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Design, development and experimental results of a solar distillery for the essential oils extraction from medicinal and aromatic plants
Available online at www.sciencedirect.com
ScienceDirect Solar Energy 108 (2014) 548–559 www.elsevier.com/locate/solener
Design, development and experimental results of a solar distillery for the essential oils extraction from medicinal and aromatic plants Anjum Munir a,b,⇑, Oliver Hensel b, Wolfgang Scheffler c, Heike Hoedt c, Waseem Amjad b, Abdul Ghafoor a b
a Faculty of Agricultural Engineering, University of Agriculture, Faisalabad, Pakistan Department of Agricultural Engineering, University of Kassel, D-37213 Witzenhausen, Germany c Solar Bruecke, G.v.Werdenbergstr.6, D-89344 Aislingen, Germany
Received 30 September 2013; received in revised form 13 June 2014; accepted 28 July 2014 Available online 3 September 2014 Communicated by: Associate Editor I. Farkas
Abstract Distillation of medicinal and aromatic plants for essential oils extraction can be done by utilizing heat in medium temperature range. These essential oils are used in foods, medicines and cosmetics etc. and are money earning business for the farming community. This research is focused to develop an on-farm solar distillery for the processing of different plant materials. The system comprises of a Scheffler reflector and a complete set of distillation system. An 8 m2 ‘projected area of the Scheffler solar concentrator was coupled with the distillation still for the extraction of essential oils. In this paper, a complete mathematical description has been explained to design different components of solar distillation system. In order to provide a fixed focus on a receiver from morning to evening and in summer and winter, flexible crossbars have been used to achieve the desired shapes of the reflector. The paper also covers all the details regarding design, development, site specific installation and tracking system etc. Different types of Florentine apparatuses were used to separate the essential oils from the hydrosol. Necessary instrumentation was used for the performance evaluation of solar distillery. The system was capable of producing 300–450 °C temperature at the receiver section within the beam radiation range of 800–850 W m2. The efficiency of solar distillery was calculated to be 33.21% with 1.548 kW thermal power available for processing in the distillation still. The system was operated for 10–12 h a day during summer. About 18.58 kW h thermal energy was obtained from the solar distillery in a sunny day. For the processing of 10 kg batch, an average 3.5 kW h energy was consumed. In this way, about 4–5 batches were processed successfully using different kinds of plant materials with 10–20 kg per batch. The research concluded that different kind of medicinal and aromatic plants could be processed effectively using solar distillery. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: Solar distillery; Essential oils; Scheffler reflector; Crossbars; Thermal energy
1. Introduction In the last decades, the increasing energy crisis in developing countries and climate change hazards has created awareness to promote the renewable energy technologies. ⇑ Corresponding author at: Faculty of Agricultural Engineering, University of Agriculture, Faisalabad, Pakistan. E-mail address: [email protected] (A. Munir).
http://dx.doi.org/10.1016/j.solener.2014.07.028 0038-092X/Ó 2014 Elsevier Ltd. All rights reserved.
As a result, the technologies devoted to the utilization of medium temperature heat sources have been evolving. (Bertrand et al., 2011; Calise et al., 2014). Moreover, fossil fuels are depleting at a very fast rate due to increase in population and industrial development (Okoro and Madueme, 2004). There are many fields which can be run using solar energy. Sterilization of medicinal equipment, extraction of oil, milk pasteurization, dehydration, solar cooling and
A. Munir et al. / Solar Energy 108 (2014) 548–559
distillation etc. can be successfully carried out using solar energy (Kalogirou, 2003; Govind et al., 2008; Liu et al., 2012). In the field of agriculture, solar energy can be successfully used as most of the agricultural processing take place in medium temperature range. Presently, solar energy utilization in agriculture sector is limited only to lower range temperature applications. But there are different types of processing that can also be carried out in medium to high temperature range. Solar heating for dairy applications and micro-irrigation are the dominant areas of solar energy utilization in the field of agriculture (Oparaku and Iloeje, 1991; Jenkins 1995; Essandu-Yeddu 1993). By using solar energy, small scale agro-based industries can be promoted at farm level which can improve the farmer’s living standard in developing countries. Essential oils are used for the medicinal and other food ¨ ztekin and applications and these oils are very expensive (O Martinov, 2007). Industrialized countries have been using the essential oils since long for the aromatherapy business. There are several extraction methods for the essential oil extraction but out of all the methods, the distillation method is the best method which is used to extract the pure essence of the plant material by evaporation process (Malle and Schmickl, 2005). Presently, the essential oils are extracted in big distillation plants which are situated in the big cities. These distillation plants are very expensive and small farmers cannot afford these distillation units to process their own medicinal plants. If we process the fresh plant material, then not only more oil contents can be achieved but also a lot of money can be saved under the heading of transportation expenses. For rural development, a decentralized distillation system is required. The solar distillation at farm level can enhance the oil extraction by using the fresher plant materials. Examples of the plants are Peppermint, Lemon Balm (Melissa), Lavender, Cumin, Cloves, Anise, Rosemary, Patchouli, Caraway, Cassia, Oregano, European Silver Fir, and Fennel etc. It has been noticed that the Scheffler reflector is a better design when compared with different solar concentrators. Scheffler reflectors provide temperature in the medium temperature range and different processing can be carried out successfully by using this technology (Bhirud and Tandale, 2006). Scheffler (2006) described that about 50% of the sun energy could be used for cooking applications. The payback period of Scheffler reflector is almost two years when they are used daily (Jayasimha, 2006). In Scheffler reflectors, the vessel is placed at the focus to utilize the thermal energy of the sun. The receiver absorbs all the reflected beam radiation and transfers them to fluid in the form of heat with minimum losses (Kumar and Reddy, 2007; Munir and Hensel, 2010). At present, solar energy is successfully utilized for cooking applications and steam generation. Extraction of essential oils using solar energy is a new research area in postharvest sector. This study was conducted for development and experimental performance a solar distillery for the processing of medicinal plants.
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2. Mathematical calculation and design detail of a Scheffler reflector The paper is about the design and development of a solar distillery based on the Scheffler reflector technology and is detailed below. In Scheffler reflector, equinox position is considered as the standard for design purpose. If the reflector is considered from the side view, paraboloid is seen like a parabola curve and reflector frame looks like a straight line. The general equation of a parabola can be written as: P ðxÞ ¼ mp x2 þ C p
ð1Þ
Differentiating Eq. (1) for the slope 0
P ðxÞ ¼ 2mp x
ð2Þ
We commence from a point Pn of the parabola curve where a beam radiation is reflected at right angle as detailed in Fig. 1. At this point, the tangent is drawn at 45° angle. In this way, the value of y-coordinate is half as compared to the xcoordinate. The study is based on two aims, first is to construct a Scheffler reflector having 8 m2 area, secondly there should be a balanced reflector. For the achievement of these two aims, the following procedure is adopted (Munir et al., 2010). First of all, we have to select x-coordinate of the point Pn(xP) in such a way that a reasonable distance from the focal point can be obtained; then calculate the y-coordinate of the same point and slope mP using Eqs. (1) and (2). Then we have to select xE1 and xE2 for the construction of 8 m2 Scheffler reflector having balanced structure. From these points, we can calculate yE1, yE2 and angle of reflector frame. As the reflector stand is elliptical in shape with semiminor axis as 1.36990 m and semi-major axis as 1.88016 m. The formula for the ellipse is p times minimum
E2
90°
Tangent at Pn 45° Pn(2.86575, 1.433287)
E1 43.23° O(0,0)
XE1 = 1.32387
XE2 = 4.06387
Fig. 1. Detail of Scheffler parabola curve.
