Economic Analysis of Parabolic Solar Concentrator Based Distillation Unit

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Economic Analysis of Parabolic Solar Concentrator Based Distillation Unit Article ¡ July 2017 DOI: 10.5958/2322-0430.2017.00218.9

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Economic Analysis of Parabolic Solar Concentrator Based Distillation Unit Digvijay Singh1, A.K Singh2, S.P Singh1 and Surendra Poonia2* 1 2

School of Energy and Environmental Studies, Devi Ahilya University, Indore-452017 ICAR-Central Arid Zone and Research institute, Jodhpur- 342003

*Corresponding author's email: poonia.surendra@gmail.com Accepted: July 31, 2017

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ABSTRACT The experimental analysis revealed that the system was found suitable to overcome the problems of corrosion, salt scaling and algae. The system was able to provide 2.65 litre of distilled water per day for about 320 days per annum. The economic evaluation of the distillation unit revealed that high value of IRR (62.88 per cent) and low value of payback period (1.9 Years) make the unit very cost efficient. The economic attributes of the system revealed its economic viability. The system is useful for getting distilled water which can be used in batteries, laboratories. It can also be used for drinking by mixing with saline water in places where water quality is saline.

Keywords Agriculture, alternative energy sources, cost benefit ratio, life cycle cost, renewable resources JEL Codes D61, D91, Q15, Q25, Q42

INTRODUCTION Most of our earth surface is covered by water.

However, less than 1 per cent of total available water is fresh water which is mostly available in lakes, rivers and underground. Again, about one-third of that potential fresh water can only be used for human needs due to mixed factors. Approximately 1.1 billion people in this world have inadequate access to safe drinking water.

There are 26 countries which do not have enough water to maintain agriculture and economic developments. At least 80 per cent of arid and semi-arid countries have serious periodic droughts. A third of Africans and most of Middle-East people live without enough water (Bouchekima, 2003). The population growth -coupled with industrialization and urbanization results in an increasing demand for water. In India, the scarcity of desalinated water is severe in coastal areas, especially in the remote coastal areas. Renewable energy based desalination plants can solve this fresh water production problem without causing any fossil fuel depletion, hydrocarbon pollution and environmental degradation. In spite of the limitations of being a dilute source and intermittent in nature, solar energy has the potential for

meeting and supplementing various energy requirements.

Solar energy systems, being modular in nature, can be installed in any capacity.

Solar stills can serve the purpose of basic drinking water requirements of man. For countries like India, the domestic solar still is a viable safe water technology (Avvannavar et al., 2008). India occupies better position regarding solar energy potential. During winter from November to February most of the Indian stations receive 4.0 to 6.3 kWhm-1day-1 solar irradiance, while in summer season this value ranges from 5.0 to 7.4 kWhm-1day-1 (Pande et al., 2009). There are, on an average 250–300 clear sunny days in a year, thus it receives about 5000 trillion kWh of solar energy in a year (Arjunan et al., 2009). From its operational feasibility and associated costs, it can be inferred that solar still technology is capable of providing desalinated water to households in rural India. The fresh water crisis is already evident in many parts of India in varied scale and intensity at different times of the year. Also, the demand for fresh water increases with the growth of its population. The conventional desalination technologies are expensive for the production of small amount of fresh water. Also, use of

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Indian J Econ Dev 13(3): 2017 (July-September)

conventional energy sources is costly and not always ecofriendly. Solar distillation is most attractive and simplest technique among other distillation processes especially for small-scale units located at places where sufficient solar energy is available.

The basin-type solar still is in the most advanced stage of development. Several researchers have investigated the effect of climatic, operational and design parameters on the performance of such still (Garg & Mann, 1976).

Researchers have done different types of analysis on basin –type solar still (Baum et al., 1970; Nayak et al., 1980; Sodha et al., 1980; Tsilingiris, 2009). A part from this, other types of stills are also proposed with modelling and analysis (Oltra, 1972; Akhtamov et al., 1978; Frick & Sommerfeld, 1973; Umarov et al., 1972; Selcuk, 1971).

