I had a few Idea I thought about while wondering how geothermal could be reworked to be "realistic" and less exploitable.
Those Ideas could be implemented in IC²-exp or more likely in GT, but I doubt it will. Though, it's still a source of inspiration for any modder.
Basically, my idea was that Geothermal should generate energy depending on ground Heat, and not consume Lava. I know it have been suggested already, for instance by SpwnX (and me as well), but I've got some new Ideas.
The whole system would be based on scanning the underground. Each biome would have some values of Heat, Oil sources, Mineral ressources. To exploit them, you would at first scan the ground. This wouldn't be necessary, but given the following process would be expensive, you'd better do it before mining in a blind way 
To scan this underground, you would have several means, giving different informations.
By using Dynamites in small machines that you would put at different points, you would have informations about the density of the underground, especially if there are liquids.
For that sake, let's assume under the Bedrock is a huge amounts you would try to exploit, and below that, an even harder than Bedrock layer.
This would mean that, with the vibrations you would generate by detonating dynamites in those machines, and collecting all the results in an other machine (that you would put where you want, but all informations being distance-between-the-explosion-and-this-machine-related, you'd better not put it randomly), you would be able to guess where are huge Oil Sources (lowest density = lowest speed of waves in it = highest delay of waves coming after having bounced on it, delay that you could measure if you placed the machines and the explosion intelligently), Lava Lakes (Low density), uninteresting rock (unless you REALLY want tons of cobble stone, medium density) and high-density minerals, containing metals and ressources you are looking for.
Such a system could of course be even more expanded (different kinds of Oil, such as Shale, Bituminous, Natural Gasses, "conventional" Oil, different kinds of Minerals Deposit), but I guess it would need as well some others way to get informations than just detonating dynamites ^^.
Once you'd have located the ressource you want, you would have to use a Drilling Machine that would use HUGE amounts of EU (like 2048EU/t and more than 50 000 000 EU per layer, if a depth is implemented as well as the rest of the system), or more likely run on Fuel (IC² definitely needs its own one, but GT Diesel would be enough) or Nuclear Fuel (using "more powerful" non-renewable sources of energy is a good way to nerf it IMO) and consume Steel/Tungsten/even Diamonds Bore Heads (that you must replace if you don't wanna damage your Drilling machine). The Drilling Machine in itself would be multiblock, and why not consume as well water (to be cooled down) and chemicals (to consume like 20 times less energy with GT, given Greg would do it like 1 000 000 000 EU per layer, and with an engine not taking electrical energy but only chemical and nuclear Fuels ^^). Of course the recipies would be extremly expensive (or maybe there could be a "cheap" version, reachable before Quantum Suit, but that wouldn't dig fast/deep etc ...)
Once the Hole is drilled, you would remove the Drilling Stuff from the Machine (The Bore Head) unless it's to mine mineral ressources. You could stop the Machine before it reached the unbreakable layer, but then you may miss some interesting stuff.
To know what you'll be able to collect you would then pick up some rocks at the depth you want (each cells of picked-up rocks would cost a bit more of energy/chemicals), and then you would have to analyze those cells using Centrifuge/Thermal Centrifuge or some new machine including Computers. This point is extremly important to me since it could even help to implement a useful research system (and if so, what about a chemical reactor in which you would test your cells to know what they contains ? ^^)
Then you would setup your pump/Thermal Pipe installer and chose at which layer you want it to process.
You would have a GUI in which you would chose those stuff you want to install (you could put several Thermal Pipes, those being able to collect Heat from Geothermal sources): of course at this point itwouldn't be testing anymore, unless you hadn't done test enough before with the rocks picked up.
At the last stage you would either: Pump Oil for a bit of energy (and get extremly larges Oil sources, comparable to a Nether Lava Lake), generate Steam from Geothermy with an insane output or generate some ressources while consuming Steel/Chemicals/what you want to nerf it and above all, to avoid it to be infinite and to make it time-spending.
In the end this system would give IMO an interesting gameplay once you've reached "EndGame" (or Late game, before the Fusion Reactor with GT), possible new ressources without implementing Ores (as an example, GT Fusion reactor should then be even more expensive and require ressources you would find in large amounts using those machines), a nice "research" system (several ones into a big one!), the ability to generate lots of energy infinitely with Geothermy, but at a quite high cost (not really enjoyable without the nerf of GreenGens from GT), and give any moder the possibility to create a whole "Oil Industry" to be played without BC (or not compatible, cause Oil Industry could be funny, but OP with BC sources).
