homeGeek CultureWebstoreeCards!Forums!Joy of Tech!AY2K!webcam

The Geek Culture Forums


Post New Topic  New Poll  Post A Reply
my profile | directory login | | search | faq | forum home
  next oldest topic   next newest topic
» The Geek Culture Forums   » Other Geeky Stuff   » Let's Get Creative!   » solar cookers

 - UBBFriend: Email this page to someone!    
Author Topic: solar cookers
Zim'et
Alpha Geek
Member # 2448

Member Rated:
5
Icon 5 posted April 08, 2004 08:29      Profile for Zim'et         Edit/Delete Post   Reply With Quote 
Hello. My physics class is having a competition with one of the calculus classes to see who can build the best solar cooker. The ovens will be placed in the sun for thirty minutes and temerature readings will be taken every five minutes. If anyone has any good ideas or websites with great info it would be greatly appreciated.Oh, and we've only been given four days notice, the competition is on Tuesday.

--------------------
3 2 1... Let's Jam

Posts: 254 | From: Montana | Registered: Nov 2003  |  IP: Logged
Allan
SuperFan!
Member # 1717

Member Rated:
5
Icon 1 posted April 08, 2004 09:27      Profile for Allan     Send New Private Message       Edit/Delete Post   Reply With Quote 
I'll prolly get laughed out of the forums, but I think you should make it out of conductive material and paint the outside matt black.

Edit: come to think of it maybe it should have a magnifying glass 'roof'

Posts: 1280 | From: Edinburgh, Scotland / Frankfurt, Germany | Registered: Oct 2002  |  IP: Logged
Gibbonboy
Geek
Member # 2426

Member Rated:
5
Icon 1 posted April 08, 2004 10:27      Profile for Gibbonboy   Author's Homepage     Send New Private Message       Edit/Delete Post   Reply With Quote 
You really need a Fresnel lens, a big one, like this one here. Not sure where you could get one on short notice. Barring that, a double reflector design would not be hard- if one of you is ok to use tinsnips, see if you can find aluminum coil stock- it's what they make gutters and roof flashing from. You want the shiny unfinished aluminum type, not painted. It's stiffer than foil (obviously), and will reflect better. If you can focus the heat enough, you can really burn some stuff up. Of course, it's all dependent on having good sunlight to start. Good luck! [devil wand]

--------------------
"It's not the end of the world, but you can see it from here."

Posts: 155 | From: A Very Small Hole in the Forest | Registered: Nov 2003  |  IP: Logged
Orpheus
Highlie
Member # 2397

Member Rated:
3
Icon 1 posted April 08, 2004 12:17      Profile for Orpheus     Send New Private Message       Edit/Delete Post   Reply With Quote 
here's what ya do if you can, don't know if there's a size limit but this is one way of collecting solar power. Have a central pillar to support your cooking pot, ideally paint the outside of the pot black or just buy a black pot. Then array around it as many mirrors as you can get your hands on and focus the reflections onto the pot et voila a solar cooker.

They use something like this to collect solar energy to boil water and drive steam turbines, or at least they used to, though with that array they had computer controlled mirrors so the light would always fall on the pot but for 30 minutes you should be fine... just get a big pot.

--------------------
my cats make me crazy

Posts: 554 | From: Galveston, TX | Registered: Oct 2003  |  IP: Logged
Flashfire
Assimilated
Member # 2616

Member Rated:
4
Icon 1 posted April 08, 2004 13:46      Profile for Flashfire   Author's Homepage     Send New Private Message       Edit/Delete Post   Reply With Quote 
quote:
Originally posted by Gibbonboy:
You really need a Fresnel lens, a big one, like this one here. Not sure where you could get one on short notice. Barring that, a double reflector design would not be hard- if one of you is ok to use tinsnips, see if you can find aluminum coil stock- it's what they make gutters and roof flashing from. You want the shiny unfinished aluminum type, not painted. It's stiffer than foil (obviously), and will reflect better. If you can focus the heat enough, you can really burn some stuff up. Of course, it's all dependent on having good sunlight to start. Good luck! [devil wand]

Fresnel lenses are so much fun... [evil] A friend of mine worked at an optics factory for a while and smuggled one out of there -- we used to burn aluminum cans with it.