All these stills work at temperatures well below 100°C for conversion process. For achieving conversion at higher temperature (>100°C), thermal devices like flate-plate collector and concentrators were used, such system are called “active'' system given in the literature by (Malik et al., 1982). Concentrator powered solar distillation systems play a significant role in producing desalted water. Presently many researchers are involved in these activities to accumulate high quality de-salted water through concentrator-assisted systems. The effect of water flow on concentrator coupled hemispherical basin solar still has been analyzed with maximum productivity of 1.67 L (Thirugnanasambantham & Ahsan, 2013). A solar still augmented with flat plate collector is analysed with different operating modes for still alone and still with collector on different dates by (Badran et al., 2005).

Chaouchi et al. (2007) designed and built a small solar desalination unit equipped with a parabolic concentrator.

The experimental and theoretical study concluded with an average relative error of 42 per cent for the distillate flow rate. Many authors have performed the distillation process with concentrator-assisted techniques (Omara & Eltawil, 2013; Shiva et al., 2014; Chaichan & Hussein, 2015; El-Samadony et al., 2015; Hasan & Mousa, 2013; Khalifa & Ibrahim, 2011). Solar desalination units made of building materials overcome the problems of corrosion but salt scaling and algae problems exists. All metallic solar stills whether multi step basin or single basin are prone to corrosion, salt scaling and algae problem and have less life (Nahar et al., 2013). To overcome these problems a concentrator based distillation device was developed at Devi Ahilya University, Indore, India.

However, economic analysis has not been carried out in earlier reports. In the present paper, an experimental and economic analyses of a distillation unit equipped with a parabolic solar concentrator have been carried out in order to study the real-time possibilities for its use in desalination.

Experimental Apparatus and Procedure The experimental device shown in Figure 1 is comprises a solar parabolic concentrator type SK 14 unit.

It's having a diameter of 1400 mm and a performance of

up to 700 Watts (EG-Solar, 2007). The net power of the concentrator is approximately 600 watts in good sunshine hours and the stagnation temperatures of 300°C can be achieved. The number of reflector sheets varies from 24 to 36 in different designs manufactured by different manufacturers. Polished, anodized hardened aluminium sheets are used as reflectors (Chaouchi et al., 2007). The aperture area of concentrator is 1.57 m2 and absorber is mounted at its focus having a cylindrical shape vase, with absorber area of 0.0314 m2. This absorber is completely insulated except the part lit by the solar rays reflected by the parabolic surface. The sun tracking mechanism for this solar distiller has two axes according to previous researches and it is a manual system (Nuwayhid et al., 2001; Kaushika & Reddy, 2000). The saline water is kept inside the absorber. The steam produced passes in a condenser where it is condensed. The rate of distillate produced per hour is collected in a jar and measured.

The solarimeter Testo 454 was used in the experiments of the solar distillation unit, with a measurement range of 0 to 1400 Wm-2 and an accuracy of 0.1 per cent.

Temperature was measured using K type thermocouples (Chromel–Alumel) with 0.2 mm diameter and accuracy of ± 2 per cent were connected to a Testo 935 digital temperature indicator. The range of temperature extends from-40°C to 900°C with an accuracy of 0.7°C. The water distillate flow rate was measured using a measuring jar.

