Two Cardboard Boxes and Some Paint = a $6 Solar Cooker to Save the World

By Rachel Cernansky | April 10, 2009 4:02 pm

solar cookerThe Kyoto Box, a $6 solar cooker made from cardboard, has won the Financial Times-sponsored Climate Change Challenge contest for innovative ways to decrease the human impact on the environment. Its capacity to not only cook food but also sterilize water could help three billion people reduce their greenhouse gas emissions. The Kenya-based Norwegian creator of the cooker, Jon Bøhmer, has been awarded $75,000 to put the idea into production.

Named after the United Nations’ Kyoto Protocol, the cooker is made from two cardboard boxes, one inside the other, with either paper or straw insulation placed in between; an acrylic cover on top lets in and traps sunlight. Black paint on the inner box, and silver foil on the outer one, help concentrate the heat. The trapped rays make the inside hot enough to cook casseroles, bake bread and boil water [CNN]. Covering the cooking pot with a transparent cover retains heat and water [BBC], and temperatures inside the pot can reach about 175 degrees Fahrenheit.

With as many as 3 billion people dependent on firewood for fuel, it is hoped that the cooker will eliminate the small-scale deforestation that has cumulatively become a major contributor to global warming worldwide. By allowing users to boil water, the simple device could also potentially save the millions of children who die from drinking unclean water [CNN]. The Kyoto Box was chosen from five finalists; the other four included a garlic-based feed additive to cut methane emissions from livestock, an indoor cooling system using hollow tiles, a cover for truck wheels to reduce fuel use and a “giant industrial microwave” for creating charcoal [Reuters].

The box can be produced in standard cardboard factories, and Bøhmer is already working with one factory in Nairobi. Bøhmer, who has started a design firm called Kyoto Energy, also designed a sturdier version made of recycled plastic, which he says would also be extremely cheap to produce. His next step is to conduct trials with 10,000 cookers in 10 countries, including India, Indonesia, South Africa, Kenya and Uganda []. “We’re saving lives and saving trees” [Reuters], he said. “I don’t want to see another 80-year-old woman carrying 20 kilos of firewood on her back. Maybe we don’t have to” [CNN].

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Image: John Bohmer

  • Brian M

    This is amazing — but if “temperatures inside the pot can reach about 175 degrees Fahrenheit” how does that boil water? Never mind bake bread, etc?

  • Loch Eddy

    Perhaps that should read175 Celsius, or 347 Fahrenheit

  • Bob Snyder

    “Covering the cooking pot with a transparent cover retains heat and water, and temperatures inside the pot can reach at least 80C.” From the BBC link.

  • Gary W.

    “Bohmer’s contest win notwithstanding, solar cooking with a cardboard oven isn’t new. Two American women, Barbara Kerr and Sherry Cole, were the solar box cooker’s first serious promoters in the 1970s. They and others joined forces to create the non-profit Solar Cookers International — originally called Solar Box Cookers International — in 1987.

    Further, the organization’s executive director, Patrick Widner, said that the plans for a solar box cooker were found in a book published by the Peace Corps in the 1960s.”

  • Jim Evans

    This article makes this idea sound so novel. I have been contributing to (and using the product of) a non profit organization called “Solar Cookers International” that has been making and distributing a similar device for decades. They also promote local citizens to become involved in the distribution.

    Please see (and donate to or buy the product of):

  • Dob Bole

    What if it’s raining or overcast?

  • Bill Woods

    80 °C is hot enough for sterilization, though it won’t *boil* water. From Wikipedia,

    Food safety: “Cooking food until the CORE TEMPERATURE is 75 °C or above will ensure that harmful bacteria are destroyed.
    However, lower cooking temperatures are acceptable provided that the CORE TEMPERATURE is maintained for a specified period of time as follows :

    * 60 °C for a minimum of 45 minutes

  • Ken Erickson

    Years ago, when I was teaching elementary school, my students and I made siimple solar ovens. Then I asked if any would be interested in making a more complicated device. Nine thought it would be interesting.

    I had do figure out how to make a parabola but once the challenge was there the answer came quickly.

    We made three complete solar ovens (basically cardboard and aluminum foil), mounted them on A/V trolleys, and added potatoes to one, veggies to another, and a roast from a moose I’d shot to the last.

