Hydrogen Fuel Cell Generator.

Here is the rationale:
In the vanilla game, hydrogen-powered vehicles carry hydrogen and an onboard fuel cell that converts chemical energy into electricity to drive the wheels. Logically, this setup can be scaled up into a large, high-capacity stationary generator. It would provide instant load-following power generation, with steam as its only byproduct. This feels like a very lore-friendly, vanilla-style solution.

To put the numbers into perspective: your tier-4 "Uber Excavator" consumes 10 hydrogen per minute. Converting that hydrogen directly into electricity equals exactly 2.083 MW of power, and that is while the vehicle is actively moving. For a massive stationary fuel cell unit, a power output of around 5 to 8 MW with dynamic load-following capability would be highly reasonable. Balancing the hydrogen consumption based on these metrics should be quite straightforward.

To make things more challenging and logistically engaging for the player, this generator should also require a supply of Pure Oxygen. This makes perfect physical sense—the internal catalysts responsible for this chemical reaction are prone to poisoning and degradation. The fact that vehicles can drive around for hundreds of years without changing their fuel cells is just a developer abstraction. In a stationary industrial plant, maintaining and supplying the catalyst reaction with oxygen fits the gameplay loop perfectly.