The performance evaluation of the parabolic solar concentrator based distillation unit has been carried out by measuring distilled water obtained per day by a measuring jar and average output of the system. The distillation efficiency and system efficiency were computed by using the following formulae, ç distillation (per cent)=

me × L × 100 Ibav, × Ap × hr ×3600

mwater × mpw (Tf - Ti) + me × L ç system= Ibav, × Ap × hr ×3600

-----------(1)

-------------------(2)

RESULTS AND DISCUSSION The performance evaluation experiment to determine the distillation efficiency and system efficiency was carried out during clear sky condition in the month of June, 2015. The developed parabolic solar concentrator based distillation unitwas tested at Indore, India. All experiments were started at 10:30 hr and carried out upto16:30 hr local time. The still is made to face the south and the saline water is poured inside the vessel in the early morning. The absorber is fixed at the focus of the concentrator with the help of the iron stand. The variations of water temperatures of both units as well as the productivity are recorded with time during the entire experiment. During the testing of the solar distillation unit, the following parameters are measured every hour for a period of 7 h: solar irradiation, distillate hourly yield

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Singh et al.: Economic analysis of parabolic solar concentrator based distillation unit

CONCENTRATOR

Evaporating vessel CONDENSOR

HOT WATER OUTLET

Figure 1. Parabolic solar concentrator based distillation unit

Table 1. Instantaneous distillation efficiency on 14th June, 2015 Time (Hr)

10:30 11:30 12:30 13:30 14:30 15:30 16:30

Hourly yield (L/h)

Beam radiation (Ib) w/m2

distillation (Per cent)

0.17 0.51 0.63 0.79 0.41 0.23 0.21

641 678 756 774 747 573 438

11 31 34 42 22 16 19

According to Table 1, it was found that the outputs of distillate increases in the beginning of the day and reach their maximum towards 13:30 hrs and decreases thereafter as shown in Figure 2. This evolution is closely linked to solar lightening, which is responsible for this production and therefore has a similar rate. This deviation can be explained by the fact that in the morning, only a small part of absorbing surface is covered with water because of the strong tilt in addition to the geometry

imperfection and the sun's manual follow-up.

The hourly instantaneous distillation efficiency was calculated by equation (1) and the experimental instantaneous efficiency and solar irradiation vs. local time was shown in Table 1 and Fig. 2. The efficiency presents an increase in the beginning; then it has a decrease thereafter. The deviations of efficiency can be explained by the fact that in the beginning, only one part of the absorbing surface is covered with salt water, the manual sun pointing and the existence of imperfections in the concentrator surface. In the other case, the maximum efficiency corresponds to the maximum solar lightning obtained towards 13:30. At this hour, the boiler is nearly in a horizontal position, which maximizes the offered heat transfer surface.

900

0.9

800

0.8

700

0.7

600

0.6

500

0.5

400

0.4

300

0.3

200

0.2

100

0.1

0

Hourly yield (L/h)

and instantaneous distillation efficiency. The experimental data are presented in Table 1. The water (coolant) resulting in hot water during this desalination process is collected in the other container that can be used for different purpose. All components of the solar desalination system were developed at the School of Energy and Environmental Studies, Devi Ahilya University, Indore, India (Figure 1).

Solar irradiation (w/m²)

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Distillate output

0 Time (Hr)

Figure 2. Experimental distillate hourly yield and solar irradiation vs. local time

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Indian J Econ Dev 13(3): 2017 (July-September) Instantaneous efficiency(ç) 45%

800

40%

700

35%

600

30%

500

25%

400

20%

300

15%

200

10%

100

5%

0

0%

Instantaneous efficiency

Solar irradiation (w/m²)

Solar irradiation 900

Time (Hr)

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Figure 3. Experimental instantaneous efficiency and solar irradiation vs. local time

The average distillation efficiency and system efficiency for June month were calculated using the equations (1 and 2) as shown in Table 2 and Table 3, and water quality analysis is shown in Table 4. Two different water samples were tested for pH and electrical conductivity (dSm-1), values which were measured before and after the samples were desalinated. Before desalination, the level of electrical conductivity in the saline water was around 1dSm-1. However, it gets decreased to 0.1 dSm-1, which is drinkable, by mixing the same amount of saline water. The typical pH varies from one water sample to another depending on the nature of the construction materials used in the water distribution system. It is usually in the range of 6.5 to 8.

