Solar Cooking Archive Discussion Forums

terrysunderland · Joined: 22 Jan 2007 Posts: 5 Location: North East England

Greetings! I live in North-East England, not the best part of the world to experiment with Solar Ovens! (It is snowing as I write). Anyway, I have had the germ of an idea. I wondered if pressure cooking would speed things up?
What I have in mind is the cheap, lightweight plastic type designed for microwave ovens, such as:
http://www.tvproducts4less.com/04-hwmmpc-12.html

I don't know if the pressure cooker would be placed inside the black pot, or painted black and used independently. Anyway, would some kind person, blessed with wall to wall sunshine, like to do the experiment? I would love to know if my idea has merit!
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Cheers and Beers,
Terry in Sunderland, North East England.
Boroudah village, Bangladesh.

http://www.thewearsurmaclinic.com/

Bill Bradley · Joined: 26 Nov 2006 Posts: 21 Location: Springfield MA USA

Pressure cookers definately can be used with solar cookers. I have an old metal pressure cooker that I have been intending to test with solar cookers but haven't done it yet. I suspect that metal would work better than plastic because metal is a much better conductor of heat than plastic which is somewhat of a natural insulator. In the microwave oven, the energy enters the pot as microwave radiation and heat energy does not have to be concucted through the walls of the pressure cooker. The outside surface of the plastic would get much hotter than the inside of the plastic cooker. Even metal cookers may have plastic or wood handles that will not stand the heat

It would take a relatively powerful solar cooker to get the pressure cooker hot enough to pressurize it in a reasonably short length of time. Some of the less powerful cookers might not ever get the pressure cooker up to pressure. I don't know what pressure is used in pressure cookers, but according to steam tables, the contents would be about 227 degrees F at 5 pounds per sq in above ambient, and 239 degrees F at 10 pounds per sq in above ambient.

How you use the pressure cooker might depend upon the type of cooker you have. However, in most cases I would suggest painting the pressure cooker black and putting it directly in the cooker.
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Bill Bradley, EarthboundTech

terrysunderland · Joined: 22 Jan 2007 Posts: 5 Location: North East England

Hello, thanks for the interest.

I did have plastic pressure cookers in mind as possibly cheaper and more portable (lighter) for use in more remote locations such as Bangladesh, where I will be shortly.

Nice to know that somebody else has the same idea. Let us know how you progress!
_________________
Cheers and Beers,
Terry in Sunderland, North East England.
Boroudah village, Bangladesh.

http://www.thewearsurmaclinic.com/

alexkee · Joined: 12 Nov 2006 Posts: 3 Location: Malaysia

Back to first principles.

What's the workings of a pressure cooker?

Pressure to raise the temperature of boiling water above the atmospheric pressure where the pressure cooker is deployed.

This presupposes that you have access to a heat source that can raise the temperature of the liquid in the pressure cooker to a temperature that would otherwise be turned into latent heat from the change of state from liquid to gas (water to steam).

In a box or panel oven, it is unlikely that you would have enough surface area to capture enough solar energy in net balance against the lost to of captured solar heat to the ambient.

For a parabolic concentrator solar cooker with a sufficient collector-reflector surface area and good direct sunlight, it is more probable that there is enough harvested solar energy to fuel the pressure cooker to a higher than usual boiling point than using a usual utentsil.

Given the above, the deployment of a pressure cooker in circumstances where the solar fuel source is not sufficient to raise it to pressurized boiling point, the justification would be one of conservation and avoidance of the lost of heat to the ambient. Where the solar fuel source is strong, pressure cooking will help speed up cooking as it is with conventional fuel cooking paradigm.

Nothwithstandingly, the deployment of a dark outer surface pressure cooker even in conditions where solar energy may not be strong will always enhance performance, but always mitigated by the additional capital cost input vis-a-vis where just ordinary utensils where deployed.

