My suggestion based on playing the modpack and GregTech 5 is that there could be some sort of weird form of energy from stainless steel age, railcraft boilers are currently the form of energy we use, but they require steel and the next big step would be to nuclear power. I'm putting it blunt, my friend made a notion when I was talking about this feedback post that currently the gregtech solars aren't there.
He also likes oil and liquids as much as we all do- but oil rarely gets used. We did use it a bit in the start, but our bio-steam plant replaced that need entirely, why not use oil as in real world in CSP power production? http://en.wikipedia.org/wiki/Solar_thermal_energy