Sorry to bother, maybe I'm just dumb.
When placing the Solar Power Tower and adding the Heliostat Mirrors I get a "No input fluid" message on the tower.
A Heat exchanger with water is connected and the tower only seems to have in-/outputs for heat pipes.
Can somebody enlighten me?

• Has to be daytime, obviously
• You need a certain number of mirrors before temperature will start to rise, something like 50 odd (about 10% capacity, I can't remember)

Oh damn. Yes, that was it. I just hadn't enough.

Thanks for your help.
Great mod by the way as far as I can tell (not at the laser beams yet ^^)