One of the major complaints with IC today is the over-poweredness of solars. This could be combated by providing another renewable (free) energy source. As it stands, geothermals only use lava. I suggest that they instead should use the heat of the earth.
Real geothermal power pumps water down into the earth, then uses a turbine to produce power as the steam comes up. In Minecraft this is impossible; however, we could have geothermal generators produce power when placed underground. The EUs produced could be based on height, like wind farms: i.e. the deeper you go the more energy is produced. But what to do with all that lava? Lava could be used to increase the eu production, somewhat similar to how scrap works with the UU machine. This would also let us use our BC pipe systems to pump the buckets in and out. The recipe would probably need to be changed for balance reasons, but who really cares what that looks like.
Anyway, let me know what you think and any gaps I left.