Environmental Engineering Reference
In-Depth Information
edges of the blades themselves, not on the tower, leading to inaccuracies when
trying to correlate the weather station data on the tower or nacelle to the active
portions of the blade. Wind velocity is another factor which affects ice formation
and accumulation on the blade which is not taken into account in most existing
indirect ice detection methods.
Direct ice sensing methods are more accurate for direct detection of ice on the
blade with better spatial resolution. Some examples of direct ice sensing methods
are resistance, impedance, and capacitance based methods, as well as optical
techniques. In Ref. [
10
], capacitance, inductance, and impedance sensing are
introduced as effective on-blade ice sensing methods for wind turbines. These
sensors can detect ice formation within a localized area, and their thin sensing
elements or electrodes can conform to blade surfaces [
10
,
13
]. More information
on these methods are available in [
12
] and [
14
]. Ice removal technology coupled
with an early detection of ice formation on the blade for reducing aerodynamic
degradation (shown in Fig.
8.1
) appears to be an essential feature for future
generations of wind turbines in cold climates. There are currently no widely
available and sufficiently reliable ice detection systems suitable for wind turbines
[
10
,
15
]. Figure
8.3
shows a summary of different approaches to ice sensing and
anti-icing and de-icing [
12
-
14
], including our technique which will be detailed
further in this chapter. Direct sensing and active actuation methods are the most
energy efficient methods of de-icing. In Sect.
8.5
, we discuss our experimentally
demonstrated optical ice sensing method which is capable of high resolution and
fast detection of ice existence, type, and thickness with micron-range accuracy.
8.3.2 Thermal Actuation
De-icing and anti-icing methods in the literature can be divided into active and
passive methods. While many wind turbines operating in cold climates encounter
icing conditions, very few of them are equipped with active de-icing and/or anti-
icing systems. Currently, wind turbines installed in cold regions use passive
methods such as ice repellant (ice-phobic) coatings on the blades. However, these
coatings are only effective for short-term operations in slight icing conditions and
are not effective in harsh cold conditions with varying forms of ice. As an
example, silicon paints exhibit promising ice repellant characteristics on soft rime
under slight icing conditions; however, hard rime ice exhibits greater adhesion
strength to silicon paint than an uncoated surface. In addition, these passive ice
prevention techniques have been shown to have poor durability when tested on
wind turbines [
15
,
16
].
Active heating systems are more effective for ice prevention. After sensing and
detecting icing conditions, anti/de-icing systems are activated to mitigate turbine
downtime. Active heating systems either affect the aerodynamic efficiency and/or
the generation capacity of the turbine. Both hot air injection and resistive heaters
can consume more than 10 % of the generated power [
12
,
17
].