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radius (semi-minor axis) and maximum radius (semi-major axis). The semi-minor and semi-major axes for this ellipse were taken as 1.44 and 1.88016 m respectively. In this way, the ‘projected area of Scheffler concentrator was calculated to be 8.09 m2. Now we have to check whether our required aims are achieved or not, otherwise we have to select new set of Pn, E1 and E2. At the end, both axes of the reflector are calculated. We take x-coordinate of point Pn (xP) as 2.86575 for the given 8 m2 Scheffler reflector. All calculations are based on the point Pn with x-coordinate as 2.86575. Actually, this coordinate delineates the distance between the focal point and this point. A value is chosen in order to keep this distance smaller but at the same time still leaves some space between inner edge of the reflector and the focus, thus preventing shading of the structure or building that normally found around the focus of the reflector. This is the reason that the point Pn with higher x-coordinate is required for higher projected area of the Scheffler reflector. It is clear from Fig. 1 that the tangent at point Pn makes an angle 45° with x-axis. If we differentiate this equation, the answer is unity. In a parabola equation, the y-coordinate is half of the x-coordinate i.e. 1.43287. The values for mp and Cp were calculated using Eqs. (1) and (2) and found to be 0.17447 and 0 respectively. As the Scheffler reflector is designed for equinox position, so the parabola equation for this position is as follows: P ðxÞ ¼ 0:17447x2
ð3Þ
Two points (xE1 and xE2) are selected as 1.32387 and 4.06387 on a graph so that a balanced reflector can be constructed. In fact, these two points were selected to make an 8 m2 Scheffler reflector e.g., the difference of these x-coordinates is 2.74 by subtracting second x-coordinate xE2 (1.32387) from first x-coordinate xE1 (4.06387). This distance will be the diameter of the projection of the ellipse formed on the horizontal plan. It represents the minor axis of the elliptical frame of the Scheffler reflector. The major axis is calculated by dividing this semi-minor axis by cos 43.23 which is equal to 3.76058. Later, recalculating these points with respect to the angle is necessary to crosscheck all numbers. The line E1E2 denotes the cutting section of the elliptical shaped frame on the parabola curve of the Scheffler reflector and this line makes 43.23° angle with x-axis as shown in Fig. 1. In this way, the straight line equation formed is given below: GðxÞ ¼ mg x þ C g
ð4Þ
Taking first derivative of Eq. (4) and by considering the angle of straight line (43.23°), the slope mg is determined as 0.94. We select x-coordinate of point E1 as 1.32387 and calculate y-coordinate and found to be 0.31. By putting the values of x, y and mg in Eq. (4), the y-intercept (Cg) can be calculated as 0.94 and the straight line equation is given as: GðxÞ ¼ 0:94x 0:93866
ð5Þ
The x-coordinate of point E2 (xE2) is calculated by using Eqs. (1) and (2), the quadratic equation formed in general form is given below: mg Cp Cg 2 xþ x ¼0 ð6Þ mp mp Two points of intersection (xE1 and xE2) of the parabola curve and straight line are obtained by solving Eq. (6) using quadratic equation. The line that cuts the curve represents the ellipse cutting plane having axes ratio as a/b = cos a, where “a” and “b” represents the semi-minor and semimajor axes respectively. The ellipse so formed makes circle on the horizontal plane. So, the radius of this circle becomes equal to the length of the semi-minor axis of the ellipse. A circle is formed if the projection of the ellipse is drawn on horizontal plane which is equal to 2a. In this way, the diameter of circle (2a) is determined by the following relation: sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 mg Cp Cg 2a ¼ ð2Þ ð7Þ 2mp mp The semi-minor and semi-major axes of the ellipse are calculated to be 1.37000 m and 1.88029 m respectively. For an 8 m2 Scheffler reflector, seven crossbars are used for the construction of required section of a paraboloid. The crossbars are fixed at ±0.48 m, ±0.96 m, ±1.44 m from the center of the reflector along major axis and on the minor axis, the respective points are selected as ±1.3246 m, ±1.17798 m and ±0.8809 m respectively. These points are clear on the frame of the reflector after the construction work. 2.1. Determination of ellipses for the crossbars The cutting planes of the crossbars are perpendicular to the cutting plane of the reflector frame and are represented by seven straight lines (q1 to q7) in Fig. 2. The cutting planes of crossbars make an angle 46.77° and these cutting lines represent ellipses as shown in Fig. 2. The middle crossbar equation is given below: q4 ðxÞ ¼ mq4 x þ C q4
ð8Þ
Middle crossbar slope is calculated by taking tan (46.77), x-coordinate of the point of intersection (Cf) which is the midpoint of xE1 and xE2 .The y-coordinate is determined by putting this value of x in Eq. (8) and is found to be 1.59357. Substituting the values of mq4, q4(x) and x in Eq. (8), the y-intercept (Cq4) for the central crossbar is calculated. The crossbar equation (q4) of the central crossbar for an 8 m2 reflector projected area is given in Eq. (9): q4 ðxÞ ¼ 1:06377x þ 4:45923
ð9Þ
All the crossbars are at right angles to the cutting section of the Scheffler concentrator, so all the crossbars have the same slopes. Referring Fig. 2, 0.48 m is the difference
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sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi 2 mqn C p C qn aqn ¼ 2mp mp
Projection of cross bar (middle)
Projection of Scheffler frame (aperture area)
ð10Þ
where “n” denotes the number of crossbar of the ellipse. 2.2. Calculation of required parameters for the development of Scheffler reflector
q7 q6
Table 1 shows parameters calculated for the preparation of the required crossbars of the Scheffler reflector. Using above calculations, the depths (Dn)and lengths of arcs (bn) for seven crossbars have been determined to construct the Scheffler reflector using simple trigonometric equations and are given in Table 2 (Munir et al., 2010). With the help of Table 2, crossbars are prepared to form the Scheffler reflector and are welded on the marked points of the Scheffler reflector frame. A jig was used to check the accuracy of the bent crossbars. Aluminum profiles were used to provide base for the Aluminum reflecting sheets to shape it lateral part of the paraboloid.
q5 q4
1.37
1.37
q3 q2 q1
0.70080 0.48
Cf (2.69387,1.59357)
Cf Pc
46.77°
43.23°
Fig. 2. Description of parabola curve and crossbars for 8 m2 Scheffler reflector.
2.3. Installing and tracking of Scheffler concentrator between two consecutive crossbars along the reflector frame which looks like a straight line in the side view. As the crossbars are inclined at 46.77° (90–43.23°) with x-axis (on drawing), the distance between two consecutive crossbars along the axis of parabola is calculated to be 0.70080 m by dividing 0.48 m with cos 46.77°. Other crossbar equations are calculated by adding and subtracting 0.70080 m from the adjacent equation as shown in Fig. 3. The coordinates shown in Fig. 3 are relative to the center of the reflector, not the absolute coordinate. The general equation for the crossbars is written as qn(x) = mqx + Cqn. In a similar way, for semi-minor axis of any ellipse of a crossbar, Eq. (7) can be written in general form as given below:
During the installation of a Scheffler reflector, the axis of rotation is set equal to the latitude of the project area. In this way, the axis of rotation of the reflector and polar axis become parallel to each other as shown in Fig. 4. Scheffler reflector undergoes daily and seasonal tracking. In daily tracking, the reflector rotates along a line parallel to the polar axis at one revolution per day (angular velocity) to counter balance the effect of earth rotation. Photovoltaic (PV) tracking device is used to rotate the reflector by solar energy. In this PV tracking system, four small photovoltaic panels (each having 0.5 v, 300 mA) are pasted on two Vshaped aluminum plates (two on either side) and covered by cylindrical glass. This glass behaves like a lens and produces concentrated line image for precise tracking. DC
(0, 1.37000) (-0.48, 1.32460)
(0.48, 1.32460)
(-0.96, 1.17798)
(0.96, 1.17798)
(-1.44, 0.88090)
(1.44, 0.88090)
(0,0) q1
q2
q3
q4
0.44 m
0.48 m
0.48 m
0.48 m
q5
q6
q7
(-1.88, 0)
(1.88, 0) 0.48 m 0.48 m
0.48 m
0.44 m
a
b
(1.44, -0.88090)
(-1.44, -0.88090) (-0.96, -1.17798)
(0.96, -1.17798)
(-0.48, -1.32460) (0.48, -1.32460) (0, -1.37000)
Fig. 3. Details of intersection points of seven crossbars (q1 to q7) on elliptical reflector frame for 8 m2 Scheffler reflector.
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Table 1 Equations, semi-minor and semi-major axes of different crossbars of Scheffler reflector used solar distillery. Crossbar “n”
Y-intercept “Cqn” (m)
Equation of cutting section of crossbars on xyplane
Semi-minor axis “aqn” (m)
Semi-major axis “bqn” (m)
1 2 3 4 5 6 7
2.35683 3.05763 3.75843 4.45923 5.16003 5.86083 6.56163
q1(x) = 1.06377 q2(x) = 1.06377 q3(x) = 1.06377 q4(x) = 1.06377 q5(x) = 1.06377 q6(x) = 1.06377 q7(x) = 1.06377
4.77516 5.17870 5.55299 5.90360 6.23452 6.54874 6.84855
6.97176 7.56093 8.10740 8.61929 9.10244 9.56120 9.99892
x + 2.35683 x + 3.05763 x + 3.75843 x + 4.45923 x + 5.16003 x + 5.86083 x + 6.56163
Table 2 Depths and lengths of different arcs of the crossbars for 8 m2 Scheffler reflector. Crossbar “n”
Yn (m)
Depth “Dn” (m)
Radius “Rn” (m)
Angle “ßn” (degree)
Half arc length “bn/2”(m)
Arc length “bn”(m)
1 2 3 4 5 6 7
0.88090 1.17798 1.32460 1.37000 1.32460 1.17798 0.88090
0.11965 0.19820 0.23403 0.23529 0.20781 0.15595 0.08305
3.30255 3.59969 3.86552 4.10612 4.32536 4.52695 4.71331
15.46997 19.10163 20.03966 19.49036 17.83280 15.08281 10.77170
0.89169 1.20008 1.35199 1.39678 1.34623 1.19169 0.88611
1.78338 2.40016 2.70398 2.79356 2.69246 2.38338 1.77222
Fig. 4. Installation details of a Scheffler reflector.
motor was employed to track the reflector and is actuated as a result of current difference in PV plates which ultimately rotate the reflector very precisely at the required position. The structure of primary reflector is completely balanced and needs very low power to track the sun. In this way, the primary reflector rotates with the help of this motor by chain-sprocket mechanism to track the sun very precisely as shown in Fig. 5a. The seasonal tracking system comprises of telescopic clamps and three triangular pivot points at the reflector. Two pivot points “A” are attached with reflector frame while the third point B is attached on parabola curve (center bar). By applying forces on the telescopic clamps to
rotate the reflector at half the angle of the solar declination, it automatically induces the desired shape of the paraboloid in order to get the fixed focus throughout the year. In one year, total seasonal twist of the Scheffler reflector is 23.5° (half the solar declination = 47°). The complete structure of the Scheffler reflector is constructed as a flexible assembly to attain the desired shape. The detail of seasonal adjustment is shown in Fig. 5b. 2.4. Development of solar distillery The reflector is taken as a lateral part of a paraboloid and is equipped with daily tracking system to record the
A. Munir et al. / Solar Energy 108 (2014) 548–559 Photovoltaic panels (each panel 0.5 Volts, 300 m A) Cylindrical glass object
Resultant solar intensity
Differential current
Two way DC motor
Anticlockwise rotation
Sun displaced from central position
Fig. 5a. Schematic of photovoltaic daily tracking system.
