Cooking with the SUN and nothing else

Aug 282017
 
diy-solar-cooker

Once we were able to get into and out of the tiny house :grin: and once we got a fridge ultimately able to keep foods fresh even during summer heat thanks to energy autonomy achieved earlier, it was time to cook a meal. :mrgreen:

Hey, not so fast, we still didn't have a way to cook at all. You may be wondering "why didn't you get a small gas burner to make a meal for that poor dog?" (I am not worthy a meal?)

Well finally, here is the answer: You can't just set up your cooking pot on gas or other open fire when you are outdoors here, nor will I use gas or any other flammable inside this widely unfinished mobile tiny house. And speaking of gas, I don't ever want to have gas in a house if I can avoid it:

solar energy autonomy
Solar energy autonomy
  • I feel uneasy to build and use something that's flammable and explosive
  • when you really think about it, using up non-renewable resources in our generation is not socially responsible
  • and being dependent on non-renewable resources that others control is risky, and can become costly
  • the stress of shopping for any kind of fuel, possibly even carrying fuel home, is avoidable.

Thus the plan is, I repeat, the plan :roll: is to do everything with the free energy of the SUN, if possible (and I am the one to try that out, right). Charging vehicle batteries from the SUN I have already learned. Next is:

  1. cooking with the SUN
  2. house heating with the SUN
  3. and water heating with the SUN.

A backup generator for emergencies (week-long solar eclipse anyone?) I would accept - if it is SUN-powered :mrgreen: - but that's all.

real sheep wool insulationNow seriously: The first TEST will be the coming winter (if I can get the house insulated before winter). The last winter didn't count as we didn't have anything, and certainly no energy autonomy. So we were both freezing inside the house. I hope we won't be freezing again this coming winter, but that's subject to being able to buy some thin tongue & groove wood planks to put over the sheep wool for insulation that I have already acquired (we are up north again where winters are cold, for truck inspection).

Today is all about the first point: cooking with the SUN.

Namely how we got from this:

Stocking up on tin food
Stocking up on costly tin food :cry:
= COLD meals!
to this:
Fresh foods cooked with the solar cooker
Fresh foods cooked with the solar cooker
= HOT meals :grin:
Making alu insert with rims for glass tube
1. Making alu insert with rims for glass tube
Making tray to shove on rims of alu insert
2. Making tray to shove on rims of alu insert
Testing cooking tube with just alu insert and tray inside
3. Testing cooking tube with just
alu insert and tray inside
Welder making two cooking pans to fit tube
4. Welder making two cooking pans to fit tube
Welder making bases of stand for cooker
5. Welder making bases of stand for cooker
Meanwhile risky cooking without stand
6. Meanwhile risky cooking without stand
Closing bases for stylish finish
7. Closing bases for stylish finish
Riveting bases to baseplate to make stand
8. Riveting bases to baseplate to make stand
Cushioning delicate nub of glass tube
9. Cushioning delicate nub of glass tube
Finished stand with glass tube
10. Finished stand with glass tube
Making rings to turn reflector
11. Making rings to turn reflector
Making reflector and having GSD guarding solar cooker
12. Making reflector and having GSD guarding
solar cooker - this is important! :-)
Finished DIY Solar Cooker
13. It works: Finished DIY Solar Cooker!

Thanks to site member Mark with GSD Max (thanks again!), I am happy to say that finally I can cook again and make the dog happy - after a full year of both of us existing on tin food and not much else.

