Design procedures and experimental verification of an electro-thermal deicing system for wind turbines
Authors: Getz David , Palacios Jose 
Published: October 2021

Abstract. There has been a substantial growth in the wind energy power capacity
worldwide, and icing difficulties have been encountered in cold climate
locations. Rotor blade icing has been recognized as an issue, and solutions
to mitigate accretion effects have been identified. Wind turbines are
adapting helicopter rotor and propeller ice protection approaches to reduce
aerodynamic performance degradation related to ice formation.
Electro-thermal heating is one of the main technologies used to protect
rotors from ice accretion, and it is one of the main technologies being
considered to protect wind turbines. In this research, the design process
required to develop an ice protection system for wind turbines is discussed.
The design approach relies on modeling and experimental testing.
Electro-thermal heater system testing was conducted at the Adverse
Environment Rotor Test Stand at Penn State, where wind turbine
representative airfoils protected with electro-thermal deicing were tested
at representative centrifugal loads and flow speeds. The wind turbine
sections tested were half-scale models of the 80 % span region of
a generic 1.5 MW wind turbine blade. The icing cloud impact velocity was
matched to that of a 1.5 MW wind turbine at full power production. Ice
accretion modeling was performed to provide an initial estimate of the power
density required to de-bond accreted ice at a set of icing conditions.
Varying icing conditions were considered at −8 ∘C with liquid
water contents of the cloud varying from 0.2 to 0.9 g/m3
and water droplets from 20 µm median volumetric diameter to 35 µm. Then, ice accretion thickness gradients along the span of the
rotor blade for the icing conditions were collected experimentally. Given a
pre-determined maximum power allocated for the deicing system, heating the
entire blade was not possible. Heating zones were introduced along the span
and the chord of the blade to provide the required power density needed to
remove the accreted ice. The heating sequence for the zones started at the
tip of the blade, to allow de-bonded ice to shed off along the span of the
rotor blade. The continuity of the accreted ice along the blade span means
that when using a portioned heating zone, ice could de-bond over that
specific zone, but the ice formation could remain attached cohesively as it
is connected to the ice on the adjacent inboard zone. To prevent such
cohesive retention of de-bonded ice sections, the research determined the
minimum ice thickness required to shed the accreted ice mass with the given
amount of power availability. The experimentally determined minimum ice
thickness for the varying types of ice accreted creates sufficient tensile
forces due to centrifugal loads to break the cohesive ice forces between two
adjacent heating zones. The experimental data were critical in the design of
a time sequence controller that allows consecutive deicing of heating zones
along the span of the wind turbine blade. Based on the experimental and
modeling efforts, deicing a representative 1.5 MW wind turbine with a
100 kW power allocation required four sections along the blade span, with
each heater section covering 17.8 % span and delivering a 2.48 W/in.2
(0.385 W/cm2) power density.