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Paul Alfrey
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Hi all here is some info about some experiments we tried this summer.
For the same info with photos go to

https://sites.google.com/site/permaship1/permaculture-practice/solar-ovens

or
www.permaship.org and click on projects

So this is about how we built a Parabolic Solar Oven, Panel Cooker and a Box Oven and the results of our experience, but first a brief overview of Solar cooking.
The idea behind solar ovens is to harness the energy from the sun and use this energy to cook and prepare food and drink. The praticalities of this concept is somewhat dependant upon, how much sun you recieve ,how much time you have and what type of cooking you prefer. A solar oven will only work when the sun is shining, will require attention and adjustments throughout the cooking period and will require a thoughtful approach to what you will cook. However it is a free source of clean energy and in some cases where sunshine is plentiful a very useful one that just requires a change of habits for it to be both efficient and convenient
Principles

Most solar cookers work on basic principles: sunlight is converted to heat energy that is retained for cooking.

Sunlight is the "fuel." A solar cooker needs an outdoor spot that is sunny for several hours and protected from strong wind, and where food will be safe. Solar cookers don't work at night or on cloudy days.


Convert sunlight to heat energy

Dark surfaces get very hot in sunlight, whereas light surfaces don't. Food cooks best in dark, shallow, thin metal pots with dark, tight-fitting lids to hold in heat and moisture.
black pot absorbing sun's rays white pot reflecting sun's rays


Retain heat

A transparent heat trap around the dark pot lets in sunlight, but keeps in the heat. This is a clear, heat-resistant plastic bag or large inverted glass bowl (in panel cookers) or an insulated box with a glass or plastic window (in box cookers). Curved concentrator cookers typically don't require a heat trap.
black pot with bag black pot in box cooker


Capture extra sunlight

One or more shiny surfaces reflect extra sunlight onto the pot, increasing its heat potential.


So now we move onto our experience when as part of our Earth and Sun Energy Learn and Create Course this summer we put together a variety of Solar Ovens for testing.

After a little discussion we split into 3 groups with each group making a different model. The models we covered were Parabolic, Funnel and the Easy Lid.

Parabolic

This was Stoyans baby, he had sourced a highly reflective aluminum allode material which he ordered pre cut and ready to asemble with just a drill ,5mm drill bit and nuts and bolts. Once the unit was built a tripod was erected around it to suspend the cooking vessel in the focus point of the sun.


Results

The Unit heated 4 litres of water with starting temperature of 23 C up to 53 C in 2 hours during a partially cloudy part of the day and served us with lukewarm tea for our break ,not a roaring success but when the sun broke later in the day the temperature quickly rose to 79 C. We also prepared a snack of Ufka( a light pastry cooked in milk and mixed with honey and yogurt) using the Parabolic which took 20 minutes to cook and was delicious.

Improvements

Research indicates we could have easily improved the performance of the cooker by using black pots with black lids and using a bigger suspension plate to allow a clear plastic bag or glass container to envelope the black pot thereby providing a insulative layer of air. We also should have made more periodic movements during the day . We will try these methods and post results in the future.

Pros and Cons

The pros for this model are

* it is made from durable material resistant to rain and will last a long time without needing much maintanance.
* Can cook as fast as a conventional electric burner.
*
Can fry foods.

The cons for this model are

*
not easy to pack away
*
not easily portable
*
more expensive than other models due to special material used
*
requires periodic realignment to the sun.
*
can cause damage to eyes due to its highly reflective nature

Comments

Stoyans model has the potential to reach very high temperatures quickly and with some getting used to can provide a good alternative to the electric oven on sunny days .Its bulkiness eliminates it from becoming a camping and hiking utensil but its durable structure means it will serve its purpose for a long time .

Funnel


The Funnel was Filips choice and was quickly put together using only Cardboard ,tinfoil some glue and a box to hold the unit up-right. Filip and co. also made a pot to fit the unit out of an old tin of dog food painted black with a tin lid also painted black than sealed this tin with an oven bag . For full construction instructions see http://www.solarcooking.org/plans/funnel.htm

Results

The Unit heated the tin of water with rice with starting temperature of 17 C upto 74 C in 2 hours during a partially cloudy part of the day.The rice was well cooked after 6 hours.

Improvements

It could be made bigger to hold a bigger vessel,it could suspend the vessel in the focus using a tripod therefore reflecting more heat to all surfaces and we could have attended to making more movements to improve the focus. Further tests will be carried out bearing this in mind and results posted.

