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326 CHAPTER 9 Design Principles of Photovoltaic Irrigation Systems

where I b is the total irradiance over the inclined plane where the PV modules are
arranged and PP is the peak power of the PV system. With the equations discussed
in this chapter, this parameter can be calculated at different times of the year.

4.1.4.2 Power Transmitted to the Pump Shaft
The shaft power supplied to the pump, P, can be calculated as a function of the PV
power, P PV, provided by the PV array by applying Eq. (9.52).
P ¼ P PV $h $h C (9.52)
M
where h C is the efficiency of the converter. This value is higher than 0.95 for most
commercial converters. h M is the efficiency of the asynchronous motor, and this ef-
ficiency increases as the frequency of the electrical current diminishes. A constant
value of 0.8 can be used as a conservative criterion.
4.1.4.3 Net Power Transmitted to the Water Flow
The power transferred to the water flow can be calculated by multiplying the shaft
power by the pump efficiency, h .
P
P u ¼ g$Q$H ¼ P=h P (9.53)
where g is the specific weight of the water.

5. DESIGN OF PHOTOVOLTAIC IRRIGATION SYSTEMS

The procedure recommended by the authors to the design and size the PV irrigation
system is based on performing a simulation of the system performance. This simu-
lation is based on the equations that describe both the PV generation subsystem and
the irrigation subsystem that have been discussed in this chapter. The following
stages in the design process should be considered.
First of all, the study period must be defined. This study period may be a whole
year or the period in which the PV is going to operate (cropping cycle). The study
period should be disaggregated into shorter periods (weeks, months) for which the
invariance of the main variables of the system, such as irradiance, solar position, irri-
gation requirements, etc., will be assumed. The shorter the selected period, the more
precise the simulation will be. A simulation of the system is then performed for a
representative day within this period (for example, the middle of the period). This
simulation includes the following stages:
1. Input data and initialization of the design variables. The first stage in the
design process is to initialize the parameters and variables required in the
simulation of the PV irrigation system:
• Type of PV plant and initial PP
• Type of irrigation system: number of pumps and performance curve of the
pumps, total area to irrigate, number of irrigation sectors, type and discharge
of the emitters, crops, etc.