Congratulations on your Great Work! Such a great feeling to get something that substantial under construction. Solar farm was the first one I ever built, too, and I was very happy with it. I've built solar farm a couple of times, and they always worked great for me. Gotta love lots of clean power!
Been a while since I constructed any GW, but I think the numbers reported are part of that whole disconnect between regional view and city view numbers. The last couple I've built have been Arcologies and once they're built it is a nightmare trying to figure out what is actually coming in to the city. The city population data map will show commuters from the "region" - sometimes - but the regional map never shows anything coming from or going to the arcology. This is, of course, the opposite of what you're seeing during building.
The likeliest answer is - this is another one of those things that drive data crunchers crazy. The good news is you only have to make sure you have the correct number of "unemployed" or "commuting" workers to keep it running and hope you can concentrate your attentions elsewhere so it doesn't drive you mad.