I've been trying to crack this nut for awhile now. I have a Generac 36KW (with Nexus controller) residential unit and want to interface it with Indigo. So far I found a guy that has setup a Raspberry Pi3 connection with WIFI and some Python code. I was able to duplicate his design because he documented so well.
https://github.com/jgyates/genmon/wikiIt works with the two most common generator controllers, Nexus and Evolution which are found in many of the home generators.
I have that installed and working it has both a web interface and a socket interface that we can connect to. The next step is to figure out how to interface that to Indigo. I'm hoping that maybe someone here might also have a home backup generator with an Evolution or Nexus controller and might be interested in setting up the same (genmon) hardware/software setup. If so, we can collaborate on integrating with Iindigo.
At this point I'm not overly confident in my programming skills to do it by myself, but given enough time, I'll have it figured out but not sure it will be "clean" enough for other people to use.