fixed focus which can be used during various experiments. The solar distillery consists of a primary reflector, Aluminum profiles based secondary reflector, PV tracking sys-
553
tem, Stainless steel (SS) distillation still, counter current flow condenser (SS), Florentine vessels etc. The Aluminum profiles based secondary reflector is used to divert the direction of beam radiations upward which are absorbed by the bottom of distillation still. The distillation unit is fabricated of an SS material (2 mm thickness) having 1210 mm column height and 400 mm diameter. The upper part of the still is insulated with rockwool (100 mm thickness) to minimize heat losses during experiments. The distillation still is equipped with all necessary mountings and fittings like safety value, water level indicator, make up water line, drain valve etc. to run the distillation experiments successfully. In order to record this temperature, a high temperature thermocouple was fixed in an insulated metallic round plate to record available temperature at focus from the Scheffler reflector. Another thermocouple was used to record the water temperature inside the distillation still (point was located about 10 mm high from the bottom of the still). A data logger was used to record the data for continuous monitoring of the system during the experiments. Both water and steam distillations were carried out by the solar distillation system. A counter current tubular type condenser was used to condense the steam. The schematic of solar based distillery is shown in Fig. 6. Three types of Florentine flasks/oil separator were used to separate the oil from water depending upon the experiments performed as shown in Fig. 7. Florentine/Separator
Fig. 5b. Layout of seasonal tracking.
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Type S-1 is used when the specific gravity (SG) of oils is less than 1, Type S-2 is used for specific gravity greater than 1 and Type S-3 when the specific gravity of the products is not known and it automatically settles down in the bottom part or floats up in the upper part (in the dotted portion). Most of the experiments were conducted using Florentine of Type S1 as most of the essential oils are lighter than water.
cw is the specific heat of water, ms is the quantity of steam produced, hfg is the latent heat of vaporization (2260 kJ kg1 for water), cf is the heat capacity of fiber, x is the steam dryness fraction and is calculated using a barrel calorimeter. During small intervals, the performance evaluation of the solar distillery can be carried out by re-writing the above expression as follows:
2.5. Performance of solar distillery Ep ¼ C1 The efficiency of solar distillery is calculated using Eq. (11) 3
System efficiencyðg%Þ ¼ R tp t¼0
10 Ep Gbave As dt
ð11Þ
100
where Ep is the total thermal energy during distillation, t is the time required during distillation process; Gbave is the beam radiation for t, As is the aperture area of reflector. The total thermal energy (Ep) during distillation of medicinal and aromatic plants in kW h can be calculated using following equation: Ep ¼
½ðmw þ M w mh Þcw þ mh ð1 M w Þcf DT þ xms hfg 3600
ð12Þ
where mw is mass of water in the distillation still (mw P 15 kg, volume equivalent to the bottom area of still exposed to radiation), Mw is the moisture content of medicinal plants (on wet basis), mh is the mass of herbs (medicinal and aromatic plants), DT is the temperature difference,
p X
DTi þ C2
i¼1
q X
ð13Þ
xj msj
j¼1
where C1 and C2 are constants for the particular batch during solar distillation experiments. The values of C1 and C2 are given as: ðmw þ M w mh Þcw þ mh ð1 M w Þcf 3600 hfg C2 ¼ 3600 C1 ¼
ð14Þ ð15Þ
(C2 = 0.62777 at atmospheric pressure). The first part of Eq. (13) provides the sum of total sensible heat (taken in small time intervals from the start of the experiment to the boiling point “p”) and the second part provides sum of total latent heat (time is taken in small intervals starting from first interval to last interval of steam generation “q” where the distillation experiment is completed). In order to determine the average power for the solar distillery, following equation was used
Thermocouple (steam temperature)
Safety valve Photovoltaic tracking system
Axis of rotation
Barrel calorimeter Steam
51.3° Plant material
B
Distillation still Column height 1210 mm Diameter 400 mm
Condenser
Water level indicator
Computer
Water connections
Pyranometer
Reflector stand
Water Thermocouple (H.T) (Temperature at F)
F Essential oil
Telescopic clamp mechanism
Secondary reflector
Florentine flask Thermocouple (water temperature)
Primary reflector 8 m 2
Fig. 6. Schematic of solar distillation system.
Data logger
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Fig. 7. Florentine vessels/oil separators.
Ep tp
inside the solar still was significantly lower than the temperature at focus. This was due to the reason that the distillation experiments were performed under atmospheric conditions and the temperature in the still could not exceed beyond 100 °C. This temperature gradient offers an excellent opportunity to be used for different experiments by employing a solar based distillery. The temperature range recorded to be 300–450 °C at the focus. Moreover, the total thermal energy gained by water (sensible and latent heat) in this experiment was determined to be 9.136 kW h. The system efficiency was calculated to be 33.21% and the power was determined to be 1.548 kW at average beam radiation of 863 W m2 under the existing specification of the solar distillery. This efficiency figure includes all the optical and thermal losses in the solar distillery.
ð16Þ
where tP is the total process time of the experiment. A number of experiments were carried out to determine the efficiency of solar distillery. According to Funk (2000), the uncontrolled variables should be maintained in a certain range in order to reduce the impact of test conditions on the results. He suggested using water for the evaluation of cookers in terms of power. Performance evaluation of one sample experiment of solar based distillery using 20 kg of water on a sunny day (from 9:00 to 15:00 h) has been presented in Fig. 8. Fig. 8 shows the beam radiation, temperature at focus and the water temperature in the distillation still versus time. Fig. 8 also illustrates the temperature in the solar still remained constant during the constant range of beam radiation showing the profile accuracy of the reflector and crossbars as well as the effectiveness of installed solar tracking system. It is also evident from the figure that the temperature
3. Experimental results of solar distillery The solar based distillery for the essential oils extraction of medicinal and aromatic plants is shown in Fig. 9.
1000
1000
Temperature, °C
800
800 Beam radiations (max.)
600
Variation due to clouds 600
Temperature at Focus
400
400
Water temeperature (distillation still)
200
200
0 9:00
10:00
11:00
12:00
13:00
14:00
Time, h Fig. 8. Performance evaluation of solar distillation system.
0 15:00
Beam Radiations (max.), W m-2
P ave ¼
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The fresh herbs were easily available at farm level and were used for the solar distillation system. So, a number of experiments were performed by utilization different plant materials. All the necessary data regarding total thermal energy consumption for various medicinal and aromatic plants were recorded using thermocouples installed at the system. Quantity of hydrosol (kg) and essential oils extracted (ml) were recorded throughout the experiment. Beam radiation were recorded by using the Pyranometer at the Scheffler reflector. Temperatures at various points of the solar distillation system were also recorded. 3.1. Distillation experiments with medicinal and aromatic plants Three varieties of Peppermint were available to conduct the distillation experiments at the solar distillation experimental site. All the three varieties (Mentha Piperita L., Mentha spec. and Mentha spicata) were processed using
Boiler (for backup)
Distillation still
condenser Florentine vessel Primary reflector
PV tracking Pyranometer system Secondary reflector
Fig. 9. A photograph of solar distillery.
solar distillery and the process curves for all these varieties (10 kg weight on fresh weight basis) are shown in Fig. 10. Regression analysis was performed for oil extraction against total thermal energy and the best fitted regression model for all the experiments with peppermint was found to be sigmoid/logistic with three parameters. The reliability of the developed model was assessed by comparing the observed and predicted curves. The results have shown that the model fitted well with the observed data for different plant materials which are indicated by high values of regression coefficient (R2 = 0.9834–0.9916). Similar results were obtained from solar distillation of Peppermint. A number of experiments were carried out with all these three varieties of Peppermint (M. piperita L., Mentha spec., and M. spicala), a comparison of 10 kg batch on fresh weight basis is shown in Fig. 11. The mean values of essential oils extracted for M. Piperita L, Mentha Spec. and M. Spicala L. was found to be 20.07, 24.95 and 22.20 ml respectively. Their corresponding standard errors were found to be 0.4676, 1.6791, and 0.9338 respectively. Low values of standard errors indicate the consistency of the results. Research concluded that the Peppermint varieties (M. piperta L, Mentha spec., and M. spicala) can be successfully processed by using solar distillery. The solar distillery was operated for 10–12 h a day during summer season. About 18.58 kW h thermal energy was achieved from the solar distillery per day. For the processing of 10 kg batch, an average 3.5 kW h energy was consumed. In this way, about 4–5 batches were processed successfully using different kinds of plant materials with 10–20 kg per batch. The variation of thermal energy (kW h) for different plant materials to complete one batch is shown in Table 3. During summer, many distillation experiments with solar distillery and at laboratory scale were performed simultaneously using the same medicinal plant material
30
Essential oils extracted. ml
Essential oil extracted, ml
30
20
10 Mentha piperita L. Mentha spec. Mentha spicata L. Regression line
20
10
0
0 0
2
4
6
8
Total thermal energy, kWh Fig. 10. Process curves of Peppermint varieties (Mentha piperita L., Mentha spec., and Mentha spicala) for 10 kg batch (Fresh weight basis).
Mentha Piperita L Mentha spec. Mentha spicata L.
Pepperrmint varieties Fig. 11. Comparison of Peppermint varieties (Mentha Piperita L., Mentha spec., and Mentha Spicala) (10 kg batch, fresh weight basis).
