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Power Hardware Technology

Making a Better Solar Cooker 167

Posted by Soulskill
from the making-high-tech-low-tech dept.
New submitter jank1887 writes "Back in 2010, the aid organization Climate Healers gave a number of solar-powered cookstoves to rural Indian villages. The stoves were rejected by the communities, mainly because they were useless when they were wanted most: for the evening meal sometimes after the sun goes down, and for breakfast before the sun has risen. Following this, the group issued a challenge to EngineeringForChange. Details of the challenge include the need to provide 1kW of heat at about 200C for two hours in both early morning and late evening, and the users should be able to cook indoors, while sitting. A number of groups, mainly at U.S. and Indian engineering institutions, accepted the challenge, and developed potential solutions. Now, almost a year later, the ten finalist designs have been selected. The actual papers have been posted to the E4C challenge workspace. The goals of most of the designs are to keep the technology simple, although there are a few exceptions, and many include sand-, oil-, and salt-based concentrated thermal storage. Many reports include some level of discussion on the social and economic considerations, barriers to acceptance and sustainability, and how to overcome initial resistance to adoption."
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Making a Better Solar Cooker

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  • Re:My Solution (Score:5, Interesting)

    by Asic Eng (193332) on Friday February 17, 2012 @02:02PM (#39077575)
    Try to build it within their cost requirements, present your prototype and compare it with the other designs. If you think you can do better, then help out - you could really make a difference to the lives of many people. I suspect you'll find that your initial idea won't be quite as good as what the other guys came up with, but generally there is always a better solution around somewhere. One more person looking for that can't hurt.
  • by Powercntrl (458442) on Friday February 17, 2012 @02:09PM (#39077663)

    There are actually government subsidies on kerosene in place in India specifically to prevent deforestation. The kerosene stoves are actually quite safe, efficient, clean burning and relatively inexpensive (by developed nation standards). Now before you start with the "OMG fossil fuels BAD!!!", remember that the grid-connected electric ranges that are so popular here in the USA are running on varying percentages of power derived from nasty, dirty coal - with the added bonus of generation and transmission losses. Since we're talking about a point-of-use fuel, these "third world" kerosene stoves are actually a pretty green solution. Perhaps instead of providing these people with pie-in-the-sky solar stoves that we wouldn't even use ourselves, we should offer good old kerosene stoves and maybe take a closer look at our own wastefulness.

  • by Firethorn (177587) on Friday February 17, 2012 @02:10PM (#39077673) Homepage Journal

    Reading the article, the first contender came with a proposal to give them efficient wood stoves first, to displace the open fires they're currently using. Doesn't imply that they have gas.

    Of course, it makes me want to point out that a modern high efficiency wood stove might sufficiently solve the problem to the point that it renders the solar stove unnecessary. Wood is a renewable resource, they apparently have sufficient quantities of it, and from what I remember, ye old wood stoves were ~10x as efficient as open pit fires at heating and cooking, and modern high efficiency ones are ~50% more efficient than the ye old varieties.

    So you're lookng at using 1/15th the wood. At which point you have to convince people that using the solar stove is more convienient/valuable than dealing with the much smaller amount of wood the solid fueled stove needs. Well, don't forget cleaning requirements.
    Let's see, stove rating areas:

    • Convienence of use
    • Stability of temperature
    • Range ot temperature
    • Maintenance/cleaning requirements
    • Cost of fuel
    • cleanness of fuel
    • availability of fuel
    • endurance of the stove
    • longevity of the stove

    The more you get, the better the product.

  • Re:I'm betting.. (Score:2, Interesting)

    by Anonymous Coward on Friday February 17, 2012 @02:16PM (#39077759)

    Of course. There's a difference between food, and a fuel for humans that's certified safe by the FDA:
    http://usnews.msnbc.msn.com/_news/2012/01/31/10282876-mcdonalds-drops-use-of-gooey-ammonia-based-pink-slime-in-hamburger-meat [msn.com]

  • Baking bread (Score:5, Interesting)

    by Firethorn (177587) on Friday February 17, 2012 @02:16PM (#39077761) Homepage Journal

    Doh... Of course you're correct, and I'm mostly thinking of my micro-production at home. Of course, back in the day you had the village baker, the average family didn't bake their own bread. What I get for trying to be among the first to post. ;)

    I should have stated a concern more for how easy it is to control the temperature of the stove - keeping it reliable is more important than the exact temperature, and many older ovens were large enough that if you wanted hot you used the back of the fire/oven, if you wanted lower temperature you kept it nearer the front.

    As for the outdoor brick/mud oven - if it's solar powered you need something to control the damper, and if you're using stored heat you need a way to moderate the heat from extremely sunny/hot days, while still keeping it hot enough on rainy days.

    Supplimental heat from a fire, or like in the one case it's 'add water here, get steam there', so if you have some sort of steam limiter, you have temperature control.

