Fundamentals of wind energy - Wind Power Generation and Wind Turbine Design - page 40

Figure 15: Flex-drive planetary gearbox. Courtesy of [109].
the supply chain to investigate design-level root causes of fi eld problems and
solutions that will lead to higher gearbox reliability [111].
7.8 Integration of wind and other energy sources
One of the notable characteristics in the wind power generation is its uncertainty
due to the sudden change in both wind speed and direction, especially for off-grid
wind power generation systems. Therefore, the power output from wind turbines
fl uctuates from time to time. When wind turbines are connected to a small or
isolated grid, the power output from other generators must be varied in response
to these variations and fl uctuation in order to keep system frequency and voltage
within predefi ned limits. For this purpose, it is benefi cial to integrate wind and
other complementary energy sources to form hybrid power systems for assuring
the stability and reliability of power supply and reducing the requirement for the
wind energy storage.
7.8.1 Wind-solar hybrid system
Both wind and solar energy are highly intermittent electricity generation sources.
Time intervals within which fl uctuations occur span multiple temporal scales,
from seconds to years. These fl uctuations can be subdivided into periodic fl uctua-
tions (diurnal or annual fl uctuations) and non-periodic fl uctuations related to the
weather change.