Performance Tests on the Solar Dryer with the Latent Heat Storage
7.7 Economic Analysis
Economic analysis of the dryer is carried out based on the annualised cost method (Sreekumar, 2010; Jain and Tewri, 2015). The cost of drying of 1 kg of dried product in the solar dryer has
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been compared with the cost of the product dried in the electric dryer. The cost per kg of dried product is calculated by the following equation.
a dr
dpa
C C
ο½ m (7.20)
where πΆπ is the annualised cost of the dryer, and ππππ is the quantity of product dried in the dryer per year.
The quantity of the product dried in the dryer per year is calculated as follows
dpb y dpa
b
m N
m ο½ N (7.21)
where ππππ denotes the mass of dried product per batch, ππ¦ is the number of days of operation of the dryer per year, and ππ is the number of drying days per batch. The mass of dried chilli removed from the solar dryer per batch was 6 kg and the drying was completed in 4 days operating the dryer daily for 10 h. The dryer is expected to be operated for 250 days per year.
The annualised cost of the dryer is calculated by employing the following equation.
a ac m a rf re
C ο½C ο«C ο ο«V C ο«C (7.22)
where πΆππ is the annual capital cost, ππ is the annual salvage value, πΆπ is the annual maintenance cost, πΆππ is the annual running fuel cost, πΆππ is the annual electricity cost for running the blower or fan. The annual capital cost is given by
ac cd c
C ο½C F (7.23)
where πΆππ is the capital cost of the dryer and πΉπ is the capital recovery factor. The capital recovery factor is given by Eq. (7.24).
(1 ) (1 ) 1
n
c n
i i
F i
ο½ ο«
ο« ο (7.24)
The interest rate (i) is assumed to be 10% and the life period (n) is assumed to be 10 years. The annual salvage value is calculated by Eq. (7.25).
a s
V ο½VF (7.25)
The salvage value (V) is taken as the 10% of the capital cost of the dryer. The salvage fund factor (πΉπ ) is evaluated by the following equation.
(1 ) 1
s n
F i
ο½ i
ο« ο (7.26)
The annual running cost of the solar dryer is the running cost of the blower. However, the annual running cost of the electric dryer is the sum of the annual energy cost for running the dryer and the running cost of the fan of the dryer. The annual running cost of the solar dryer is calculated by the following equation.
re hr bl ele
C ο½ ο΄ ο΄ t p C
(7.27)where π‘βπ is the annual running hour of the dryer, πππ is the power consumed by the blower (250 W), and πΆπππ is the unit cost of electricity (Rs. 6.25 per unit).
Table 7.1
Cost of the components of the dryer.
Components Cost (Rs.)
Solar air heater 25,000
Thermal energy storage 12,000
Blower 8,000
Drying chamber with trays 20,000
Pipe and fitting 5,000
Total cost 70,000
The annual fuel cost of the electric dryer is given by the following equation.
100 3600
fg ele db
rf dpa
d
M h C
C m
Ξ·
ο©ο¦ οΆ ο¦ οΆοΉ
ο½ οͺο«ο§ο¨ ο·οΈ ο¨ο΄ο§ ο΄ ο·οΈοΊο» (7.28)
where πππ denotes the moisture content in dry basis, βππ is the latent heat of evaporation, and ππ is the efficiency of the electric dryer. The efficiency of the electric dryer is assumed to be
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75%. The cost of the electric dryer is assumed to be 50% of the solar dryer. The cost breakup of the components of the solar dryer is given in Table 7.1 and the summary of the cost analysis is given in Table 7.2.
Table 7.2
Summary of the economic analysis.
Particulars Solar dryer Electric dryer
Capital cost of the dryer πΆππ, (Rs.) 70,000 35,000
Life of dryer, n (years) 10 10
Interest rate, i (%) 10 10
Number of operation of the dryer per year (days) 250 250
Annual capital cost, πΆππ (Rs) 11,392 5,696
Maintenance cost, πΆπ (Rs)
10% of annual capital cost (πΆππ) 1,139 569
Salvage value, V (Rs.)
(10% of the capital cost) 7,000 3,500
Annual salvage value, ππ (Rs.) 439 220
Running cost of the dryer (Rs.) 3,906 24,583
Annualized cost of the dryer (Rs.) 15,998 30,628
Quantity of product dried (kg) per year 375 375
Cost of drying per kg of dried product (Rs.) 42.7 81.4
It has been found from the economic analysis that the cost of drying per kg of dried product in the solar dryer is Rs. 42.7 while the cost of drying per kg of dried product in the electric dryer is Rs. 81.4. Thus, the drying cost in the solar dryer is Rs. 38.7 lower than that of the electric dryer. The percentage saving on the cost of drying per kg of dried product is 47.5%.
However, it is costlier than the product dried in the open sun. The drying cost in the open sun is almost negligible. The only drying cost involved in the open sun drying is the labour cost.
The labour cost in the sun drying is 100% more than in the solar drying since the product in the open sun dried in 8 days while it took 4 days in the solar dryer (Fig. 7.9). The colour quality of the product dried in the sun drying is inferior to the product dried in the solar dryer. The product dried in the open sun is not hygienic. It was observed that the open sun dried product was contaminated with dust during the drying period due to the blowing of dusty wind. Though, the solar drying incurs some expenses in comparison with the open sun drying, the solar drying
is preferable particularly for drying high value and photosensitive agricultural products such as Ghost chilli, Ginger, large cardamom, medicinal plants, and black pepper as the solar drying products preserve its colour, texture, and nutritional values.