Energy Conversion and Management 51 (2010) 1219–1229

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Energy Conversion and Management

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Design, fabrication and performance of a hybrid photovoltaic/thermal(PV/T) active solar still

Shiv Kumar a,*, Arvind Tiwari b

a Centre for Energy Studies, Indian Institute of Technology, Hauz Khas, New Delhi 110 016, Indiab Department of Electronics and Communication Engineering, K.I.E.T., 13 Km Stone, Meerut-Ghaziabad Road, Ghaziabad (UP), India

a r t i c l e i n f o

Article history:Received 24 December 2007Received in revised form 29 May 2009Accepted 28 December 2009Available online 9 February 2010

Keywords:Hybrid photovoltaic/thermal (PV/T)Solar stillsWater depthElectrical efficiencyThermal efficiency

0196-8904/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.enconman.2009.12.033

* Corresponding author. Tel.: +91 9868878227.E-mail address: skdubey_1966@rediffmail.com (S.

a b s t r a c t

Two solar stills (single slope passive and single slope photovoltaic/thermal (PV/T) active solar still) werefabricated and tested at solar energy park, IIT New Delhi (India) for composite climate. Photovoltaic oper-ated DC water pump was used between solar still and photovoltaic (PV) integrated flat plate collector tore-circulate the water through the collectors and transfer it to the solar still. The newly designed hybrid(PV/T) active solar still is self-sustainable and can be used in remote areas, need to transport distilledwater from a distance and not connected to grid, but blessed with ample solar energy. Experiments wereperformed for 0.05, 0.10, and 0.15 m water depth, round the year 2006–2007 for both the stills. It hasbeen observed that maximum daily yield of 2.26 kg and 7.22 kg were obtained from passive and hybridactive solar still, respectively at 0.05 m water depth. The daily yield from hybrid active solar still isaround 3.2 and 5.5 times higher than the passive solar still in summer and winter month, respectively.The study has shown that this design of the hybrid active solar still also provides higher electrical andoverall thermal efficiency, which is about 20% higher than the passive solar still.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

All ecosystems and every field of human activity depend onclean water and it is one of the most precious earth’s resourcesin today’s world. Water is a primary need of life, health, and sani-tation and is the most important issue in the international agenda.Water resources around the world are under pressure. The world’ssupply of fresh water is running off because of increasing demanddue to increasing population, industrialization, and draught at var-ious locations, followed by desertification. Water available in riv-ers, lakes, and underground reservoirs is being polluted due toindustrial, agricultural and population growth during the currentyears. The global consumption of water is doubling in every20 years, more than twice the growth rate of human populationas estimated. According to the United Nations, more than one bil-lion people already lack access to fresh drinking water. The presentfresh water resources, which are less than 1%, are inadequate tosupport life and vegetation on the earth and will not be able tomeet the requirements in future. If current trends persist, by2025 the demand for fresh water is expected to rise by 56% morethan the amount of water that is currently available.

Decline in drinking water quality is affecting millions in devel-oping countries. Many developing countries including India have

ll rights reserved.

Kumar).

given utmost priority to rural water supply in their developmentplans. At present India has 16% of world population but only 4%of its fresh water supplies. To distillate the saline/brackish waterto fresh water for human consumption and for other utility, differ-ent technologies has been used for about century and the use ofdistillation technology has been accelerated after world war-II.Many options (conventional and non-conventional) are availableto distillate the brackish/saline water. Among the non-conven-tional methods, to disinfect the polluted water, the most promi-nent method is the ‘solar distillation’ to get the potable/distilledwater by utilizing the solar energy and has been practiced for cen-turies. Comparatively this requires simple technology, eco-friendly, lower maintenance and no energy costs, due to which itcan be used anywhere with lesser number of problems. However,these advantages of simple passive solar stills are off set becauseof low yield, approximately 2–3 L/m2 day, low efficiency anddependent on solar intensity, which varies with location.

Broadly, solar distillation systems are classified as passive andactive solar stills and various scientists throughout the world havecarried out numerous research works on design, fabrication meth-ods, testing and performance evaluation, etc. as historically re-viewed by Tiwari et al. [1]. Cooper [2] reviewed the factorsaffecting the absorption using shallow basin passive solar still.An ideal solar still has been proposed to attain maximum ideal effi-ciency of 60% over a day’s operation. However, maximum experi-mental efficiency for solar still operating near to ideal (cover

Nomenclature

Ac area of collector (m2)Am area of PV module (m2)As area of solar still (m2)Ic (t) total solar intensity on the glass covers of collector pa-

nel (W/m2)Im (t) total solar intensity on the glass covers of PV module

(W/m2)Is (t) total solar intensity on the glass covers of solar still (W/

m2)Ic;d (t) instant diffuse solar intensity on the glass covers of col-

lector panel (W/m2)Is;d (t) instant diffuse solar intensity on the glass covers of solar

still (W/m2)ISC short circuit current (A)IL load current (A)

Tb basin temperature (�C)L latent heat of vaporization (J/kg)_mew distillate yields (kg/m2 h)

Tgo glass outer surface temperature (�C)Tgi glass inner surface temperature (�C)Tv vapor temperature (�C)Va wind velocity (m/s)VOC open circuit voltage (V)VL load voltage (V)

Greek symbolsge electrical efficiencygeth equivalent thermal efficiencygth thermal efficiencygo overall thermal efficiency

1220 S. Kumar, A. Tiwari / Energy Conversion and Management 51 (2010) 1219–1229

inclination 10� and 0.0095 m water depth) rarely exceeds over 50%,as predicted. Gomkale and Datta [3] designed a simple double-sloped solar still using aluminum components and black polyethyl-ene film as the base liner and insulation bed of sand and sawdust atthe bottom using wooden basin. They predicted annual averageproductivity of 2.51 L/m2 day, i.e. an efficiency of 28% at Bhavnagar(India). Garg and Mann [4] reported that the distillate output fromthe solar stills depend on climatic conditions, thermo physicalproperties of construction material, its orientation, cover tilt angle,water depth, vapor leakage and operating parameters. They re-ported 26% heat loss through the base of solar stills and recom-mended insulated base to lower down the loss. Al-Hinai et al. [5]studied the effect of effect of climatic, design and operationalparameters on the yield of a simple solar still. They recommendedoptimum thickness of insulation as 0.1 m, under the Omani cli-matic conditions, after which the increase in the still yield doesnot justify the additional insulation cost. They have also recom-mended the brine water depth in the range of 0.02–0.06 m for bet-ter yield and found an increase in daily yield by 8.2% with rise inambient temperature from 23 to 33 �C. Malik et al. [6] includedimportance, history and background of solar distillation and pre-dicted maximum efficiency of 30% for passive solar still. Fathet al. [7] designed the pyramid shaped passive solar still and foundthat average daily annual productivity from both pyramid and sin-gle slope solar still was nearly same and close to 2.6 L/m2 day.

