parabolic solar heater

[S and M Wind]

Parabolic trough solar heater is impressive. This is larger than my first one.

I made a three way bypass valve and installed it after the filter. The 1 1/2" pvc lines run to and from the bypass valve. The header pipe is 1 1/2"cu and the pipe that is in the focal point of the concentrator is 1"cu painted flat black. There is a pressure relief valve on the high side of the system in case the water steams.

The actual parabolas are sheet aluminum from an old car hauling trailer with reflective mylar glued on them for greater efficiency each in a plywood frame. The parabolas are 39" wide, 65" long and about 8" deep. I downloaded a free program that helped to determine the focal point. The system worked well. On a day where the high temp was lower than the starting temp of the water I was able to raise 13,000 gallons of water 1 degree per hour. I figured that the surface temp of the 1"cu was over 600F when focus into the sun. The whole project was a great learning experience. Solar concentrators are powerful.

NOTE OF WARNING!!

When focused into the sun you could be BLINDED, BURNED OR MAIMED!!

USE CAUTION!!

 

[sdscott]

Cool!  I like the simplicity...  Thanks for sharing!

Cheers!

[chadking]

Nice looking setup!  Learning is one of the main benefits from these projects...well that and some free energy.  Haha...it's amazing what a little sun can do.

Raising the temp on 13,000 gallons of water with this is pretty impressive!

[johnlm]

I don't mean to sound amazed here but something is wrong with your numbers.

You have about 35 square feet of collector, and if you were able to convert all 35 sq ft of sunshine at 100 % effeciency you would only be able to collect 300 BTU / Hr per sq ft. or about 10,562 BTU per hr total.  That would raise about 10,000 pounds of water 1 degree F in one hour.  10,000 lbs of water is 1272 gallons. Either your numbers are of by 10X or you got alot of heating just by having the ambient temp heat the pool of water.

Nice looking collectors by the way.

Johnlm

[bob g]

a couple of questions if i might?

i am trying to make sense of your measurements

are they 8 feet in length,, i would appear so from the pics?

i assume the 39" is the width across the curve?

the reason i ask is,, if the 39 inches is the width, and if the curve is half a circle then the focal point should be approx 19.5 inches (the radius of a 39" circle)

if your radius is larger then the focal point will be correspondingly longer in length, it appears in the pictures that you focal point is far too close.

what radius is your setup based on, and what is your focal distance,, the pictures might distort the actual dimensions, i dunno.. but would like to know.

what is your focal length and mirror radius?

looks like neat project

bob g

[richhagen]

I thought about that too.  He's got about 4 square meters in the collector give or take, so about 4000 Watts in full sun even if he could collect all of it.  That's not enough to heat it that fast, but the sun would also have been shining on the pool at a 1000 W/square meter too, a percentage of which would be absorbed, in addition to any conduction from a warmer environment.  Rich

[wdyasq]

Just to clear uo a few points:

http://www.mathwords.com/f/focus_parabola.htm

Hey - it's the way the things work....

Ron

[bob g]

Ron:

thank you for the link,, it has been over 30 years since i worked with this sort of thing and we used a radius trough,, of which the focal point was the center of the radius,,

thanks again

bob g

[thefinis]

Dang sure not where I would have thought the focal point would be. Live and learn thanks for the link will have to bookmark it.

It looks like there is a coiled pipe solar water heater setup on the side of the building too.

Great setup I have been wanting to try the solar mirrored trough and would be interested in seeing how well the mylar lasts. What grade/thicknees did you use?

Finis

[sdscott]

bob g;  If this structure was half a circle, the focus would be the centre of the circle (or distance of the radius).  The structure is parabolic, more efficient at collecting and concentrating the light, with a shorter focal length.

[Ungrounded Lightning Rod]

If this structure was half a circle, the focus would be the centre of the circle (or distance of the radius).

Nope.  With a half-circle the middle chunk of the reflector produces an approximate focus halfway between itself and the circle's center.  (This is because it approxiates a parabola of that focal length.)

But as you move outward the circular reflector "focuses" progressively further back.  At 60 degrees offcenter the "focus" has moved to the reflective surface at the center of the mirror.  By 90 degrees the focus is at minus infinity, i.e it doesn't focus the light at all.

= = = =

It's easier to understand why the pin/string/T-square construction produces the correct shape to produce a point focus (ie. the parabola) if you consider the incoming light as a flat wavefront rather than a bundle of parallel rays.

The wave front travels in a stright line except when bouncing from the mirror.  If the wave is to come to a focus, the distance traveled from a reference line at right angles to the incoming light to a point on the refletor, plus the distance traveled from that point on the reflector to the focus, must be a constant.

With the pin/string/T-square construction the pin holds one end of the string at the focus, the point where the other end of the string connects to the T-square tracks the arbitrary reference line, the string provides the constant total length, and the pencil keeping the string tight against the T-square forces the string to sum the straight-line distances in the correct directions.  This forces the pencil to track the reflecting surface's correct position.

[Ungrounded Lightning Rod]

If you're just heating pool water you'll collect the same amount of heat with a flat collector as you will with parabola troughs of the same area.

More even:  Aim won't be as critical, you won't lose heat through misaming from reflector shape imperfections, and you can more easily recapture reradiated infrared in a flat collector using a flat glass plate than you can in a line-focus collector using a glass tube around the collector pipe.

The line focus doesn't increase the amount of heat you gather.  It only increases the temperature you can gather it at.  This is a big deal for collecting the heat for overnight storage or use in the hot end of a heat engine.  But the only advantage for pool heating is that you don't need to pump as much water to transport the heat to the pool.

[healerenergy]

I can't remember where I found this but It is a great picture and math in one.

George