Pros and Cons

The pros for this model are

* it is made from cheap and ready available materials
* it can be constructed very quickly
* It is very portable
* Demonstrated good results from the offset

The cons for this model are

*
a few rainfalls will destroy it
*
too small to provide a familly size meal (athough a bigger model would solve this).
*
requires periodic realignment to the sun.
*
can cause damage to eyes

Comments

The Funnel is my favourite as it demonstrated from the start how effective it can be and what potential it has. Its very easy and cheap to build and is the ideal cooker to take camping with you as its so lightwieght and packs up nicely. We are looking forward to many a beach holiday with the funnel.

Easy Lid


Ivan and Emil cracked on with the easy lid which is basically a cardboard box lined with foil with black tin floor plate and a perspex or glass screen with foil lined lid which can be tilted to reflect the sun into the box. look here for concise instruction how to assemble one http://solarcooking.org/plans/easylid.htm

Results

The Unit heated 1 liter of water with a starting temperature of 17 C up to 30 C in 2 hours during a partially cloudy part of the day. By 6.00 p.m that same day the temperature was 74C. Not remarkable by any means. We also made a fruit juice with this cooker. Sava filled a jar with Cornellian Cherries and added some water after a few days in the sun the mix was ready for straining and with some sugar added made a very appetising juice.

Improvements

The cooking vessels we used could have been better i.e black and sealed in glass or plastic. A further box inside the outer box would also provide better insulation and the perspex we used was not totally clean. Also more attention to periodic movements of the lid would have undoubtedly increased the performance.

Pros and Cons

The pros for this model are

* it is made from cheap and ready available materials
* it can be constructed relatively quickly
* It is sealed so can be used for uncovered food i.e drying ,heating

The cons for this model are

*
a few rainfalls will destroy it.
*
lower temperatures.

Comments

The easy lid is very easy to setup and does not require to much movement but it does not really operate well for cooking that requires high temperatures .However with the low temperatures we were reading makes it an ideal tool for drying fruit and we had great success in drying figs and apples in the unit. The sealed box keeps the flies and insects out and a few days in the sun was more than enough for the apple chips ,3 days for the figs although if the figs had been halved than 2 days would have been enough.


Sashkos Solar Oven Night Light

We discovered a dual purpose for our cookers whilst we were relaxing around the fire at night , Sasho had the good sense to place a candle within the ovens. The effect was very beautiful ,even more so under the influence of the home made rakia we were knocking back, and you can achieve a good enough light to work around. The funnel oven ,the most portable of the units also works as the best night lamp making it a perfect travel companion.


Summary

Our experiments with solar ovens so far have revealed a few things. Firstly these units are very easy to make and do work but to get the most out of them requires time and attention and more importantly a changing of habits and expectations. They are by no means an all out answer to off grid cooking but do provide a good alternative when conditions are correct . They are an easy thing to demonstrate to other people who may be interested and making these with children is a great way to teach a variety of principles whilst having fun. For beach camping the funnel will really come into good use serving as a cooker by day and lamp by night.
We are really looking forward to more experiments to test how useful we can make the units we built and will post updates. Thanks to all involved with the experiments.

https://sites.google.com/site/permaship1/permaculture-practice/solar-ovens

hope you find it useful

www.permaship.org
 
rose macaskie
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i have a big problem trying to think how to prop up a pot in a funnel cooker.  I have read lots of instructions on how to make the cookers but as a unhandy woman i want a lot more on tripodes with platforms on them and such.
  I imagine that if industry got its back in to solar cooking they couldl make some reflective surfaces that were more power full than a normal box cooker one without getting to be as dangerouse as a parabolic curve reflector or a fresnel lense. agri rose macaskie.
 