El-Sebaii [8] selected different designs of the passive and activesolar stills to study the effect of wind velocity, water and glass cov-er temperatures, and water depth on the yield. The single slope sin-gle basin still with water flowing in the basin and the vertical solarstill were selected as an active solar still. He reported that dailyyield of the active basin type, wick-type and vertical solar stills in-crease as wind velocity increases up to the typical velocity, possi-bly because their overnight yields equal zero. However, for singleeffect passive stills, there is a critical depth (0.05 m) beyond whichthe yield increases with increase in wind velocity. Boukar and Har-mim [9] reported that daily yield from simple double basin solarstill increases nearly two times after coupling it to a flat plate col-lector during clear days in summer.

The simple basin solar still has several advantages over otherknown desalination methods. It is simple in construction, directuse of free solar energy, minimal need for maintenance, self-oper-ation and long lifetime, but the low yield offsets these advantages.The yield can be increased by feeding the hot water in the basinand to achieve so, the different designs of active solar distillationsystems have been proposed by various researchers. Singh and Ti-wari [10] evaluated the monthly performance of passive and active

solar stills for different Indian climatic conditions for differentwater depths and reported that the yield significantly dependson water depth and annually maximum for glass cover inclinationequal to the latitude of the place. Voropoulos et al. [11] reportedthat by coupling of the solar still with thermal storage, heated byflat plat collectors, the yield increased by two times than that ofthe solar still only. Zaki [12] carried out experimental investigationon an active system under thermosyphon mode of operation andreported that the maximum increase of yield by 33%, when thewater in the single slope solar still was preheated in the flat platecollector. Recently, Tiwari et al. [13] developed a thermal model forintegrated active solar still coupled with different types of the solarcollectors and validated with experimental values for 0.05 m waterdepth. They concluded that active solar still integrated with evac-uated tube collector with heat pipe gives yield 4.24 kg/m2 day,maximum among all other type of solar still. The yield in these ac-tive methods of solar distillation has been increased significantly,but operation depends on power supply and if PV operated, thethermal energy of solar cells convected from back surface wasnot utilized usefully.

Once thermal energy withdrawal is associated with the photo-voltaic (PV) module, it is referred as hybrid (PV/T) system. The con-cept behind the hybrid is that a solar cell converts solar radiationto electrical energy with peak efficiency in the range of 9–12%,depending on specific solar-cell type and thermal energy dissi-pated for air or water heating. More than 80% of the solar radiationfalling on photovoltaic (PV) cells either reflected or converted tothermal energy. In view of this, hybrid photovoltaic/thermal (PV/T) collectors are introduced to simultaneous generate electricityand thermal power, Je et al. [14]. Fujisawa and Tani [15] have donethe annual exergy based evaluation of hybrid photovoltaic/thermal(PV/T) collector. They predicted the higher output density from thesystem than in a unit PV module or in a liquid flat plate collector.Hung et al. [16] have studied the experimental performance of un-glazed PV integrated solar collector for water heating under natu-ral mode and found primary energy saving efficiency exceeds 60%,which was higher than for a conventional solar water heater orpure PV system.

Chow [17] has analyzed the performance of PV/T water collec-tor with single glazing in transient conditions, including theinstantaneous thermal/electrical gains efficiencies, and thermalstate of various collector components. He reported an increase ofelectric efficiency by 2% at mass flow rate of 0.01 kg/s and reported60% thermal efficiency of the system. Later, Chow et al. [18] haveconcluded that the tube-in-plate absorber collector with singleglazing regard as one of the most promising design. They have ob-

Fig. 1b. Schematic of a passive solar still (sectional side view).

S. Kumar, A. Tiwari / Energy Conversion and Management 51 (2010) 1219–1229 1221

tained that partial covered PV/T flat plate collector gives betteroverall thermal and electrical efficiencies.

Further, Zakharchenko et al. [19] have studied unglazed hybrid(PV/T) water heating system and reported that the area of moduleand collector in the PV/T system need not to be equal for higheroverall efficiency. To operate the PV module at low temperature,the PV module should be cover low temperature part of the collec-tor. They inferred that with suitable thermal contact between thePV module and collector, 10% increase of the power generated bypanel can be obtained. Tiwari and Sodha [20] have carried outthe parametric study of different configuration of hybrid (PV/T)air collectors (unglazed and glazed PV/T air heaters), with andwithout tedlar. They reported that glazed hybrid PV/T without ted-lar gives the best performance. Recently, Dubey et al. [21] have re-ported the higher annual average efficiency of glass-to-glass typePV module with and without air duct as 10.41% and 9.75%, respec-tively. Many solar till configurations have been investigated andreported on in literature; however none has considered and evalu-ated the performance of hybrid (PV/T) active solar still.

The motivation for this configuration arises from problemsidentified in the remote areas, facing power problems and goodquality of water for commercial use. The pure water have to betransported from a distance to meet the requirements (i.e. drink-ing, hospital use, battery charging, schools, laboratories, etc.),which cost more. We have designed, fabricated and tested the hy-brid (PV/T) active solar distillation system to operate in remotelocations with the view point of higher yield and increase in elec-trical efficiency of PV module. For comparative assessment, a pas-sive solar still of same specification was also fabricated. Thecomparative experimental performance has been presented forboth the solar stills on typical days of each month in a year.

Fig. 1c. Photograph of a passive solar distillation unit.

2. Experimental setup

2.1. Single slope passive solar still

The schematic of single slope passive solar still is shown inFig. 1a (top view) and Fig. 1b (side view). This conventional singleslope solar still has an effective basin area of 1 m � 1 m and fabri-cated using glass reinforced plastic (GRP) material, which is 2–3times more durable than fibre reinforced plastic (FRP). The bodywas prepared by coating unsaturated polymer resin on 3-D matof glass wool (trade name Parabeam 3-D mat). It consists of 30–40% mat and 60–65% resin. Ultimately, the hardened body of glassreinforcement plastic (GRP) offers corrugated layers of glued matafter drying. The air that has been entrapped between its corru-gated cavities after drying provides a high degree of insulationfor heat flow that is highly desired quality for the body of solar

Fig. 1a. Sectional top view of the passive solar still.

stills. The lower height (front side) of the basin is kept at 0.30 m toaccommodate different water depths and to fix the distillationtrough.

