Hybrid Car – More Fun with Less Gas

Looking for some guidance for my own power generation - Page 6

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Posted by Curbie on February 20, 2009, 8:30 pm
You've run headlong into three areas of engineering with some pretty
intense math:
1) Thermal dynamics (heat exchange between two things I.E. oil and
2) Steam properties
3) Turbine dynamics

I know because I did the same thing!

I'll skip the intense stuff and boil the problem down to the basics.

Sunshine produces 295 BTU per square foot (on a crystal clear day).
Boilers need to produce 34.5 pounds of steam per hour for a one
horsepower engine.
33,468 (34.5 * 970.1) BTUs of heat is needed for enough steam to drive
a one horsepower engine.
It takes 113.5 (33,468 / 295) square feet of solar collection surface
to generate steam for a one horsepower engine.

To drive a 10hp steam engine you'll need 1134 (113.5 x 10) square feet
of solar collection surface (using basic math) but more like 2269 in
reality after thermal losses.

If you use 4' x 8' sheets of metal covered reflective material (what
the commercial guys do) shaped into a parabola you end up with 32
square feet of solar collection surface per collector.

32 / 2269 and you'll need 70 collectors for 10hp or 8000 watts.

I was also attracted to steam turbines, but turbines like higher RPM
and lower torque. Generator like lower RPM and higher torque. Gears
solve this problem but at the expense of cost, simplicity,
maintenance, and reliability. (The things that attracted me to

Steam gives up its energy though expansion; small single stage
turbines (say 75-100hp) don’t have enough interior space to permit
full expansion of the steam before it exits the exhaust. Any steam
expansion that doesn’t happen inside the turbine is energy lost to the

Reciprocating (piston) steam engines on the other hand confine the
steam and force it to fully expand within the engine.  Generating
electricity requires three things 1) a conductor, 2) a magnetic field,
and 3) motion. Motion doesn’t necessarily mean rotation, motion is
motion, it can mean reciprocation. A linear generator with no
crosshead, connecting rod, flywheel...

You still have problems involving storage, we don’t get sunshine 24
hour a day and have to store energy for non-sunshine hours or days
with poor sunshine. Who knows, you may have to produce 16,000 watts
while there is clear sunshine to store enough energy for when there
isn’t. Google "Typical Meteorological Year" data for answers for your

It may seem like this idea doesn't have enough feathers to fly, but I
still play with it although I'm moving to an area with a good wind

Good luck.

Posted by vaughn on February 21, 2009, 12:05 am

If only that were true!  There is nothing to say that the steam is done
expanding when the piston hits BDC.  If the steam is not done expanding when
the exhaust valve pops open, then the rest of the energy is lost to the
engine.  Now you need to Google the term "triple expansion engine" to learn
how this problem is solved by adding additional complexity and greatly
increasing the size of steam engines.

When you get a chance, go check out a real triple expansion engine, perhaps
in a museum ship somewhere.  Note that the low pressure cylinder may easily
be 10x the volume of the high pressure cylinder, and then contemplate that
the engines are normally engineered so that all three cylinders produce the
same horsepower, even though they are vastly different in size.


Posted by Curbie on February 21, 2009, 12:53 am
 As my post said; I was boiling the problem down to the basics.
My point was in small steam engines say less than 75hp, a
reciprocating (piston) steam engines may be a better choice than a
single stage geared turbine. (cost, simplicity, maintenance, and

Sorry for any confusion.

On Sat, 21 Feb 2009 00:05:03 GMT, "vaughn"

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