i guess efficiency is more important if you are making heat with a fuel source
however if you can make sufficient heat with a solar concentrator maybe you can deal with less efficiency?
iirc the geo thermal driven turbine i referenced earlier ran on around 50psi wet steam, certainly not the most desirable form of steam, and not the fluid for the turbine, but it was basically a free heat source and it worked out fine (likely still working out there).
personally i think this might be a really interesting project, one that might need a quite large collector to make a reasonable about of power, but nevertheless a cool project.
this is how i would approach the project
1. i would determine just how large a collector i would need to make enough steam at 50-100psi to make maybe 1000watts. (figuring in the end with all the other losses maybe i could get lucky and net a couple hundred watts to start with and work to improve that )
2. i would work with an automotive alternator, only because they are cheap and are built to take input rpm over a wide range and make power, this would negate the need for transmissions and their losses.
3. i would either use the tesla turbine design or the air vane motor design, and use the alternator shaft as the rotor shaft, therefore no coupling issues and a tightcompact package, not unlike the hydro boys do things.
4. i would use a balmar controller, in lieu of the oem automotive regulator, the idea being one could tailor the alternator to match the available power from the collector.
5. i would place the turbine assy at the base of the collector, no long pipe runs and therefore less heat losses to battle
maybe one starts by doing the research on the collector and determine its size requirment, then he builds a prototype turbine/alternator and tests it with air pressure
to determine how much air pressure @ X cfm to produce Y amount of watts electrical output, and tweaks the programming of the controller to optimize output to the input available.
then if the research tells you that a collector of perhaps 12ft diameter will produce the amount of steam required (volume and pressure) one could then couple the two (collector and turbine) and run a batch test to see if it really does work? if it does as planned or acceptably so then you have to work out the plumbing, condenser, feedwater return pump, tracking mechanism etc, all of which will present their unique challenges i am sure, but at least you know or have a good idea that the thing will work when you are done?
me personally? i would love to see it done! and i would get very excited to hear it run!
bob g