small wind turbines and wind pumps - välkommen till kth · pdf filethomas ackermann...

Thomas Ackermann November 2015
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Small Wind Turbines & Wind Pumps & Wind Diesel Systems
Thomas Ackermann, Ph.D.
[email protected]
Expert User of DIgSILENT PowerFactory for Power Systems Studies
Contents
Part 2: Wind Pump Systems
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Part 1: Small Wind Turbines
Part 3: Wind-Diesel Systems

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Contents
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Typical Markets for Small Wind Turbines (< 50 kW)
Remote Homes
Telecommunications
Village/ Rural Electrification
Water Pumping
Oil Well Pumping
Refrigeration
Desalination
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Rural Electrification
World Bank projects in:
Brazil;
Russia;
Indonesia;
China;
Mexico ...
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Features of Small Turbines for Power Generation
Larger tower, compared to turbine size;
Mainly variable speed, direct driven systems (no gearbox) for 2 to 10 kW; direct driven systems are also under development for turbines between 10 to 50 kW (Reason: High rotor speed well suitable for direct driven systems);
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Generators
Low Cost Alternatives:
Alternators are very popular (Advantage: cheaper, long life time);
Induction motor (washing machine);
Advanced Alternatives:
AC generators (very seldom DC);
Permanent magnet generators;
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Power regulation
Yaw (~ 10 %);
Stall (~ 8 %);
No Control (~ 14 %);
Pitch (~ 35 %);
Tilt (~ 33 %)
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Yaw/ Horizontal Furling
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Tilt/ Vertical Furling
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Pitch Control
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Blades
Often very bad aerodynamic design for small blades, e.g.
455 kW/ m2 for Bonus 600 kW
260 kW/ m2 for Bergey 10 kW;
Good research in this area is done by the University of New South Wales, Newcastle, Australia
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Maintenance
Low maintenance costs is the key, however, it is often very difficult ton achieve;
Also, very difficult and risky to climb up a large tower to repair/ maintain a small wind turbine;
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Grid Connection I
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Induction Generator
Easy to synchronize with the network;
Cheap and easy;
BUT: Requires reactive power, hence a reactive power source needed!
Voltage different to regulate;
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Synchronous Generator
Reactive power generation possible;
Easy to control;
BUT: Must be synchronized in frequency, phase and current;
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DC Generator
Direct connection to battery possible (Battery charger);
No synchronisation required;
Low efficiency;
Repair of DC generator can get very expensive;
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Battery & Inverter
Power output can be regulated;
Easy to synchronise;
Can supply reactive power;
Expensive;
Control might be difficult;
Lifetime of Battery limited.
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Water - Pumping
Cut subsidies to save water and to find economic ways to pump water (India has estimated 12 million electric pump sets, but only several thousand wind/solar pump sets)
Without subsidies (Yemen): 50-60 cents US/ kWh for electricity;
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WIND PUMP SYSTEMS
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Electrical Water Pumping
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Wind Pump Systems
32Pump
mechanical coupling
gearbox
belt drive

Typical Situations
Small pumped volumes high pumped heads (> 20 m), often drinking water;
Medium pumped volumes medium pumped heads (5 - 20 m), often livestock;
Large pumped volumes small pumped heads (< 5 m), irrigation, drainage.
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Operating Principle Pump
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Pmech = 2 Pi M n
Ppump = pw g Q H

Pumps
A: Piston pump
B: Diaphragm pump
C: Eccentric screw pump
D: Single-stage centrifugal pump
E: Multistage centrifugal pump
F: Screw pump
G: Chain pump
H: Mammoth pump
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A: piston pump
B: diaphragm pump,
C: eccentric screw pump,
D: single-stage centrifugal pump,
E: multistage centrifugal pump,
F: screw pump,
G: chain pump,
H: mammoth pump
Which Pump?
drinking-water supply/ livestock watering: Volume = small to medium; Height = large to medium;
Piston pump (A), multistage centrifugal pump (E), eccentric screw pump (C), mammoth pump (H)
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Which Pump?
Irrigation; Volume = large; Height = small
Single-stage centrifugal pump ( D), diaphragm pump (B), screw pump (F), chain pump (G);
often pumps that can handle dirty water
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A: piston pump; B: diaphragm pump
C: eccentric screw pump; D: single-stage centrifugal pump
E: multistage centrifugal pump; F: screw pump
Total
pumped
head H
Rotational speed n

Important Aspects
Rated Wind Speed (1.4 ..1.6 of Vm)
Cut in Wind Speed;
Gearbox efficiency (reduces overall efficiency);
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Operating Points
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Piston pump Centrifugal pump
Starting moment for piston pump
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Position of the crank drive
Rotational speed
Performance characteristics of
the wind turbine
Torque

Centrifugal Pump & Gear Box
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Power PW of the
wind turbine
Rotational speed nW of the wind turbine
curve of operating
points
Wind Pumps ...
Can be a very easy and cost effective solution if appropriate designed!
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Contents
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Wind Diesel Systems
In many remote locations in the world, power generation with diesel generators is the common;
Fuel prices, however, are often very expensive: InAustralia/China, fuel costs per kWh can reach up to 20 Uscents;
Wind power can be used as fuel saver!
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Wind Diesel Systems
Different design concepts possible, from very basic to extremely complicated;
Costs versus reliability, power quality, lifetime of diesel generator & battery, redundancy of equipment.
Larger number of different concept are in use.
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Diesel/ Battery
Diesel: Cascade Design;
Battery: Short term storage up to 5-10 minutes; Short lifetime due to large number of cycles, Extra building, Air-condition ?, Environmental problematic;
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Practical Steps
Important: Define Max, Min and average load
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Wind-Diesel-Battery Systems
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System 1: Wind / Diesel Controlled by Frequency (Droop Mode)
The grid frequency is used as a measure for loadsharing between the WTG and the diesel genset;
If the load increases, speed of diesel drops and frequency decreases;
If diesel power output is less than 50 % than wind turbine would sense a rise and would start to pitch (reduce output), hence increase load on the diesel generator
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System 1
Advantages
WTG can be installed without communication link;
Minimum load on diesel genset is ensured;
Disadvantages
Wind speed fluctuations affect grid frequency
Need

small wind turbines and wind pumps - välkommen till kth · pdf filethomas ackermann...

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