25-07-2012, 10:27 AM
Small Wind Turbine Testing and Applications Development
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Introduction
Small wind turbines offer a promising alternative for many remote electrical uses where there is a good
wind resource. The National Wind Technology Center (NWTC), part of the National Renewable Energy
Laboratory (NREL), helps to further the role that small wind turbines can play in supplying remote power
needs by both testing and developing new applications for small turbines.
The goal of this work is to characterize small wind turbines, wind-diesel hybrid system components, and
wind-hybrid systems and to develop new off-grid applications for small wind turbines in order to expand
the international market for these systems. Projects fall into two classifications: applications development
and testing. Testing includes both small turbines and wind-hybrid systems. Although the projects that
fall under applications development and testing are varied, they all focus on the remote power market and
all include small wind turbines as the power source. Specific project descriptions follow.
Peak Power Tracker.
Many small wind turbine generators consist of a variable-speed rotor driving a
permanent-magnet synchronous generator (alternator). The principal application of such wind turbines is
battery charging, in which the generator is connected through a rectifier to a battery bank. The wind
turbine electrical interface is essentially the same whether the turbine is part of a remote power supply for
telecommunications, a stand-alone residential power system, or a hybrid village power system; in short,
any system where the wind generator output is rectified and fed to a DC bus. Field experience with such
applications has shown that both the peak power output and the total energy capture of the wind turbine
often fall short of expectations based on rotor size and generator rating.
The performance of permanent-magnet wind turbine generators (WTG) in battery charging applications is
limited by a mismatch, over most of the operating wind speed range, of the rotor, generator, and load
characteristics. The power available in the wind, for a given swept area, increases as the cube of the wind
speed. A given wind turbine rotor has a certain tip-speed ratio at which it converts wind power to shaft
power most efficiently. In order to convert the maximum possible fraction of available wind power to
mechanical power, the rotor must operate at this optimal tip-speed ratio, with its revolutions per minute
(RPM) varying in proportion to wind speed.
Health Clinic Replication.
In a given community,
the local health clinic and school are often the first
facilities to be electrified6. To better demonstrate
these applications, NREL is building a mock health
clinic/school at the NWTC. The purpose of this
replica is to provide a hands-on demonstration of
applications that are compatible with stand-alone
renewable energy systems. The mock-up is
currently under construction. It will consist of a 10’
x 20’ prefabricated building on a concrete slab.
Power will be provided by a hybrid system composed of two Windseeker 503 wind turbines and a 240 Wp
solar panel array. Applications will include lighting, communications, TV/video, water purification,
medical appliances, and solar water heating and disinfection.
Data Acquisition Development.
Reliable technical monitoring of hybrid power systems is crucial for
evaluating their performance and cost and trouble shooting problems. Valid data sets can be fed into
analytical models for a long-term simulation of the system’s performance and development of
recommendations to improve a system’s operational characteristics. Typical monitoring systems for winddiesel
hybrid sites include the following major components: datalogger; wind speed/direction, solar
radiation (depending on site) and temperature sensors; power measuring equipment (voltage, current,
power transducers); fuel consumption gages (optional). The number of sensors and measurement
frequency depends on the system’s complexity and monitoring objectives.