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Table 3 Total thermal energy consumed and essential oil extracted during solar distillation of different plant material. Plant material
Part used
Weight (kg)
Moistures contents (w.b) (%)
Total thermal energy (kW h)
Essential oil extracted (ml)
Melissa Peppermint Rosemary Cumin Cloves
Leaves Leaves Leaves Seeds Buds
11.6 9.1 3.0 1.2 0.8
78 74 72 9 11
3.868 3.180 4.626 8.910 7.744
1.425 28.2 4.6 12.4 44
Table 4 Comparison of laboratory and solar distilled essential oils of different medicinal and aromatic plants.
Melissa Peppermint Rosemary Cumin Cloves
Part used
Leaves Leaves Leaves Seeds Buds
M.C (w.b) (%)
78 74 72 9 11
Weight (kg)
Essential oil extracted (ml)
Essential oil per unit d.m (ml kg1)
Lab
Solar
Lab
Solar
Lab
Solar
200 100 100 100 100
11.6 9.1 3.0 1.2 0.8
0.027 0.324 0.162 1.081 5.500
1.425 28.20 4.60 12.40 44.00
0.614 12.462 5.786 11.879 61.798
0.558 11.918 5.476 11.355 61.798
for comparison. The laboratory distillation unit comprises of a glass boiler (2 L capacity), glass still, a condenser and glass Florentine flasks (oil tube of Florentine flasks were graduated to measure 1/40 mm of oil), an electric oven and energy meter. For Peppermint, Rosemary, Cloves and Cumin, 100 g of the plant material was used and for Melissa 200 g for Melissa was used (as it has very low contents of oils and was difficult to measure with existing apparatus). Medicinal and aromatic plants like Melissa, Peppermint, Rosemary, Cumin and Cloves having different weights and moisture contents were used to conduct experiments of solar based distillery. Necessary data regarding the quantity of essential oils extracted per unit dry matter (d.m.) were recorded for each experiment. Different plant materials resulted different amounts of oil extraction per unit dry matter. The comparison of laboratory and solar distilled experiments for different medicinal and aromatic plants are shown in the following Table 4. The results depict that the essential oils extracted using solar distillery were comparable to that of laboratory experiments. This concludes that the solar distillery based on Scheffler reflector can be successfully utilized for the processing of medicinal and aromatic plants. The percentage of oil extracted during field experiments with different plants (Cloves, Cumin, Melissa, Peppermint, Rosemary) have been shown in Fig. 12. The results have shown that fresh plant materials require lower input energy as compared to dry plant materials. Therefore, it provides excellent opportunity to process more batches by on-farm processing for the benefits of stakeholders. Best statistical model during the processing of medicinal plants was found to be sigmoid curve. The results in terms of extraction rates are shown in Fig. 13. These results show that the higher oil extraction rates at the start of the distillation process and lower extraction
Thermal energy used (solar) (kW h)
3.868 3.180 4.626 8.910 7.744
100
80
Oil extracted, %
Plant material
60
40 Cloves Cumin Melissa Peppermint Rosemary Regression line
20
0 2
4
6
8
Total thermal energy, kWh Fig. 12. Process curves of different plant material during solar distillation.
rates toward the end of the process. It is concluded that different kind of medicinal and aromatic plants can be processed successfully by employing solar distillery. 3.2. Cost analysis The investment cost for the development of Scheffler reflector and its accessories was 2000 US $. The cost of the complete distillation system (distillation still along with water level indicators, counter current condenser, Florentine vessel) was 1500 US $. The cost analysis of solar distillation was carried out and payback period of solar distillation system in terms of essential oils produced was calculated. The break-even point (BEP) is the point at which cost or expenses and revenue are equal: there is no net loss or gain, and one has “broken even”. A profit or a loss has not been made, although opportunity costs have been “paid”, and
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Essential oils extracted, ml
50
40
30
20 Cloves Cumin
10
Melissa Peppermint Rosemarie
0 0
50
100
150
200
250
300
350
400
450
500
Distillate starting time , Minutes Fig. 13. Essential oils extraction rates of different medicinal and aromatic plants.
1500 1000 500 3200
3000
2800
2600
2200
2400
1800
2000
1600
1400
1200
1000
0 800
where, TR is the total revenue, P is the cost per h, TFC is the total fixed cost and TC is the total cost. In this study citrus peels were used for the extraction of essential oils, the average yield of fresh and fermented citrus peels essential oils for one batch was 17.8 ml and time required for the completion of extraction was about 4 h. In one day two batches of experiment could be run easily. Therefore total oil yield in a day (8 h) was 35.6 ml and price of 10 ml citrus peels essential oil using conventional energy resources was 2.50 US $ (Amazon.com: Sweet orange 100% pure).
2000
600
TFC P V
Income
2500
400
X ¼
Cost
3000
0
P X ¼ TFC þ V X
fixed cost
3500
200
TR ¼ TC
4000
Revenue & Cost, US $
capital has received the risk-adjusted, expected return. In short, all costs that need to be paid are paid but the profit is equal to 0.
Time, h Fig. 14. Break even analysis.
breakeven point show that payback period of solar distillation system is 2336 h which is equal to 0.799 year. After completion of payback period system will run free of cost. 4. Conclusions
10 ml of citrus peel essential oil = 2.50 US $. 1 ml of citrus peel essential oil = 0.25 US $. 35.6 ml of citrus peel essential oil = 8.90 US $. As 35.6 ml oil could be attained from 8 h working of solar distillation system and price of essential oil was 8.90 US $. Therefore earning from 1 h would be 1.1125 US $. The break even analysis of solar distillery is shown in Fig. 14. 427 1:1125 0:9297 X ¼ 2335:886 h: X ¼
In its simplest form, the break-even analysis is a graphical representation of costs at various levels of activity shown on the same chart as the variation of income (or sales, revenue) with the same variation in activity. The point at which neither profit nor loss is made is known as the “break-even point” and is represented on the chart below by the intersection of the two lines. The value of
In this paper, the development and experimental results of a solar distillery using 8 m2 Scheffler reflector have been presented for the processing of medicinal plants. The results conclude that the high temperature at the fixed focus (300–450 °C) was capable of maintaining the required constant temperature inside the distillation still for continuous processing of the medicinal and aromatic plants. This shows the profile accuracy of the reflector and crossbars as well as the effectiveness of installed solar tracking system for solar based distillery. The average power and efficiency of the solar distillation system was calculated to be 1.548 kW and 33.21% respectively. The solar distillation system was operated for 10–12 h a day during summer. About 18.58 kW h thermal energy was obtained from the solar distillery in a sunny day. For the processing of 10 kg batch, an average 3.5 kW h energy was consumed. In this way, about 4–5 batches were processed successfully using different kinds of plant materials with 10–20 kg per batch. The research concluded that different kind of
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medicinal and aromatic plants could be processed successfully using solar distillery. The cost analysis of solar distillation was carried out and payback period of solar distillation system in terms of essential oils produced was calculated to be 2336 sunny hours. Acknowledgement The authors would like to thank “International Center for Development and Decent Work (ICDD)” and “German Academic Exchange Service (DAAD)” Germany for financing the research project entitled “Value Addition to Agricultural Products using Solar Energy”. References Bertrand, G.L., Tchanche, F., Frangoudakis, A., Papadakis, G., 2011. Low-grade heat conversion into power using organic Rankine cycles – a review of various applications. Renew. Sustain. Energy Rev. 15, 3963–3979. Bhirud, N., Tandale, M.S. 2006. Field evaluation of a fixed-focus concentrators for industrial oven, Advances in Energy Research (AER – 2006). In: Proceedings of the 1st National Conference on Advances in Energy Research, Mumbai, Macmillan India, December 2006. Calise, F., Capuozzo, C., Carotenuto, A., Vanoli, L., 2014. Thermoeconomic analysis and off-design performance of an organic Rankine cycle powered by medium-temperature heat sources. Sol. Energy 103, 595–609. Essandu-Yeddu, J.J., 1993. Prospects for using solar energy power systems to meet energy requirements of agricultural facilities located in remote areas. In: Proceeding of National Energy Symposium 93, vol. 5, 1993. Funk, P.A., 2000. Evaluating the international standard procedure for testing solar cookers and reporting performance. Sol. Energy 68, 1–7.
