Is the solar duty distribution transformer used for zig-zag or autotransformer grounding transformers?

No, the solar duty distribution transformer is meant to be used as a low voltage grid tie transformer to correctly adjust the voltage between the solar inverters, energy storage, utility grid and/or facility, especially where a bi-directional feed is used. HPS does supply zig-zag and autotransformer grounding but not under the solar duty distribution transformer heading. Grounding transformers are a different application than the solar duty distribution transformer,