11. Splitting the solar pumping system
11.1. Introduction.
To maximize the efficiency and reliability of a solar pumping system, instead of using a single high-power pump, it
is possible to split it into two or more pumps in parallel, each controlled by a variable speed inverter and powered
by the same photovoltaic system.
When the system consists of a single pump, in conditions of low irradiance, the pump is often stopped as the
photovoltaic power is not sufficient to guarantee its operation.
Vice versa, when the system is split into several lower power pumps, even in conditions of poor irradiation, at least
one or more pumps continue to operate supplying water.
This results in a significant increase in the total efficiency of the system.
In addition to this, the following are ensured:
• greater system reliability as, if one pump or inverter fails, the other pumps can continue to operate
• uniformity of pump wear thanks to the alternation of operation managed by the inverters in the unit.
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1: Inverter; 2: Pump; 3: Check valve; 4: PV system; 5: Gate valve; 6: Strings combiner with protections; 7: DC
disconnector
11.2. Solar pumping unit with two or more pumps in COMBO Solar.
The unit consists of two or more pumps (up to 8) each controlled by an inverter. The inverters are connected to
each other via COMBO RS485 serial port.
One inverter is configured as master (address 00) whereas the others are configured as slaves (addresses 01 to
07).
11.2.1. Cascade operating principle.
When the unit is started, a single pump is started at variable speed to maximize the available photovoltaic power
(MPPT).
If the photovoltaic power is sufficient to reach the maximum frequency of the pump, the second pump of the unit is
started.
If the photovoltaic power is sufficient to reach the maximum frequency also of the second pump, the third pump of
the unit is started and so on according to the number of pumps present in the group.
When the irradiation decreases, the pumps are progressively slowed down and stopped in sequence.
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