Not sure if this is going to make the balance of the intended game tip, but i suggest mid game availability of Solar and Wind power generation with high component cost, low power production and intermitent power availability (inground).
But of course a lot of people (including me) will criticize the solar option, as there is no silicone in game.
In all honesty the installation and completion of the space elevator should provide solar power generation from the elevator itself. and in return in ground gases and liquids should be processed and sent up (Diesel/RP1, Oxygen, water, etc).