My home made solar water heater

[ChainsawGrandpa]

I found a design for a solar water heater on the 'net.

The builder said the first unit caught fire and burned-up.

The second design attained 600 F.

Sounds just like what I was looking for!

I've been using a lot of white gas (Coleman fuel, naptha) to heat my shower water. decided to reduce my dependency on the gas stove by using solar power.

The images:
http://s287.photobucket.com/albums/ll154/rbuchananlogman/
show the building sequence of the insulated parabolic box, and the last image is the unit out in my field with two of eight reflectors in use.
The reflectors are to be attached with door hinges. Removing the hinge pins
allows the unit to be quickly disassembled. The hinges are expensive at the local hardware store but Brown's Building Supply in Spokane had them for 75 cents each. Good thing they were cheap, I needed twenty four hinges.
I positioned the unit to catch the setting sun. With only a short exposure to the sun at day's end it still managed to get the water in the stainless steel cylinder up to about 155 F. Plenty hot for a nice shower.

When I'm finally finished the unit will have eight reflectors with a power of "9 suns". I designed it to gather as much heat as possible on an overcast winter day. A plywood gymbal will allow the unit to be oriented to the sun for time of year, and time of day.

A heater that warms the water during the day is no good when you need a shower at 10:00 PM. No photos yet, but I've been building an insulated box to hold the stainless steel cylinder. The cylinder fits into a sleeve made from layers of Reflectix insulation and a Harbor Freight wool blanket. The whole affair lays in the foam insulated box. Preliminary tests show I should have almost boiling hot water for a shower the next morning.

Already have a design for another unit. Should boil five gallons of water, cook a pot roast, and bake 33 loaves of bread all at once (no, I have no desire to bake 33 loaves of bread...ever!). The larger unit should cost less than $75 and have all season, all weather durability.

-Rick

[ChainsawGrandpa]

Should have mentioned....

There are some changes that should be made if you want to build a unit for yourself.

The focal plane should be the width of the cylinder (4") x 3.1416 + the diameter of the cylinder. In this case
it would be 16 5/8". That would make the parabolic chamber close to being a square instead of rectangle.

The unit should be positioned at an angle to the sun in
the summer. You may just accidentally set the unit on fire.

For all weather use the unit should be covered in fiberglas or
made of metal. Exterior grade plywood just isn't good enough.

-Rick

[ponyboy]

Or should I say Hot... :-)

How hot do you think it would get during an overcast winters day?

As for the bread...
http://www.youtube.com/watch?v=_L8zsDurc_I

P.S. Here's a great program to stitch together a bunch of photos into one.
http://www.cs.ubc.ca/~mbrown/autostitch/autostitch.html

[rreidnauer]

I'm sure I don't have to tell Rick, but for others who may read this should know, that safety precautions need to be taken when working with unregulated high temperatures and water. Essentially, rick built a bomb if not fitted with pressure relief valves. While they post 600F for temps, it's unlikely the heated fluid would achieve that. Never the less, water pressure increases exponentially with temperatures above the ambient atmospheric boiling point temperature. For example, a sealed vessel of water heated to 281F will have 50 PSI of pressure, but heat it just another 47F and the pressure doubles. 100F above 281F and the pressure quadruples!!! If you continue to heat it to 545F, the pressure would be 1000 PSI!!!

But the real danger comes with a rupture of the vessel containing the superheated water, as any pressure drop at a given temperature will cause the water to flash to steam, and steam expands 1680 times the volume of water. So pieces of your now rupturing vessel gets an extra push from the instantly expanding gas, and basically you have a water powered pipe bomb.

