Navitron Renewable Energy and Sustainability Forum

SOLAR THERMAL => Solar Cooking (using vacuum tubes or more conventional methods) => Topic started by: Paulh_Boats on December 07, 2009, 08:03:58 PM



Title: Indoor Solar Oven?
Post by: Paulh_Boats on December 07, 2009, 08:03:58 PM
The BBC program "Bang Goes the Theory"  (http://www.bbc.co.uk/iplayer/episode/b00p8469/Bang_Goes_the_Theory_03_12_2009/) managed to cook a chicken using 2 filament bulbs - to demonstrate how much energy was wasted.

They used a box of 6in thick polystyrene, foil lined with 2 bulbs inside. After 90 minutes the chicken was cooked and edible.

So I thought.......build such a box with a copper coil/heat sink inside. Pipe in solar hot water which can get to 93C in February and beyond boiling in Summer. With good insulation all you need to do is get the food hot, then balance heat loss.
The power available from a solar thermal panel is huge compared to 2 light bulbs, so the idea is quiet achievable.

Bacteria is killed at 66C, 82C in a chicken thigh is considered safe. Solar can easily achieve those temperatures.


My other idea is a very well insulated electric slow cooker - 150 Watts of PV might be enough.

Mad or what?  ;D

cheers
Paul


Title: Re: Indoor Solar Oven?
Post by: daftlad on December 07, 2009, 08:10:00 PM
Why are "normal" ovens so poor? Typically they are 2.2 kw, they take half an hour to warm up and they would take not far off 90 minutes to cook a chicken?
I wonder how hot the oven on Bang goes the theory got?
good luck Paul
ta ta


Title: Re: Indoor Solar Oven?
Post by: breezy on December 07, 2009, 08:29:22 PM

My other idea is a very well insulated electric slow cooker - 150 Watts of PV might be enough.

Mad or what?  ;D

cheers
Paul


I've just finished eating my dinner, a chicken chasseur (made with free range chicken), cooked in an ageing Russell Hobbs slow cooker - it uses 50W at max (old tech bimetallic thermostat in the base), so I think you could get away with a lot less than 150W of PV.


Title: Re: Indoor Solar Oven?
Post by: Paulh_Boats on December 07, 2009, 08:59:47 PM

My other idea is a very well insulated electric slow cooker - 150 Watts of PV might be enough.

Mad or what?  ;D

cheers
Paul


I've just finished eating my dinner, a chicken chasseur (made with free range chicken), cooked in an ageing Russell Hobbs slow cooker - it uses 50W at max (old tech bimetallic thermostat in the base), so I think you could get away with a lot less than 150W of PV.

I just measured our modern Breville slow cooker at 154W on Lo and 169W on Hi

I guess its all about "Insulation, insulation and insulation!"

-Paul


Title: Re: Indoor Solar Oven?
Post by: breezy on December 07, 2009, 09:21:07 PM
By co-incidence, I've been musing over a relevant idea over the last few days. I found a small Pyrex casserole dish (estimate 1.5 litres) with lid. I have a small mountain of PU foam offcuts and a couple of rolls of foil tape. I'd been considering making up a modern equivalent of the "hay box" cooker. The second iteration (of the idea) was a 12V slow cooker powered by 2/3 halogen spots controlled by a simple (PIC based??) circuit. I say 12V because the bulbs are cheap and easy to source, and, as we know, most of their output is given to heat, especially when under-driven (by a PWM circuit, maybe?).

I can't find my temp probe at the moment but my recollection is that slow cookers don't get much hotter than about 75 or 80 C

Have you measured yours?


Title: Re: Indoor Solar Oven?
Post by: Ivan on December 08, 2009, 02:20:26 AM
Paul,

You mean like this? I can't remember the temperature we reached - around 120C I think. The main problem was a big leak on the front door as the insulation was cut with a handsaw, and the front face wasn't particularly flat. With a bit of effort, this oven should be capable of reaching 180C.

(http://www.navitron.org.uk/forum/index.php?action=dlattach;topic=6912.0;attach=3116;image)


Title: Re: Indoor Solar Oven?
Post by: tony. on December 08, 2009, 06:56:47 AM
what about using a old microwave as a enclosure?
my local dump has a few!

tony