A transparent glass cover with an inclination of 30� to the hor-izontal optimized for 28.34� N latitude of New Delhi is fixed on thetop of the solar still using iron clamps. Further, it is sealed usingwindow-putty to prevent vapor leakage to out side. A rubber gas-ket is placed between the glass and iron frame. The bottom andside walls are painted black from inside to increase the absorptiv-ity to solar radiation. The transparent glass cover allows solar radi-ations to inter inside, which get absorbed by water and basin liner.A trough is fixed at the end of the smaller front vertical wall of thestill basin to collect distillate that has been taken to an external jarby connecting a plastic pipe to this trough. An inlet pipe is alsofixed at the rear wall of the still for feeding saline/brackish water.An opening in the bottom is also provided to flush/clean out thelayer of sludge that develops in the bottom of the tank as oftenas necessary. A plastic scale is fixed at the center of basin using

Fig. 2a. Sectional top view of the hybrid (PV/T) active solar still.

1222 S. Kumar, A. Tiwari / Energy Conversion and Management 51 (2010) 1219–1229

m-seal (Adhesive). The position of thermocouples is also shown inFig. 1b. A hole is also drilled in the side body of the solar still to takethe wire of respective thermocouple externally. The whole unit ismounted on an angle iron stand of size 1 m � 1 m � 1 m. The solarstill is oriented due south in order to receive maximum solar radi-ation throughout the year. The photograph of fabricated singleslope deep basin solar still is shown in Fig. 1c.

2.2. Single slope hybrid (PV/T) active solar still

The schematic of self-sustainable hybrid (PV/T) active solar stillis shown in Fig. 2a (top view) and Fig. 2b (side view). The fabri-cated system consists of following components:

Fig. 2b. Schematic of a hybrid (PV/T) active solar still (sid

(i) PV integrated flat plat collector.(ii) Solar still.

(iii) DC motor pump.

Two flat plate collectors are connected in series and integratedto the basin of solar still by using insulated pipes. Each collectorhas an effective area of 2.0 m2. The whole absorber is encased inan aluminum metallic box with 0.1 m glass wool insulation at baseand side to reduce thermal losses. The toughened glasses of0.004 m thick are fixed on the top of the box using aluminumframe and screw. The rubber seal is placed between the metallicbox and glass cover as well as between glass and aluminum frame.

e view). The position of sensors is same as in Fig. 1b.

Table 1Specifications of the fabricated passive and hybrid (PV/T) active solar distillation unit.

Specification Hybrid (PV/T) activesolar still

Passive solarstill

Area of basin 1 � 1 m2 1 � 1 m2

Area of glass cover 1.16 � 1 m2 1.16 � 1 m2

Thickness of glass cover 0.004 m 0.004 mAngle of glass cover with horizontal 30� 30�Lower vertical height of basin (front

side)0. 30 m 0.30 m

Higher vertical height of basin (backside)

0.88 m 0.88 m

Total surface area of solar still 3.36 m2 3.36 m2

Weight of solar still 21.17 kg 21.17 kgHeight of iron stand from the

ground1.5 m 1.0 m

Area of PV module 0.55 � 1.20 m2 –Diameter of the copper tubes 0.0127 m –Angle of FPC with the horizontal 45� –Number of copper tubes in the FPC 20 (10 in each) –Size of each collector 1.9 m � 1.25 m –Number of tube in each collector 10 –Length of each tube 1.8 m –Diameter of each tube 1.27 cm –Thickness of collector glass

(toughen)0.004 m –

Size of PV module 1.25 m � 0.55 m –No. of solar cell in the PV module 36 –Effective area of first collector under

glass1.34 m2 –

Effective area of first collector underPV module

0.66 m2 –

Effective area of second collectorunder glass

2.0 m2 –

Fig. 2d. Photograph of the hybrid (PV/T) active solar still.

Fig. 2c. Photograph of the DC water pump.

S. Kumar, A. Tiwari / Energy Conversion and Management 51 (2010) 1219–1229 1223

A photovoltaic glass-to-glass module of area 0.55 � 1.20 m2

(75 Wp) is integrated with one of the collector at lower side [18],towards the inlet of low temperature water. The electrical energygenerated by the photovoltaic (PV) module is used to operate theDC water pump, which is used to circulate water under forcedmode of operation to compensate the pressure drop in the collec-tors and piping arrangement. The solar radiations which are beingtransmitted through non-packing area of module, directly ab-sorbed by the blackened surface of the collector as well as con-vected thermal energy from back surface of the module is alsobeing utilized for water heating below the PV module. The wholesystem is made vapor tight using silicone rubber sealant, becauseit remains elastic for quite long time. The photograph of DC waterpump is shown in Fig. 2c.

The fabricated single slope solar still of the same specification asexplained in Section 2.1 is mounted on another iron stand of size1.5 m � 1 m � 1 m and connected to the PV integrated collectorsthrough insulated piping. The entry of hot feed water from collec-tors is kept at 0.05 m level in solar still at one side. The position ofthermocouples is kept similar to passive solar still. The outlet pipefrom the solar still to DC pump connected diagonally on other sideof the still at 0.025 m level from the base. In a hybrid active solarstill, the water in the basin gets heated directly as well as indirectlythrough flat plate collectors. The complete unit is oriented duesouth in order to receive maximum solar radiation throughoutthe year. The photograph of complete fabricated hybrid (PV/T) so-lar still is shown in Fig. 2d, while specifications in Table 1.

3. Instrumentation

The following instruments were used during the experimenta-tion for measuring the various parameters of the passive and hy-brid (PV/T) active solar stills.

(i) Solarimeter: The instrument was used to measure the hourlytotal solar radiation intensity (local name ‘‘Suryamapi” makeCentral Electronic Limited (CEL), India). The diffuse radiationwas also measured by manually providing a shade over itsphotovoltaic sensor. It was calibrated with the help of a Pyr-anometer and has a least count of 20 W/m2.

(ii) Temperature sensors: The temperatures of water and glasscover were recorded with the help of calibrated copper-con-stantan thermocouples and a digital temperature indicatorhaving a least count of 0.1 �C. The thermocouples were cali-brated with the standard Zeal thermometer (0–110 �C).

(iii) Mercury thermometer: The ambient temperature wasrecorded with the help of a calibrated mercury thermometerhaving a least count of 1 �C. It was hanged at the height of solarstill in an open-air shade to prevent direct exposure toradiation.

(iv) Measuring cylinder: The distillate output was measured usinggraduated measuring cylinders of a least count 10 ml and1 ml, respectively.