So, always be sure to have a pressure relief valve (sized safely below the vessel pressure limits) any time you consider heating water above the boiling point in a closed container.
~~~~~~~~~~~~~~
Side note: I once asked a steam locomotive engineer what pressure they operate their boilers at. When he told me 180 PSI, I was shocked to say the least. I can imagine that a catastrophic rupture in something that size would probably darn near take out a city block, and send train parts a mile from ground zero. Come to think of it, I believe I recall some WWII aerial gunsight footage of steam locos be shot, and doing just as I envision.

[ponyboy]

[quote=rreidnauer] So pieces of your now rupturing vessel gets an extra push from the instantly expanding gas, and basically you have a water powered pipe bomb.
.
.

That's why he's going to install it in his favorite neighbor lady's yard and run a long pipe.... :-)

[ChainsawGrandpa]

"That's why he's going to install it in his favorite neighbor lady's yard and run a long pipe.... :-)"

I'll get two! On for each neighbor!

Actually...Rod is right. I knew I had a bomb, but the engineer & I both came up with
about 400PSI ultimate strength. I may not reach 400 PSI, but it is certainly possible.
The unit is mounted out in the field about 50' away from me...MUCH TOO CLOSE!
Mounting it in the next county might be safer. I need to install a pressure regulator
on top, or maybe a simple pop-off valve. When I open the ball valve the burst of water
takes about 3-4 seconds to fly into the air and fall to the ground. This is at low temperatures!
I've seen videos of a BLEVE (Boiling Liquid Expanding Vapor Explosion) and they're
not pretty. People several blocks away are killed. Good thing my unit is small. I know
it takes a short exposure to the sun to reach comfortable shower temperatures. Set
and forget for several hours with all the reflectors in use could be catastrophic.
Thanks for the heads-up Rod, I'll get a valve...or you can read about my exploits in the
Darwin Awards. =8-O

Would like to build the big unit...eight reflectors at 13' long...maybe a parabolic chamber.
Better build a lot of safety features into that unit. Materials, money, and design are no
problem to building the next unit. The safety feature is that I don't have enough time to
dedicate to building the next unit. Too much mad scientist in me.
(That's "Fronkenschteen!" Gene Wilder)

-Rick

[hemlock77]

With all this talk about your water heater temps and potential steam bomb, it got me to thinking(this could get dangerous). Would it be possable to utilize those high temps to generte electricity. Basicly a solar powered steam turbine generator for off grid power. Rick/ Rod is there enough potential for a viable system?
Stu

[ChainsawGrandpa]

Already looked into it. The water heater generates a lot of power but slowly over
a period of time. Despite the large size (71 sq. ft.) of the reflectors I would only be
able to generate about 15 watts if the sun was always shining directly on the
reflectors. Works best for heating water & food. Would take ten stainless steel
cylinders filled with water to heat my storage shed for just one hour. On an average
winter day I might get three cylinders of hot water, but would need 250 cylinders to
keep the place up to temperature for 24 hours. Would also work for generating ice,
but the best I could expect is to keep my Coleman ice chest cool.

The numbers show that for the area of the reflectors I should generate close to 500
watts of power, but with occasional sunshine, friction losses, etc. the real numbers
are far from the theoretical numbers.

Too bad. It does sound exciting to have free energy.

-Rick

[christinex]

Hi Rick,

I was wondering if you still use your home made water heater?

Also, do you have a link to the design descriptions/materials list? What material is used for the reflectors? Perhaps I am missed the link but I did not see it amongst your photos.

I will be building in Sweden where the days are very short (latitude around 64-65) and most likely off-the-grid. So I am very interested in your invention project(s).

Thanks

Christine

[StressMan79]

rick has two separate solar collectors on that photobucket site. The one I like best is a "solar trough" (google that). I will be making one of those soon. Here is my list of materials:

1] 10' long x 1" (2" would be better) diameter black steel/galvanized pipe, threaded at each end If not black, use some hi temp grill paint to make it so. Mask off the threads while painting.

?] sheets of 1/2 inch exterior grade ply

2] sheets of tagboard/sharpies to make stencils

?] Marine grade lacquer.

2] sheets of flexible stuff. .005" stainless would be fine. I wouldn't use galvanized or aluminum as the oxide layer will prevent full reflection. I plan to use some 1/16 melamine, laquered and sprayed with spray adhesive and finally coated with some mylar

If you are worried about the environmental resiliency of the surface, cover the box with single pane of glass (I wouldn't use plastic--UV degradation).

put the pivot point at the black tube (also at the focus), build 7 frames that are no more than 4' wide and 4' tall (depending on collector geometry), space the frames at 16" centers and fasten to a 4x8 sheet of plywood. Reinforce with 1x1. Brad and construction adhesive in place. finish sides of box. Let dry.

use HVLP sprayer to put on a few (thin) layers of the marine laquer/poly.

Install the reflective surface using appropratie means. This may be self tapping screws, brads+glue or whatever. finish the box with the glass if needed. Hook up a thermocouple/digital logic circuit or even mercury switch on bimetallic strip to a relay to a motor or something. You don't want this to overheat. you effectively have to come up with some way of dumping heat or preventing the collection. you wouldn't have to tip the collector much (maybe 10 degrees) to make the focus not a point and not lie on the tube. I prefer the motor, as you can track the sun too. Otherwise it is only effective at noon.

I am excited now. I gotta make me one!

-Peter