Robert Ray
gardener
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Location: Cascades of Oregon
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I use an aluminum double boiler ring to elevate my pots in a funnel cooker. It fits within my cooking pots and is always there when I use it.
  A tuna fish can works for flat bottom pots as well.
I have used a ten inch dutch oven and find that it is a better container to cook bread in when using a funnel cooker.
I have a large parabolic that gets extremely hot and is incredibly effective if high heat is desired. The funnel cooker is slow and easy I like it better. At least my cooking style likes it better.
Robert
 
Paul Alfrey
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Hi Rose

The easiest way would be to rest the pot on a heat retentive platform (to reduce heat loss from the bottom of the pot) .This could be anything from a flat stone to an upside down pot of similar size. If you look at the photo of the funnel cooker on this link you will see what i mean.
http://sites.google.com/site/permaship1/projects/solar-ovens.
Its a basic design but provides the principal. The alternative is to set up a tripod or two support stands either side of the funnel and suspend the pot using wire as shown on this link. The photo is about half way down the text.
http://www.solarcooking.org/plans/funnel.htm


Hope this helps

Paul

http://sites.google.com/site/permaship1/Home

 
Robert Ray
gardener
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Rose,
mollybakersolaroven.com  Shows the use of the double boiler ring on it's pages. I like the ability for reflection to hit the base of the cooking vessel as well as the sides. That is why I opt for a ring or tripod.
Stacking cooking vesels within a funnel cooker seems to work for two seperate dishes, much better than side by side.
 
rose macaskie
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  lampinerobert. Gosh, i would like to see a foto of stacking dishes with in a funnel cooker i made one but could not think how to use it how to stick dishes in it. Yours must be big if you can stack dishes in it. Its an easy sort of reflector to make.
  i have just looked at the foto permaship has given the connection for, it seems to have a sort of chimney coming up through the bottom of the funnel cooker which you can place a pot on. I had imagined the funnel at an angle to catch a less high sun and then what? Maybe i have to look at the other foto paul gives the address for. Have seen the other site, they have one foto of a pot hung into the funnel cooker. that coudl work if i got good at making stands. agri rose macaskie.
 
Robert Ray
gardener
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Location: Cascades of Oregon
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Rose,
Here is a picture of a cone oven with two pots stacked you can just see the riser beneath the bottom pot. This doesn't show the secondary cover of an oven bag that covers the pots and bumps up maximun temp.
14-folding-front-lip-for-low-sun-.JPG
[Thumbnail for 14-folding-front-lip-for-low-sun-.JPG]
 
Joel Hollingsworth
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Location: Oakland, CA
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It's interesting that everyone seems to use metal to prevent heat loss.

My first idea would be wine corks, perhaps a bundle of them a few inches wide.
 
rose macaskie
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  That is a beautifull solar cooker. Its a lovely open gesture too.
  I thought of corks even suggested them to solarcookingnut on youtube I think she thought i was messing around with her.  As a child in a house which was very damp my father used to cut cork into slices and stick it on the back of pictures to hold them of the wall and away from the damp and as cork aislats well it should be good unde pots to hold them of fthe bottom of the oven and stop the pots losing heat through the floor. agri rose macaskie
 
Robert Ray
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I had never even thought of corks as a riser in the cooker.
Stability would be the key in this design since it is often used outdoors on the ground and not on a level surface. But on a design that has a rigid bottom/base it would help in heat loss to a degree.
I'll try it in the future.
 
rose macaskie
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Permaship says that solar ovens require time and attention and a changing of cooking habits.
    If you look up the video on youtube "slow cooking fresnal lense solar powered italian cooking" then you will see that solar cooking can be fast and pretty normal.
   
  iI you want to see how too fast cooking could be, look up "30"x40" crystal clear fresnal lens sun collector" that shows how you can leave concrete red hot in a few seconds.  They are both videos of the Dan and Denise Rojas. Dan Rojas is an incredibly busy fertile interesting solar cooking experimenter. He will make us some really functional soalr cookers in the end. agri rose macskie.
 
Paul Alfrey
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Even with these super fast cookers you will still need to plan your meals around sunlit hours and be aware of the weather before and during  cooking .Its not the same as flicking a switch whenever you feel like it  , this is what is meant by changing of habits ,you could say re-learning your expectations.


Tx for the you tube link ,good work they are making.



 
rose macaskie
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I read one mans talking about solar cookers, in google i think, and he put something into the oven each morning before starting work or doing things on the farm or somesuch and his father did not seem very convinced about it when the son first started doing solar cooking but his father came round to it in time, one morning the man had not put in anything and his father complained, the idea of cooking free had in the end got to him as so irresistible, even if you can't cook your dinner free too, that he too fell for it.