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Govind, N.K., Shireesh, B.K., Santanu, B., 2008. Design of solar thermal systems utilizing pressurized hot water storage for industrial applications. Sol. Energy 82, 686–699. Jayasimha, B.K., 2006. Application of Scheffler reflectors for process industry. In: International Solar Cooker Conference 2006 in Granada, Spain. Jenkins, N., 1995. Photovoltaic systems for small-scale remote power supplies. Power Eng. J. 9, 89–96. Kalogirou, S., 2003. Potential of solar industrial process heat applications. Appl. Energy 76, 337–361. Kumar, N.S., Reddy, K.S., 2007. Numerical investigation of natural convection heat loss in modified cavity receiver for fuzzy focal solar dish concentrator. Sol. Energy (Elsevier) 81, 846–855. Liu, Z., Lapp, J., Lipinski, W., 2012. Optical design of a flat-facet solar concentrator. Sol. Energy 86, 1962–1966. ¨ therische o¨le selbst herstellen, Verlag die Malle, B., Schmickl, H. 2005. A Werkstatt GmbH Lotzestraße 24 a, D- 37083 Go¨ttingen, pp. 23–27. Munir, A., Hensel, O., 2010. On-farm processing of medicinal and aromatic plants by solar distillation system. Biosyst. Eng. (Elsevier) 106 (3), 268–277, ISSN 1537 5110. Munir, A., Hensel, O., Scheffler, W., 2010. Design principle and calculations of a Scheffler fixed focus concentrator for medium temperature applications. Sol. Energy (Elsevier) 84 (8), 1490–1502, ISSN: 0038-092X. Okoro, O.I., Madueme, T.C., 2004. Solar energy investments in a developing economy. Renew. Energy 2, 1599–1610. Oparaku, O.U., Iloeje, O.C., 1991. Design considerations for a photovoltaic-powered water-pumping facility in a rural village near Nsukka. Nigerian J. Renew. Energy 10, 64–69. ¨ ztekin, S., Martinov, M. 2007. Medicinal and Aromatic Crops, O Harvesting, Drying and Processing, Haworth Food & Agricultural Products PressTM, An Imprint of the Haworth Press Inc, 10 Alice Street, Binhamton, New York, 13904–1580, USA. Scheffler, W., 2006. Introduction to the revolutionary design of Scheffler. In: SCIs International Solar Cooker Conference, Granada, Spain.
ScienceDirect Solar Energy 108 (2014) 548–559 www.elsevier.com/locate/solener
Design, development and experimental results of a solar distillery for the essential oils extraction from medicinal and aromatic plants Anjum Munir a,b,⇑, Oliver Hensel b, Wolfgang Scheffler c, Heike Hoedt c, Waseem Amjad b, Abdul Ghafoor a b
a Faculty of Agricultural Engineering, University of Agriculture, Faisalabad, Pakistan Department of Agricultural Engineering, University of Kassel, D-37213 Witzenhausen, Germany c Solar Bruecke, G.v.Werdenbergstr.6, D-89344 Aislingen, Germany
Received 30 September 2013; received in revised form 13 June 2014; accepted 28 July 2014 Available online 3 September 2014 Communicated by: Associate Editor I. Farkas
Abstract Distillation of medicinal and aromatic plants for essential oils extraction can be done by utilizing heat in medium temperature range. These essential oils are used in foods, medicines and cosmetics etc. and are money earning business for the farming community. This research is focused to develop an on-farm solar distillery for the processing of different plant materials. The system comprises of a Scheffler reflector and a complete set of distillation system. An 8 m2 ‘projected area of the Scheffler solar concentrator was coupled with the distillation still for the extraction of essential oils. In this paper, a complete mathematical description has been explained to design different components of solar distillation system. In order to provide a fixed focus on a receiver from morning to evening and in summer and winter, flexible crossbars have been used to achieve the desired shapes of the reflector. The paper also covers all the details regarding design, development, site specific installation and tracking system etc. Different types of Florentine apparatuses were used to separate the essential oils from the hydrosol. Necessary instrumentation was used for the performance evaluation of solar distillery. The system was capable of producing 300–450 °C temperature at the receiver section within the beam radiation range of 800–850 W m2. The efficiency of solar distillery was calculated to be 33.21% with 1.548 kW thermal power available for processing in the distillation still. The system was operated for 10–12 h a day during summer. About 18.58 kW h thermal energy was obtained from the solar distillery in a sunny day. For the processing of 10 kg batch, an average 3.5 kW h energy was consumed. In this way, about 4–5 batches were processed successfully using different kinds of plant materials with 10–20 kg per batch. The research concluded that different kind of medicinal and aromatic plants could be processed effectively using solar distillery. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: Solar distillery; Essential oils; Scheffler reflector; Crossbars; Thermal energy
1. Introduction In the last decades, the increasing energy crisis in developing countries and climate change hazards has created awareness to promote the renewable energy technologies. ⇑ Corresponding author at: Faculty of Agricultural Engineering, University of Agriculture, Faisalabad, Pakistan. E-mail address: [email protected] (A. Munir).
http://dx.doi.org/10.1016/j.solener.2014.07.028 0038-092X/Ó 2014 Elsevier Ltd. All rights reserved.
As a result, the technologies devoted to the utilization of medium temperature heat sources have been evolving. (Bertrand et al., 2011; Calise et al., 2014). Moreover, fossil fuels are depleting at a very fast rate due to increase in population and industrial development (Okoro and Madueme, 2004). There are many fields which can be run using solar energy. Sterilization of medicinal equipment, extraction of oil, milk pasteurization, dehydration, solar cooling and
A. Munir et al. / Solar Energy 108 (2014) 548–559
distillation etc. can be successfully carried out using solar energy (Kalogirou, 2003; Govind et al., 2008; Liu et al., 2012). In the field of agriculture, solar energy can be successfully used as most of the agricultural processing take place in medium temperature range. Presently, solar energy utilization in agriculture sector is limited only to lower range temperature applications. But there are different types of processing that can also be carried out in medium to high temperature range. Solar heating for dairy applications and micro-irrigation are the dominant areas of solar energy utilization in the field of agriculture (Oparaku and Iloeje, 1991; Jenkins 1995; Essandu-Yeddu 1993). By using solar energy, small scale agro-based industries can be promoted at farm level which can improve the farmer’s living standard in developing countries. Essential oils are used for the medicinal and other food ¨ ztekin and applications and these oils are very expensive (O Martinov, 2007). Industrialized countries have been using the essential oils since long for the aromatherapy business. There are several extraction methods for the essential oil extraction but out of all the methods, the distillation method is the best method which is used to extract the pure essence of the plant material by evaporation process (Malle and Schmickl, 2005). Presently, the essential oils are extracted in big distillation plants which are situated in the big cities. These distillation plants are very expensive and small farmers cannot afford these distillation units to process their own medicinal plants. If we process the fresh plant material, then not only more oil contents can be achieved but also a lot of money can be saved under the heading of transportation expenses. For rural development, a decentralized distillation system is required. The solar distillation at farm level can enhance the oil extraction by using the fresher plant materials. Examples of the plants are Peppermint, Lemon Balm (Melissa), Lavender, Cumin, Cloves, Anise, Rosemary, Patchouli, Caraway, Cassia, Oregano, European Silver Fir, and Fennel etc. It has been noticed that the Scheffler reflector is a better design when compared with different solar concentrators. Scheffler reflectors provide temperature in the medium temperature range and different processing can be carried out successfully by using this technology (Bhirud and Tandale, 2006). Scheffler (2006) described that about 50% of the sun energy could be used for cooking applications. The payback period of Scheffler reflector is almost two years when they are used daily (Jayasimha, 2006). In Scheffler reflectors, the vessel is placed at the focus to utilize the thermal energy of the sun. The receiver absorbs all the reflected beam radiation and transfers them to fluid in the form of heat with minimum losses (Kumar and Reddy, 2007; Munir and Hensel, 2010). At present, solar energy is successfully utilized for cooking applications and steam generation. Extraction of essential oils using solar energy is a new research area in postharvest sector. This study was conducted for development and experimental performance a solar distillery for the processing of medicinal plants.
549
2. Mathematical calculation and design detail of a Scheffler reflector The paper is about the design and development of a solar distillery based on the Scheffler reflector technology and is detailed below. In Scheffler reflector, equinox position is considered as the standard for design purpose. If the reflector is considered from the side view, paraboloid is seen like a parabola curve and reflector frame looks like a straight line. The general equation of a parabola can be written as: P ðxÞ ¼ mp x2 þ C p
ð1Þ
Differentiating Eq. (1) for the slope 0
P ðxÞ ¼ 2mp x
ð2Þ
We commence from a point Pn of the parabola curve where a beam radiation is reflected at right angle as detailed in Fig. 1. At this point, the tangent is drawn at 45° angle. In this way, the value of y-coordinate is half as compared to the xcoordinate. The study is based on two aims, first is to construct a Scheffler reflector having 8 m2 area, secondly there should be a balanced reflector. For the achievement of these two aims, the following procedure is adopted (Munir et al., 2010). First of all, we have to select x-coordinate of the point Pn(xP) in such a way that a reasonable distance from the focal point can be obtained; then calculate the y-coordinate of the same point and slope mP using Eqs. (1) and (2). Then we have to select xE1 and xE2 for the construction of 8 m2 Scheffler reflector having balanced structure. From these points, we can calculate yE1, yE2 and angle of reflector frame. As the reflector stand is elliptical in shape with semiminor axis as 1.36990 m and semi-major axis as 1.88016 m. The formula for the ellipse is p times minimum
E2
90°
Tangent at Pn 45° Pn(2.86575, 1.433287)
E1 43.23° O(0,0)
XE1 = 1.32387
XE2 = 4.06387
Fig. 1. Detail of Scheffler parabola curve.
