power for a house

[monkeyman_1027]

Is it possible to us a satellite dish with a metallic surface to
focus the light of the sun (kind like a magnify glass) and get
extremely high temperatures? Take the heat you get from their store
it in heat cells and deliver a constant temperature to a large-scale
Stirling engine to create power for your house. Also by storing the
heat in the cells, during peek power usage times you could up the
heat to create more power. During low power usage times of the day
lower the heat to create less power.

[keritoot]

I have thought about this idea for quite a number of year. I am not sure of the title of a book I read which I think was "the solar energy boat book" I should be able to contact the friend I lent it to in a few weeks. Anyway it turns out that brick is a pretty good material for storing heat at the temperatures which could be obtained from a solar reflector. I supose the heat storage unit could be insulated with "rock wool" insulation.

As for the construction of a solar reflector. I have thought about taking an old parabolic tv satelite reflector (at least 6 feet dia) and laying it out in a dark room with a transit type level type laser suspended overhead via some kind of a etch a skech like mechanism to move it above the layout of the antena with a spherical target at the focal point.
The task then would be to break old glass mirrors into semi square fragments and cement them onto the parabolic surface while the laser is adjusted to shine down on it. (If the laser beam is in line with the string supporting it, gravity would then cause the laser to simulate parallel light from the sun.)

The craftsman would tap on the corners of the mirror segments as they are setting up in bondo or cement.

I am currently working on the math to make a frensel type refelctive cone I remember reading about in popular mechanics or popular science way back in 1963 or before. This would allow a spiral to be cut from a piece of masonite with reflective mylar on top and layed out of some stepped cone support structures radiating outward and upwards. I have done some of the prelimnary math in the quattro spreadsheet format which uses succesive approximation via macros and allows me to select various cone angels and focal point elevations till I end up with a spiral which doesn't waste too much masonite or close back on itself.

I would be happy to share this openly with any math/geometry enthusiast who would consdier using an old lotus spreadsheet or quattro up to version 5 for windows. (which has a keystoke record option)

I hope to have a web site soon where I will explain these ideas further. I hope that enthusiast with varios areas of experties and who would like help protect the plannet would support such an enterprise spontaniosly rather than waiting for government or business to do this for us... Something like what is happening in the linux open source code environment.

Sincerely
Richard
keritoot@hotmail.com

[twmudd]

I have a method I used for making a fair sized parabolic reflector quite easily if its any help.

1. create a cylinder with the same circumferance as the edge of your desired reflector.
In my case I used an old oil drum although a dustbin would also work.

2. Stretch a plastic or rubbery material over the end of the cylinder and secure it over the cylinder using rope / gaffa tape / cable ties etc.
For this I used a sheet of latex rubber which I held in place using an anysize Jubilee clip kit.

This creates a diaphram over your cylinder.

3.Place the cylinder so the diaphram is perfectly horizontal and pour into the middle of this some Plaster of Paris mix.

with the rubber diaphram, the weight of the plaster starts to sag the diaphram downwards. depending on how full of plaster you make it or how tight the diaphram is, you get varying shapes of a perfect parabola being 'pressed' into the rubber.

4. once the plaster is set, this can be removed from the diaphram.

you then have your negative or mold for making your reflector dish.

5. with the convex side of the mold facing upwards, start to place small mirror pieces all over the surface (shiny side facing down)

Hold these in place by using a fibre glass car body repair kit to bind the mirror segments together.

6. Once cured, the fibre glass with the mirror pieces embedded can be lifted off the mold.

You now have a parabolic shaped array of mirror pieces which should produce a focal point about the size of the average size of your mirror pieces.


Please let me know if anybody manages to go bigger than an oil drum size.

Cheers

Tom Mudd

[kevfromtheboo-lastcall]

Hello All,

I also have been fascinated with the Stirling Engine for some time but only recently (2 days ago) have begun to research them. So... please forgive me if this suggestion is way off base.

If you are approximating a parabolic reflector using broken pieces of a mirror, why not construct a geodesic dome from same sized isosceles mirror triangles.

It seems to me (from a lay perspective)that this radiator would be more efficient/focused than an inside out "disco ball".

I am extremely interested in hearing any and all responses. Thanks in advance.

Best Regards,

Kev

[i2lzy]

http://www.cc.jyu.fi/~hvirtane/cooker/node8.html

this link shows how to simply create a perfect parabolic curve on a flat piece of rigid material (ie plywood) that you could then use to create a form for the dish by rotating the profile around the center point of the mold material. I remember seeing a website that made a plaster cast of a big parabolic hole in firm soil. Which was then used to mold the solar dishes they used for their cookers. I was thinking that if one were to make a casting then one could use insulating foam and a box to make a vacuum form from the plaster cast on which one could lay a large acrylic sheet which could be heated (maybe a heat gun for the diy guy) to flexibility and "sucked" down into the form using a household vacuum cleaner with the hose inserted tightly in a hole in the deepest portion of the form. Then polished foil or mylar could be fastened to the acrylic dish to create the reflective surface desired.

Thoughts?