  You will probably be able to cook at night too usign the sun, they save heat in salt in big solar energy farms, and one man Roland L Conte suggests that maybe we could make a solar cooker like a masonary stove surronded by a large amount of some material that collects heat,  the masonary or salt surrounding the oven that willwill collect and hold the heat. You would have to shut aislating lid when the sun went down and have a sun chasing devise. He call it the "heat retention solar oven" and you can find his articles if you put the words heat retention oven into google.  webplaces.org/solaroven/design. agri rose macaskie.
 
rose macaskie
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  Solar cooking is for sunny places. Some climbers took a solar cooker up Everests to make their coffee, those mountainouse places have a lot of sun.
    They use Them in poor countries, in Tibet for example, where they have big parabolic reflectors to cook  for their regular everyday cooking. YOu can see a video of them using parablic reflectors to cook with in Tibet in you tube with the words, "solar cooking Tibet.
        One big killer of women and children in second world countries is smoke that gives pneumonia. They cook with fires and dont' have chimneys on their stoves or fires and which fill their homes full of smoke and give them lung problems.
      My mother loved big  fire places and real fires and i remember my baby sister with croop, weezing away, we had to call the doctor she was breathing so badly, i did not think of it at the time but when i heard that lots of women and children die from smokey rooms i wonder if maybe those fires weren't pretty bad for us.  I think they might introduce chimneys into South America and Africa to make cooking less smokey but still cooking without fires is better it stops people going to look for wood and so causing desertification. Solar cooking is a modern technique that is more used in third world countries than rich ones. Rich countries who depend on petrol for their fuel don't appreciate how the land in many poorer countries gets desertified because they use all the wood to cook with.   
      Looking for fire wood is also time consuming. There are people who say that it keeps people occupied, they are the wealthy who don't value the company and wisdom of people in a group they find it hard to converse with, it is good for children to have their mother teaching them rather than working unless there wother is really stupid, oranutangs have their mother on the job full time till they are five, lots of animal mothers are on the job full time teaching them to hunt and collect till the children grow up and leave.
      Even if solar cooking not a hundred percent satifactory i bet there is a big market out there for ever more efficient solar cookers, be it only for novelty value, in the west and because people are worried about global warming. i certainly would buy one or several if they sold them here and have spent a lot of money buying equipment to make them. Sheets of aluminium, black paints of variouse types, there is a paint for barbacues but its expensive, black pots, iron girdles to put in box cookers that i haven that will take up the suns heat and hold it making the oven hotter. I just still have not got all the ingredients together and cooked and writting here is one reason why as well as the fact that i have been making about ten types of cookers at once. Writting takes up so much of my time i do enjoy but it but it has to affect some other things. 
    Just think, boy scouts learning to make their own cooker instead of learning to build fires. agri rose macaskie.
 
bunkie weir
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it would be wonderful rose! i remember in girl scouts cooking over an open fire. it would've been fun to have cooked then using the sun!

i have a solar cooker we purchased a year ago last August from a place that provides them to countries like rose mentioned. i found only one month we couldn't use it here and that was January. i cooked brownie cupcakes in the sun when it was 27F outside. it took four hours to cook them, but they were mighty tasty.

http://www.imageuploads.net/ims/pic.php?u=27615PDlUo&i=164684

it's true one can only cook when the sun is out, but, if there are a few clouds passing over, this oven still retains it's heat and will cook, just takes a bit longer. i always shelter it a bit from the wind, too, but that doesn't seem to affect it much.

i never thought of stacking pots in it. neat idea. it has  a little shelf that swings to keep the pot level as i adjust the angle for the sun. i have removed this shelf to use bigger pots. i imagine that it would work for stacked pots too.

chicken and veggies...

http://www.imageuploads.net/ims/pic.php?u=27615PDlUo&i=169169

great ideas all!
 
rose macaskie
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  Bunkie weir,.That looks like a really solid heavy duty cooker ,it is strange that you could only use it in january. Why, what happened, is that the time with least cloud cover were you are?
 
bunkie weir
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Location: eastern washington
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hi rose. January was the only month out of last year that we could not use it. we had snow storm after snow storm and mostly cloudy days all that month. otherwise, we used it all the rest of the months. it was amazing to cook in it when it was sunny and tempraatures were in the 20's.
 
Seth Pogue
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Here's my favorite solar oven...so far...

http://www.backwoodshome.com/articles/radabaugh30.html
 
Adrien Lapointe
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Here is an interesting video of how to make a grilled cheese sandwich using a parabolic mirror.

 
paul wheaton
master steward
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Location: missoula, montana (zone 4)
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Look at this one! A bit of clear plastic and water will burn wood, fry eggs and pop popcorn!



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