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Fig. 12.1 Block diagram of the wind-solar installation supported with hydrogen
supervisory control and data acquisition system. Figure 12.1 depicts the block
diagram of the hybrid system.
In summer, solar energy is sufficient to supply the load to maintain a high state
of charge of the batteries, and to feed the electrolyzer (model Hart-250 of Hydrogen
Works) to produce hydrogen which is stored in the metal hydrides. In winter, when
the state of charge of the batteries is low, the fuel cell recharges the batteries avoiding
any cut in electric power supply. The electrolyzer plays a key role in the operation and
performance of the hybrid system, as remarked by different research works (Ulleberg
2004 ; Calderón et al. 2010 ; Calderón Godoy 2010 ; Calderón et al. 2011 ).
The test-bed monitoring and control system is implemented by the PLC S7-313C-
2DP. This device incorporates electronic modules, Siemens SM331 and SM334
models, to connect analogue sensors with both voltage and current outputs. Data
are displayed and stored on a TP277B touch panel (Siemens) running a SCADA
(Supervisory Control and Data Acquisition) application. The touch panel logs the
variables of interest at one minute intervals from the PLC's memory by a permanent
MPI (Multi-Point Interface) connection.
The hydrogen generator and the PVmodules are connected by a DC-DC converter
that carries out the conditioning of voltage and current provided by the PV modules
to the electrolyzer levels. Using one of the analogue outputs of the module SM334,
the PLC applies a voltage level to the control input of the converter. This voltage
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