The one drawback -- they're expensive. [Frown]

The other option -- enter someone's car. [Big Grin] We all know how hot the inside of a car gets on sunny days...

but that's probably against the rules, isn't it?

--------------------
"No silicon heaven? That's absurd!
Where would all the calculators go?"
--Kryten, Red Dwarf
-------------------------------
My Web Comic: NSTA: Semper Vigilantis

Posts: 368 | From: State of Denial | Registered: Mar 2004  |  IP: Logged
The Famous Druid

Gold Hearted SuperFan!
Member # 1769

Member Rated:
4
Icon 1 posted April 08, 2004 14:39      Profile for The Famous Druid     Send New Private Message       Edit/Delete Post   Reply With Quote 
A fresnel lens is overkill for what you're doing, you want to cook the food, not vaporise it. My high-school physics project was a solar furnace, basically a fresnel lens in a frame, I estimated the temperature obtained by putting different metals in it and seeing which ones would melt.

I got the fresnel lens from Canon (they make overhead projectors).

For a solar cooker, the two standard designs are the solar barbecue and the solar oven.

The barbecue is basically a big reflector, cardboard covered with foil should work well enough for a short-notice school project. 2 or 3 square metres of reflector should do nicely. The heat generated will depend on how accurately you focus the suns rays. A proper parabolic reflector that sze would be way too hot for cooking, but that would be very hard with cardboard and foil anyway. A reasonable approximation to parabolic shouldbe fine.

The oven is basically Allans black box, possibly augmented with 1-2 square metres of reflector to speed things up a bit, or a glass front so you can see what's going on. It's quite scary how how a black metal box can get in the sun.

We hd heaps of fun doing this in school, you've brought back all kinds of fond memories, like the time our teacher nearly lost a hand trying to find the focal point of a fresnel lense by waving his bare hand around.....

--------------------
If you watch 'The History Of NASA' backwards, it's about a space agency that has no manned spaceflight capability, then does low-orbit flights, then lands on the Moon.

Posts: 10680 | From: Melbourne, Australia | Registered: Oct 2002  |  IP: Logged
littlefish
BlabberMouth, a Blabber Odyssey
Member # 966

Member Rated:
4
Icon 1 posted April 08, 2004 15:51      Profile for littlefish   Author's Homepage     Send New Private Message       Edit/Delete Post   Reply With Quote 
Or if you want to win by thinking laterally, get some solar panels and a big fuck off battery, powering an oven. Charge the battery with solar power hours before the cook off, and kick ass.
Posts: 2421 | From: That London | Registered: Nov 2001  |  IP: Logged
TheMoMan
BlabberMouth, a Blabber Odyssey
Member # 1659

Member Rated:
4
Icon 1 posted April 09, 2004 03:34      Profile for TheMoMan         Edit/Delete Post   Reply With Quote 
Zim'et______Seeing that you have the weekend to do this there are commercial ones for camping, try Gander Mountan, Cabela's or even K-mart in the sporting goods then arrange some tin foil glued to card board to reflect on the areas of the oven that are shaded be its self.

--------------------
Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.


Benjamin Franklin,

Posts: 5848 | From: Just South of the Huron National Forest, in the water shed of the Rifle River | Registered: Sep 2002  |  IP: Logged
Doco

SuperFan!
Member # 371

Member Rated:
5
Icon 1 posted April 09, 2004 08:25      Profile for Doco   Author's Homepage     Send New Private Message       Edit/Delete Post   Reply With Quote 
I'm guessing that the teacher gave some restrictions as to size or the measuring point, or something like that. Not knowing any of those items it is hard to give specific advice.

General advice though - you want as much surface area as possible to reflect the light towards your target. As others have said - You want your target to be black. If you can make your target bigger you don't have to worry about focusing the light as percisely, BUT you then also have the larger mass of a big target to heat up. A big black iron pot might not be a good target for a 30 minute competition as the mass of the pot will slow you down. A thin-walled aluminum sheet or tube painted black would probably be better. Aluminum transmits heat very well so the power that hits it in one area will be quickly transmitted throughout. The smaller your target the hotter you can heat it - but the harder to focus the light on it.

