Solar Drying: Fundamentals,Applications and Innovations - National ...

It was seen that for all fish, hot air drying exhibited highest moisture diffusivity followed
by solar cabinet and freeze drying, whereas, open sun drying showed the lowest
diffusivity values. Freeze-drying was the best method of drying for Bombay duck and
Prawns resulting in high quality dehydrated product, but it was high energy intensive
process. Solar cabinet drying was found to be low energy intensive process compared to
freeze and hot air drying resulting in acceptable quality dehydrated fish product.
1.12.1. Economics of Solar Dryers
Solar dryers are generally capital intensive and therefore the financial viability is the
key to successfully compete with any of the other dryers. The financial analysis generally
includes the cost of dryer (fixed cost), cost of drying (operating expenses) and payback.
They can be viable only if the annual cost of extra investment (on the solar dryer)
could be balanced against fuel savings, or if the equipment cost could be reduced
(Jayaraman, 1995). The user or dryer designer looks for a favourable combination of
cost, energy efficiency, quality, and price of the final product (Crapiste and Rotstein,
1997). Payback is the measure of time (number of days/months/years) it takes to recoup
the total investment made on a dryer, in the form of operational cash inflow. Payback
analysis does not measure the profitability of dryer as it does not take the service
life of dryer into consideration. This is discussed in detail by Brenndorfer et al. (1987).
Continued use of the dryer rather than seasonal use will decrease the drying cost and
payback (Arinze et al., 1996). Economic analysis on a solar dryer should also incorporate
the cost benefits due to improved quality, higher yields, less floor area and quicker
drying (Sreekumar, 2010).
1.12.2. Dynamic Methods of Economic Evaluation
The economic evaluation of solar dryer ultimately aims at determining the payback time.
For the calculation of payback time the dynamic method of calculation takes into account
the influence of inflation. The following considerations summarize this method,
according to Boer (1978). Payback occurs when the accumulated savings S equals the
sum of investment capital (I) plus yearly interest and the accumulated costs (E):
S = I + E (1.18)
The annual accumulated savings can be calculated from the net income D by reducing
the mass and quality losses and thus by increasing the marketing price of the product in
case of natural solar dryers.
For passive solar dryers, savings can be calculated from the price of the substituted conventional
energy D. Considering the annual interest rate r and the yearly inflation rate (e)
for the prices of energy, for n years the annual accumulated savings can be calculated as
follows:
S = (1+r)n −(1+e) n
D (1.19)
r−e
The sum of first investment cost (C) with interest will be, during n years,
I = C(1 + r) n (1.20)
Accumulated yearly costs, taking the annual fixed charge rate mC and inflation rate i for
equipment into consideration, will be
E = mC(1+r)n −mC(1+i) n
(1.21)
r−i
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