    Every 15 minutes I sent out one of the nine to re-aim the ovens. By noon the meal was ready to eat. We had a great lunch.

    That was with Grade 5 students in Prince Albert, SK. What a great bunch.

    I tried it years later with Grade 9 students on a reservation but the results were disappointing.

  • Dean

    too bad some parts of the world its raining for a season at a time

  • Claire C Smith


    This is one of the best posts I have seen in a long time.


    I am going to have a go at making this. I mean, it’s simple and already obvious. Retaining heat, insulation, duration of heat. Cheap materials we already have in the home, how to think. This is augmentation of materials, how they work together. Capacitising their uses to the fullest dregree, but then so many things can be…


  • Angela

    This isn’t new. I remember making one to roast hot dogs in elementary school. However, the concept could be extremely beneficial in areas that need to heat water to purify it, but since it’s just a cardboard box, obviously they’ll need some other kind of vessel for the water. As I remember how long it took for my hot dog to cook in my admittedly less high tech version (aluminum foil + a shoe box), I (like others) can’t imagine how one could cook a casserole or bake bread in one of these!

  • Ris

    The idea may not be novel, but we must note that this solar cooker is much cheaper than the one sold by Solar Cooker International (SCI) ($25, perhaps even after considering economics of scale). The target audience of this project are firewood-users, who are likely poorer. They are more sensitive to the prices of goods.
    However, SCI’s cookers can reach mid 200 degrees Farenheit…. Hopefully, when this guys improves his idea, his cooker wouldn’t cost too high…..

  • JDH

    It will boil water…
    at 8000 meters!

  • Jon Bohmer

    The solar box was invented in 1767 by De Sasseur in Switzerland. I was just wondering why everybody did not have them already. Solar cookers have been DIY projects for years and so is the Kyoto Box but the important thing is the ease of mass manufacturing of this particular design.

    I boiled water and rice with it – so it reaches at least 212F/100C. Pasteurization of water happens at 154F/68C and cooking is done at 185F/85C so it is pretty good for many tasks. At night you just fold down the lid and it keeps the food warm for hours.

    The cardboard version is a fun and easy DIY project but we are bringing a plastic version to market that is more professional and will last through rain and spilling. The $6 price is in fact offset by carbon credits (cap and trade) so it will be free for the users. This way we will make this the VW bug of solar cookers.

    In the countries with the largest deforestation the sun is also most plentiful. As global warming increases the conditions for solar cooking will only improve. The Kyoto Protocol also mandated “adaption”, where victims of global warming is compensated (with appropriate tools, we suggest) so that they can continue their lives. We are bringing out a number of adaptation products, including water pumps. See for more information.

  • Shannon Carr-Shand

    Thanks for all the comments regarding the Kyoto Box winning the FT Climate Challenge Competition. There have been a few posts pointing out that the solar-powered oven is not a new idea. The point of the competition was not to reward a eureka moment but to help an innovative approach to climate change reach the market. As Kyoto Energy founder and competition-winner Jon Bøhmer acknowledges in his company literature and on his application, the concept of solar cooking has been around since the eighteenth century.

    There are other versions of solar cookers available on the web and there are also detailed explanations of how to make a version of a similar device. What distinguishes this approach is that the cooker will be mass-produced cheaply in existing factories, the finished item is to be flat-packed for bulk transportation to end users and is extremely cheap at $6.

    The $75,000 prize money is going to enable Kyoto Energy to test durable, plastic versions of the cooker with 10,000 people currently burning fossil fuels to clean their water and heat their food. The expert judges and the thousands of members of the public who voted for the Kyoto Box agreed that this simple idea offered the best opportunity amongst the five short-listed ideas for an innovation to help tackle climate change on a big scale.

    Please see the press release and our site for more information on the competition and its objectives.

    Shannon Carr-Shand, Forum for the Future

  • Zeek wolfe

    Six dollars for a cooker? Hey, you could charge six cents but it won’t change a thing. These dopes in the third world don’t even know how to boil water and this technological upgrade is quite beyond them. They would try it once or twice and then use the box for firewood. Tell me how I’m wrong!

  • Uncle B

    Folks in India use large reflectors and slots in the walls of homes to ovens for cooking, and have done so for a number of years. Sunny climate folks have few excuses – they must use solar wherever possible. Folks in Northern Canada, where it is too dark and clod most of the year, denpend on wind if they have any, otherwise they burn wood, coal oil, natural gas, anything to keep from freezing – they have but one choice, to move to an environmentally more friendly zone to save the environment!