Not that you misunderstand though: not the tin food you can get in the "pet food" aisle, but REAL FOOD tin food: human-grade, thus controlled quality, not incinerated toxins. Hence why the local animal hospital was able to confirm that despite existing primarily on tin peas and tin champignons for a year(!) Miguel is very healthy indeed. :-)

Here's the photo story how we came to cooking with the SUN and nothing else:

  • While there exist many ways to cook with the sun, I had done my research (and Gary's site is excellent) that the most efficient way is a double evacuated glass tube
  • because you already know that a vacuum is the best insulator, and so when sunlight heats up the inner glass tube, the heat cannot escape back out through the outer glass tube :idea:
  • I instantly loved the ingenious concept and the so much smaller footprint and therefore convenience of this style of solar cooker (NB: tiny house!)
  • The problem: pretty much all evacuated glass tubes are made in China and importing anything here to Portugal they make more difficult than getting an engineer degree and building it yourself :mrgreen:
  • but I knew that someone (with the most absurdly secretive business you can imagine) somewhere in the USA had imported a container of such tubes and sells them very successfully
  • Be aware that all that comes next was before anyone here could buy that amazing GoSun stove.
  • And the GoSun sport is way too small to cook for a hungry German Shepherd Dog. :roll:

I can't remember how site member Mark with GSD Max got to know of all of this but somehow he kindly offered to organize proper repackaging as family gift :mrgreen: and overseas postage of that truly great value for money solar cooking tube from that business that don't even disclose where they are. Note though that this overly secretive amazon.com vendor will only sell to mainland USA and just the glass tube with lid.

Placing a glass tube somewhere when sharing a mobile tiny house with a German Shepherd Dog is impractical of course! Therefore when I received the tube (UNBROKEN thanks to Mark's thorough repackaging) I went on to turn the glass tube into a complete cooker, trying to make it as stunning as the now available GoSun stove.

I hope you enjoy this illustrated project report. :-)

Going through the photos:

Step 1: By all means, give the glass tube an aluminum insert for safety. While the borosilicate glass is extremely shockproof, this does not include thermal shock.

The alu insert prevents that a preheated evacuated double glass tube disintegrates when say chilled food were to touch the glass directly. The alu insert also makes cleaning the cooker a breeze because nothing sticks to the glass (I can get my arm inside but it's not convenient).

Note that aluminum conducts heat the best - unless you can afford an insert made of copper or silver?

Therefore I had a blacksmith cut and roll an alu sheet in a way that it got two small rims like you see in the photo. The rolled alu insert is sized to be squeezed a bit such that it nicely fills out the tube when I shove it in.

 

Step 2: The same blacksmith then cut and bent me a stainless steel (inox) sheet to function as tray for the tube. The photo shows how smoothly the tray glides on the rims of the alu insert. No lubrication needed: Inox on alu.

 

Step 3: When I got those two parts back it was a sunny evening, and so I decided to quickly test the tube's temperature gain with the alu insert and tray inside (without food):

  • From 6pm to 7pm the tube's temperature rose from 40C / 104F to 110C / 230F
  • At 19.45 I stopped the test because the sun was about to set
  • Tube temperature: 121C / 250F
  • I felt this was good, no?

 

Step 4: So then I gave the blacksmith the design for two cooking pans sized to fit on the tray and to be shoven in the tube. I cut the inox sheet myself in a way that he could cleanly bend it with a machine and then simply weld the edges close.

It turned out, my "friend" couldn't weld my chosen 0.5mm thin (and therefore light!) pan material. Thus for this small job of welding the pans close I had to find an "artistic" welder who would weld such thin inox. The result looks and feels disastrous: One could easily cut his fingers on that rough weld! At least the outside of the pans I was able to deburr with my cordless drill.

 

Step 5: When I got back the two pans, I gave my trusted "friend" blacksmith the design for two bases that will make the stand for the cooker, so that he would cut and bend a stronger inox sheet for me.

He also welded an inner channel to accommodate my fear that otherwise the glass tube would knock against the 1mm edges of the bases, each time we hit road bumbs. :roll:

 

Step 6: While I was waiting for his work, the sun was shining and Miguel was hoping for a cooked dinner, which is why I dared to place the yet naked glass tube on a lounger to test cook some food inside the two pans:

  • At 1pm I shove FROZEN food in the tube when the tube's temperature was 40C / 104F
  • Because the food was frozen, by 2pm the temperature in the cooking tube was only 57C / 134.6F
  • Another hour later: 73.5C / 164.3F
  • At 4.30pm 92.3C / 198.1F
  • At 5pm (thus after 4 hours!) 93.7C / 200.7F - either there was a cloud in the meantime or I forgot to adjust the lounger for the movement of the sun?
  • FINALLY at 6pm (after 5 hours!) the cooker temperature reached a meager 100C / 212F.