One idea - find a nice parabolic dish - say something like a 9' satalite antenna and cover it with very shiney foil. Put a black target at the focal point and cover the whole deal with some 0.5 mil clear plastic. The plastic will help keep the heat from going away by convection. Of course you need some wood sticks to keep the plastic well away from your target as it might get quite hot. Once you get past the logistical parts of acquiring a large dish and covering it with foil there is the non-small issue of aiming it.

Another idea might be to create a parabolic shaped trough and then put a black painted pipe (say a 1" copper pipe) at the focal point. Again cover with glass or plastic to reduce convection losses. The wider the trough the more energy you can harness. Don't go for a very deep trough though as the edges don't contribute as much energy as the "flatter" parts.

Well - that is enough rambling for me for now....

Posts: 419 | From: Minneapolis, MN | Registered: Mar 2000  |  IP: Logged
The Famous Druid

Gold Hearted SuperFan!
Member # 1769

Member Rated:
4
Icon 1 posted April 09, 2004 14:38      Profile for The Famous Druid     Send New Private Message       Edit/Delete Post   Reply With Quote 
quote:
Originally posted by Doco:
One idea - find a nice parabolic dish - say something like a 9' satalite antenna and cover it with very shiney foil. .

Bad idea!
Very bad idea!

A 1' fresnel lens gathers enough heat to set fire to wood instantly, and melt metal in a few of minutes. A 9' parabolic dish has around 60 times the area of the fresnel lens, it would be a lethal weapon. Remember, this is for a school project, telling a school kid "stay back, this is dangerous" is like a red rag to a bull.

--------------------
If you watch 'The History Of NASA' backwards, it's about a space agency that has no manned spaceflight capability, then does low-orbit flights, then lands on the Moon.

Posts: 10680 | From: Melbourne, Australia | Registered: Oct 2002  |  IP: Logged
quantumfluff
BlabberMouth, a Blabber Odyssey
Member # 450

Member Rated:
5
Icon 1 posted April 09, 2004 18:41      Profile for quantumfluff     Send New Private Message       Edit/Delete Post   Reply With Quote 
Totally wrong. You should go for the biggest parabolic dish you can make, and when the teachers see your food varporize, you should point out that they should have deliniated the parameters better. You're only young and stupid once - enjoy it.

I would take every junk AOL CD i can find and build a reflector. They are not perfect mirrors, so it won' be too powerful, but it will be the most memorable project in the class.

Posts: 2902 | From: 5 to 15 meters above sea level | Registered: Jun 2000  |  IP: Logged
somnabulist
Geek
Member # 2403

Member Rated:
4
Icon 1 posted April 10, 2004 14:46      Profile for somnabulist   Author's Homepage     Send New Private Message       Edit/Delete Post   Reply With Quote 
makesure whatever foil you use is completely flat- no wrinkles. also take the time to use a protractor to figure the optimum angle of all flat refleecive surfaces. (angle of reflection=angle of incidence)
Posts: 109 | From: in the chair | Registered: Oct 2003  |  IP: Logged
hey-U
SuperBlabberMouth!
Member # 2128

Member Rated:
5
Icon 1 posted April 10, 2004 15:09      Profile for hey-U     Send New Private Message       Edit/Delete Post   Reply With Quote 
quote:
Originally posted by somnabulist:
makesure whatever foil you use is completely flat- no wrinkles. also take the time to use a protractor to figure the optimum angle of all flat refleecive surfaces. (angle of reflection=angle of incidence)

So... no point in offering my tinfoil hat as a contribution, then?
[Razz]

Posts: 1263 | From: London | Registered: Apr 2003  |  IP: Logged
Zim'et
Alpha Geek
Member # 2448

Member Rated:
5
Icon 1 posted April 10, 2004 19:50      Profile for Zim'et         Edit/Delete Post   Reply With Quote 
If I brought in a Hummer with a fresnal lens as a roof and entered it my physics teacher would giggle and be thrilled. He's insane, we don't have any restrictions. Great suggestions though, thank you!

