Hot water heating using a 15 foot dish

[windjunkie]

My current project is a 15 foot diameter satellite dish that I am going to coat with mirrors in order to focus LOTS of sun for heat.

Current arguments are for a sterling engine set up to generate electricity.

OR, and this is my wish, and why I posted this question in water. A coil setup to heat water in order to augment our current hot water solar panels. The current solar panels dump into a 2000 gallon tank which we use to heat our house.

My question is this, has anyone had experience with these mirrors

http://www.allelectronics.com/make-a-store/item/MIR-22/SHINY-METAL-MIRROR/1.html

Specifically regarding their use in this type of application. i.e. outdoors for extended periods of time, reflectivity, wear, corrosion, mounting etc...

And what type of mirrors have you used, or seen?

All info is welcome, especially any info on mirror coatings.

WindJunkie

[scottsAI]

 Windjunkie,

Unless you have burning need for high temperature water...

www.builditsolar.com

Has great design for solar hot water at $4/sq foot total cost for the collector.

Your design is not cheaper with many parts that can fail and things go wrong.

These collectors can provide 190F maybe higher, water?

Stirling engines are expensive and difficult to DIY. Most of the designs are models, power is l/10HP at best.

Good design steam engine is a different story, yet much more complicated than heating home.

And more dangerous with live steam.

Have fun,

Scott Beversdorf.

[Basil]

Take a look at this. http://krawlr.com/solarfurnace/solarfurnace.htm

I have spoke to this guy and I plan to copy a lot of his work with my 10 foot dish that I am working on now.

3 or 4 inch mirrors work great and last for ever almost. I am going to use Mylar for now. It's cheap and fast. Only 2 to 5 year life I heard. If it works out then I can go with mirrors. Send me an Email and we can talk about it. basilkey at bellsouth dot net.

[Bruce S]

Windjunkie;

 I have to agree with Basil on this one. Mirrors are expensive and Mylar will give you much more controll over the curvature of the reflective material.

The one item that will make just as much of a contribution to the working product will be the focal point.

Builder beware, once you start getting even a few sheets on it; anything,person,part remotely close to the focal point or any sub-set of it will quickly find a burning sensation.

A 15 foot dish reflecting all that sun into a specific point will equal 15+ suns worth of heat/energy in seconds.

Did a small test using an old 3 foot Dish given to me by a good friend. I lined it with mylar, setup an old cast iron pot at the focal point, then turned it into the sun. I reached for my morning coffee and by the time I turned around, the old seasonings was already starting to smoke, the temprature <using an IR meat therometer> read 250F. Took me little more than 5 more seconds to turn it back away and the pot was smoking !!!

Now of course this was a good warm summer day with lots of pretty sunshine, but you get the idea.

When designing this, make sure and use high-temp everything, knowing that temps can get up way up there in mere seconds, and you might need a good "robust" pump to move the water fast enough to keep things at a low enough temp.

Might be a good idea for a hot tub :-)

VERY doable, but do be careful :-()

Cheers

Bruce S

[GaryGary]

Hi,

You might ask Duane at www.Redrok.com -- there is little he does not know about concentration collectors.

I think that he uses reflectorized Mylar for most of his projects.  He attaches it with grease so that it can be peeled off easily at the end of its about 3 year life and replaced.

More stuff on concentrating collectors that might be helpful here:

http://www.builditsolar.com/Projects/Concentrating/concentrating.htm

It does seem like for heating water to moderate temperatures that flat plate collectors would be easier and probably more efficient?

Gary

[Tritium]

Bruce, that is a lot more than 15 suns. If a 15 foot dish is focused on a 1 square foot area then it would be over 176 suns at the focal point. Area of a circle is Pi time radius squared and there is even more area since this circle is concave.

Thurmond

[Bruce S]

Tritium;

 I concurr, but was in Medical equipment tech-support mental mode and couldn't remember right off hand the math formula :-).

Which is why I put 15+.

However with your numbers, that's an even more important reason the play safe 1st with these.

Can we say, cast iron smelter :-?, exploding hot dogs anyone :-))

Cheers

Bruce S

[WineGuy]

I also recommend Red Rock Energy.

Call the guy and talk to him if you can. I is a real character, but has LOTS of good info about building concentrators using old dish setups.

[Gordy]

Hi all,

As to the safety issue, I met Duane http://www.Redrok.com about 4years ago at an Alt. Energy show in Custer WI. He had an 18" satellite dish with the milar liner and his tracker set up. At the focal point he had a stop set up, that he would hold a pop can against. With those high thin wispy clouds the dish would burn a hole through one side of the can in 4-5 seconds. http://www.Redrok.com is a good site tons of info.

Gordy

[hvirtane]

I think that if you are going to use

that mirror for heating it might be better

to use it to heat air and circulate air.

That because I think that you can get water easily boiling and then the steam pressure would create lots of problems.

- hv