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308 CHAPTER 9 Design Principles of Photovoltaic Irrigation Systems

3.1.3 Other Types of Photovoltaic Array Arrangements
In intensive crop farms or greenhouses farms, the lack of space to lay the PV system
is an important problem that must be faced because the price of land is usually high
and most of the surface area is occupied by farm facilities such as greenhouses, res-
ervoirs, warehouses, and irrigation facilities. The development of PV energy gener-
ation technology currently offers different alternatives to cope with this problem.
Different research works have proposed mounting the PV cells on greenhouse roof-
tops. In this way, the excessive sunlight irradiating greenhouses could be used to pro-
duce both crops and energy (Fig. 9.13).
Several research works analyzing the effect of partial shading on crop yield
[36e39] have pointed out that moderate partial shading does not have a significant
effect on crop yield reduction. Kitta et al. [40] recommended a shading factor no
higher than 20% for sweet pepper in Mediterranean climate conditions.
Different types of materials and technical solutions have been proposed to inte-
grate solar-based energy generation systems into greenhouses, from conventional
opaque flat hard or planar flexible PV modules with various arrangements (straight
line and checkerboard) to semitransparent PV modules [41e47] (Fig. 9.14).
More recently, progress in PV cell technologies has provided new possibilities
for solar cell applications. Biancardo et al. [48] developed a semitransparent PV
module composed of spherical solar microcells, characterized by its small size
and isotropic ability for photoreception. Yano et al. [49] subsequently tested the per-
formance of this new type of PV System on a greenhouse. These studies showed that
although conscientious design is necessary, it is possible to generate enough elec-
tricity for the control of greenhouse environment appliances using PV systems
that are compatible with plant cultivation [41,44,45] (Fig. 9.15).
Another alternative is to cover the irrigation reservoirs with floating solar mod-
ules so that, in addition to producing solar energy, water losses from evaporation and
algae formation in the water could be reduced (Fig. 9.16).

FIGURE 9.13
Photovoltaic (PV) generator on the greenhouse rooftops.