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It is all about available capacity. The biggest apples and oranges distinction can be kept clear if the heat engine is remembered as an essential thing between burning fuel and either mechanical or electrical energy. That can be the car engine or the central power plant steam turbine, or whatever kind they are using. All of our heat engines discharge a huge amount of wasted heat; some even a lot worse than others.
Surprisingly, the production Prius turns out to get about 38% efficiency out of its specially loaded engine. Good diesels get 35%. Engines in coal fired power plants get about 33% (and that includes the electric generator losses as well.) Some natural gas combined cycle plants get about 50%, and maybe a little more. But in every case all those efficiencies are a lot less than 100% and the difference is the heat wasted.
They locate these central power plants out away from population centers so they can get rid of the heat without bothering people much. This system was dumbed out 100 years ago when fuel was almost free; not so dumb then, but it sure looks dumb now.
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