The temperature very slowly rose a bit further, but I stopped cooking at 7pm (after SIX HOURS). The food was cooked, but the fries weren't crisp by any means. That wasn't too exciting! :roll:

 

Step 7: The next day the blacksmith had welded close the stand bases that you saw in photo 5, to give them an Apple-style finnish. As you can easily confirm, this welder indeed does "artistic" quality work. :grin:

 

Step 8: I decided to use rivets to connect the bases with the baseplate to become a strong stand for the solar cooker.

 

Step 9: Before I gently pushed the glass tube in its stand, I cushioned the nub that connects the outer and inner glas tube, because this nub is the most fragile part!

I also put some scrap cork cushioning around the tube where it meets the two metal bases of the stand.

 

Step 10: The finished stand with cooking tube: I immediately loved the looks!

 

Step 11: I got some scrap inox strips bent into two smoothly fitting rings, lubricated the inner rings outer side, and riveted two brackets each on the outer rings. For reference, the photo shows the right one finished, and the left one in work.

I figured that this ring arrangement is a quick, cheap solution to fix a reflector to the solar cooker. At some point I hope to find (or make) ball bearings for smoother operation though!

 

Step 12: I riveted scrap metal strips to a shiny inox sheet to be used as reflector, and their other ends I screwed to the rings' brackets such that the reflector is connected to the tube via the rings. Here I screwed because this connection needs to be done when the rings already are tightly around the tube, and you really don't want to rivet near a glass tube! :shock:

Note that by now the DIY solar cooker is so precious that a German Shepherd Dog must guard it during the cooking process. :mrgreen:

Indeed: No one dared to come close. Although that may have been because no one was around - which is why Miguel looks so bored.

 

Step 13: Here you see the finished DIY solar cooker, complete with the most simple sun dial to gauge the ideal orientation of the cooker towards the sun, and with a cheap Chinese meat thermometer pierced through the silicone lid that comes with the glass tube.

Not to worry: The piercing is so tight that nothing leaks out. I must commend the vendor again, he has chosen exactly the right dimensions and weight for the silicone stopper:

  • no pressure buildup inside the tube
  • yet hardly any heat/steam escapes from the cooking process.

In fact, the stopper sits just loose enough that it would fall out if you were to place this glass tube horizontally: Indeed, when during preheating the cooker I forget the tray that arrests the long meat thermometer underneath the tray, the stopper has nothing to hold onto and promptly falls out. I feel this is good: It reminds to use a tray.

Be aware that for now my reflector is not exactly in the shape of a parabola. I might bend and attach it more accurately when I get to fit proper ball bearings to the tube for smoother rotation of the reflector.

Hands-on experience with this DIY solar cooker

While I am happy to finally be able to cook some meals again(!), I am not satisfied with:

  1. the maximum temperature that this cooker achieves: The highest I recorded before stopping the cooking process was just 115C / 239F. Not a temperature you can make anything crisp with, for example!
  2. the cooking speed of this cooker: It hardly ever reaches even only water boiling point (100C / 212F) before THREE HOURS have passed. And that is in the summer now!

Not sure yet why. I have to find out.

I will not test-use the tube without the alu insert though: I won't be able to get another one here if this tube breaks. Also Mark mentioned that his highest temperature was 250F too, although he does not use an alu insert.

And I can't imagine the alu insert to be the reason: As long as it touches the glass everywhere, there should be zero impact on temperature because aluminum conducts heat about 200 times better than glass. In fact, over a year ago I had suggested to one Chinese manufacturer to make the inner chamber in alu, and while at that time they replied "technically not possible" I see that meanwhile a selected few Chinese vendors offer just that.

