Page 354 - Advances in Renewable Energies and Power Technologies

5. Design of Photovoltaic Irrigation Systems 327

• Economic data: installation costs of the PVand irrigation equipment, price of
energy and products, discount rate and useful life of the system, etc.
2. Simulation of the energy received and power supplied by the PV array:
• Determination of direct, diffuse, and global irradiance on the horizontal
plane.
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• Determination of the three components of the solar vector ( s ) for every
period.
• Determination of the three components of the normal vector to the collector
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plane ( n ), applying the right equation depending on whether it is fixed or
not.
• Calculation of the PV power produced by the PV array and the shaft power
transferred to the pumps by the electric motor.
3. Calculation of the operating point of the pumping system. This depends on
the type of irrigation system: pumping to an elevated tank or direct irrigation. In
the latter case, the use of noncompensating emitters, the number of irrigation
sectors, and the number of sectors in operation have to be considered. In this
stage, the frequency of the AC, the discharge, and head of the pumping system
are determined.
4. Calculation of the irrigation water requirements. This is to estimate
the irrigation application time and the volume of water that has to be pumped by
the pumping system. The irrigation water requirements depend on many
factors, such as the weather conditions of the area, the type of crop and cropping
systems, and the efficiency of the irrigation system. The FAO approach [51] has
been widely used worldwide to calculate these crop water requirements
because of its good level of precision and ease of use. According to this
methodology, crop evapotranspiration (ET c ) is calculated by the following
equation:

ET c ¼ ET o K c (9.54)
where ET o is the reference evapotranspiration for a standardized crop whose can-
opy characteristics do not change. ET o depends on climate conditions. K c is the
crop coefficient, which is the ratio between the evapotranspiration of a specific
crop and the evapotranspiration of the reference crops. ET o can be calculated
using the PenmaneMonteith equation [51]. Appropriate values for the K c must
be chosen depending on the type of crop. Calculating the irrigation water needs
is a complex task; therefore consulting specific literature on this issue is recom-
mended for this purpose.
5. Establishing a water and energy balance. Both water and energy balances can
be established. As a result, the total volume of irrigation water pumped by the
pumping system and the total energy consumed can be calculated.