I'd like to propose the following mod idea: A steam engine to generate mechanical power, producing about the overall torque as 2 large windmills in a storm at sea level, but more compact and convenient but at the expense of maintenance and resources.
It has 3 parts to it that are placed individually:
- A boiler
- A normal fire pit
- A piston that connects to a flywheel, which in turn is the attachment point for your axles
Water is placed into the boiler. It has an interface similar to a barrel, but instead of one bar showing how full it is, it also shows pressure.
When the fire pit is burning beneath the boiler, the temperature in the boiler raises. when at 100°C, it generates pressure. Depending on the pressure, the system generates torque. Depending on the pressure at the time, an amount of water proportional to that pressure is released from the boiler if the system is moving. If the system is not moving the pressure will raise more. Once the system is moving the pressure will be constant.
The speed should be fairly slow, encouraging to build a transmission.
Adding additional torque sources will reduce the amount of water being used, but not the fuel consumption. No pressure can be had beneath 100°C.