(v) Anemometer: It is a conventional instrument (electronicdigital anemometer model of LUTRON AM-4201) usedto measure airflow velocity over the glass cover of solarstill.

(vi) Clamp for multi-meter(Tong meter): The instrument was usedto measure the short circuit current (ISC), load current (IL),open circuit voltage (VOC) and load voltage (VL). The leastcount of the instrument for measuring current and voltageare 0.1 A and 0.01 V.

1224 S. Kumar, A. Tiwari / Energy Conversion and Management 51 (2010) 1219–1229

4. Methodology

The extensive experiments were conducted throughout the yearfrom April 2006 to March 2007 for different water depths (0.05,0.10 and 0.15 m). The underground brackish water (TDS = 724)used to be filled in the solar stills to a desired depth at least 24 hbefore the commencement of the experiment in order to bringthe filled water in a steady state. The experiments were startedat 7 am (local time of New Delhi), and continued until 7 am nextday. The solar radiation were recorded on the inclined glass surfaceof the solar still, flat plate collectors and PV module itself at centersand used for computational proposes. The following parameterswere measured hourly for a period of 24 h (7–7 am) for each waterdepth during the experiments:

a. Basin liner temperature (Tb).b. Water temperature (Tw) at different depth i.e. 0.025 m (T2.5),

0.05 m (T5), 0.10 m (T10) and 0.15 m (T15) to measure ther-mal stratification inside the water.

c. Inner glass temperature (Tgi).d. Outer glass temperature (Tgo).e. Vapor temperature (Tv).f. Total radiation on the solar still cover, Is (t)and on the collec-

tor, Ic (t).g. Diffuse radiation on the solar still cover, Is,d (t)) and on the

collector, Ic,d (t).h. Ambient temperature (Ta).i. Hourly distillate output ( _mew).j. Air velocity (Va).k. Open circuit voltage (VOC), load voltage (VL), short circuit cur-

rent (ISC), load current (IL) were measured during sunshinehours of the day.

5. Experimental observations and discussion

The solar stills were tested throughout the year 2006–2007 inoutdoor conditions for three water depths (0.05, 0.10 and0.15 m). Water comes out at 0.025 m level of the solar still, whichis lower temperature (Twi1) and inters at the inlet of PV integrated

Table 2aHourly variation of various parameters for passive solar still at 0.05 m water depth on Ap

Time (h) Is (t) (W/m2) Is,d (t) (W/m2) Tgo (�C) Tgi (�C) Tv (�C)

0700 0 0 14.3 14.5 13.50800 0 0 16.1 16.3 14.90900 540 40 31.9 31.3 38.21000 680 60 47.4 48.3 57.21100 740 60 54.9 55.5 59.21200 780 60 56.7 58.9 60.61300 700 60 59.1 61.5 59.61400 560 60 59.7 64 66.81500 440 60 55.8 63.6 68.31600 160 20 47 54.3 61.61700 0 20 45.6 51.3 551800 0 0 40 42.1 44.81900 0 0 33.3 33.7 35.82000 0 0 28.1 28.5 30.22100 0 0 24.1 24.2 252200 0 0 21 21.3 21.62300 0 0 18.6 18.7 192400 0 0 17 17.5 16.80100 0 0 16.9 17 15.70200 0 0 16.1 16.5 13.90300 0 0 15.2 15.4 12.50400 0 0 15 15 10.80500 0 0 14 14.6 9.80600 0 0 13 13.2 8.90700 0 0 14 12.9 9.3

collector through DC pump. The outlet of water (Two1) at the end ofabsorber below the covered part of PV module becomes inlet toremaining portion of PV/T integrated collector. The outlet waterat the end of first collector (Two2) becomes inlet to the second flatplate collector and finally fed into the integrated solar still at high-er temperature (Two3), as read out in Fig. 2b.

The typical experimental parameters recorded at differentwater depth (0.05, 0.10 and 0.15 m) in the typical clear days, inthe summer month (April 2006) for both the stills are illustratedin Tables 2-4. These values contain hourly data of solar intensity,wind velocity, temperatures namely ambient, water, inner andouter surface of glass cover, vapor temperature, and distillate yield.

From the tables it has been observed that the inner glass covertemperature of hybrid (PV/T) active solar still is higher than outerglass cover temperature in the most of observations and higherthan passive solar still due to the release of more heat of conden-sation on the inner surface of glass cover. It has also observed thatbetween 7 am and 8 am, the outer glass surface is at higher tem-perature than the inner glass surface. This is due to low intense so-lar radiation during sunrise, which encountered first by the outersurface and being absorbed. The observations also show that at0.05 m water depth on April 13, 2006 the highest value of watertemperature reached in passive solar still (i.e. Tw � 59�C at1500 h) is lower than in hybrid (PV/T) active solar still (i.e.Tw � 90�C at 1300 h).

From tables it can be clearly seen that in all cases there is a sig-nificant increase in water yield from the system, when the solarstill is integrated with the hybrid PV/T collectors. The daily yieldobtained from hybrid (PV/T) active solar still (7.22 kg) is higherthan passive solar still (2.26 kg) at 0.05 m water depth for typicalday of summer. The yield is reduced significantly to 5.0 kg and1.51 kg with increase in water depth to 0.10 m and 0.15 m, respec-tively. In both cases (Tables 3 and 4) too, the daily yield in the caseof hybrid active solar still is about 3.5 times higher than yield ob-tained from passive solar still. Decrease in daily yield has been ob-served with increase in water depth. Almost same daily yield at0.10 and 0.15 m water depth is observed, which is due to intensesolar radiation on April 08, 2006 (4.54 kW/m2 day) in comparisonto solar radiation available on April 03, 2006 (4.21 kW/m2 day).

ril 14, 2006 (daily yield = 2.26 kg).

T5 (�C) T2.5 (�C) Tb (�C) Ta (�C) Va (m/s) _Mew (kg)

17.4 17 19.6 16 0 015.9 15 17.7 23 0 0.0420.2 18.5 21.9 28 1.8 0.03431.3 29.5 32.5 32 2.1 0.01542.1 40.1 42.3 33 1.9 0.00549.7 50.3 53.2 35 2.1 0.05854.7 57.1 60.1 36 2.5 0.1557.5 60.2 66.9 36 5.5 0.358.9 63.3 66.1 37 6 0.2959.3 60.6 63.2 36 3.5 0.2856 57.2 59.8 34 2.5 0.2148.6 49.2 51.5 29 1.8 0.1941 41.6 43.8 23 2.1 0.1635.7 36.1 38.2 21 1.8 0.0930.5 30.7 32.9 20 0.9 0.08627 26.8 28.2 20 0.6 0.0623.3 24.3 25.8 18 0.4 0.04621.8 21.5 22.1 17 0 0.04520.1 19.7 20.3 17 0 0.03718.7 19.5 19 16 0 0.03217.3 17 17.6 15 0 0.03115.7 15.3 15.9 15 0 0.0314.6 14.1 14.7 14 0 0.02713.3 13.2 13.6 14 0 0.02313 13 12.7 15 0 0.022

Table 2bHourly variation of various parameters for hybrid (PV/T) active solar still at 0.05 m water depth on April 13, 2006 (daily yield = 7.22 kg).

