Rossi said that the latest e-cat operates at high temperatures and thereby achieves roughly 40% Carnot efficiency. It would be better to operate at lower Carnot efficiency. Conventional nuclear fission reactors operate at roughly 33%, and a much lower temperatures than Rossi describes. This is better because the fuel is very cheap, whereas increasing the operating temperature increases the wear and tear on the steam turbines. In the case of cold fusion, the fuel costs nothing, so you should optimize to produce the lowest equipment cost over the life of the machine.
You do not want to go down to 5% Carnot efficiency because you would end up with a machine looking like a 19th-century steam tractor, with a gigantic engine. Like this: http://upload.wikimedia.org/wikipedia/commons/3/35/Ruston_and_Hornsby_steam_tractor_sn_115100_of_1922.JPG In other words, 40% efficiency would be an advantage only insofar as it allows compact engines, and it reduces waste heat. In many applications, waste heat is not a problem. If you can achieve 40% efficiency for the same equipment cost as 30%, then go for it. - Jed
