Design and development of small wind turbines - Wind Power Generation and Wind Turbine Design - page 275

Given the relatively limited resources of the industry at present, many design
refi nements can be expected in the future, in such areas as:

￿ Rotor design

Although most manufacturers have adopted the horizontal axis confi gura-

tion, signifi cant research is ongoing with vertical axis machines.
A number of overspeed control mechanisms have been considered, but the

most prevalent (the furling tail) does not scale up very easily, and different
concepts are being explored such as pitch-to-stall rotors, coning rotors, and
deformable blades.
Most rotors are made of reinforced plastics, however there is active research

into modifi ed wood blades as well as other materials.
Drivetrain design

￿

Permanent magnet alternators are available up to about 10 kW, above which

induction machines tend to be used. However, with advances in permanent
magnet technology, it is possible that this technology will become available
in larger size, along with larger grid-tie inverters.
Variable speed drives are commonly used in industry for variable speed mo-

tor applications using induction machines. It is possible though less com-
mon for “regenerative” drives to be used on e.g. elevator applications, where
power is returned to the grid. This technology could be applied to induction
generator-based wind turbines.
Though gearboxes have been traditionally used for power transmission in

induction generator-based turbines, recent advances in timing belt materials
mean that this technology can now be used, offering the advantages of low
noise, high shock load capability and lack of need for lubrication.
Tower design ￿

Advances in laminated wood technology (“glulam”) may result in the

possibility for high-technology wood towers. This would result in low
embodied energy/low CO 2 towers made from sustainable forests.
Control systems ￿

With mass production of small wind turbines even more advanced, micro-

processor-based control and monitoring systems are expected. These will
provide remote communications capability, detailed operator/owner displays
and more advanced condition monitoring capability.

3 Conclusions

Although less signifi cant in an energy sense than large wind turbines (which have
the potential to supply a signifi cant percentage of the world's electricity), small
wind systems have a bright future. Demand is rising rapidly, and costs should
correspondingly decline. Until now, R&D has been limited to the rather small
budget of the few companies that have been able to survive in the small wind busi-
ness. Therefore there will be a signifi cant increase in R&D on small wind systems,
which will result in improvements in reliability and value.