Version 0.1.0 (Factorio 0.16.x)

Power production slightly more nuanced:
Boilers remain 50% efficient and have been tinted slightly red/rusty.
"High efficiency boilers" are 70% efficient and crafted from a boiler, steel furnace, copper, and concrete.
Steam engines are 70% efficient and steam turbines are 80% efficient (so are useful even with boiler steam).

Boiler/exchanger/engine/turbine ratios remain the same, only the rates of fuel consumption and power output are changed. (Overall, you get less power and consume more fuel, making power production slightly more of a consideration.)