Sunday, January 29, 2012

from rice cooker to solar oven in three hours

the results of today's tinkering
It was seasonably cold today- meaning that it was much colder than it has been for most of the winter. Ice on the windows and some fresh snow on the sidewalk.  I wanted to go outside to play, but the kids just started being a bit sniffly and coughing (also seasonable) and it's never a good idea to take them outside when that's the case.  Even if it is an old wives tale that cold weather will bring on a cold or flu, I have a wife that believes very much in that conventional wisdom, and I'll be in trouble if I take them outside with me.

So, since Gita isn't feeling very well either after her fourth chemo session, I mostly stayed inside, played with the kids and looked for ways to stay sane.

I haven't puttered in the workshop for a while.  Most of my tools are stranded at the vacant apartment at our rental place which is in a state of suspended animation since cancer became an unwelcome part of our lives.

I brought up the banana plants from the root cellar, thinking it may be an early spring after all, and maybe I'll get them re-started in the bay window and get a jump on that early spring.  And I noticed in the corner near the bay window, for the tenth time, the small but growing pile of stuff that is old or broken or otherwise useless that I should take out to the trash, but which I haven't gotten around to yet.  Mostly because there is some good left in those things that I just haven't gotten around to figuring out yet.

But today, when I saw in the pile the old rice cooker that doesn't quite completely cook the rice, and which has been on the verge of being tossed out for a while, I had a revelation.  It's a solar oven waiting to happen.

It already has a good number of the features of a solar oven- a nice heat-proof cooking box, a glass lid, an airspace all around the cooking box that can accommodate some insulation.  All it needed was the addition of that insulation, a solar collector and a thermometer.

I've been thinking about making a solar over for a while now.  It's been on my to-do list for maybe two years now, and I've been looking for some scavenged parts in order to make one.  But what's better than scavenging something that hasn't even been thrown out yet?

So I took it downstairs and started puttering.  I took out the innards of the thing- the heating element and switch and various electrical wires.  That left about two inches under the cooking box of empty space and about three-quarters of an inch on the sides.

It was easy enough to cut some polystyrene insulation to fill the gap at the bottom- but how to insulate the sides?  I've never actually taken any sort of class on how to make a solar cooker, but have seen one or two prototypes, and was pretty sure I had to insulate the cooking box with something non-flammable, in case the solar oven was more successful than I had anticipated.  I also had to adhere the insulation to the cooking box with something that also isn't flammable, and more, won't start to smell horrible when it heats up to 200F or so.

So I looked around the basement.  I could use polystyrene, but it's not very bendable and might melt or even catch fire at high temperatures.  I toyed with the idea of using some scrap carpet we had laying around, but that's polyester or nylon, and that wouldn't smell so good when heated either.

But we had lots of lint in the basket next to the dryer!  Lint is a fantastic insulator- which you can confirm for yourself by holding it in your hand.  Most of our clothing is cotton, which won't melt, and won't combust until it reaches a higher temp than I'm likely to get in this oven.  But how to adhere it to the aluminum cook box?  I didn't have any spray glue, and probably wouldn't use it if I did- I doubt that would smell good at high temperatures.

But I had some soft hand soap in a big bottle.  I slathered that on the aluminum, and it turned out that lint bonds very very well to semi-tacky hand soap.  I stuck as much lint to the cook box as I thought would fit, and slid the thing into place, hoping the lint wouldn't all fall off.

And it stayed on pretty well.  I finished the passive part of the cooker off with a little caulk around the rim to hold the cook box in place and create a seal to keep the heat from seeping out.

So at this point, I had to find a solar collector, and a way to attach the thing to the stove, so I went for a walk.  I ended up at the hardware store, where they had a hinge that would work, and a candy thermometer, which was also good, but no concave mirror, which was the part- the solar collector- that would really finish it off nicely.  No lightweight flat plastic mirrors either.  I was starting to think I wouldn't be able to finish the project, or at least not today, until the sales guy suggested, half joking, that I buy a stainless wok, pointing over at the kitchenwares.

That's when the light went on over my head.  We had a wok cover, an aluminum one, in our basement, that we haven't used for years and which I had also been thinking about throwing away, but hadn't gotten around to.

I'm lucky they didn't have concave mirror, because I was able to fit yet another piece of useful junk into the design of my solar oven and began feeling very good about myself.  As it turns out, it really was a very useful piece of junk.  I was able to polish it to a fairly high sheen with some fine steel wool, and make a serviceable parabolic mirror out of it, which will stand up to abuse far better than a glass or even plastic mirror.

I don't know how well it'll focus the sun, but I wasn't shooting for perfect- just good enough, and done with stuff I had on hand.
finished solar cooker.  and my messy worskhop.

So the finished product is actually much more attractive than I had expected it to be.  It looks more like something I ordered from a catalog than something I put together from junk in my messy basement man cave.

The total for the hinge and candy thermometer was about $2.50, since I had $10 of unused Ace rebate coupons in my wallet that I had forgotten about.

By the time I was done, it was dark, so there was no way to tell if the thing will actually work, but I tried a few different 'sun angles' with a flashlight, and it seems like the collector reflects pretty well.  The hinge doesn't keep it in place as well as I'd like, but if I have a stick to prop it up with, it should be OK.

This sort of thing makes me really happy.  It doesn't take much really.

I'm looking forward to grilling this spring- with deadfall from our maple tree, then throwing some veggies or rice into the solar cooker to slow cook while I tend the fire.  Both sustainable and free of charge.

So go put that in your gas grill and smoke it.


  1. I was outside with a flashlight last night ... checking the reflection on my newly finished solar oven too !

  2. Hi Anon- send a picture or post a link- I'd love to see your solar oven!

  3. Very cool!

    One thing I'd like to point out: perlite and vermiculite make good insulators too, and there is no danger of them igniting. Granted, you probably don't have any lying around your basement, but a lot of gardeners do use them as soil amendments. Granted also, as energy prices go higher, eventually those will prohibitively expensive, but while energy is still relatively cheap, I think those are wonderful investments.

  4. Thanks for the tip John! I never even considered vermiculite. I was trying to think of a mineral insulator and all I could think of was rock wool or fiberglass and didn't want to chance either one mixing with food. I've heard some vermiculite is contaminated w. asbestos, so I suppose I should exercise caution there too.

    None lying around my basement- but I like to go to nurseries- I know where to find it if I need it.

    I think perlite is polystyrene, so it might combust given enough heat, but it would take a lot. I had some old polystyrene that I considered breaking up and stuffing into the spaces, but thought I'd give the lint a try first. Thanks for the thoughts.

  5. Somehow, after your last few posts, thought you might appreciate this article:

  6. Thanks Amy! I really enjoyed the article. It's nice to see that this idea is catching on in academia. I had no idea that St. Benedict's was doing any of this. Gives me new respect for them.

  7. I like to know if your solar oven works. Hope you will know it by summer.

  8. I really enjoyed the insign you bring to the topic, awesome stuff about the
    "Solar Energy Project"..Thanks for sharing it.... solar panels