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radius (semi-minor axis) and maximum radius (semi-major axis). The semi-minor and semi-major axes for this ellipse were taken as 1.44 and 1.88016 m respectively. In this way, the ‘projected area of Scheffler concentrator was calculated to be 8.09 m2. Now we have to check whether our required aims are achieved or not, otherwise we have to select new set of Pn, E1 and E2. At the end, both axes of the reflector are calculated. We take x-coordinate of point Pn (xP) as 2.86575 for the given 8 m2 Scheffler reflector. All calculations are based on the point Pn with x-coordinate as 2.86575. Actually, this coordinate delineates the distance between the focal point and this point. A value is chosen in order to keep this distance smaller but at the same time still leaves some space between inner edge of the reflector and the focus, thus preventing shading of the structure or building that normally found around the focus of the reflector. This is the reason that the point Pn with higher x-coordinate is required for higher projected area of the Scheffler reflector. It is clear from Fig. 1 that the tangent at point Pn makes an angle 45° with x-axis. If we differentiate this equation, the answer is unity. In a parabola equation, the y-coordinate is half of the x-coordinate i.e. 1.43287. The values for mp and Cp were calculated using Eqs. (1) and (2) and found to be 0.17447 and 0 respectively. As the Scheffler reflector is designed for equinox position, so the parabola equation for this position is as follows: P ðxÞ ¼ 0:17447x2
ð3Þ
Two points (xE1 and xE2) are selected as 1.32387 and 4.06387 on a graph so that a balanced reflector can be constructed. In fact, these two points were selected to make an 8 m2 Scheffler reflector e.g., the difference of these x-coordinates is 2.74 by subtracting second x-coordinate xE2 (1.32387) from first x-coordinate xE1 (4.06387). This distance will be the diameter of the projection of the ellipse formed on the horizontal plan. It represents the minor axis of the elliptical frame of the Scheffler reflector. The major axis is calculated by dividing this semi-minor axis by cos 43.23 which is equal to 3.76058. Later, recalculating these points with respect to the angle is necessary to crosscheck all numbers. The line E1E2 denotes the cutting section of the elliptical shaped frame on the parabola curve of the Scheffler reflector and this line makes 43.23° angle with x-axis as shown in Fig. 1. In this way, the straight line equation formed is given below: GðxÞ ¼ mg x þ C g
ð4Þ
Taking first derivative of Eq. (4) and by considering the angle of straight line (43.23°), the slope mg is determined as 0.94. We select x-coordinate of point E1 as 1.32387 and calculate y-coordinate and found to be 0.31. By putting the values of x, y and mg in Eq. (4), the y-intercept (Cg) can be calculated as 0.94 and the straight line equation is given as: GðxÞ ¼ 0:94x 0:93866
ð5Þ
The x-coordinate of point E2 (xE2) is calculated by using Eqs. (1) and (2), the quadratic equation formed in general form is given below: mg Cp Cg 2 xþ x ¼0 ð6Þ mp mp Two points of intersection (xE1 and xE2) of the parabola curve and straight line are obtained by solving Eq. (6) using quadratic equation. The line that cuts the curve represents the ellipse cutting plane having axes ratio as a/b = cos a, where “a” and “b” represents the semi-minor and semimajor axes respectively. The ellipse so formed makes circle on the horizontal plane. So, the radius of this circle becomes equal to the length of the semi-minor axis of the ellipse. A circle is formed if the projection of the ellipse is drawn on horizontal plane which is equal to 2a. In this way, the diameter of circle (2a) is determined by the following relation: sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 mg Cp Cg 2a ¼ ð2Þ ð7Þ 2mp mp The semi-minor and semi-major axes of the ellipse are calculated to be 1.37000 m and 1.88029 m respectively. For an 8 m2 Scheffler reflector, seven crossbars are used for the construction of required section of a paraboloid. The crossbars are fixed at ±0.48 m, ±0.96 m, ±1.44 m from the center of the reflector along major axis and on the minor axis, the respective points are selected as ±1.3246 m, ±1.17798 m and ±0.8809 m respectively. These points are clear on the frame of the reflector after the construction work. 2.1. Determination of ellipses for the crossbars The cutting planes of the crossbars are perpendicular to the cutting plane of the reflector frame and are represented by seven straight lines (q1 to q7) in Fig. 2. The cutting planes of crossbars make an angle 46.77° and these cutting lines represent ellipses as shown in Fig. 2. The middle crossbar equation is given below: q4 ðxÞ ¼ mq4 x þ C q4
ð8Þ
Middle crossbar slope is calculated by taking tan (46.77), x-coordinate of the point of intersection (Cf) which is the midpoint of xE1 and xE2 .The y-coordinate is determined by putting this value of x in Eq. (8) and is found to be 1.59357. Substituting the values of mq4, q4(x) and x in Eq. (8), the y-intercept (Cq4) for the central crossbar is calculated. The crossbar equation (q4) of the central crossbar for an 8 m2 reflector projected area is given in Eq. (9): q4 ðxÞ ¼ 1:06377x þ 4:45923
ð9Þ
All the crossbars are at right angles to the cutting section of the Scheffler concentrator, so all the crossbars have the same slopes. Referring Fig. 2, 0.48 m is the difference
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sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi 2 mqn C p C qn aqn ¼ 2mp mp
Projection of cross bar (middle)
Projection of Scheffler frame (aperture area)
ð10Þ
where “n” denotes the number of crossbar of the ellipse. 2.2. Calculation of required parameters for the development of Scheffler reflector
q7 q6
Table 1 shows parameters calculated for the preparation of the required crossbars of the Scheffler reflector. Using above calculations, the depths (Dn)and lengths of arcs (bn) for seven crossbars have been determined to construct the Scheffler reflector using simple trigonometric equations and are given in Table 2 (Munir et al., 2010). With the help of Table 2, crossbars are prepared to form the Scheffler reflector and are welded on the marked points of the Scheffler reflector frame. A jig was used to check the accuracy of the bent crossbars. Aluminum profiles were used to provide base for the Aluminum reflecting sheets to shape it lateral part of the paraboloid.
q5 q4
1.37
1.37
q3 q2 q1
0.70080 0.48
Cf (2.69387,1.59357)
Cf Pc
46.77°
43.23°
Fig. 2. Description of parabola curve and crossbars for 8 m2 Scheffler reflector.
2.3. Installing and tracking of Scheffler concentrator between two consecutive crossbars along the reflector frame which looks like a straight line in the side view. As the crossbars are inclined at 46.77° (90–43.23°) with x-axis (on drawing), the distance between two consecutive crossbars along the axis of parabola is calculated to be 0.70080 m by dividing 0.48 m with cos 46.77°. Other crossbar equations are calculated by adding and subtracting 0.70080 m from the adjacent equation as shown in Fig. 3. The coordinates shown in Fig. 3 are relative to the center of the reflector, not the absolute coordinate. The general equation for the crossbars is written as qn(x) = mqx + Cqn. In a similar way, for semi-minor axis of any ellipse of a crossbar, Eq. (7) can be written in general form as given below:
During the installation of a Scheffler reflector, the axis of rotation is set equal to the latitude of the project area. In this way, the axis of rotation of the reflector and polar axis become parallel to each other as shown in Fig. 4. Scheffler reflector undergoes daily and seasonal tracking. In daily tracking, the reflector rotates along a line parallel to the polar axis at one revolution per day (angular velocity) to counter balance the effect of earth rotation. Photovoltaic (PV) tracking device is used to rotate the reflector by solar energy. In this PV tracking system, four small photovoltaic panels (each having 0.5 v, 300 mA) are pasted on two Vshaped aluminum plates (two on either side) and covered by cylindrical glass. This glass behaves like a lens and produces concentrated line image for precise tracking. DC
(0, 1.37000) (-0.48, 1.32460)
(0.48, 1.32460)
(-0.96, 1.17798)
(0.96, 1.17798)
(-1.44, 0.88090)
(1.44, 0.88090)
(0,0) q1
q2
q3
q4
0.44 m
0.48 m
0.48 m
0.48 m
q5
q6
q7
(-1.88, 0)
(1.88, 0) 0.48 m 0.48 m
0.48 m
0.44 m
a
b
(1.44, -0.88090)
(-1.44, -0.88090) (-0.96, -1.17798)
(0.96, -1.17798)
(-0.48, -1.32460) (0.48, -1.32460) (0, -1.37000)
Fig. 3. Details of intersection points of seven crossbars (q1 to q7) on elliptical reflector frame for 8 m2 Scheffler reflector.
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Table 1 Equations, semi-minor and semi-major axes of different crossbars of Scheffler reflector used solar distillery. Crossbar “n”
Y-intercept “Cqn” (m)
Equation of cutting section of crossbars on xyplane
Semi-minor axis “aqn” (m)
Semi-major axis “bqn” (m)
1 2 3 4 5 6 7
2.35683 3.05763 3.75843 4.45923 5.16003 5.86083 6.56163
q1(x) = 1.06377 q2(x) = 1.06377 q3(x) = 1.06377 q4(x) = 1.06377 q5(x) = 1.06377 q6(x) = 1.06377 q7(x) = 1.06377
4.77516 5.17870 5.55299 5.90360 6.23452 6.54874 6.84855
6.97176 7.56093 8.10740 8.61929 9.10244 9.56120 9.99892
x + 2.35683 x + 3.05763 x + 3.75843 x + 4.45923 x + 5.16003 x + 5.86083 x + 6.56163
Table 2 Depths and lengths of different arcs of the crossbars for 8 m2 Scheffler reflector. Crossbar “n”
Yn (m)
Depth “Dn” (m)
Radius “Rn” (m)
Angle “ßn” (degree)
Half arc length “bn/2”(m)
Arc length “bn”(m)
1 2 3 4 5 6 7
0.88090 1.17798 1.32460 1.37000 1.32460 1.17798 0.88090
0.11965 0.19820 0.23403 0.23529 0.20781 0.15595 0.08305
3.30255 3.59969 3.86552 4.10612 4.32536 4.52695 4.71331
15.46997 19.10163 20.03966 19.49036 17.83280 15.08281 10.77170
0.89169 1.20008 1.35199 1.39678 1.34623 1.19169 0.88611
1.78338 2.40016 2.70398 2.79356 2.69246 2.38338 1.77222
Fig. 4. Installation details of a Scheffler reflector.
