:You mean right now? see - PACER power which has a lot of references that it is commercially viable(although politically a hot potato and therefore unlikely to be tested). As for steady state sources. Well apart from the worldwide international effort to build the first steady state fusion reactor - ITER, a project that has more nation state collaborators than any other construction project in the history of mankind, because everyone and their cat knows it will be commercially viable and sustainable. Well then no I don't -D 

 : Moreover, are you honestly trying to argue the most common source of visible energy in the entire universe -Fusion, is not sustainable for billions of years? The very processes that power our star and every other star in the entire universe... is not sustainable? 

 : Am I in the twilight zone? 
 :