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Stewart



Joined: 10 Jul 2007
Posts: 10
Location: London

PostPosted: Wed Jul 25, 2007 8:42 am    Post subject: First Post Reply with quote

Great to find this forum. I'm an architect with a long term interest in energy conservation.

I've been trying to perfect a decent UK box solar cooker for a few years now, here in north east London. However the temperate maritime weather is usually the problem.

My first attempts were laughable, porous boxes with plastic covers.......these usually got soaked and trashed, but could get to about 60-70C but not keep the temp. in the cloudy times. I thought I had it sussed with double cardboard design insulated with warmcel newspaper insulation, and a double glazed unit. Got it to 80 once and baked a potato, but when left to slow cook it invariably rains at some point, the achilles heel of cardboard box cookers in this climate...........i'll post some pics of the remains sometime!.

I've now got two boxes on the go, London is good to harvest good free materials from. One i'm concentrating on at the mo. is a plastic box, with silver backed insulation batts forming the inner oven bit, and a aluminium thermally broken frame and double glazed unit.

Unfortunately since I've got this one cooking (get's to 60C even in overcast times) the weather has been the pits.

I'll keep you updated as time go's by.

Sorry about the longwinded first post
all the best

Stewart
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coconino



Joined: 21 Nov 2006
Posts: 77
Location: Sunny Brixton

PostPosted: Wed Jul 25, 2007 1:09 pm    Post subject: Reply with quote

Yes, London weather is completely rubbish this summer! It's incredibly frustrating to try and do anything with solar. I was at the Lambeth fair on Saturday in Brockwell Park, trying to demonstrate solar cooking, but it was obviously hopeless given the overcast and rain we had. Sunday was better weather but I was booked elsewhere.

On 7th July I did a demonstration at a school fair in Streatham and that was reasonably successful, actually managing to cook rice and bean stew. I even got a half page in the local newspaper.

Have a look at my posts around this forum, and the solar pics on my flickr page.

You might find, as I did, that a different design of cooker works better here.
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Stewart



Joined: 10 Jul 2007
Posts: 10
Location: London

PostPosted: Wed Jul 25, 2007 6:07 pm    Post subject: Solar cooking in adversity - UK Reply with quote

Thanks for the swift reply.

I've got a heavens flame collector ready to put on the high efficiency box..................but going on hol's next week, so its on hold till late august.

Its been my evolving conclusion so far that reflective foil and a sealed void between boxes is only good for near constant sunshine. This design doesnt have the mass to keep temps. up for long when the sun goes in.

Since the sun 'goes in' a lot around here, i've been superinsulating the boxes.

I've found that it can stay at above 60C 2 hours after no sun on a nice afternoon.

any body else used thermal insulation?

Stew
ps
Cant wait to try the heavens flame collector.
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SharonID



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

PostPosted: Wed Aug 08, 2007 4:59 am    Post subject: Re: Solar cooking in adversity - UK Reply with quote

Stewart wrote:
any body else used thermal insulation?


If you mean the silver-coated bubble stuff, I'm using it as the first layer of insulation for the outer box of the Easy Lid cooker I'm building for a friend. I'd be leery of using it in the inner box, because I don't think the plastic would take the heat well, but it should work fine as the outermost insulation layer, since there'll be some cardboard and airspace layers between that and the inner box, where it really gets hot.

Also, I think using a good grade of steel for your bottom tray can give you an edge on holding heat when the sun is playing it coy. I bought 18-guage steel for my wonderful Easy Lid oven (which I spray-painted flat black with the non-toxic-when-dry spray paint), and I really think it holds the heat better than the flimsier scrap metal I've used in another cooker. Another thing that will give you an edge (especially if you pre-heat) is putting some rocks or bricks in your oven if the food won't come close to filling it, so you've got more thermal mass when the sun goes behind a cloud. You really need to preheat those rocks though, because otherwise it will take the whole thing too long to get hot when the food goes in.

We are having more clouds and haze where I live this summer, too (though no more rain than usual, more's the pity), so I know how frustrating that can be! One cooker that is pretty much impervious to rain is the one you make out of a car windshield cover that is in the "Build a solar cooker" section of this website (or you could do a similar thing with the foil/bubble insulation material if the windshield covers are not available where you live). If you don't want to mess with sewing on velcro, use clamps. If you use a big truck windshield cover and plastic tub instead of car windshield cover and bucket, you can make a monster funnel that can heat/cook large amounts of water/food or heat small amounts much more quickly than a smaller funnel. If you find some arrangement of rigid glass or plastic items to 'greenhouse' the food instead of using oven bags, your food will hold heat somewhat better when the sun plays hide-and-seek for short periods or if it is windy. My monster windshield cooker does better-than-average in hazy conditions.

Hope that helps! Good luck!

Regards,
SharonID
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