WHO-Unicef JMP, Progress on Drinking Water and Sanitation, (2008). [2] H. Al-Hinai, M.S. Al-Nassr, B.A. Jubran, Effect of climatic, design and operational parameters on the yield of a simple solar still, Energy Convers. Manag. 43 (2002) 1639–1650. [3] G.M. Cappelletti, An experiment with a plastic solar still, Desalination 142 (2002) 221–227. [4] I.A. Hayek, O.O. Badran, The effect of using different designs of solar stills on water

11

Desalination xxx (xxxx) xxx–xxx

B. Praveen kumar et al.

[38]

[39] [40]

[41]

[42]

[43] Z.M. Omara, A.S. Abdullah, A.E. Kabeel, F.A. Essa, The cooling techniques of the solar stills' glass covers–a review, Renew. Sust. Energ. Rev. 78 (2017) 176–193. [44] S.W. Sharshir, G. Peng, L. Wu, N. Yang, F.A. Essa, A.H. Elsheikh, A.E. Kabeel, Enhancing the solar still performance using nanofluids and glass cover cooling: experimental study, Appl. Therm. Eng. 113 (2017) 684–693. [45] Y.A.F. El-Samadony, A.E. Kabeel, Theoretical estimation of the optimum glass cover water film cooling parameters combinations of a stepped solar still, Energy 68 (2014) 744–750. [46] S. Praveen, D. Prince Winston, Protection and Performance Improvement of a Photovoltaic Power System, Advances in Electronic and Electric Engineering, 4.1 (2014), pp. 41–48. [47] A. Muthu Manokar, D. Prince Winston, Experimental analysis of single basin single slope finned acrylic solar still, Mater. Today Proc. 4 (2017) 7234–7239. [48] A. Muthu Manokar, D. Prince Winston, A.E. Kabeel, Ravishankar Sathyamurthy, T. Arunkumar, Different parameter and technique affecting the rate of evaporation on active solar still - a review, Heat Mass Transf. (2017), http://dx.doi.org/10. 1007/s00231-017-2170-9 (In press).

operation, 19th European Photovoltaic Solar Energy Conference, 2004, pp. 3091–3094. Shiv Kumar, Arvind Tiwari, Design, fabrication and performance of a hybrid photovoltaic/thermal (PV/T) active solar still, Energy Convers. Manag. 51 (2010) 1219–1229, http://dx.doi.org/10.1016/j.enconman.2009.12.033. G.N. Tiwari, Solar Energy: Fundamentals, Design, Modelling and Applications, CRC Publication/Narosa Publishing House, New Delhi/New York, 2002. J. Je, J. Ping Lu, T.T. Chow, W. He, G. Pai, A sensitivity study of a hybrid photovoltaic/thermal water heating system with natural circulation, Appl. Energy 84 (2007) 222–237. A.M. Manokar, K.K. Murugavel, G. Esakkimuthu, Different parameters affecting the rate of evaporation and condensation on passive solar still–a review, Renew. Sust. Energ. Rev. 38 (2014) 309–322. P.N. Kumar, A.M. Manokar, B. Madhu, A.E. Kabeel, T. Arunkumar, H. Panchal, R. Sathyamurthy, Experimental investigation on the effect of water mass in triangular pyramid solar still integrated to inclined solar still, Groundw. Sustain. Dev. 5 (2017) 229–234.

12