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< prev - next > Energy Mechanical Power KnO 100432_Windpumping (Printable PDF)
Practical Action
Other common pump types used for windpumping are the progressive cavity or ‘Mono’ pump
and the centrifugal pump. Both have advantages in certain circumstances but both also tend
to be expensive and less commonly used.
Figure 3 illustrates a typical example of a modern multi-bladed windpump. The high solidity
means high starting and running torque and low running speed which is desirable for use with
the piston pump.
It is obviously important to match the water pumping demand with the available wind and
hence decide upon a suitable rotor size. To calculate the demand we need to know the
following data:
The head to which the water is to be pumped - in metres
volume of water to be pumped per day - in metres cubed
For water at sea level the approximate energy requirement can be calculated using the
following equation:
E = 0.002725 x volume x head (in kilowatt-hours)
Typically pumping heads can vary between a few metres and 100m (and occasionally more),
whilst the volume of water required can vary from a few cubic metres a day for domestic use to
a few hundred cubic metres for irrigation.
Anatomy of windpump
A borehole is by far the most common
water source from which the
windpump will draw water. A classic
multiblade farm windpump has a
piston pump pumping to an elevated
storage tank. There are many other
configurations possible, depending on
the nature of the water source and the
demand. These machines have rotor
diameters of between 1.5 and 8
metres but seldom exceed 4 or 5
metres. The power is transmitted from
the rotor to the pump rods via a
gearing system or via a direct drive
mechanism. The movement of the
pump rods cause the pump to lift
water to the tank. Water can then be
fed into the distribution network from
the tank. The function of the tail vane
is to keep the rotor orientated into the
wind. Most windpumps have a tail
vane, which is designed, for automatic
furling (turning the machine out of the
wind) at high wind speeds to prevent
Windpumping with electricity
Although the multiblade windpump is
by far the most common windpump in
use, it is not the only option available.
Another option, especially where there
is a requirement for the pump to be
sited remote from the wind machine,
Figure 3: The Kitjito Windpump used to pump ground
water in the Bhel region of Turkana for the nomadic
pastoralists. Photo: Practical Action.