motor was employed to track the reflector and is actuated as a result of current difference in PV plates which ultimately rotate the reflector very precisely at the required position. The structure of primary reflector is completely balanced and needs very low power to track the sun. In this way, the primary reflector rotates with the help of this motor by chain-sprocket mechanism to track the sun very precisely as shown in Fig. 5a. The seasonal tracking system comprises of telescopic clamps and three triangular pivot points at the reflector. Two pivot points “A” are attached with reflector frame while the third point B is attached on parabola curve (center bar). By applying forces on the telescopic clamps to
rotate the reflector at half the angle of the solar declination, it automatically induces the desired shape of the paraboloid in order to get the fixed focus throughout the year. In one year, total seasonal twist of the Scheffler reflector is 23.5° (half the solar declination = 47°). The complete structure of the Scheffler reflector is constructed as a flexible assembly to attain the desired shape. The detail of seasonal adjustment is shown in Fig. 5b. 2.4. Development of solar distillery The reflector is taken as a lateral part of a paraboloid and is equipped with daily tracking system to record the
A. Munir et al. / Solar Energy 108 (2014) 548–559 Photovoltaic panels (each panel 0.5 Volts, 300 m A) Cylindrical glass object
Resultant solar intensity
Differential current
Two way DC motor
Anticlockwise rotation
Sun displaced from central position
Fig. 5a. Schematic of photovoltaic daily tracking system.
fixed focus which can be used during various experiments. The solar distillery consists of a primary reflector, Aluminum profiles based secondary reflector, PV tracking sys-
553
tem, Stainless steel (SS) distillation still, counter current flow condenser (SS), Florentine vessels etc. The Aluminum profiles based secondary reflector is used to divert the direction of beam radiations upward which are absorbed by the bottom of distillation still. The distillation unit is fabricated of an SS material (2 mm thickness) having 1210 mm column height and 400 mm diameter. The upper part of the still is insulated with rockwool (100 mm thickness) to minimize heat losses during experiments. The distillation still is equipped with all necessary mountings and fittings like safety value, water level indicator, make up water line, drain valve etc. to run the distillation experiments successfully. In order to record this temperature, a high temperature thermocouple was fixed in an insulated metallic round plate to record available temperature at focus from the Scheffler reflector. Another thermocouple was used to record the water temperature inside the distillation still (point was located about 10 mm high from the bottom of the still). A data logger was used to record the data for continuous monitoring of the system during the experiments. Both water and steam distillations were carried out by the solar distillation system. A counter current tubular type condenser was used to condense the steam. The schematic of solar based distillery is shown in Fig. 6. Three types of Florentine flasks/oil separator were used to separate the oil from water depending upon the experiments performed as shown in Fig. 7. Florentine/Separator
Fig. 5b. Layout of seasonal tracking.
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Type S-1 is used when the specific gravity (SG) of oils is less than 1, Type S-2 is used for specific gravity greater than 1 and Type S-3 when the specific gravity of the products is not known and it automatically settles down in the bottom part or floats up in the upper part (in the dotted portion). Most of the experiments were conducted using Florentine of Type S1 as most of the essential oils are lighter than water.
cw is the specific heat of water, ms is the quantity of steam produced, hfg is the latent heat of vaporization (2260 kJ kg1 for water), cf is the heat capacity of fiber, x is the steam dryness fraction and is calculated using a barrel calorimeter. During small intervals, the performance evaluation of the solar distillery can be carried out by re-writing the above expression as follows:
2.5. Performance of solar distillery Ep ¼ C1 The efficiency of solar distillery is calculated using Eq. (11) 3
System efficiencyðg%Þ ¼ R tp t¼0
10 Ep Gbave As dt
ð11Þ
100
where Ep is the total thermal energy during distillation, t is the time required during distillation process; Gbave is the beam radiation for t, As is the aperture area of reflector. The total thermal energy (Ep) during distillation of medicinal and aromatic plants in kW h can be calculated using following equation: Ep ¼
½ðmw þ M w mh Þcw þ mh ð1 M w Þcf DT þ xms hfg 3600
ð12Þ
where mw is mass of water in the distillation still (mw P 15 kg, volume equivalent to the bottom area of still exposed to radiation), Mw is the moisture content of medicinal plants (on wet basis), mh is the mass of herbs (medicinal and aromatic plants), DT is the temperature difference,
p X
DTi þ C2
i¼1
q X
ð13Þ
xj msj
j¼1
where C1 and C2 are constants for the particular batch during solar distillation experiments. The values of C1 and C2 are given as: ðmw þ M w mh Þcw þ mh ð1 M w Þcf 3600 hfg C2 ¼ 3600 C1 ¼
ð14Þ ð15Þ
(C2 = 0.62777 at atmospheric pressure). The first part of Eq. (13) provides the sum of total sensible heat (taken in small time intervals from the start of the experiment to the boiling point “p”) and the second part provides sum of total latent heat (time is taken in small intervals starting from first interval to last interval of steam generation “q” where the distillation experiment is completed). In order to determine the average power for the solar distillery, following equation was used
Thermocouple (steam temperature)
Safety valve Photovoltaic tracking system
Axis of rotation
Barrel calorimeter Steam
51.3° Plant material
B
Distillation still Column height 1210 mm Diameter 400 mm
Condenser
Water level indicator
Computer
Water connections
Pyranometer
Reflector stand
Water Thermocouple (H.T) (Temperature at F)
F Essential oil
Telescopic clamp mechanism
Secondary reflector
Florentine flask Thermocouple (water temperature)
Primary reflector 8 m 2
Fig. 6. Schematic of solar distillation system.
Data logger
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Fig. 7. Florentine vessels/oil separators.
Ep tp
inside the solar still was significantly lower than the temperature at focus. This was due to the reason that the distillation experiments were performed under atmospheric conditions and the temperature in the still could not exceed beyond 100 °C. This temperature gradient offers an excellent opportunity to be used for different experiments by employing a solar based distillery. The temperature range recorded to be 300–450 °C at the focus. Moreover, the total thermal energy gained by water (sensible and latent heat) in this experiment was determined to be 9.136 kW h. The system efficiency was calculated to be 33.21% and the power was determined to be 1.548 kW at average beam radiation of 863 W m2 under the existing specification of the solar distillery. This efficiency figure includes all the optical and thermal losses in the solar distillery.
ð16Þ
where tP is the total process time of the experiment. A number of experiments were carried out to determine the efficiency of solar distillery. According to Funk (2000), the uncontrolled variables should be maintained in a certain range in order to reduce the impact of test conditions on the results. He suggested using water for the evaluation of cookers in terms of power. Performance evaluation of one sample experiment of solar based distillery using 20 kg of water on a sunny day (from 9:00 to 15:00 h) has been presented in Fig. 8. Fig. 8 shows the beam radiation, temperature at focus and the water temperature in the distillation still versus time. Fig. 8 also illustrates the temperature in the solar still remained constant during the constant range of beam radiation showing the profile accuracy of the reflector and crossbars as well as the effectiveness of installed solar tracking system. It is also evident from the figure that the temperature
3. Experimental results of solar distillery The solar based distillery for the essential oils extraction of medicinal and aromatic plants is shown in Fig. 9.
1000
1000
Temperature, °C
800
800 Beam radiations (max.)
600
Variation due to clouds 600
Temperature at Focus
400
400
Water temeperature (distillation still)
200
200
0 9:00
10:00
11:00
12:00
13:00
14:00
Time, h Fig. 8. Performance evaluation of solar distillation system.
0 15:00
Beam Radiations (max.), W m-2
P ave ¼
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The fresh herbs were easily available at farm level and were used for the solar distillation system. So, a number of experiments were performed by utilization different plant materials. All the necessary data regarding total thermal energy consumption for various medicinal and aromatic plants were recorded using thermocouples installed at the system. Quantity of hydrosol (kg) and essential oils extracted (ml) were recorded throughout the experiment. Beam radiation were recorded by using the Pyranometer at the Scheffler reflector. Temperatures at various points of the solar distillation system were also recorded. 3.1. Distillation experiments with medicinal and aromatic plants Three varieties of Peppermint were available to conduct the distillation experiments at the solar distillation experimental site. All the three varieties (Mentha Piperita L., Mentha spec. and Mentha spicata) were processed using
Boiler (for backup)
Distillation still
condenser Florentine vessel Primary reflector
PV tracking Pyranometer system Secondary reflector
Fig. 9. A photograph of solar distillery.
solar distillery and the process curves for all these varieties (10 kg weight on fresh weight basis) are shown in Fig. 10. Regression analysis was performed for oil extraction against total thermal energy and the best fitted regression model for all the experiments with peppermint was found to be sigmoid/logistic with three parameters. The reliability of the developed model was assessed by comparing the observed and predicted curves. The results have shown that the model fitted well with the observed data for different plant materials which are indicated by high values of regression coefficient (R2 = 0.9834–0.9916). Similar results were obtained from solar distillation of Peppermint. A number of experiments were carried out with all these three varieties of Peppermint (M. piperita L., Mentha spec., and M. spicala), a comparison of 10 kg batch on fresh weight basis is shown in Fig. 11. The mean values of essential oils extracted for M. Piperita L, Mentha Spec. and M. Spicala L. was found to be 20.07, 24.95 and 22.20 ml respectively. Their corresponding standard errors were found to be 0.4676, 1.6791, and 0.9338 respectively. Low values of standard errors indicate the consistency of the results. Research concluded that the Peppermint varieties (M. piperta L, Mentha spec., and M. spicala) can be successfully processed by using solar distillery. The solar distillery was operated for 10–12 h a day during summer season. About 18.58 kW h thermal energy was achieved from the solar distillery per day. For the processing of 10 kg batch, an average 3.5 kW h energy was consumed. In this way, about 4–5 batches were processed successfully using different kinds of plant materials with 10–20 kg per batch. The variation of thermal energy (kW h) for different plant materials to complete one batch is shown in Table 3. During summer, many distillation experiments with solar distillery and at laboratory scale were performed simultaneously using the same medicinal plant material
30
Essential oils extracted. ml
Essential oil extracted, ml
30
20
10 Mentha piperita L. Mentha spec. Mentha spicata L. Regression line
20
10
0
0 0
2
4
6
8
Total thermal energy, kWh Fig. 10. Process curves of Peppermint varieties (Mentha piperita L., Mentha spec., and Mentha spicala) for 10 kg batch (Fresh weight basis).
