I agree with others saying primary and secondary are dangerous words to use. The "primary" needs to be the winding that is the source of magnetic excitation of the core, the utility side. The "secondary" is the side connected to loads, even if they are negative loads like generators. This is important because the inrush will be affected by which winding provides excitation. Using a transformer in "reverse" where the nominal "secondary" is now the winding supplying excitation may lead to unpleasant surprises.

Another thing to consider is the losses. Transformers have no load losses that exist 24x7 and load losses. Over a year these may eat up 2-4% of the energy generated by the system. Select the transformer with that impact in mind. Just because it is DOE-compliant does not make it a low-loss transformer.