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:about the power conversion, however you also have to realize that even if your running a 2k rpm, or 6k rpm the electric setup will still draw the same "power" from the system to pump the same amount of fluid, Even with a mechanical device, its load on the crank will be proportional to the load on it. That whole torque/rpm/horsepower relationship comes into play, in other words if you're drawing 746 watts from an alternator, it's going to require 1 HP to turn it (in a perfect world) regardless of how many RPM's it is turning. What that means is that if your engine is turning at half the rpm's, the torque required to turn the alternator will be twice as high as it would be if you were turning at twice the rpm. Same goes with pumps. If a pump has a load on it, it's going to require a certain amount of power to overcome that load. Once that load is overcome it doesn't just scale the load proportionally with RPM. In other words, if a pump takes 1 hp to turn, it's going to try to suck up 1 hp no matter how fast you spin it, or what you spin it with. If you spin it slower it will get harder to turn or else its total output will decrease. Even in electronics it works this way. The Torque,RPM, and horsepower relationship is the same as amps, volts and watts. To maintain a HP, if you cut your RPM in half you will have to double your torque. To maintain a watt, if you cut your voltage in half you will have to double your amperage. In any system, the law of conservation of energy will always come into play. There is a definite limit to how much desired work you can get out of a given power input, but there is no limit to how much undesired inefficiency you add into a system by repeatedly converting energy forms. Running an alternator with a crank, generating electricity and using that to drive a motor which turns another crank is a good way to lose efficiency.
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