--------------------
3 2 1... Let's Jam

Posts: 254 | From: Montana | Registered: Nov 2003  |  IP: Logged
Zim'et
Alpha Geek
Member # 2448

Member Rated:
5
Icon 1 posted April 13, 2004 15:43      Profile for Zim'et         Edit/Delete Post   Reply With Quote 
I ended up nicking a lens from a projector at school and placing it on top of a box completely lined with tin foil. I didn't win but the experiment went quite well and I received full credit for it. thanks again!

--------------------
3 2 1... Let's Jam

Posts: 254 | From: Montana | Registered: Nov 2003  |  IP: Logged
Katie
Geek
Member # 2502

Member Rated:
4
Icon 1 posted April 14, 2004 00:31      Profile for Katie   Author's Homepage     Send New Private Message       Edit/Delete Post   Reply With Quote 
*Get ready for lame line*
"This chicken is out of this world"
*Can't say I didn't warn yee*

--------------------
I am not the type of person to do shamless plugging,how dare you
http://freewebs.com/lordofmuffins

Posts: 183 | From: Florida land of the retired | Registered: Dec 2003  |  IP: Logged
Jace Raven

Solid Nitrozanium SuperFan!
Member # 2444

Icon 1 posted April 14, 2004 09:22      Profile for Jace Raven         Edit/Delete Post   Reply With Quote 
You should have gone for the 9' parabolic dish. You probably would have won.
Posts: 1791 | Registered: Nov 2003  |  IP: Logged
Doco

SuperFan!
Member # 371

Member Rated:
5
Icon 1 posted April 14, 2004 10:30      Profile for Doco   Author's Homepage     Send New Private Message       Edit/Delete Post   Reply With Quote 
So out of geeky coursity - what was the design that did win?
Posts: 419 | From: Minneapolis, MN | Registered: Mar 2000  |  IP: Logged
Gibbonboy
Geek
Member # 2426

Member Rated:
5
Icon 1 posted April 14, 2004 12:11      Profile for Gibbonboy   Author's Homepage     Send New Private Message       Edit/Delete Post   Reply With Quote 
quote:
Originally posted by Jace Raven:
You should have gone for the 9' parabolic dish. You probably would have won.

Or at least started a large fire.

--------------------
"It's not the end of the world, but you can see it from here."

Posts: 155 | From: A Very Small Hole in the Forest | Registered: Nov 2003  |  IP: Logged
Jace Raven

Solid Nitrozanium SuperFan!
Member # 2444

Icon 1 posted April 14, 2004 12:53      Profile for Jace Raven         Edit/Delete Post   Reply With Quote 
quote:
Originally posted by Gibbonboy:
quote:
Originally posted by Jace Raven:
You should have gone for the 9' parabolic dish. You probably would have won.

Or at least started a large fire.
Absolute enjoyment, either road.
Posts: 1791 | Registered: Nov 2003  |  IP: Logged
Zim'et
Alpha Geek
Member # 2448

Member Rated:
5
Icon 2 posted April 14, 2004 15:01      Profile for Zim'et         Edit/Delete Post   Reply With Quote 
One of my friends in the AP calculus class created a parabolic dish made of tin foil and mirrors, then instead of rigging up a motor to do it for him, rotated the dish with the rotation of the earth. He deserved to win, there was a 61 degree Celcius change in temperature and he got his water to boil.

--------------------
3 2 1... Let's Jam

Posts: 254 | From: Montana | Registered: Nov 2003  |  IP: Logged


All times are Eastern Time  
Post New Topic  New Poll  Post A Reply Close Topic    Move Topic    Delete Topic next oldest topic   next newest topic
 - Printer-friendly view of this topic
Hop To:

Contact Us | Geek Culture Home Page

2015 Geek Culture

Powered by Infopop Corporation
UBB.classicTM 6.4.0

homeGeek CultureWebstoreeCards!Forums!Joy of Tech!AY2K!webcam