I am so sorry, I am new to this forum. Below is the formula used when trying to add a drop down list. Cell P3 was just recently added as a BU (Business Unit) only to try out the equation.

=LOOKUP(2,1/(((COUNTIF($W$2:W2,Turbines[Location]))+($P$3<>Turbines[BU]))=0),Turbines[Location])