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A multi stage steam turbine is very efficient by itself. It can be 80-90%. You end up with waste heat in the condensate, and you can have inefficient ways of making the steam in the first place.
So old ships burned fuel oil to make steam, then steam to turn the propeller and steam to run generators to make electricity. The condensate heat was just wasted into the ocean because it was simple and reliable and needed to be handled on a large scale. Modern ships use jet fuel to run a gas turbine and eliminate the steam middle man. Then nuclear ships use the nuclear reactor to superheat water at pressure, that water is used to boil other water and make steam, steam runs propulsion turbines, and turbine generators, and again the condensate heat is wasted.
So if you used an efficient method to make steam like nuclear, used efficient turbine generators, and put the condensate heat to some use, I'm sure it would be by far the cleanest and most efficient way to make electricity.
I know some fossil fuel power plants up north use the condensate heat to melt sidewalks in the towns nearby. That is sort of a luxury and seasonal, but there has to be some use of heat year round. In a desert neat saltwater you could probably use it for desalination. If you put water at a high vacuum it will boil at a lower temperature.
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