Post by Kirk Wallace
I have been giving this some thought. If the grid is available, the only
way off-grid power makes since is if it's almost free. One of my
thoughts is to run my generator head with a steam engine which could
burn, wood, waste oil, propane, whatever. If necessary, enough batteries
would be needed to fill the gap when the mains get interrupted. There
would be enough batteries to to keep the power up until the
hydro-generator kicks in. The hydro source would be a tank on a tower,
or a tank at the top of my hill with the turbine at the bottom. The tank
would be pumped up when I have excess power. Hopefully there would be
enough hydro to allow enough time to get the steam engine up to speed.
Or maybe have the hydro turbine do double duty as a water and steam
turbine. Anyway, this is some of what I think about when I do my morning
With 2 sq km of forest on the farm, my original reason for buying the
lathe and mill was to build a steam engine, or convert an old horizontal
IC engine with fat flywheels. (There's one in a corner of the shed.)
It's only progressed as far as calculations of power output vs RPM,
average steam pressure, cylinder dimensions, etc. The other calcs are
for the boiler. Due to stiff regulations, having one made isn't cheap.
So ... flash steam (monotube boiler) is very tempting. (They need a
constant load, because there's no hot water to provide a steam reserve.
I figure that batteries could substitute.)
We don't have much clean water out there. (18,000 L total, for domestic
use.) That mandates a condenser. Dam water could be used on the outside
of that. All that's lacking is the round tuit.
Gasification is an alternative, but cleaning the tar and crap from the
gas generator output necessitates filters, which need regular cleaning.
That's a grubby and non-trivial job, from the writings of those who've
Ideal would be a stirling engine with integral alternator:
http://www.stirling.dk/ # Nifty, but still in one-off production,
# after about 5 years. Smallest is 9 kw.
# Larger units use woodchips.
It's a while since I went through:
Maybe someone's within cooee of thinking hard about going commercial
PS: If my simple script for calculating steam engine power vs various
% cut-off, etc., would amuse, then just yodel off-list. It looks
like this in use:
Input: Pressure(PSI) Stroke(cm) Bore(cm) RPM
200 10 8 400 <- User input
Cutoff HP kW
25% 3.7 2.8
33% 4.2 3.1
37.5% 4.6 3.4
50% 5.2 3.9
62.5% 5.7 4.2
67% 5.8 4.3
75% 6.0 4.5
87.5% 6.1 4.6
100% 6.2 4.6
There's also two pages of maths & musings for engine & boiler to
hand, from last time I nudged closer toward something workable.
PPS: Water and steam turbines look very different, unfortunately.
A single Pelton wheel could do for the former, but alternating
stator and rotor wheels of increasing diameter are needed in the
latter, to utilise the expanding steam. (AIUI, anyway. ;-)
PPPS: Hope there's some ideas in that lot.