[irfeld]

I am looking for just what the link above mentions: a way to make a parabolic curve out of a sheet of plywood. The link is not working. Does anyone have an idea how to do this?
#-irfeld@yahoo.com

[i2lzy]

sorry that the link is dead now...

A sheetrock square and a piece of string no longer than 8 ft... Attach one end of the string to the tip of the long leg of the square. get a rigid piece of 4'x8' material. If you mark a point at the center of the long side and put a nail there to attach the other end of the string to then you just put the short side of the square aqainst the (opposite from the nail) long side of the stock to be cut with the string attached to the appropriate locations and the long leg of the square against the nail... a pencil is used to trace the curve by keeping it against the leg of the square with the string looped around the pencil from the top of the square's leg, around the pencil, and back up to the nail (focal point). Just keep that pencil against the square and string and move the square to the outside edge of the material. Then repeat for the other side of the nail. As you move the square accross the plywood the string will move from the other side of the plywood (accross from the nail side) and the path it follows will be a curve that has the nail you used as a focal point.

The string's length depends on the depth that you are going for and the focal point position, but is simple to find and is not more than twice the depth of your dish (ie the width of your template material) for reasons not the least of which is that it keeps the focal point of the dish within the volume of the dish instead of above it where there is more potential damage to cause.

I played with some foil and sand that I had from a trench and got over 160 with about a 3 square foot trough enclosure. I'm sure that it was much higher but that is as high as the thermometr would read...

[i2lzy]

BTW, for small dishes, I love that drum procedure. I would tweak it a little but it is perfect simplicity and I love that...

[kevin.jackson]

Yes it is very possible and your approach makes good sense. Edison (the utility company) has contracted to have a plant built using 38 ft. parabolic (satellite style) dishes that will provide enough solar energy to produce 25 kW of electricity each. That is about 22 watts per square foot of dish. Your house probably uses much less than that so you can use a much smaller collector (dish).
I have been wanting to try to make a large collector using a method described in Scientific American (and discussed on some home made telescope forums). This method doesn't make very good telescope mirrors but should work great for a solar collector. Essentially you use the fact that a liquid spinning in a container will take the shape of a parabola (liquid mercury telescope mirrors). In the article a round pie pan is used on a record player turntable to spin some slow drying epoxy. When the epoxy hardens you have a near perfect parabolic surface that only needs to be made into a mirror. This can be done with commercially available kits. Slow drying epoxy is used because it will average out record player vibrations, allow time for air bubbles to rise and pop and prevent warping (caused by uneven heating during the cure because the epoxy is thicker on the outsides than near the center). I want to scale up this approach a lot. I'm thinking a 6' sattelite dish. One of the old fashioned solid (fiberglass) ones that will hold the epoxy. It is important to have a parabolic shape to begin with so you don't have to use massive amounts of epoxy which would be expensive and heavy when finished. First glue on a dam around the outside to contain the epoxy, plug/cover any hole in the middle and seal any seams, this is your form. Mount your dish/mold to your variable speed mold spinning thing (probably easier to say than do, I'm considering a electric potters wheel, mabe you guys can think of some better ideas). Mix-up enough epoxy to put a thin layer on the surface of your dish, pour it in, spin slowly up to the speed that makes an even coating from the bottom to the top and hold that speed until the epoxy hardens. Apply the mirror metalization and you are ready to catch some serious solar energy.
P.S. A nail, string and pensil does not a parabola make. If you swing the pensil all the way around you will make a circle not a parabola.
P.S.S. If you want to make a "broken mirror refelector" I would suggest the following: Make the mirrors the same size as the target area you want to heat, this will minimize the number of mirrors you will have to cut and place and will be as effective and probably more effective than many smaller mirrors. As you get further from the center you can make the mirrors even larger in one dimension because of the angle of incedence will be increasing. I think I would mount the mirrors in the sun. Mount a pole with a plate on the end of it (the plate will be slightly larger then the target you will have for your project) to the center of your refelector long enough to establish what will be your focal point. Point the refelector at the sun (the plate's shadow will be centered on the base of the pole) glue the most inner mirror down first making sure they reflect the sunlight centered on the target. Cover that mirror, check your sun alignment (the sun moves in the sky!) and glue the next one. I suggest you cover each mirror as you go so you can see the refelected light of the mirror you are working on and so the pole/plate doesn't burn up! One feature of the broken "mirror" that I think is really cool is it doesn't have to be dish shaped. Because each mirror is "doing it's own thing" the refelector can be a flat sheet of plywood or any shape you like.
Next time I'd like to talk about a low buck ($100-150), high power Stirling engine idea I have.
Good Luck,
Kevin

[i2lzy]

I have thought of the fresnel approach with all the little mirrors but what I suspect is that it would be less efficient than a dish of comparable area. Maybe would still get plenty of energy, but more is better. due to the loss of light intensity as it travels from the flat mirrors to the focal point. As far as the string and t-square thing, you mis-understand how to trace the curve. The pencil is held so that it travels up the leg of the square (y-axis) as the square is being slid accross the material away from the focal point (x-axis).