Time (h) Is (t) (W/m2) Is,d (t) (W/m2) Ic (t) (W/m2) Ic,d (t) (W/m2) Tgo (�C) Tgi (�C) Tv (�C) T5 (�C) T2.5 (�C) Tb (�C) Ta (�C) Va (m/s) _mew (kg)

0700 0 0 0 0 13.6 14.5 15.7 16.8 17.8 17.1 16 0 00800 400 40 420 40 27.4 26.9 22.9 18.8 19.4 19.5 23 0 0.0620900 580 60 600 60 54.2 54.1 52.8 51.4 40.7 43.7 28 1.8 0.0161000 680 80 700 80 61 66.1 65.1 64.1 45.7 50.7 32 2.1 0.2551100 740 60 760 60 78.6 80.5 81.2 81.9 56.7 65.4 33 1.9 0.641200 780 80 780 60 82 87.4 88.7 90 68.4 79.8 35 2.1 0.981300 700 60 680 60 81.5 88 89.9 91.7 76.9 82.2 36 2.5 0.991400 560 60 540 40 79 84.1 88.2 92.3 82.3 89.8 36 5.5 1.351500 440 40 300 40 71.8 73 75.9 78.8 76.5 79.2 37 6 0.851600 160 40 60 20 64 67.1 69.6 72.1 73 74.7 36 3.5 0.671700 0 0 0 0 42.2 47.8 54.4 61 51 50.4 34 2.5 0.351800 0 0 0 0 35.9 41.1 46.3 51.5 48 46.2 29 1.8 0.261900 0 0 0 0 27.6 32.7 38.7 44.6 40.5 38.3 23 2.1 0.1852000 0 0 0 0 22.9 26.9 32.7 38.5 36.6 33.3 21 1.8 0.1252100 0 0 0 0 20 23.2 28.4 33.5 32.4 29 20 0.9 0.0962200 0 0 0 0 18.1 21 25.5 30 28 26.1 20 0.6 0.092300 0 0 0 0 15.9 18.3 22.4 26.5 25.7 24.1 18 0.4 0.0552400 0 0 0 0 14.5 16.6 20 23.4 22.3 21.5 17 0 0.0460100 0 0 0 0 13.5 15.2 18.4 21.5 20.7 20 17 0 0.0380200 0 0 0 0 12.2 13.7 17.1 20.5 19.2 18.6 16 0 0.0340300 0 0 0 0 11.1 12.4 15.5 18.5 17.9 17.2 15 0 0.0310400 0 0 0 0 9.4 11.1 14.3 17.5 16.3 15.5 15 0 0.030500 0 0 0 0 8.9 10.2 13.4 16.5 15.3 14.6 14 0 0.0280600 0 0 0 0 8.1 9.6 12.2 14.7 14.4 13.7 14 0 0.0220700 0 0 0 0 9.9 9.5 11.6 13.6 13.3 12.6 15 0 0.02

Table 3aHourly variation of various parameters for passive solar still for 0.10 m water depth on April 03, 2006 (daily yield = 1.51 kg).

Time (h) Is (t) (W/m2) Is,d (t) (W/m2) Tgo (�C) Tgi (�C) Tv (�C) T10 (�C) T5 (�C) T2.5 (�C) Tb (�C) Ta (�C) Va (m/s) _mew (kg)

0700 0 0 19 19.5 20.9 23.6 24 23.7 24.4 18 0 00800 0 0 20.4 20.4 19.4 20.6 20.5 20.1 21 22 0 0.0370900 400 60 32.1 32.2 34.8 23.2 20.7 21.3 24 27 0 0.0321000 560 100 45.2 46.8 52.8 29.5 24.6 24.8 27 31 0.5 0.0161100 640 100 51.4 52.4 52.9 37.4 32.7 32.3 34.2 34 0.5 0.0051200 720 120 53.1 56.1 54.5 42.5 37.4 39.2 41.5 35 2 0.0051300 680 120 55.9 60.8 57.2 47.5 42.9 46.2 48.6 37 4.5 0.0221400 500 100 52.1 58.7 57.7 49.4 45.5 48.3 51.4 36 5 0.0451500 400 80 51 53.3 61.4 52.4 52.6 53 54.2 36 5.2 0.071600 200 80 45.2 50 54.4 52.1 52.2 52 55 35 6 0.121700 40 20 42.1 46.9 49.8 51.1 51.8 52.2 53.9 32 3.5 0.151800 0 0 38.5 40.7 43.3 47 47.4 47.4 49.2 30 2.5 0.141900 0 0 35 36.6 39 43.2 43.7 43.6 45.2 26 2 0.142000 0 0 32.3 33.5 35.5 39.8 40.5 40.4 41.9 24 0.5 0.112100 0 0 29.2 30.3 31.9 36.6 37.2 37.1 38.7 21 0.5 0.092200 0 0 26.8 27.1 28.7 33.2 33.8 33.7 35.3 21 0.5 0.0872300 0 0 25.2 25.2 26.3 30.7 31.5 31.3 32.9 20 0.5 0.072400 0 0 23.5 23.3 24.4 29.1 29.5 29.3 30.8 19 0 0.0670100 0 0 21.6 21.3 22.1 26.7 27.3 27.1 27.7 18 0 0.060200 0 0 20.2 19.9 20.4 25.1 25.6 25.4 26 18 0 0.0550300 0 0 18.8 18.5 18.7 23.2 23.7 23.2 24 17 0 0.0520400 0 0 17.4 17 17.2 21.6 22.1 21.6 22.4 17 0 0.0410500 0 0 16.9 16.2 15.9 20.3 20.5 20.2 21 17 0 0.0350600 0 0 16.6 16.2 16.1 19.7 20.1 19.6 20.6 17 0 0.0330700 0 0 17.2 16.7 16.4 19.5 19.8 19.3 20.3 17 0 0.027