Therefore where cost-benefit or price-performance comparison values are contextualized in the evaluation, pressure cookers in solar cooking scenarios may be indifferent to or inferior to usual cooking utensils.
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The Sun, Humanity's Ultimate Equalizer

Irenes · Joined: 02 Jun 2009 Posts: 2

I am quite new to solar cooking, but I could not imagine a plastic pressure cooker doing the trick. Are they not meant for microwave use only? Seems to me that the plastic would melt or deform considerably if exposed to such heat. Microwaves work differently and have very little affect on the temperature of most plastics. Correct me if I am wrong.

I recently conducted an interview on sous vide cooking - a relatively new cooking technique. The interview can be accessed from the right Featured Articles panel on Recipes Cookbook
- the cooking technique has similarities to pressure cooking, as food is cooked in a vacuum sealed bag. Do you think such a technique would work with a solar cooker? It would be interesting to combine the two.

SharonID · Joined: 24 Jun 2007 Posts: 74 Location: northern Idaho

In case anyone is still interested in this topic, if I wanted to try pressure cooking and could afford it, I would try it with one of the lightweight black ones designed for camp use, such as the one here: http://www.campmor.com/outdoor/gear/Product___82051

I don't know anything about plastic pressure cookers, but I don't think they'd work well for solar, since plastic is not a particularly good heat conductor. I'm sure if I had one I could get one of the light black metal ones to work though, in any one of a number of my panel cookers, especially with a rigid 'greenhouse'. All you need is to get the water to boil—the special lid and valves, etc., take care of the rest. Once there is steam, pressure will build, and I know I can make steam. Smile

Regards,
SharonID
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Idaho Regional Representative, International Women's Writing Guild
Visit the Guild at: http://www.iwwg.org/

micsolaire · Posted: Sat Oct 03, 2009 9:35 pm Post subject:

Solar cooking with a pressure cooker is possible.

As you can see, I close vapor exit.

Temperature in my oven cannot exceed 150�C, so there is no danger to close the vapor exit.

http://micsolaire.aliceblogs.fr/blog/_archives/2008/5/21/3703663.html

SharonID · Joined: 24 Jun 2007 Posts: 74 Location: northern Idaho

micsolaire · Posted: Sun Oct 04, 2009 9:29 am Post subject:

Don't worry, there is a security valve which opens when the inner pressure exceeds 2 bars.
In my oven temperature never exceeds 150�C and according to "loi de Mariotte" for the gas,

P x V = constant for the temperature and pressure of the test.

p is the pressure of the system.
V is the volume of the gas.

A balance will be established and steam will be contained since temperature is constant (150�C).

With this process, there is no more mist in the oven or on the glass during cooking.

gaiatechnician · Joined: 06 Jan 2008 Posts: 32 Location: Victoria BC

I do not think a 150 C reading means a whole lot. I think the sunlight beating down on the theremometer causes a lot of "Phantom" degrees to show. And even if the 150 C reading is a correct temperature, it is way too hot to be cooking food. autoclave temp is 121C or so. You need that temperature at the bottom of your pressure cooker to get enough pressure. Having 150 at the top does not mean you have pressure inside.
If you buy a probe and stick it into food, you will find a much lower temperature than is shown on the oven thermometer. Typically less than 100C.
Brian

micsolaire · Posted: Mon Oct 05, 2009 8:55 am Post subject:

gaiatechnician · Joined: 06 Jan 2008 Posts: 32 Location: Victoria BC

Yeah, but! you might be putting yourself in great danger if the pressure cooker explodes!
Why not just put the weight on the cooker and leave it at 15 pounds pressure? That should stop the steam until 120C inside the pressure cooker anyway. With a pressure cooker, you only get a lot of steam released when you turn up the heat, so amount of heat in is important. A solar cooker is only putting 300 or 400 watts in so there should be very little steam.
Have you tried that, just the weight on top?

micsolaire · Posted: Wed Oct 07, 2009 3:03 pm Post subject:

Brian,

gaiatechnician · Joined: 06 Jan 2008 Posts: 32 Location: Victoria BC

I am glad it works, hopefully it works in the oven too. (My pressure cooker loses a tiny bit of steam round the rubber seal.)
I admire your inventiveness.
Well done.