Actually, I've never used Greg's GeoGens, but I like his Diesels. Not sure why, but... they seem good.
They're crap when you start looking at relative output.
One of the reasons everybody uses lava is the a geothermal produces 24EU/t while a diesel produces 12. One uses a fuel that is widely available and usable as soon as it's pumped up. The other has irregular, limited, spawnings and must be processed (...and both can be made from bees, but lava made easier)[DOUBLEPOST=1368827316][/DOUBLEPOST]
as i said previously, multi block structures should be the way to go with solar power, to strike the balance with server load and space required
There's also relative use to other generation. Solar should be the worst generator in both resource cost as well as space allocated.
Start with advanced solar, turn the curent IC2 solar into a dead box, used only in construction of the second tier. The second tier is ALSO a dead box, only used to create the third. The third level generates 1EU/t. Eliminate the fourth tier altogether.
Now, solar is relatively balanced.