Mentha Piperita L Mentha spec. Mentha spicata L.
Pepperrmint varieties Fig. 11. Comparison of Peppermint varieties (Mentha Piperita L., Mentha spec., and Mentha Spicala) (10 kg batch, fresh weight basis).
A. Munir et al. / Solar Energy 108 (2014) 548–559
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Table 3 Total thermal energy consumed and essential oil extracted during solar distillation of different plant material. Plant material
Part used
Weight (kg)
Moistures contents (w.b) (%)
Total thermal energy (kW h)
Essential oil extracted (ml)
Melissa Peppermint Rosemary Cumin Cloves
Leaves Leaves Leaves Seeds Buds
11.6 9.1 3.0 1.2 0.8
78 74 72 9 11
3.868 3.180 4.626 8.910 7.744
1.425 28.2 4.6 12.4 44
Table 4 Comparison of laboratory and solar distilled essential oils of different medicinal and aromatic plants.
Melissa Peppermint Rosemary Cumin Cloves
Part used
Leaves Leaves Leaves Seeds Buds
M.C (w.b) (%)
78 74 72 9 11
Weight (kg)
Essential oil extracted (ml)
Essential oil per unit d.m (ml kg1)
Lab
Solar
Lab
Solar
Lab
Solar
200 100 100 100 100
11.6 9.1 3.0 1.2 0.8
0.027 0.324 0.162 1.081 5.500
1.425 28.20 4.60 12.40 44.00
0.614 12.462 5.786 11.879 61.798
0.558 11.918 5.476 11.355 61.798
for comparison. The laboratory distillation unit comprises of a glass boiler (2 L capacity), glass still, a condenser and glass Florentine flasks (oil tube of Florentine flasks were graduated to measure 1/40 mm of oil), an electric oven and energy meter. For Peppermint, Rosemary, Cloves and Cumin, 100 g of the plant material was used and for Melissa 200 g for Melissa was used (as it has very low contents of oils and was difficult to measure with existing apparatus). Medicinal and aromatic plants like Melissa, Peppermint, Rosemary, Cumin and Cloves having different weights and moisture contents were used to conduct experiments of solar based distillery. Necessary data regarding the quantity of essential oils extracted per unit dry matter (d.m.) were recorded for each experiment. Different plant materials resulted different amounts of oil extraction per unit dry matter. The comparison of laboratory and solar distilled experiments for different medicinal and aromatic plants are shown in the following Table 4. The results depict that the essential oils extracted using solar distillery were comparable to that of laboratory experiments. This concludes that the solar distillery based on Scheffler reflector can be successfully utilized for the processing of medicinal and aromatic plants. The percentage of oil extracted during field experiments with different plants (Cloves, Cumin, Melissa, Peppermint, Rosemary) have been shown in Fig. 12. The results have shown that fresh plant materials require lower input energy as compared to dry plant materials. Therefore, it provides excellent opportunity to process more batches by on-farm processing for the benefits of stakeholders. Best statistical model during the processing of medicinal plants was found to be sigmoid curve. The results in terms of extraction rates are shown in Fig. 13. These results show that the higher oil extraction rates at the start of the distillation process and lower extraction
Thermal energy used (solar) (kW h)
3.868 3.180 4.626 8.910 7.744
100
80
Oil extracted, %
Plant material
60
40 Cloves Cumin Melissa Peppermint Rosemary Regression line
20
0 2
4
6
8
Total thermal energy, kWh Fig. 12. Process curves of different plant material during solar distillation.
rates toward the end of the process. It is concluded that different kind of medicinal and aromatic plants can be processed successfully by employing solar distillery. 3.2. Cost analysis The investment cost for the development of Scheffler reflector and its accessories was 2000 US $. The cost of the complete distillation system (distillation still along with water level indicators, counter current condenser, Florentine vessel) was 1500 US $. The cost analysis of solar distillation was carried out and payback period of solar distillation system in terms of essential oils produced was calculated. The break-even point (BEP) is the point at which cost or expenses and revenue are equal: there is no net loss or gain, and one has “broken even”. A profit or a loss has not been made, although opportunity costs have been “paid”, and
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Essential oils extracted, ml
50
40
30
20 Cloves Cumin
10
Melissa Peppermint Rosemarie
0 0
50
100
150
200
250
300
350
400
450
500
Distillate starting time , Minutes Fig. 13. Essential oils extraction rates of different medicinal and aromatic plants.
1500 1000 500 3200
3000
2800
2600
2200
2400
1800
2000
1600
1400
1200
1000
0 800
where, TR is the total revenue, P is the cost per h, TFC is the total fixed cost and TC is the total cost. In this study citrus peels were used for the extraction of essential oils, the average yield of fresh and fermented citrus peels essential oils for one batch was 17.8 ml and time required for the completion of extraction was about 4 h. In one day two batches of experiment could be run easily. Therefore total oil yield in a day (8 h) was 35.6 ml and price of 10 ml citrus peels essential oil using conventional energy resources was 2.50 US $ (Amazon.com: Sweet orange 100% pure).
2000
600
TFC P V
Income
2500
400
X ¼
Cost
3000
0
P X ¼ TFC þ V X
fixed cost
3500
200
TR ¼ TC
4000
Revenue & Cost, US $
capital has received the risk-adjusted, expected return. In short, all costs that need to be paid are paid but the profit is equal to 0.
Time, h Fig. 14. Break even analysis.
breakeven point show that payback period of solar distillation system is 2336 h which is equal to 0.799 year. After completion of payback period system will run free of cost. 4. Conclusions
10 ml of citrus peel essential oil = 2.50 US $. 1 ml of citrus peel essential oil = 0.25 US $. 35.6 ml of citrus peel essential oil = 8.90 US $. As 35.6 ml oil could be attained from 8 h working of solar distillation system and price of essential oil was 8.90 US $. Therefore earning from 1 h would be 1.1125 US $. The break even analysis of solar distillery is shown in Fig. 14. 427 1:1125 0:9297 X ¼ 2335:886 h: X ¼
In its simplest form, the break-even analysis is a graphical representation of costs at various levels of activity shown on the same chart as the variation of income (or sales, revenue) with the same variation in activity. The point at which neither profit nor loss is made is known as the “break-even point” and is represented on the chart below by the intersection of the two lines. The value of
In this paper, the development and experimental results of a solar distillery using 8 m2 Scheffler reflector have been presented for the processing of medicinal plants. The results conclude that the high temperature at the fixed focus (300–450 °C) was capable of maintaining the required constant temperature inside the distillation still for continuous processing of the medicinal and aromatic plants. This shows the profile accuracy of the reflector and crossbars as well as the effectiveness of installed solar tracking system for solar based distillery. The average power and efficiency of the solar distillation system was calculated to be 1.548 kW and 33.21% respectively. The solar distillation system was operated for 10–12 h a day during summer. About 18.58 kW h thermal energy was obtained from the solar distillery in a sunny day. For the processing of 10 kg batch, an average 3.5 kW h energy was consumed. In this way, about 4–5 batches were processed successfully using different kinds of plant materials with 10–20 kg per batch. The research concluded that different kind of
A. Munir et al. / Solar Energy 108 (2014) 548–559
medicinal and aromatic plants could be processed successfully using solar distillery. The cost analysis of solar distillation was carried out and payback period of solar distillation system in terms of essential oils produced was calculated to be 2336 sunny hours. Acknowledgement The authors would like to thank “International Center for Development and Decent Work (ICDD)” and “German Academic Exchange Service (DAAD)” Germany for financing the research project entitled “Value Addition to Agricultural Products using Solar Energy”. References Bertrand, G.L., Tchanche, F., Frangoudakis, A., Papadakis, G., 2011. Low-grade heat conversion into power using organic Rankine cycles – a review of various applications. Renew. Sustain. Energy Rev. 15, 3963–3979. Bhirud, N., Tandale, M.S. 2006. Field evaluation of a fixed-focus concentrators for industrial oven, Advances in Energy Research (AER – 2006). In: Proceedings of the 1st National Conference on Advances in Energy Research, Mumbai, Macmillan India, December 2006. Calise, F., Capuozzo, C., Carotenuto, A., Vanoli, L., 2014. Thermoeconomic analysis and off-design performance of an organic Rankine cycle powered by medium-temperature heat sources. Sol. Energy 103, 595–609. Essandu-Yeddu, J.J., 1993. Prospects for using solar energy power systems to meet energy requirements of agricultural facilities located in remote areas. In: Proceeding of National Energy Symposium 93, vol. 5, 1993. Funk, P.A., 2000. Evaluating the international standard procedure for testing solar cookers and reporting performance. Sol. Energy 68, 1–7.
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