S. Kumar, A. Tiwari / Energy Conversion and Management 51 (2010) 1219–1229 1225

It has also been observed that there is large variation in thetemperature of water (i.e. thermal stratification) in hybrid activesolar still, between each layer across the water depth at 0.025,0.05, 0.10, and 0.15 m level with reference to the base during daytime, which is higher than the passive solar still. This is due tofeeding of hot water from integrated flat plate collectors, whichis significantly higher at 0.05 m level unlike in passive solar still.This trend has been reversed in the case of passive solar still forhigher water depth (at 0.10 and 0.15 m) due to increase in attenu-ation as well as the top surface water is being exposed to vaportemperature, which is higher than water surface temperature ascan be observed from the tables. The stratification in the water col-umn has also been observed for 0.15 m water depth. The water

temperature is maximum at 0.05 m water depth and minimumat top surface (0.15 m) in hybrid active solar still. The thermalstratification is almost zero during off sunshine hours in both thesolar stills. It can be further seen that the basin temperature (Tb)is higher than water temperature (Tw) in the passive solar still (Ta-ble 2a) unlike an active solar still (Table 2b). The thermal stratifica-tion across water depth for 0.05 m water depth is shown in Fig. 3.

It is also observed that the hourly yield increases with increasein solar radiation. However, there is time difference between max-imum radiation and maximum distillate yield to occur. The maxi-mum radiation (780 W/m2) measured at 1200 h on the collectorand solar still surface, while the maximum distillate yield(1.35 kg) occurs at 14 h due to time lag between evaporation and

Table 3bHourly variation of various parameters for hybrid (PV/T) active solar still for 0.10 m water depth on April 03, 2006 (daily yield = 4.94 kg).

Time (h) Is (t)(W/m2)

Is,d (t)(W/m2)

Ic (t)(W/m2)

Ic,d (t)(W/m2)

Tgo

(�C)Tgi

(�C)Tv

(�C)T10

(�C)T5

(�C)T2.5

(�C)Tb

(�C)Ta

(�C)Va

(m/s)_mew

(kg)

0700 0 0 0 0 19.4 19.8 21.3 22.8 23.1 22.9 22.5 18 0 00800 300 60 300 60 27.1 26.5 22.5 18.5 18.9 16.1 16.8 22 0 0.050900 460 80 460 80 42.2 40.7 35.3 29.8 32.6 27.7 29.9 27 0 0.0221000 600 100 600 100 57.7 58.2 51 43.8 48 41.2 44.3 31 0.5 0.011100 640 120 620 100 73 74.2 68 61.7 70 57.2 62.9 34 0.5 0.121200 720 120 700 100 73.2 75.6 70.5 65.4 72.2 57.4 63.8 35 2 0.41300 680 120 640 120 72.8 76.8 73.6 70.4 76.8 72.1 76.1 37 4.5 0.621400 480 100 440 100 72.2 74.3 74.5 74.6 77.6 73.1 76.2 36 5 0.71500 300 100 220 100 67.9 73.5 73.8 74.1 77.4 73.5 76.4 36 5.2 0.681600 160 60 100 60 61.5 63.7 64 64.2 67.9 63.5 66.1 35 6 0.61700 0 0 0 0 49.2 52.1 54.3 56.5 58.9 55 55.9 32 3.5 0.351800 0 0 0 0 41.8 44 47.3 50.5 52.6 49.5 49.6 30 2.5 0.251900 0 0 0 0 36.9 38.8 42.3 45.7 47.4 44.8 44.4 26 2 0.222000 0 0 0 0 32.6 34.3 38.1 41.9 43 40.6 40.3 24 0.5 0.182100 0 0 0 0 29.3 31 34.5 38 39.4 37.4 37 21 0.5 0.1252200 0 0 0 0 28.6 29.4 33.6 37.7 39 37.2 36.8 21 0.5 0.122300 0 0 0 0 24.5 25.9 29.3 32.7 33.9 32.4 32 20 0.5 0.0882400 0 0 0 0 21.9 23 26.6 30.2 31 29.8 29.3 19 0 0.0790100 0 0 0 0 20.1 21.7 24.9 28 28.8 27.8 27.3 18 0 0.0710200 0 0 0 0 18.5 19.5 22.8 26 26.8 26 25.4 18 0 0.0680300 0 0 0 0 16.8 17.7 21 24.2 24.7 24.2 23.6 17 0 0.0560400 0 0 0 0 15.6 16.1 19.3 22.5 23.1 22.9 22.2 17 0 0.0460500 0 0 0 0 14.8 15.6 18.6 21.5 21.7 21.8 21 17 0 0.0360600 0 0 0 0 14.6 15.2 18 20.8 20.9 21.1 20.4 17 0 0.0350700 0 0 0 0 15 15 17.7 20.3 20.3 20.5 20 17 0 0.027

Table 4aHourly variation of various parameters for passive solar still for 0.15 m water depth on April 08, 2006 (daily yield = 1.52 kg).

Time (h) Is (t) (W/m2) Is,d (t) (W/m2) Tgo (�C) Tgi (�C) Tv (�C) T15 (�C) T10 (�C) T5 (�C) T2.5 (�C) Tb (�C) Ta (�C) Va (m/s) _mew (kg)

0700 0 0 20.7 20.8 25.9 29 29.2 29.2 28.9 29.6 20 0 00800 0 0 22.8 22.4 21.9 23.8 24.2 24.5 24.1 25 25 0 0.0360900 480 60 34.6 35.7 36.6 25.6 24 23.2 24 26.7 32 0 0.0441000 640 80 50.9 51.4 59.4 35 30.2 29 30.1 32.3 35 0.5 0.0121100 720 80 59.7 60.2 60.8 43.5 36.6 36.1 34.9 36.9 38 5.1 0.0061200 740 100 60.4 62.2 60.1 47.7 41.9 40.2 41.4 43.5 39 4 0.0041300 680 160 60.7 62.5 60.7 50.3 48.1 46.3 47.4 49.1 39 4.5 0.0141400 500 120 55.4 63 61 51 48.8 47.5 48.3 52.3 39 6.2 0.0331500 400 100 54.2 61.1 62.4 51.8 50.9 49.5 51.5 54 40 6.5 0.0581600 240 40 48.3 54.1 61.6 54.4 53.3 51.6 53.4 55.3 40 5.3 0.061700 40 20 46.8 52.1 55.2 54.8 54.2 54.2 54.6 56.2 37 5.1 0.091800 0 0 43.9 46.5 49.3 52.3 52.2 51.9 52.3 54.1 32 2.4 0.111900 0 0 38.9 40.6 45.3 48.4 48.2 48.4 49.9 49.9 27 2 0.152000 0 0 38.6 40 42.2 47.2 47.2 47.1 47.2 48.8 25 2.5 0.132100 0 0 33.9 35.1 36.8 41.2 41.5 41.4 41.4 43.1 25 1.6 0.1252200 0 0 31.6 32.5 33.9 38.2 38.5 38.4 38.4 40.2 24 1.5 0.1052300 0 0 29.6 30.4 31.3 36.3 36.7 36.7 36.4 38.2 23 1.4 0.0912400 0 0 27.8 28.5 29.6 34 34.5 34.5 34.3 36.1 22 0 0.080100 0 0 26.5 27.5 28.3 32.5 32.9 32.9 32.6 33.3 21 0 0.0740200 0 0 25.5 26 26.7 30.9 31.3 31.4 31.1 32 21 0 0.0590300 0 0 24.5 24.8 25.3 29 29.6 29.7 29.3 30.3 21 0 0.0650400 0 0 23.9 24 24.5 28.1 28.5 28.7 28.2 29.2 20 0 0.0560500 0 0 23.3 23.3 23.7 26.9 27.1 27.5 27 27.9 20 0 0.040600 0 0 22.8 22.9 23.1 26 26.6 26.7 26.4 27.3 20 0 0.0420700 0 0 23.1 22.8 24.2 25.7 26 26.1 25.7 26.6 21 0 0.034