  • Chris mankey

    “Six dollars for a cooker? Hey, you could charge six cents but it won’t change a thing. These dopes in the third world don’t even know how to boil water and this technological upgrade is quite beyond them. They would try it once or twice and then use the box for firewood. Tell me how I’m wrong!”

    Are you a teabagger? What have you EVER done to make the world a better place?

  • Zeek wolfe

    I was part of an international aid group assigned to an impoverished west African nation. I personally showed hands on, one-on-one, hundreds if not thousands of the poverty stricken citizens how to operate donated equipment. This equipment would give them a better life. We returned six months later to check the results. The only results were bad. Solar cookers and water purifiers, even pipelines from distant water sources had been abandoned. We asked why they no longer used the equipment and they said that they preferred the “old ways.” Yes, Chris Mankey, I’ve been there and done that.

  • Gabriel Gadfly

    New or not, it’s a pretty good idea, and for the most part, this can be made entirely with junk materials — you don’t actually need to buy anything.

  • Jack

    Health standard in the US require dishware to be sanitized in, minimally, 175-degree F water, so even this temp achieved by the solar box has purpose to, perhaps, sanitize water if not bring it to a boil.

  • alain

    Zeek wolfe said:

    “We asked why they no longer used the equipment and they said that they preferred the “old ways.” Yes, Chris Mankey, I’ve been there and done that.”

    Perhaps you’ve pointed out why honorable efforts of so many angel-hearted westerners ofter failed so miserably on the fields.
    They disregard “the old ways” thinking, “Oh, I am from a sophisticated country. I am a college educated with PhD in several social fields. I should lecture these people how to do things. Look how the destroy the earth and oppress their women. That won’t do. We must make them change with our ways. Even though that would require them to bend over backward to adjust with the limitations we impose on them.”

  • Joe

    Tried solar cookers similar to this. In practice it doesn’t work reliably enough and the heating energy is not sufficient to heat a large mass of food or water. In practice we found a parabolic dish of about 1.5 meters or more is needed.

  • Ivo Roper

    The real revolution will be when innovators actively include people from target regions to test and refine these inventions *before* mass producing them. Linking the new solution visually and metaphorically to ideas and stories that are culturally comfortable will help bridge gaps of unfamiliarity. Such ideas need to be put through a real trial by fire to validate them.

    Also, the old ways work reliably! If the new ways fail 5% of the time, they will stop using them because going without a meal for one night is unacceptable. If you can only afford just enough food to live on, then wasting any food is a survival risk AND very damn unpleasant.

  • solar oven lover

    These solar ovens are quite literally life savers in remote regions of the world. Great that you can build one so cheaply

  • Chris G. Mankey

    Sorry about the other Chris who posted up there (#18) I really wish he was a bit more open minded…

  • Jeremy

    I don’t get why this gentleman gets credit for inviting this… My kids made these in shop class almost 20 years ago, and baked cookies, bread, pizza, you name it, they made it. Is this a really old story, just brought to light due to the ever increasing environmental crisis? Solor cookers are a great idea, just not a new idea. mass production and distribution in third world countries is a great idea though

  • Russell Blevins

    I boil water by telling thousands of lies per minute. How’s that? I have a great impact on the environment by reducing the amount of trust in my area.

  • http://Mozillafox shinie

    thank you we do use the suns heat to heat the water etc we live in a hot region and we use the fans a lot during the night can you suggest or gives us an idea how to coll the rooms at night without using the electricity.we spend a lot on electricity/

  • Srinivasan Nenmeli-k

    Jon Bohmer’s solar cooker is quite similar to SCI-Kerr-Cole type box cooker….may be a bit simpler…it has value to third world countries with deforestation growing rapidly—Hope this will spur work in those countries using local materials and produced as cottage industry there..lot of training and motivational work is required for adoption by local villagers…

  • john hand

    How can I get the specifics – plan and list of materials with detailed instructions to make this? I want to do this in an African town where the availability of materials is quite limited. Thanks.

  • karo

    maybe it is useful, to take iron plates at the bottom, to accumulate the heat.

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  • Nina

    what are the detentions of the box???


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