Friction. Tell you what, why dont you try a home experiment on this.
Get a large bucket of watr, drill a hole in the side, get some drainpipe and some properllers of some sort that will fit inside it, and place them at regular intervals along the pipe, then connect the pipe together, stick the top end into the bucket, and the bottom end into your garden drain or something, and then fill the bucket with water. Actually I just forgot, what you really need is small electric motors connected to all teh propellors, with output wires sticking out the pipe. Then you can check what energy is coming out them, and compare the differences between one turbine, 2, 3, 4, and so on.
Have you ever done any actual school level physics and thermodynamics?
Are you willing to take a scientific atttiude and subject your theories to tests?