1226 S. Kumar, A. Tiwari / Energy Conversion and Management 51 (2010) 1219–1229

condensation as well as storage effect in hybrid active solar still for0.05 m water depth. The similar observations were also obtainedfor higher water depths. Total yield obtained during daytime ishigher at lower water depth while during night results are vise ver-sa. The increase in the night yield is expected with increase inwater depth and higher for the hybrid active solar still, since thewater in basin remains hot enough so that distillation is continuedduring the night. It has been observed that distillate yield from theactive solar still is much higher at around 128 times (11 am for0.05 m water depth) and 80 times (12 pm for 0.10 and 0.15 mwater depth) than the passive solar still.

Fig. 4a shows the seasonal effect on the total daily yield ob-tained during the year 2006–2007. The maximum and minimumyields follow the solar energy trend. The highest daily yields ob-tained from hybrid (PV/T) active and passive solar still were7.22 kg and 2.26 kg, respectively in the summer month (April2006), which is about 3.3 times. It can also observe that daily mea-sured yields in rainy season (July 2006) were 1.956 kg and0.825 kg, respectively, which is around 2.4 times. The low yieldwas due to partially cloudy condition on the day. The total and dif-fuse radiations of this day were 2.79 kW/m2 and 1.57 kW/m2 (i.e.55.2%). Further, it can be noticed that in winter season (January

Table 4bHourly variation of various parameters for hybrid (PV/T) active solar still for 0.15 m water depth on April 08, 2006 (daily yield = 5.28 kg).

Time(h)

Is (t)(W/m2)

Is,d (t)(W/m2)

Ic (t)(W/m2)

Ic,d (t)(W/m2)

Tgo

(�C)Tgi

(�C)Tv

(�C)T15

(�C)T10

(�C)T5

(�C)T2.5

(�C)Tb

(�C)Ta

(�C)Va

(m/s)_mew

(kg)

0700 0 0 0 0 25.3 25.4 26.6 27.8 29 28.9 28.1 27.8 20 0 00800 340 40 360 60 31.5 31.4 26.7 22 21.5 21.7 18.7 19.4 25 0 0.0260900 540 60 520 60 46.1 44.4 36.2 27.9 31 34.3 30.3 31.2 32 0 0.021000 660 80 640 60 63.5 63.5 53.5 43.5 45.1 49.7 42.3 45.6 35 0.5 0.0081100 700 80 700 60 71.5 72.6 67.9 63.2 67.3 73.4 62.8 67.6 38 5.1 0.11200 740 120 680 100 73.5 73.4 68.5 63.6 67.9 75.4 64.1 69.2 39 4 0.321300 680 160 600 160 74.1 74.5 70.7 66.9 71.9 78.6 66.4 73 39 4.5 0.61400 440 140 420 140 74.8 75.3 72.1 68.9 73.1 79.7 68.6 73.7 39 6.2 0.591500 420 100 400 100 70.1 72.9 72.1 71.3 73.3 76.2 69.4 74 40 6.5 0.551600 140 40 100 40 62.2 64.8 64.7 64.6 66.1 70 64.9 69.4 40 5.3 0.481700 0 0 0 0 55.4 59.4 59.6 59.7 60 65.1 60 61.7 37 5.1 0.421800 0 0 0 0 49.1 53.3 54.6 55.8 57.9 60.5 58.6 55.9 32 2.4 0.391900 0 0 0 0 41.6 45.2 47.6 50 52.4 54.3 54 50.5 27 2 0.372000 0 0 0 0 38.5 41.2 43.8 46.3 48.4 50.2 47.1 46.2 25 2.5 0.232100 0 0 0 0 35.2 37.4 39.9 42.3 44.5 46 42.9 42.3 25 1.6 0.212200 0 0 0 0 32.5 34.3 37.3 40.3 41.9 43.3 40.5 39.9 24 1.5 0.182300 0 0 0 0 30.3 32.2 35 37.8 39.5 40.8 38.5 37.6 23 1.4 0.142400 0 0 0 0 28.2 29.9 32.7 35.4 37.1 38.2 36 35.4 22 0 0.130100 0 0 0 0 26.7 28.3 31 33.6 35.2 36.3 34.4 33.6 21 0 0.120200 0 0 0 0 25.3 27.1 29.7 32.2 33.6 34.4 32.7 32.1 21 0 0.10300 0 0 0 0 24.2 25.4 28.1 30.7 31.9 32.4 31.8 30.2 21 0 0.090400 0 0 0 0 23.3 24.4 26.8 29.2 30.5 31.1 29.9 29.1 20 0 0.0690500 0 0 0 0 22.4 23.6 25.8 28 29.2 29.4 28.6 27.8 20 0 0.050600 0 0 0 0 22.3 23.1 25.2 27.3 28.3 28.5 27.8 27.1 20 0 0.050700 0 0 0 0 22.4 22.6 24.8 27 28 28.2 27.6 26.8 21 0 0.04

S. Kumar, A. Tiwari / Energy Conversion and Management 51 (2010) 1219–1229 1227

2007) the yield obtained from hybrid active solar still (4.25 kg/day)is around 5.5 times higher than the passive solar still (0.784 kg/day). The similar results have been observed for higher waterdepth (0.10 m and 0.15 m) as depicted from Fig. 4b. This impliesthat the hybrid active solar still give better comparative perfor-mance than the passive solar still in the winter season. However,

Fig. 3. Thermal stratification between different water layers for 0.05 m waterdepth. (a) Passive solar still. (b) Hybrid (PV/T) active solar still.

the average annual yield obtained from hybrid active solar still isfound to be 3.5 times than the passive solar still, irrespective ofwater depths.

