The heat in the exhaust is waste.  The pressure is not.  Putting a load on the turbo would increase the backpressure in the exhaust system.  So the power you pull from the turbo comes straight out of the shaft horsepower.

The power the turbo pulls from the exhaust to run the compressor also comes out of shaft horsepower.  But the compressor gives it back by increasing the intake pressure.  Gain occurs because it gives you a higher effective compression ratio, so you use the fuel heat at a higher temperature for greater efficiency, more than making up for losses in the turbo.

But the main advantage of a turbo is that an atmosphere or so of pressure boost effectively doubles the size of your engine by increasing the cylinder charge, at negligible increase in weight.  This isn't particularly significant in stationary applications, where weight isn't an issue and wear is.  (A stationary engine can get the same effect by having a higher compression ratio in the first place.)  But it's major in vehicular applications, where boost is used for accelleration rather than cruising.  (A vehicle engine has to haul itself around in addition to the payload, so doubling the power to weight ratio means a lighter engine for a given application.  That turns into either more payload or less fuel consumption.)

while in theory you can pull the power off the turbo shaft, you will not lose an equal amount of crankshaft power, you will lose some to pumping force but not that much. There are many factors in what drives a turbo, cam profiles, pulse manifolds, heat retention,  etc..... but mainly it is the heat that drives it, not the pumping from the pistons.

in practice the connection of the turbo output shaft as stated runs from 30,000 to well over 100,000 rpm, the transmission needed to get this down to a useable rpm would be enormous and very difficult to manufacture and maintain. Also it might be worth noting that the smaller turbo's you are likely to encounter for smaller engines will work upwards of 125,000 rpm.

as for connecting magnets to the turbo shaft and mounting coils to form a small high speed alternator, nix that idea before you start, at 100,000 rpm rest assured that your  magnets will have exploded into deadly projectiles (worse case) or certainly be digested into the intake manifold, valves then cylinders of your engine (best case)

also one should consider what a turbo actually does, that is it allows an engine to make more power by pumping more air into the cylinders, allowing the ability to burn more fuel.  without the added fuel there would be no more power and likely engine destruction due to lean burn conditions.

from a seriously practical standpoint there simply is not simple way of doing what you are proposing.

be careful when working with turbo's ,,, they like to eat fingers :( , and consume alot of money if set up wrong.

http://www.aardvark.co.nz/pjet/turbine4.htm

This is also the man who got busted by the NZ government for putting plans for a homebrew cruise missile on his website.  Something about anti-terrorism, I believe.

I got to thinking about mounting a single disc magnet on the end of the inlet shaft.  You'd have to make sure it was balanced, but with three wraparound coils and some rectifiers close to them, it ought to be possible to draw off some electricity.

I'm not sure it would help you, though, since anything that retards the turbo either reduces the boost pressure or creates backpressure on the exhaust, both of which will lower the efficiency of the engine.  But you could recover waste heat by circulating the exhaust through pipes in your heat store.

Heh if it would work maybe it would help boost the power you can resell from this plan you have:

http://www.fieldlines.com/story/2004/9/9/31217/10092

T

The Truth is the Truth, even if no one believes it; and a lie is a lie even if everyone believes it