From the abstract for "NREL Airfoil Families for HAWTs" by Tangler and Somers:

“The development of special-purpose airfoils for horizontal-axis wind
turbines (HAWTs) began in 1984 as a joint effort between the National
Renewable Energy Laboratory (NREL), formerly the Solar Energy Research
Institute (SERI), and Airfoils, Incorporated.  Since that time seven airfoil
families have been designed for various size rotors using the Eppler
Airfoil Design and Analysis Code.  A general performance requirement of
the new airfoil families is that they exhibit a maximum lift coefficient
(c_l,max) which is relatively insensitive to roughness effects.  The airfoil
families address the needs of stall-regulated, variable-pitch, and variable-
rpm wind turbines.  For stall-regulated rotors, better peak-power control
is achieved through the design of tip airfoils that restrain the maximum
lift coefficient.  Restrained maximum lift coefficient allows the use of
more swept disc area for a given generator size.  Also, for stall-regulated
rotors, tip airfoils with high thickness are used to accommodate overspeed
control devices.  For variable-pitch and variable-rpm rotors, tip airfoils
having a high maximum lift coefficient lend themselves to lightweight
blades with low solidity.  Tip airfoils having low thickness result in less
drag for blades having full-span pitch control.  Annual energy improve-
ments from the NREL airfoil families are projected to be 23% to 35% for
regulated turbines, 8% to 20% for variable-pitch turbines, and 8% to 10%
for variable-rpm turbines.  The improvement for stall-regulated turbines
has been verified in field tests.”

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