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300 CHAPTER 9 Design Principles of Photovoltaic Irrigation Systems

2.2 ACCORDING TO THE TYPE OF IRRIGATION SYSTEM
PV irrigation systems are usually composed of one pump, or one set of pumps oper-
ating in parallel, which transfers water to either an elevated storage tank or directly
to the irrigation water distribution system. Therefore, two basic typologies can be
distinguished.

2.2.1 Pumping to an Elevated Tank
Storing the pumped water into an elevated storage tank is a sound procedure for
matching the renewable energy production to the crop irrigation demand. Water
can subsequently be distributed to the plants by gravity [21,29,30] (Fig. 9.1).
However, in many cases, there is no location with enough elevation to build a
reservoir to take advantage of the gravitational energy to distribute the irrigation wa-
ter. In this case, a booster station is required to provide the energy required to
discharge water through the emitters. In other cases, the elevated locations can be rela-
tively far and the construction cost of these elevated reservoirs can be unaffordable.

2.2.2 Direct Pumping
To avoid the abovementioned drawbacks, in this work a stand-alone direct pumping
PV irrigation system that pumps water directly to the irrigation distribution network
rather than lifting it to an elevated reservoir is proposed. In addition, with the aim of
matching energy production to irrigation demand, we propose a new approach that is
different to that used in other works on PV irrigation systems design [31e35]
(Fig. 9.2).
In both cases, the segmentation of the pumping stage into several units and the
use of frequency variation and frequency drives all help the system to operate effi-
ciently under variable working conditions.

FIGURE 9.1
Scheme of a grid-connected photovoltaic (PV) pumping to an elevated tank system.