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Results! A convenient, inexpensive, high-power solar cooker

March 4, 2011

This is what it’s all about right here: we’ve finished the core of our new solar cooking system.

I contend that this is one of the simplest, most convenient and most cost effective high power (1kwh+) solar cooking solutions.

I’ll go into technical and performance details in a later post but for now just check out the ergonomics and consider the facility of use. Waist high cooking console with a lever to control the mirrors and a ‘rearview mirror’ to peek at the underside of the pot to ensure that the machine is properly oriented. The cooking console is far enough removed from the mirrors that putting up a shade or umbrella will not affect the system. All while harnessing 2kwh of solar thermal energy. Enough to boil 8L of water in 40 minutes.

It’s a simplified version of our old mainstay, the Helios array that we’re calling the Phaeton coupled with something we’ve managed to develop what we’re calling an upward reflector. Thin mirror strips reflect the light upwards and onto the bottom of a cooking vessel, enabling boiling or frying in a traditional manner.

There’s a reason we call these technologies Solar Fire. No new recipes required… the Phaeton will cook anything a fire cooked and more.

The convenience factor matched with the power of the machine and leveraged using the upward reflector means that this is a significant development which helps to overcome a persistent flaw in many solar cookers of this size. Observe the following pictures of larger solar cookers which are in more or less the same size league as ours.

The bigger they get, the less accessible the focal point becomes at certain times of day, or the more extreme the angle of incoming light which hinders some processes like frying. Waist high solar cookers like the rightmost have difficulty exceeding 2 square meters of collector area. Tinytech on the far left has a very impressive 8m2 but one cannot install a shade, to access the pot you must mount a step and it cannot operate as early or late. The Phaeton can operate from sunup to sundown, though the incoming energy below a 20-degree-from-the-horizon sun is not really worthwhile. Nonetheless, in the tropics you get 8 good hours of solar cooking. I have yet to make a big test batch of rice but based on some rough figuring the Phaeton can prepare at least 50kg of rice per day. Instead of rice we’ve been making marmalade and dried pineapples 😀

Oh, and it costs less than $500 all told.

Designed to be built onsite by local tradespeople the Helios array uses common materials that are off the shelf in nearly every country on the globe.

My grandfather and I want to engage in international aid projects wherever the need is greatest. Aid organizations running camps in Haiti could see these machines work 8hrs a day and pay themselves off in less than a year, reducing fuel budgets and improving health standards by sterilization. Sub-Saharan countries ravaged by deforestation and suffering under the weight of energy poverty can use this free technology to start generating wealth at all levels of society.

Seriously, we’re mounting a project, somewhere, somehow, and we’d love your help.

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5 Comments leave one →
  1. Ken Provost permalink
    August 23, 2011 10:47 am

    Beautiful construction, Lorin! I’ve been building cookers for several years, and
    I just built a small Vesta (16 reflectors, each containing nine 4×4 facets).
    Each of my reflectors was built in a jig that gave pretty good control over
    the focal length, but every reflector is symmetrical about the center facet.
    I used 4 different focal lengths for the 16 reflectors.

    I notice a LOT of focal spread due to the off-axis reflection problem, and
    I’m wondering how you solve that. Is every one of the 35 reflectors built
    assymetrically (ie, a faceted off-center portion of a paraboloid)? Do you
    use the original plaster mold approach, or have you found a simpler way?

    Thanks, -K

    • August 23, 2011 7:23 pm

      Thanks Ken! I’d like to see some pics of your jig if you’ve got some.. or of the Vesta, for that matter!

      I’m not sure what you mean by the off-axis reflection problem…
      I use the original plaster mold approach, where each 9 facet mirror module is symmetrical about the middle facet (calibrated facing the sun) but then usually is placed off center on the mirror array. Over the course of the day there is some distortion of the focal point but generally all the light still falls on the bottom of the pot so it doesn’t affect things greatly.

      Cheers!

      • Ken Provost permalink
        August 24, 2011 10:21 am

        Lorin:

        I’m not sure how to post pictures, so here are a couple links to a
        Photobucket album:

        Vesta — http://i1177.photobucket.com/albums/x359/provost_k/11.jpg
        Jig — http://i1177.photobucket.com/albums/x359/provost_k/vesta_jig_small.jpg

        You described the focal drift problem exactly — if the mirrors are built for
        a precise focus when facing the sun, they suffer from astigmatism when tilted
        at some angle from the sun. And the Helios (or Phaeton) would be even worse
        than the Vesta, because the highest row of mirrors can be over 45 deg. off-axis.

        As you say, you just have to have a large enough window, or calibrate every
        mirror in place, reflecting to the target — lotta work:-)

        -K

      • August 25, 2011 9:09 pm

        The vesta looks great!
        The jig is interesting… do you have screws in there the adjust the mirrors?
        With the Phaeton and Helios we have 5 or 6 molds for different positions on the array and it works out pretty well. One solution for the focal drift problem is to have the oven or whatever you have at the focal point so that you can move it back and forth over the course of the day. Towards noon the focal point gets diffuse but then you pull the oven back a foot and a half and you’re back to a good tight focal point. I’ve never noticed the problem being bad on a Vesta, but maybe the pot or pan could be raised and lowered a bit to help compensate.

  2. Ken Provost permalink
    August 26, 2011 7:26 am

    Thanks! There are 4 wood screws coming up under each corner of
    the aluminum plate, so you can use the same jig for all your reflectors.
    The plate height is 8/f, which for a vesta is easy to adjust and measure
    with a calipers. Really long focal lengths would need some modifications.

    Another question — can you tell me a bit more about your upward-reflecting
    secondary mirror? I guess the strips are to tolerate the high temperature;
    are they glass or aluminum, and are they stuck to a baseplate or open
    to circulating air?

    I really appreciate you sharing your knowledge — this is a fun
    hobby for me 🙂

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