Err...I think you will find that there are far more power generation units utilising steam turbines that are fuelled by coal, oil, natural gas etc. Nuclear powered units are only one option!
Oh, I know that. I'm just being contrary to be a pain in the arse! :)
The original article as a general rule suggests, "that a steam engine of 500-horsepower is the equivalent of a 1000-horsepower internal combustion engine." so you're getting twice the power for half the size?
Is that how we should interpret that statement? I would read it as for the size of a 1000 hp unit you only get 500 hp. Or for the same HP you need an engine twice the size.
And, of course, your comment on the ancillery equipment is very true and is also where the bulk of the mass of the system is.
For example, the engine for the M1 tank is the Lycoming (now Honeywell) AGT1500C gas turbine that produces about 1500 hp and weighs about 2500 lbs. The actual gas turbine part of the engine, i.e. where the air is compressed, fuel burned and power extracted, is pretty small and only weighs about 400 lb. The regenerators. intercoolers and preheaters that allow the powerpack to be efficient enough (barely) to be practical in a tank weigh the other 1100 lb. Plus the 500 gal of fuel. And no water. And all of this is with modern materials and processes.
The Maybach engine in the Tiger 1 also weighed about 2600 lb for 690 hp. If we use the ratio from the article per my interpretation above (could be wrong, but am going with it for now) then the basic steam turbine engine to produce 690 hp would mass about 5200 lb using equivalent WW II materials and science. Using the ratio from the AGT1500 of ancillery equipment to basic engine weight of almost 4:1 (1100:400) then the steam system mass in a Tiger-sized steam turbine engine might be 20,000 lb.
Plus fuel and water.
These are just spitballin' type numbers of course, but a steam turbine engine that is efficent enough to run a tank any tactically useful distance is bound to be many times the size of a similar internal combustion engine. Once the volume starts to go up you can either reduce the protection around the entire vehicle to keep the mass down, or increase the mass greatly and suffer a significant reduction in performance.
Or, of course, you can cover the hull and turret in rivets, plant a big smokestack on the engine deck, put a smoothbore breechloader in the turret and call it a
steampunk tank and built it. :)
Paul