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Posted by Curbie on April 5, 2009, 9:20 pm

I agree with your logic.

Ok, I think I have a better picture, a bit off-topic if anything grows
in area naturally than I would play with that to see if you could
create compost for at least a food garden.

My mom subscribed to Mother Earth News and that sounds like the
article that kicked off my first experiments.  

The gap between the mirror are helpful but 100 x (12" x 12") is still
a 100 ft^2 "sail" that in my opinion has to compensated for in the
design by vastly increasing the strength of a standup structure.





electricity.  So, if the


where I


grasp on the

In another post I went through my knowledge of the metric system, (two
liters is about the size a coke bottle) it's another way of describing
the measurement of things, but the things themselves don't change when
you change the way you're measuring them. This analogy is useful in
that if I got results (for example) that said 10 liters was a gallon,
I'd know something was wrong because I know I couldn't fit 5 two liter
cokes into a gallon jug. My point being you loose your valuable "life
experience" when change to  measurement systems you don't think in,
and mixing measurement systems can lead to more problems. I would
advise sticking to whatever system you "think" in.

Also in another post someone posted a link to a little conversion
program to convert numbers of different measurement systems, I think
in old "Imperial" units but I'll try and convert my thoughts for
clarity of my explanation.

100ft^2 = 9.290304 m^2
1m^2 = 1000 watts (heat energy NOT electrical)
 or 9200 watts (heat energy)

You'll first have to pay the piper for heat conversion losses before
you can think about using what heat is left for an engine of any kind.
Because 6000 ELECTRICAL watts is about 8hp doesn't mean you can skip
the heat conversion, you still have to convert light to heat, before
you can convert heat to motion for electricity.

The heat energy from the sun, that reaches the earth is relatively
constant but isn't constant at the earth's surface basically due to
the amount of atmosphere the light needs to penetrate when the sun
isn't directly overhead. So the heat energy that reaches any
particular location is dependant on variables like time of day, time
of year, location, and elevation of location the 1000 watt per m^2
number is a rounded up number for best case situations, using imperial
measurements 295 btu per ft^2 and goes down quickly depending on the

Ok, meat and potatoes time using conservative imperial (sorry) numbers
VOLUME of heat from a parabola is a function of the area of the
collector and TEMPERATURE of heat is a function of the "Concentration
Ratio". I bring this up again (and again) because the concept is
central to understanding the first step of converting light energy to
heat energy. I really think you would get further along using my basic
solar steam math, cheesy as it is.

33475 BTUs (1 Boiler Hp/Per hour)
250 BTU's for 1 Ft.^2 (of collector on a reasonably clear day)

So 100 (ft^2) x 250 (btu/hour) = 25000 (btu/hour)  / 33475 (boiler hp)
= .75 (boiler hp NOT the 8 hp.

Now my recommendations for you:
1)    I agree with you logic to use resources on-hand, and your
situation is about the only one I can think of where small-scale solar
thermal could make sense.
2)    Santa Ana winds was what I was thinking of and 60mph winds are
a real design problem which could (I really don't know math on this)
be solved with that horizontal dish and moveable receiver idea I
posted. The design of the dish would not only protect it from the wind
but reduce cost of construction. Since the receiver is moveable by
design you could extend its functional range of motion to cower it in
high winds.
3)    Using flat mirrors are fine, I've come to think of the idea as
an array of heliostats configured in a parabolic shape.
4)    There is a "Concentration Ratio" design consideration when
using flat mirrors, the receiver opening that catches the light to
convert it to usable heat must be larger than the mirrors in your
arrays. If you think about this notion for a minute, flat mirror don't
individually concentrate light, so if the receiver opening has a
smaller area than the mirrors, some light will miss the opening. Total
collector area determines the heat per hour collected, concentration
ratio determines the temperature (max or avg), which are both driven
by solar variables.
5)    When I started my second go-round at this in 05, I started by
picking up where I left off in the 80's with that Mother Earth News
design. After running head long into concentration ratio issues I
looked for and found a fairly simple (though time-consuming) solution,
you can take a 12" by 12" mirror and score a tic-tac-toe pattern on it
to break it up into 9 4"x 4" mirrors to increase the concentration
ratio. Each GROUP of 9 4" mirrors can then be arranged to focus their
light on one 4" spot at the focal length of the theoretical parabola.
6)    I abandoned to idea a an array of heliostats configured in a
parabolic shape due to time-consumption involved with the cutting and
position of the mirrors in favor of a true parabolic shape made from
sheet metal covered in a SOLAR reflective film. The design costs were
7)    Having learned from both physical and computer models I prefer
computer models, but if you prefer the hands-on route I would build a
small (model size) horizontal collector, using sheet metal covered
with reflective film for a parabolic dish, a cavity type receiver
combined with a mono-tube boiler, measure how much your collector
raises the temperature of a fixed amount of water (55 gallon drum) in
one hour which is a measurement of how many btu per hour your
concentrator is producing. WARNING you need not need to boil the water
to measure the btu produced, so DON'T ALLOW IT TO BOIL by increasing
water flow and never letting the fixed water get above 200F, shut the
test down and increase the volume of the fixed water supply if it
does.  There is supposed to the equivalent of one stick of dynamite to
each gallon of water turned to steam so turning water to steam really
concerns me without knowing the math behind it (think BOOM)! I think
you should research and thoroughly understand cavity type receivers
and mono-tube boiler before even think about stream production, and
only when you conclude that (or IF) your model could produce the
required btu per hour if scaled-up and only then would I mess with
receivers and boilers with a model steam engine (which can be found
all over the net). There is NO reason to anywhere near a steam boiler
(remote sensors) SO DON'T, if you can't commit to this rule don't
pursue this advice or you will be killed by the endeavor! Keep a log
on every test, know what your trying to accomplish BEFORE you test,
try to predict the results before testing, and don't move on if your
results don't match your prediction until you understand why.

You'll never reach the destination if you don't enjoy the journey and
make no mistake this idea will require a LONG (maybe dangerous)


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