Renewable Energy Resources for Irrigation - Practices of Irrigation and On-farm Water Management - page 488

Considering the efficiency of photovoltaic cells, and an overall design safety
factor, the equation for calculating N PV takes the form:

N PV = ( P E × S F ) / ( R S × A PV × E PV ) (13.5)

where

S F = Overall design safety factor (1.1-1.2)

E PV =

efficiency of photovoltaic cells to convert solar irradiance to electricity
(35-42%)

13.4.4.3 Economics of Photovoltaic Irrigation Pumping

The cost of photovoltaic-powered water pumping system is progressively decreas-
ing. The cost of photovoltaic modules has already fallen 400% in the last 30
years (due to technological improvement and commercialization system), and this
trend continues. On the other hand, the cost of power derived from fossil fuel is
increasing.
In a case study in Bangladesh, Bhuiyan et al. (2000) evaluated the economics of
stand-alone photovoltaic power to test the feasibility in remote and rural areas and
to compare renewable generators using method of net present value analysis. They
found that the life-cycle cost of photovoltaic energy is lower than the life-cycle cost
of conventional energy where there is no grid, and the photovoltaic generator is
economically feasible in remote and rural areas.

13.4.4.4 Sample Work Out Problems
Example 13.1
How much energy is required to lift a discharge of 0.05 m 3 /s from a depth of 10 m?

Solution

We know, required power,
P

= Q × 9.81 × H

Here,
Q

0.05 m 3

= / s

H 10 m

Putting the values,
P

=

= 4.905 kilowatt (kW)(Ans.)

Example 13.2
In a small agricultural farm, the peak water demand rate is 250 m 3 /d and total head
requirement is 10 m. The minimum and maximum solar irradiance through the crop-
ping period at the site are 6 MJ/m 2 /d and 8 MJ/m 2 /d. Determine the number of PV
array required to meet the power demand, if the area of each array is 3 m 2 .