Actually, you just hit on the crux of the problem
Yes, there are NO machines the PRODUCE power ANYWHERE in human experience. Every machine in existance has to "live" by this principle.
But, it IS very common to use a small CONTROL power to "harness" a larger flow of power in a "separate loop". Some of that "harnessed" power from the larger loop is diverted to the smaller "CONTROL loop" to keep the process going once it's started.
Your windmills do this pretty well. But, you have to be willing to look at the system from a different perspective in order to understand.
You take time to build a generator and some blades and then you put it up in the air and wait for the wind to blow. All this wind power is free, AFTER you subtract the cost of construction, right?
So, one loop is the part where YOU provided the INPUT POWER to build your mill. Call this initial USER INPUT ENERGY quantity "A". Then the mill DRAWS IT'S POWER from a larger "WIND LOOP". It DRAWS enough wind power to do two things.
- It overcomes it's own internal bearing friction and starts turning, producing some heat, noise, etc..., with a PORTION of the wind power it COLLECTED. Call this energy quantity "B". So, "B" is what it takes just to keep the blades turning by overcoming internal losses.
- It also turns the generator against an electrical load. This is the "extra" power drawn from the wind. Call this energy quantity "B". This is what gets delivered to the power line for YOU to use.
So, the total wind power COLLECTED by the mill is "B"+"C".
The total power YOU get to use is just "C".
"B" was "diverted" to keep the mill turning (internal losses to overcome for continued rotation).
"B" is internal use (Control energy in loop 1).
"C" is power delivered TO YOU.
"A" is everything YOU PERSONALLY input to the system to get it going.
From the perspective of the USER, only a small initial input "A" results in a system that collects enough environmental energy to RUN ITSELF "B", and GENERATE EXTRA POWER "C".
If you use "coefficient of performance" to measure the system, you simply look at how much total power the system delivers "C" and compare it to how much it takes to keep the system in motion "B".
C.O.P. = "C"/"B"
So, from that perspective, lets say you have 100watts collected by the blades. 10watts is used to overcome internal losses and 90watts is delivered to the generator.
This is 90watts/10watts or C.O.P.=9
From the WINDMILL perspective, it's collecting enough ambient energy to RUN ITSELF, "B" energy, AND it's DELIVERING TO THE USER *NINE TIMES* the quantity of "B".
It's nothing magical. It's just a matter of changing perspective.
From the USER perspective, the mill is "running itself" AND providing extra "o/u" power, compared to what the USER is putting into the system, "A", to keep it going.
I'll stop here for the moment. Allow yourself fully digest how C.O.P. and "efficiency" are really issues of perspecitive. They're just a means of comparison.