4) Photovoltaic Cell: To maintain the charge of the WSU
batteries, a solar panel MPT4.8-75 was employed. Each solar
panel delivers 50 mA at 4.8 V, which is sufficient energy
to maintain the voltage of the three rechargeable batteries.
A MSS1P2U Schottky diode (Vishay, Shelton, CT) is used
to prevent the solar module and to drain the battery when
is in the dark. The solar panel is encapsulated in a 3-mm
clear polyester film with dimensions of 94 mm × 75 mm.
This flexible panel was mounted on a PVC prismatic base
(100 mm × 80 mm × 3.17 mm) that is fastened in the upper
part of a PVC pole allowing for the correct alignment of the
photovoltaic panel to the sun. The stick is 50 cm of length
and 12.5 mm of diameter; the lower end of the pole had a tip
end to be buried.