Ok. Maybe I needed to ask: " Is it possible to have higher efficiency from a water driven device as opposed to an air driven device?" . I do not have capability for any head for water so I was hoping for an alternative. Thanks for a clear response.
Vic
Are you talking water/air as a power transmission medium from some prime mover (like a gas generator) or water/air as a source of wild power to be captured.
I think we covered the first alternative, so assuming you're talking water turbines vs. wind turbines:
Two answers:
1) Water is heavy and most of its energy is in the form of it being raised from the outflow level (or this can be arranged). Under many circumstances you can capture nearly all of the energy in it, because you don't need to leave much energy in its momentum as it leaves. Air is a gas and neutrally bouyant in its environment. So all its available energy is in the form of mass-with-momentum. You have to let a lot of it flow out of your mill to let new air come in, bringing more energy with it, so you have to leave a lot of energy in it to get it out of the way. A wind turbine can never collect more than the Betz limit - 59.3% - of the energy in it. So your inefficiencies you down from there, not from 100%.
2) Why are you worried about "efficiency"? That's a red herring. When "the fuel is free" the measure of efficiency you should be worried about is how many watt-hours per buck of infrastructure and maintenance cost, not what fraction of the energy in the source ends up in your wires.
Collection efficiency is like horsepower in a Rolls Royce:
Customer: How many horsepower does this model's engine produce?
Salesman: An adequate number.