Could it be because I shoved FROZEN food in the tube? No: I have meanwhile tested it with room-warm veggies as well. I never got the tube hotter than about 115C / 239F with any food inside. Admittedly, I won't leave the cooker out forever: Once food is cooked, it doesn't get any better from being cooked longer. :roll:

Could it be the reflector? Phew. Can any kind of reflector be that bad at all? I don't think so.

Now, why did I above bold the words preheating the cooker?

Because that's another noteworthy experience: I realized that intense preheating does speed up the cooking process. I see that the vendor of the GoSun stove and the GoSun sport does not recommend intense preheating as "that might cause thermal shock when you add the food or liquid". Well, that's why I have the alu insert, tray, and pans: I cannot thermally shock my tube. :grin:

Now off we go to cook the dog some good meals. :mrgreen:

SUN cooked pork chunks, fries, spinach, broccoli, cauliflower, carrot, green beans, celery
SUN cooked pork chunks, fries, spinach, broccoli, cauliflower, carrot, green beans, celery

 

SUN cooked pork chunks, broccoli, cauliflower, carrot, green beans, celery
SUN cooked pork chunks, broccoli, cauliflower, carrot, green beans, celery

 

SUN cooked pork chunks, green beans, leek, cauliflower, carrot
SUN cooked pork chunks, green beans, leek,
cauliflower, carrot
SUN cooked pork chunks, fries, broccoli, cauliflower, carrot, green beans, celery
SUN cooked pork chunks, fries, broccoli, cauliflower,
carrot, green beans, celery

 

SUN cooked fries, spinach, cauliflower, carrot, cheese
SUN cooked fries, spinach, cauliflower, carrot, cheese
SUN cooked pork chunks, fries, cheese, carrot, cauliflower
SUN cooked pork chunks, fries, cheese, carrot, cauliflower

Why always pork chunks at this time?

It's cheapest here. :roll:

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  1.  

    Tim, your new outdoor oven looks so cool. You did a great job designing it and the sheet metal guy/blacksmith did a good job fabricating it; I love the rotation flanges. Those pork chunks and vegetables look so much better then the cold cans. I bet Miguel is having a good time eating that. Have you tried to cook rice or pasta in it yet??

    Anyway, thanks for the educational/scientific blog, in addition, to all the dog info on this site.

    •  

      Thanks Mark. I gonna try steaming rice in it from this weekend: the local takeaway where I used to get the rice cooked for cheap closed for holiday, relentless. :roll:
      Have YOU done rice or pasta??

      Was I correct above describing your own experience? Any suggestions how to get past the 230F mark?? What's the reason, you think? ;-)

  2.  

    Well, I was wondering about that myself. As you and I "spoke" before, the reflectors need to try to aim the sun back into tube. I cant tell from the pics, if you can adjust the angle of the reflectors. It looks like those rods are fixed. My next question would be is how accurate is the thermometer; did you use one that measures the air, or did you measure the meat?? I have a probe for my smoker grill that measures the air in the smoker. When I told you mine got to 250°F, i was guessing based on the temp of the meat I was cooking; i have yet to measure it accurately. The irony is that this summer here in the southern US has been very cool and wet. We have had more days with clouds and rain than with sun and temps in the 90's or above. That being said, your oven should get hotter than my lone tube does, all things being equal. I will try to get some temps and see what it does, provided the sun comes out. This weekend is supposed to be in teh upper 70's and low 80's, with a chance of rain.

    •  

      I trust you are at least spared the horrendous downpours your neighboring states get?
      I always wonder, had we had weather records a 100 years ago, would they be similar?? Ie did the weather overall get much worse?
      You may know, in your job ;-)

      "how accurate is the thermometer; did you use one that measures the air, or did you measure the meat??" phew, I'd say I measure the air inside the tube: this thermometer is a long metal stick basically (like chefs stick in meat). It nicely arrests the stopper when it hits the tray from below. :-)
      But I do compare like with like: All oven temperatures measure the air inside. I only called it "meat" thermometer because that is its name on the sales page I thought, and it CAN be used for that.

