Available HP decreases with altitude above sea level so if you are at any appreciable altitude then your generation capacity will also decrease.
Ron   

  Anyone know the caculation for reduction of HP as you gain altitude ?

 I found this site a couple of weeks ago, from a reference from a Solar PV forum. My situation is a off-grid, rural installation, with PV my primary power source (going to be a 8KW PV array). I'm highly attracted to the old, exposed pushrod as in the Rocketboy project   http://www.f1-rocketboy.com/lister.html. Hand crank, CS engine, with a " harmonic regulation" generator attached (belt, rubberband, direct drive, whatever)  What is un-attractive, is the hours needed to debug, and weed out failures in a brand new system.  I only need about 3 or 4 KW of electric out of it. 
  I had some experience with a Lister, in '77, in the USMC.  I was the custodian of the M.A.R.S. Radio station at Cherry Point, NC, and we had one parked in the back room as our backup generator. It was sweet!
  Anyway, back to the WAF (wife acceptance factor), while a modern, silent Onan or whatever unit, would be completely unacceptable, a hand crank, no wires engine would be,  only if I did not have to spend years debugging bad manufacturing techniques. Expected usage would be a couple hours a day, 3 times a week, in cloudy winter conditions, and no usage in sunnier weather. (gotta keep the batteries topped off).  I'll have a 2nd room in the battery shed to park this in.
   I've perused the messages here the last week, and rather than re-inventing the wheel, wonder what my options are for a CS, hand crank system, if any after the EPA engine Nazi's were done with their ticket books. This will be installed in northern California, so east coast shipping is likely out.