Economic Analysis The economic analysis of the present solar concentrator based desalination unit was carried out by computing the life cycle cost (LCC) and life cycle benefit (LCB) of the unit. In addition, five economic attributes, namely, Benefit-Cost Ratio (BCR), Net Present worth (NPW), Annuity (A), Internal Rate of Return (IRR) and Pay Back Period (PBP) were also determined for judging the economic viability of the technology.

Life cycle cost (LCC) Life cycle cost (LCC) of the parabolic absorber based distillation unit is the sum of all the costs associated with a solar distillation energy system over its lifetime in terms of money value at the present instant of time and takes into account the time value of money (Kalogirou, 1996). The initial investment (P) in distillation unit is `9200 as shown in Table 5. The annual cost of operation and maintenance (O&M) including labour are taken as `6000. The benefit was computed for distillate output at a rate of 2.5 litre per day for 300 days a year priced at `15 a litre. The salvage value is taken as 10 per cent of initial investment.

Economic Attributes BCR: The ratio of discounted benefits to the discounted values of all costs given as LCB/LCC NPW: It is the sum of all discounted net benefits throughout the project given as LCB-LCC The annuity (A) of the project indicates the average net annual returns given as, NPW (Annuity)= n (1 + i )n å n= 1 IRR It is that rate of interest which makes life cycle

Table 2. Average distillation efficiency for the month of June Mass of distilled water, Latent heat (L) Beam radiation me (liters) (J/kg) (W/m2) 2.65

2300000

675

Aperture area (m2) 1.57

Operating hours (hr)

ç-distillation

6

27.1

Table 3. Average system efficiency for the month of June mwater Cpw Tf Ti (kg) (C) (C) (Jkg-1C-1)

mhwo (kg)

me (kg)

Tcf (C)

Tci (C)

çsystem (per cent)

0.5 0.77 0.83 0.58 0.4 0.75

10 9.6 9.8 10.5 11.3 9.1

3 2.73 2.67 2.92 3.1 2.75

60 65 49 54 53 49

23.6 24.1 23.5 25.4 24.9 24.7

36.49 36.88 35.62 35.42 35.61 34.61

4200 4200 4200 4200 4200 4200

Table 4. Water quality analysis TDS (mg/l) Before desalination After desalination 330

35

75 68 64 72 77 65

22.4 23.3 22.6 24.1 24.5 23.4

pH before desalination

Conductivity (dsm-1) After desalination

Before desalination

After desalination

7.21

1.0

0.1

7.60 572

Singh et al.: Economic analysis of parabolic solar concentrator based distillation unit

Table 5. Cost estimates of distillation unit Item with specification

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Parabolic concentrator 1400 mm diameter Evaporating vessel 0.005 m3 Copper tube 1 m long Condensing unit m×m×m Red-oxide metal primer Blue paint Glass wool Distillate jar Binding cloth Total

benefits and life cycle cost equal (LCB-LCC=0) PBP: It is the length of time from the beginning of the project before the net benefits return the cost of capital investments(value n for LCB-LCC=0) Determination of (LCC) and Economic Attributes The procedure of life cycle cost estimation as adopted

by Sodha et al. (1993), the LCC is given as, = 9200 + 6000

X (1- Xn ) n - 920 (1+ i)(1- X)

= 9200 + 6000

X (1- X10) 10 - 920 (1+ i)(1- X)

1+ eö æ Where R = Annual benefit (`) and X = ç ÷ 1+ iø è BCR: The ratio of discounted benefits to the discounted values of all costs can be expressed as: Life cycle cost of distillation unit

53310

= 1.58NPW

=LCB – LCC = 30758 The annuity (A) of the project indicates the average net annual returns. This term can be given as, A (Annuity)=

NPW n

=

30758

(1 + i) 2.5937 å n

1 1 1 1 1/2l 1/2l 1kg 1 1m

6200/piece 900/piece 1000/m 500/piece 120/ l 150/l 60/kg 50/piece 60/m

6200 900 1000 550 60 150 60 50 60 9200

Or 9200 + 6000 X

=11859...... (5)

1 ii =

A linear relationship between NPW and discount rate (i) was shown in Table 6 and established with a R2 = 0.998

0 . 945 (1 0 . 945 n ) 0 . 945 (1 0 . 945 n ) = 11250 (1 0 . 945 ) (1 0 . 945 )

Or 9200 = 5250 .

