Seems to be incompatible with the Concrete Gate from Shall Tank Platoon (https://mods.factorio.com/mod/SchallTankPlatoon):
Failed to load mods: Error while running setup for entity prototype "flat-solar-panel" (gate): next_upgrade target (Shall-concrete-gate) must have the same fast_replaceable_group (wall != solar-panel).

I think the concrete gate must be from a different mod because I can load the tank platoon mod with this one no problem. Any chance you could share a save with me? Or find out what mod the concrete gate is from?

I think I know what's causing it, though. Uploaded a solution. Let me know if that fixes it.

Well I loaded your updated version (0.1.11? I think), and the game loads fine now. I'm going to try to load and see if the research shows up normally.

Confirmed that the new "Flat Solar" research is available for 500 red and green science. Looks like you fixed it!