Where can I build a Thermal Power generator in XCom
According to the description, Thermal generators must be built "over steam vents". Naturally, I assumed that this meant the space above the one marked "steam", so I cleared out rubble and tried to build on that space, only to find that I could not.
Do I need to actually build on the space that says "Steam", or above it as the description says? If above it, is there any reason I can't build on a space I've cleared out? (other than money, which was not an issue).
You can only build thermal generators on squares in your base view that have "Steam" in them. This is a bit confusing in the tooltip, but that's the way it's implemented.
There's no reason to avoid building on an adjacent square - there's nothing unusual about the space above a "Steam" square. However, there is an adjacency bonus for power plants. Therefore, you might want to consider building another power plant type there, in order to get the bonus power.