Table 5 shows hourly measured values of solar intensity, cur-rent, voltage, efficiency, power produced and consumed by thewater pump. It has been observed that open circuit voltage andmodule efficiency decreases with increase in solar radiation(780 W/m2 at 12:00) due to rise in cell temperature as expected.The power consumed by the DC pump/day is 0.089 kW, which is

Fig. 4a. Comparative yield of hybrid active and passive solar stills in differentmonth of the year 2006–2007 at 0.05 m water depth.

ig. 4b. Yield ratio between hybrid active and passive solar stills in different month

F for 0.05, 0.10 and 0.15 m water depth.

Table 5Hourly variation of various parameters of PV module and DC water pump observed on April 13, 2006.

Time Im (t) (W/m2) VOC (V) ISC (A) VL (V) IL (A) Power generated from ‘module (W) Power consumed by pump (W) Power net (W) ge (%) geth (%)

0800 420 19.8 1.5 18.9 0.6 29.7 11.34 18.36 8.6 22.60900 600 19.2 2.4 18.6 0.6 46.08 11.16 34.92 9.3 24.51000 700 18.5 3.5 18.2 0.6 64.75 10.92 53.83 11.2 29.51100 760 18.3 3.8 17.7 0.6 69.54 10.62 58.92 11.1 29.21200 780 18 3.9 17.5 0.6 70.2 10.5 59.7 10.9 28.71300 680 17.5 3.4 17.2 0.6 59.5 10.32 49.18 10.6 27.91400 540 18 2.7 17.2 0.6 48.6 10.32 38.28 10.9 28.71500 300 17.6 1.1 16.8 0.6 19.36 10.08 9.28 7.8 20.51600 60 17.1 0.3 11.7 0.3 5.13 3.51 1.62 10.4 27.4

1228 S. Kumar, A. Tiwari / Energy Conversion and Management 51 (2010) 1219–1229

about 22.5% of the total power generated by PV module (0.413 kW/day). Therefore, it is recommended to optimize the system by;

� utilization of un-used power in the other applications at localarea by connecting number of hybrid active solar still an arrayor,

� optimizing the size of PV to make the system more economicalor,

� increasing in the system capacity by connecting more collectorsto increase in performance.

6. An overall thermal efficiency

Following Tiwari [22], the thermal efficiency of the passive andhybrid active solar still is evaluated as

(a) Passive solar still

gpassive ¼daily yield� L

As �P

IsðtÞ � 3600ð1Þ

(b) Hybrid active solar still including PV module areas

gactive ¼daily yield� L

As �P

IsðtÞ � 3600þ Ac �P

IcðtÞ � 3600ð2Þ

(c) Hybrid active solar still excluding PV module areas

gactive ¼daily yield� L

As �P

IsðtÞ � 3600þ ðAc � AmÞ �P

IcðtÞ � 3600ð3Þ

where L is a latent heat of vaporization and expressed as

L ¼ 2:4935� 106ð1� 9:4779� 10�4T þ 1:3132� 10�7T2

� 4:7974� 10�9T3Þ

Fig. 5. Monthly variation of thermal and electrical efficiencies of th

(d) The electrical efficiency of PV module is given by

ge ¼FF � ISC � VOC

Am � ImðtÞð4Þ

where FF is fill factor of solar cell and its value is 0.8 in presentcase.

(e) The equivalent thermal efficiency of PV module [14] is givenas

geth ¼ge

0:38ð5Þ

(f) The overall thermal efficiency of the hybrid active solar stillcan be obtained by adding Eqs. (3) and (5) and it is given by

go ¼ gth þ geth ð6Þ

Eqs. (1)–(6) have been used to evaluate thermal efficiency of thepassive and hybrid (PV/T) active solar still using the data from theTables 2a and b. The results show that the thermal efficiency of thehybrid active solar still lower than the passive solar still as ex-pected due to large thermal losses in hybrid active solar still, be-cause of high operating temperature range. The thermalefficiency of the passive solar still have been found to be as28.4%, 21.1%, and 19.6% for of 0.05, 0.10 and 0.15 m water depth,respectively, while in the hybrid active solar still, these values havebeen obtained as 19.4%, 15.4% and 15.2%, respectively. However, anoverall thermal efficiency of the hybrid active solar still is muchhigher than the passive solar still and evaluated as 48.3%, 44.3%,and 44.1% for respective water depths, which is almost 20% higherthan the passive solar still in month of April 2006. It is due to factthat conversion of electrical energy of PV module to thermal en-ergy gives more thermal energy. The variation of electrical, thermalefficiency and overall thermal efficiency of the PV module, passiveand hybrid active solar still in different month is shown in Fig. 5.

e passive and hybrid active solar stills for 0.05 m water depth.

S. Kumar, A. Tiwari / Energy Conversion and Management 51 (2010) 1219–1229 1229

The electrical efficiency of PV module has been obtained in therange of 9.3–12.4% with exception in the month of October(14.2%), possible due to intense solar radiation after rainy seasonand low ambient temperature. The electrical efficiency obtainedin PV integrated hybrid solar still is found to be higher than pre-dicted using PV module alone (9–12%) as predicted. It can be fur-ther seen that the thermal efficiency of the hybrid active solarstill is higher than the passive solar still in the winter months(i.e. November 2006–January 2007), with overall thermal effi-ciency of about 41% on annual basis.

7. Conclusions

The comparative performance of two solar still configurations,the hybrid (PV/T) active and the passive system, have been pre-sented. The following conclusions have been drawn from the study.

1. The DC pump motor uses only 23% of the power generated byPV module and the remaining 77% of power can be utilizedfor other applications or the size of PV module should bereduced to make the system more economical.

2. The operating water temperature range of the hybrid activesolar still is much higher than passive solar still (Tables 2–4)for all water depth in the basin due to additional thermalenergy supplied by the collectors.

3. The hybrid active solar still gives the higher yield and is about5.5 times than that of the passive solar still during wintermonths. However, the average annual yield is 3.5 times, irre-spective of water depths and accounting all seasons.

4. The thermal efficiency of the hybrid active solar still (excludingelectrical conversion efficiency) is lower than the passive solarstill. However, the overall thermal efficiency of the hybridactive solar still is about 20% higher than the passive solar still.The electrical efficiency of PV module has been found in therange of 9.3–12.4%.

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