The prototype built followed the design presented in figure 2. This system incorporates a PV-cell 150mmx150mm, Pmax=1,12W, (Polycrystalline Silicon wafer) and the whole structure is made of aluminium alloy. In fig. 6 the global developed prototype is shown. The control unit was developed using an industrial Siemens S7-300 PLC (Programmable Logic Controller). Figure 7 details the electro-mechanical structure of the developed sun-tracker system.

The selected PLC system is a modular device that is constituted by the following modules:

Slotl = Power supply PS 307-2A Slot7 = Analog card AO4 x12bit

Slot2 = Processor CPU 315-2DP Slot8 = FM card — Counter Module (FM350)

Slot4 = Communication module CP 342 -5 Slot9 = FM card — Counter Module (FM350)

Slot5 = Digital card DI8/DO8xDC24V/0,5A SlotlO = FM card — Stepper Motor (FM353)

Slot6 = Analog card AI8 x12bit Slotll = FM card — Stepper Motor (FM353)

Additionally, the PLC-tracker has a modem for GSM communication that provides the system capacity to communicate through the mobile phone network.