      No, the reflectors ARE movable of course. I describe that in the text. I adjust them all the time... desperate for higher temps.
      I read the GoSun folks claim their grill can reach 700F!!! What's the magic?

  3.  

    Yeah, the rain we are getting now is the remnants of the hurricane that hit Texas over the weekend. There are some records from 100 years ago. It was in 1900 that a hurricane in Galveston Texas killed between 6,000 and 12,000 people. I guess, the weather hasn't changed that much but our buildings have.

    Ok, on the rods; I guess i missed that detail. As far as the air temp and the thermometers, if it is made for that, then good.

    Now, looking at GoSuns web page, they have the max temp at 550°F for the sport and 450°F for the grill with working termps of 200-450 for both. They do not say that those are the air temps or the surface of the inside of the glass. The reason I say that, is that a popular steak restaurant here in the US advertises that they cook their steaks on their broiler machine at 1500 or so degrees F, however, when you look that up, the 1500 is actually the temp of the broiler head and that goes down quickly as yoy get further away from the broiler flame. So, maybe the 550 they advertise is at the glass surface and not the air in the tube.

    Just my opinion. You can only do so much to the solar. it is fixed by GOD. So, then, what else can be done to increase the efficiency and that is the parabola shaped reflector (and you have that)?? Maybe for their sales sheet, they created the perfect environment not is not easily duplicated.

    Just my opinion.

    •  

      Ah okay. I got the 700F figure here: "Technology: Where do our temperature ratings come from?
      We have thoroughly tested the GoSun in all kinds of environments and conditions. We typically travel with an infrared temp. sensor and keep notes with a time stamp. If it is not humid, the sun at high-noon in the summer is about as hot as it gets, it doesn't matter where you are (below 40° N Lat). We've recorded temperature slightly above 700°F with an empty tube!"

      My highest when empty was 121C / 250F. But who cooks "empty"? :roll: "Miguel/Max, today for dinner you'll get empty. mmm yummy yummy!" LOL

      I know from when I had an oven that 250C! / 482F was the limit, and 220C was the minimum when it was pizza day.
      In the GoSun manual they write: "Max Temp: 450°F (232°C) / Working Temp: 250°F (121°C) – 425°F (218°C)"
      So that would be barely enough then.

      Strange, in videos people make fire that way, so I thought temps are much higher... :cry:

      •  

        Ok, you can get an infrared thermometer pretty cheap these days. Still, you're right, our oven had settings to 550; I can't imagine 700. That is HOT. I think the 500 is about right, but if you can get 400-450, that's still good. If you think about it, when baking meat, I never go more than 350 so you don't over cook it and make it tough.

      •  

        "I never go more than 350"
        I wish mine reached 350F :roll:

        But, at least IT COOKS! :grin:

  4.  

    Well I was thinking about something you said yesterday about cooking it empty. The metal pans, will absorb some of that heat, so maybe in time and some practice and tweaking, you may be able to get your 350 or so. Also remember, I don't have any pans. I put the median by itself wrapped in foil.

    •  

      That's it then! You are right, 2 thin pans, one thick tray, and the alu insert, ALL "absorb some of that heat" that the sun produces inside the tube. Indeed, all these parts can burn my fingers! :grin:
      Thanks so much for pointing that out! I didn't right away think of that. :-)

      Plus, a "solar expert" from UK mentioned "the larger the tube, the slower it will heat up" (and I believe he also wrote) the lower the ultimate temp.
      Is both correct, you as engineer? :mrgreen:

      Either way, I understand now that I will never get my cooker as hot as you get yours without those things. Odd is only that the GoSun stove/grill has way more "extra" material inside than mine (visible from the manual). And still, they reach "Max Temp: 450°F (232°C) / Working Temp: 250°F (121°C) – 425°F (218°C)", ie their LOWEST "working temp" is HIGHER than my max temp!?!? :roll:

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