Environmental Engineering Reference
In-Depth Information
W
m
Weighting matrix in de-icing performance cost function
X
De-icing performance state vector
x
Chord-wise distance from the leading edge of the blade
x
b
Chord-wise blade axis along resistor columns
y
b
Span-wise blade axis along resistor rows
x
Angular velocity of the rotating blade
8.1 Introduction
With good wind resources often in cold and wet regions, installation of wind
turbines in these regions has been growing faster than the total installed wind
power capacity in the world. From the year 2008 to 2011, the global total installed
capacity of wind turbines approximately doubled while the installed capacity in
cold regions increased more than three times from 3 GW to more than 10 GW.
Many regions of North America (Minnesota, Alaska, Canada, etc.) and Europe
experience more than 50 days per year of icing conditions.
Atmospheric icing causes several problems on wind turbine operation in cold
climates. It causes (1) significant reduction of the energy production because it
lowers aerodynamic efficiency of the wind turbine blades, (2) errors in sensing
wind speed and direction, (3) mechanical failure by increasing load and mass
imbalance on the blades and tower and also increasing high amplitude structural
vibrations and resonances, (4) electrical failure by snow infiltration in the nacelle,
and (5) safety hazard issues when ice sheds off the blades. Seifert and Richert
studied the effect of different amounts of ice accretion at the leading edge of the
blade tip on aerodynamic efficiency of wind turbines [
1
]. Their analysis showed,
for the case of severe ice accumulation, that more than 40 % of the average
generated power may be lost for the wind speed range of 5-20 m/s for a typical
300 KW wind turbine using pitch control. This was based on different power
curves calculated using the aerodynamic characteristics of the various iced sec-
tions found in wind tunnel tests and linear interpolation along the radius of the
blade (Fig.
8.1
). This analysis can be extended for a range of turbine sizes by
updating the power curve versus wind speed at hub height. Figure
8.2
shows
examples of ice build-up accretion and some of the issues that result [
2
,
3
].
This chapter includes 11 sections. In Sect.
8.2
, we introduce different types of
atmospheric ice accretions on wind turbine blades. In Sect.
8.3
, we describe
background information on existing ice sensing and thermal actuation techniques
and compare their effectiveness for active de-icing of wind turbines. In Sect.
8.4
,
we present calculations of heat flux requirements for de-icing. We describe a
proposed method of ice detection using optical sensors in Sect.
8.5
and further
discuss our experimental results on detection of different types of ice using a
particular class of optical sensors. Our optical sensing method allows direct and
