Walker remember what we talked about last night? "Synthetic Coal?"
Or, as an alternative, simply make a technology that eliminates the need for coal in Industrial & Consumer goods altogether.
I.E. "Finished Goods Coal Consumption -100%"
I've often wondered why, exactly, factories themselves need coal when they're getting all their energy from other power facilities located elsewhere.
Other new tech ideas could be trade-offs for the sake of balance. For example, "Sustainable Lumber" could be an eco-friendly tech that would raise the Environment rating by 10% but also reduce Timber Mill production by 25% (decreased logging, more time spent planting replacement trees, ect).
Another one that I always thought was really obvious: Electric vehicles. Not fuel cells, but straight up electric cars. Put it in various stages:
Fully Electric Mass Transit (-20% population oil consumption, +20% population power use, +5% environment rating.)
Fully Electric Cars (-70% population oil consumption, +70% population power use, +15% environment rating.)
Thus a fully electric transport system would be great for a country with vast fields of Advanced Solar and Cold Fusion plants. Some oil will always be used, of course, for other things (lamp oil, fertilizer, engine lubricant, cooking spray, etc). Since the game has no real reflection of the airline industry that could easily be a 90% reduction for those willing to take the hit on power use.
Fully Electric Military Vehicles - Drain power instead of oil when calculating resupply. Simple enough.
Also, there is that one laser-strategic bomber, the YBL. It is interesting because when you look at it's stats it only shows an ammunition supply of 1. This is not a bug, however - rather the YBL never runs out of ammunition. It's a laser, after all. So long as it's jet engines are producing electricity it can keep on firing. I think that's spiffy and I wish this was incorporated into other units in the game, especially considering just how many are supposed to be sporting laser weapons in the first place.
I wonder if something similar could be done for fuel supply as well? It seems to me that the next step after Cold Fusion is miniaturizing it down to vehicle size units, thus giving land units the kind of ranges previously only seen in nuclear powered naval ships. So there's something else that could be invented: Vehicular Cold Fusion. Vehicle range is now effectively infinite. Combine that with laser weapons and you'll never need supply vehicles again.
Now with all this talk of power, there is also plenty of room for more power technologies: Right now we've got solar power giving the same output all over the place. It would be more realistic to have solar output based on how far the plant is from the equator. To make up for that you could add in GeoThermal power, Tidal power and even Wind power. GeoThermal might work better in mountainous regions, tidal obviously would go on water tiles, and wind would operate opposite of geothermal by gaining effectiveness based on how flat the terrain is.
So on and so forth...