[EE]:: Operation of water pumps from Wind Turbines

TL;DR / Summary

Comments on the following are invited - especially the practicality of
using DC powered deep well water pumps to allow direct powering of water
pumps by wind turbines across a wide range of wind speeds.
Of significant uncertainty is the practicality of powering a 1-5 kW range
DC powered pump from a highly variable wind source, and the ability to load
the turbine close to maximally at all times to prevent damage.

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I'm interested in the operation of deep well water pumps powered by WT
(wind turbines.)
Direct alternator to pump action without batteries or inverter is desired.
Pumps motors are typically in the 1 kW - 5 kW range.
Smaller and larger may happen.

In the target application pumps are in most cases powered by diesel fueled
generators, but in some cases by AC mains power or solar panels.
Solar with AC motors has the cost disadvantage of requiring batteries and
inverters.
Diesel operation is costly.

When wind turbines are used the most usual method is to produce 3 phase AC,
rectify it and store energy in a battery and then use an inverter to power
the pump.
This has the advantage of decoupling the pump operation from variations in
WT output and wind energy variations. As required the pump may be operated
at a relatively constant level in start / stop mode depending on mean wind
energy availability.

While grid scale WTs can be operated in constant speed mode and provide
relatively stable AC frequency output, this is not practical with WTs of
this size. Even if constant speed was viable, energy variations would occur.
Non constant frequency operation makes operation of standard off-the-shelf
motors problematic.


Application environment:

In this application it is intended that the WTs proper, and where practical
also the alternators, will be constructed locally in countries where low
income and possibly also high energy costs make this attractive.
This replaces material costs with local labour but means that use of
battery plus inverter systems adds substantially to the capital cost.
Adequate knowledge and design resource exists in these areas, but more
relevant input is alway welcome.

DC system:

I'm interested in the possibility of using DC pump motors. WT AC output
would be rectified to DC and used to drive pumps directly or via an MPPT*
system.
This presents the DC motor with a variable voltage variable energy power
source. Voltage and available energy need to be adequate to start the water
pump from stall conditions and the pump must be able to provide the WT with
a full load across its intended power design range.
When the WT reaches maximum wind speed and power output furling systems
prevent further increases in output. "Dump load" systems to add extras load
at the top end are conceivable but undesirable if the energy is wasted.
Depending on environment two or more pumps may be able to provide a staged
load.

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* MPPT = Maximum Power Point Tracking is a system which adapts a variable
voltage level input source to a load (by adjusting the load seen at the
source so that the energy source is optimally loaded (maximum power out) at
all times.
This can be thought of as an "electronic gearbox".
A MPPT controller very usually contains an inverter



    Russell