Small pumps (<2kW ou 3HP) are mainly powered by direct current (DC) and are driven by the voltage variation.
•
Medium and heavy pumps (>4kW ou 5,5HP) are powered by alternating current (AC) and are controlled by frequency
variation. To make this possible, the DC current of the panels must be alternated or inverted, hence the name «pump
inverter».
•
For intermediate power (between 2000W and 4000W), suppliers may offer DC pumps or AC pumps, or pumps that
support both types of voltage, depending on the brand they usually supply, what they have in stock, ...
It is important not to specify a specific type of voltage so that the supplier can propose the type of pump (DC, AC or AC /
DC) for which it will be the most competitive.
When we do not know the type of pump and its supply voltage, we use the generic term «pump controller» (or «pump
control unit»).
17
SOLAR PUMPING
Guidelines - Electrical design and installation of solar pumps
PUMP CONTROLLERS
The rotation speed of the pump is controlled by its voltage supply: the higher the voltage, the higher the rotation speed of
the pump. Pump controllers are small, have at least one ON / OFF button, a display showing the status of the pump, and
faults encountered if they cause the pump to stop. Figure 6 displays 3 commonly used pump controllers.
FIGURE 6:
THREE EXAMPLES OF PUMP CONTROLLERS
ON/OFF
Display
ON/OFF
(Downside)
ON/OFF
Display
Grundfos Brand
Lorentz Brand
Generic brand
SOLAR PUMP INVERTERS
The rotation speed of the pump is controlled by the frequency (in Hertz) of the AC voltage. The solar inverter will therefore
produce a variable frequency depending on the DC voltage it receives from the panels. Typically, a solar pump inverter will
start the pump at a minimal frequency of 25Hz when there is little sunlight. It will increase the output frequency as sunlight
and thus the DC voltage of panels increase, to finally reach a maximum frequency of 50Hz (or 60Hz depending the pump)
at peak hours.
It is therefore impossible to use an inverter designed to power buildings, for a solar pump. Inverters for buildings are designed
to deliver a fixed frequency of 50 or 60 Hertz (grids and generator frequencies). If you do it anyway, the pump will only run at
the fixed frequency of 50Hz or 60Hz (its maximum power), and when the panel voltage is not sufficient to allow the inverter
to produce 50Hz (morning, evening, cloudy days, ...) the pump will not run. Therefore, you will not reach the full potential of
solar pumping, which main goal is to provide water even when there is little sun.
For most solar pump inverters it’s possible (or even necessary) to set the minimum starting frequency ; the maximum
frequency at full power ; the power of the pump ; the type of start-up ; the type of low water level probe ... Figure 7 presents
the main solar pump inverters.
FIGURE 7:
EXAMPLE OF SOLAR PUMPING INVERTERS
Grundfos Brand
Lorentz Brand
SolarTech Brand
Suoer Brand
(China)
Generic Brand
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