0 . 945 (1 0 . 945 n ) (1 0 . 945 )

9200 ( 0 . 055 ) Or (1 0 . 945 n ) = 5250 X 0 . 945 9200(0.055) Or 0.945n = 1= 0.9036 5250 X 0.945

X (1 X ) LCB = R .........(4) (1 X)

=

Amount (`)

and given as, i= -7 X10-5 (NPW) + 0.628 (Fig. 4). Putting the NPW as zero, i become internal rate of return (IRR) which comes to 62.8 per cent in the present case, which is very high for a project to be economically viable.

Pay-back period can be determined as following: LCC + LCB = 0

n

Life cycle benefits of distillation unit 84068

Unit cost (`)

Table 6. Values of NPW for different rates of discount/interest (i) NPW (`) 423.14 -331.35 -983.0 Interest rate i (per cent) 60 65 70

1+ eö 1+ 0 . 04 ö æ æ Where X = + ç ÷ ç ÷ 1 + i 1 + è ø è 0 .1 ø LCC (Unit) =Initial cost of unit (P)+PW (O & M Costs including labour)– PW (SV) -------(3) Where, e = annual escalation in cost (in fraction) i = interest or discount rate (in fraction) Life cycle benefits (LCB) can be given as,

Benefit cost ratio (BCR) =

Quantity

Or nlog 0.945 = log 0.898 n = log (0.898 – 0.945) = 1.898 years = 1.9 years Or Pay-back period (PBP) = 1.9 year Table 7. Values of economic attributes Attributes economics BCR NPW A IRR (per cent) PBP (years)

Values 1.58 30758 11.86 62.8 0 1.9 years

CONCLUSIONS In this experiment the average daily output of the still was around 2.65 L for with coolant (water). Cooling water increased the solar still productivity. The overall approach of this design and construction of the concentrator coupled system appears to be good as indicated by its

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Indian J Econ Dev 13(3): 2017 (July-September)

70 IRR = -0.0071NPW + 62.891 R² = 0.9982

68

Interest rate (per cent)

66 64 62 60 58

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-1000

-800

-600

-400

-200

0

200

400

600

800

1000

Net present worth (NPW) Figure 4. Net present worth v/s interest rate curve

system efficiency 32.4 per cent. This system provides an alternative to the single basin solar still connected to a flat plate collector for high temperature passive solar distillation and concentrator coupled hemispherical basin solar still. The economic evaluation of the distillation unit revealed that high value of IRR (62.88 per cent) and low value of payback period (1.9 Years) make the unit very cost efficient. ?

The system uses no electricity (or minimal amounts of electricity) as driving power, and is therefore especially suitable for high solar flux areas which are often poorly supplied with electric power. ?

The system is a low- cost, no pollution, alternative to incineration. ?

The system can be utilized for cooking purpose as it contains solar parabolic concentrator.

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Symbols and Notations Ap = Aperture area (m2) Cpw= specific heat (J/kg/°C) Ib =Beam radiation (W/m2) L = Latent heat (J/kg) me= Mass distill water obtained (litres) mhwo= Mass of hot water outlet mwater= Mass of water remaining in evaporator vessel Ti = Initial temperature of water in evaporative vessel Tf = Final temperature of water in evaporative vessel

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Tci = Initial temperature of cold water Tcf = Final temperature of cold water ç = Distillation efficiency çsystem = System efficiency BCR=Benefit to cost ratio NPW = Net present worth IRR = Internal rate of return A = Annuity PBP = Payback period