  • Re:My Solution (Score:4, Interesting)

    by yog (19073) * on Friday February 17, 2012 @02:19PM (#39077783) Homepage Journal

    Some day, photovoltaic panels will be dirt cheap and will be perfect for these rural villages, but right now they're too expensive even for most Americans.

    When I was a teenager, I build a solar stove out of cardboard, plywood, and aluminum foil, based on a design in a book I read. I probably could have made it totally out of cardboard; I wasn't much of an engineer/architect :)

    Anyway, the thing worked amazingly well. I demonstrated frying a hamburger (not something you would want to show the Hindu villagers, by the way) and my family was blown away. However, it had three disadvantages. First, it was extremely bright. To stand more or less in front of it to turn the food was a blinding experience.

    Second, you needed a black-bottomed pan, which we didn't have, so I painted an aluminum pie pan black on the bottom.

    Third, like the article says, it only works in full sunlight. You don't really want to cook the meat and veggies at 3pm, you want to get them started around 5:30 or 6 in most households. It's likely that the villagers are working in the fields or small workshops all day and don't get around to supper until 7pm or later.

    At least, it should be quite possible with a reflector cooker to make large pots of rice during the day, which they probably do anyway since it takes relatively long. Solar reflector cookers are perfect for that application because rice mostly wants to simmer at a lower temperature.

  • by Powercntrl (458442) on Friday February 17, 2012 @02:48PM (#39078155)

    The Japanese and the Amish use kerosene appliances quite heavily in their societies. A properly designed kerosene stove will burn just as clean as the LP/natural gas stoves that we seem to be entirely unafraid of, here in the US. Notice the incredibly clean, blue flame this stove [youtube.com] burns with.

    What it boils down to is, as you said, a problem of getting the subsidized fuel to the people who need it. It seems like that's the real issue here, not some engineering challenge to show off to some poor villagers how advanced our high tech is (again, never minding the fact many of us use electric stoves that get their power from dirty coal!).

  • by Daniel_Staal (609844) <DStaal@usa.net> on Friday February 17, 2012 @02:52PM (#39078217)

    Propane is expensive and hard to store and transport. (At least by 'developing country villager' standpoint.) Easiest way to transport it is large metal canisters, of which the canister itself would cost a month's salary, quite often. Of course, the canister is recyclable, so they'd only have to pay that once, but it's still an expensive item. Then they have to carry it back and forth from the refueling station, and pay for the actual fuel.

    From the villager's standpoint, that's not much different than using a wood stove; at least the wood will be cheap/free.

  • by sirwired (27582) on Friday February 17, 2012 @03:54PM (#39079081)

    A couple of years ago, the IEEE magazine of the Society for the Social Implications of Science and Technology had a fascinating article about this very topic. (Although it did not involve solar stoves; instead it was about combination stoves/small generators to supply low levels of lighting and communication access to a rural village, in addition to a stove.) I can't remember how the electricity was generated; it was something non-mechanical... As an added bonus the stoves vastly improved the air quality of the dwelling; at least, they would have if they were used.

    What they determined was that the style of cookstove used varies by region, and that a design put together by some appliance designer many thousands of miles away is invariably not going to design a stove that is going to get used in some isolated rural village in the boondocks.

    It'd asking somebody that's used an oven all their life to start doing all their cooking over an open fire... given the choice, I'm just going to keep doing what I've been doing.

    The project also failed to account for distribution and transportation difficulties. A bulky stove weighing a couple of hundred pounds is really hard to transport into a mountain village accessibly only via a one-week journey by donkey.

  • by Tekfactory (937086) on Friday February 17, 2012 @04:41PM (#39079631) Homepage

    I would think you think you're being clever or well informed, but I regularly cook things in my Sous Vide machine at the FINAL temperature I want them to be. With this method you cannot overcook your food, it will hold at temperature and in most cases not degrade the texture of the dish if something comes up and you wait 30 minutes to pull it out of the water bath. Some high end restaurants use this method to keep popular foods just shy of done, when an order comes in they give them a quick sear in a pan and put them on a plate.

    A lot of the 300-400 degree cooking methods are too-efficient transmission directly from the pan through the meat so when the center is 170 and safe to eat, the outside is 240+ and either beef jerky or charcoal. Likewise air is a poor heat conductor so it takes hours in an oven for the center of the meat to reach 160, see every Thankgiving turkey ever.

    With Sous Vide you never overcook and the moisture in the food isn't driven out by the cooking process.

    So I'll see your Newton's Law and raise you Fourier's Law

    "Writing about sous vide led Myhrvold to think more deeply about how heat moves through different media (which is why Modernist Cuisine may well be the only cookbook ever published with a long disquisition on Fourierâ(TM)s law, the equation for calculating heat transfer)."

    http://www.wired.com/magazine/2011/02/ff_myhrvold/all/1 [wired.com]

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