An uninvited guestWednesday, April 25, 2007
Monday, April 23, 2007
Deployable solar cooker
Ideas for a portable, deployable solar cooker
So, we have a working solar cooker (more about this on these posts), and we hope that with a couple of adjustments we will speedily boil water to our hearts content using free, renewable energy (sun permitting). Great!
I'm not quite happy with it though. It's a hefty thing, and doesn't exactly fold away for easy transportation. I'd like to improve the design to make a cooker that's far more portable, that's easy to deploy and adjust to the sun, and that (ideally) I can take to a music festival with my friends eD and Andy.
eD and Andy, however, are towing a tipi to this festival by bicycle. Yes; that means towing a tipi and a solar cooker by bicycle over roughly 5o miles of Somerset's gently sloping roads. You might say we can't do it. We can! You can read more about eD's debatable ideas here
For the deployable solar cooker, I'm thinking of using an umbrella, like so:
Click on the image to see a larger version; note the whistling kettle
I plan to reinforce two of the umbrella arms, such that the central strut (handle) and the two arms make a three point stand. The central strut can be used to orientate the cooker directly at the sun, by adjusting until there is no shadow falling from the strut onto the umbrella. We will also make an integral kettle stand.
The inside of the umbrella needs to be as smooth and reflective as possible. One idea is to adapt a survival blanket:
This happy chap can be found at OutdoorScotland.co.uk
Attaching the survival blanket to the inside of an umbrella such that it deploys with a smooth, sunlight-focusing finish is going to be somewhat of a challenge, so the thinking caps are still firmly in place. I'll probably write again when ideas develop....
This design is interactive - please feel free to either make it yourself or suggest design-changes for us to incorporate (using the 'comments'....)
So, we have a working solar cooker (more about this on these posts), and we hope that with a couple of adjustments we will speedily boil water to our hearts content using free, renewable energy (sun permitting). Great!
I'm not quite happy with it though. It's a hefty thing, and doesn't exactly fold away for easy transportation. I'd like to improve the design to make a cooker that's far more portable, that's easy to deploy and adjust to the sun, and that (ideally) I can take to a music festival with my friends eD and Andy.
eD and Andy, however, are towing a tipi to this festival by bicycle. Yes; that means towing a tipi and a solar cooker by bicycle over roughly 5o miles of Somerset's gently sloping roads. You might say we can't do it. We can! You can read more about eD's debatable ideas here
For the deployable solar cooker, I'm thinking of using an umbrella, like so:
Click on the image to see a larger version; note the whistling kettleI plan to reinforce two of the umbrella arms, such that the central strut (handle) and the two arms make a three point stand. The central strut can be used to orientate the cooker directly at the sun, by adjusting until there is no shadow falling from the strut onto the umbrella. We will also make an integral kettle stand.
The inside of the umbrella needs to be as smooth and reflective as possible. One idea is to adapt a survival blanket:
This happy chap can be found at OutdoorScotland.co.ukAttaching the survival blanket to the inside of an umbrella such that it deploys with a smooth, sunlight-focusing finish is going to be somewhat of a challenge, so the thinking caps are still firmly in place. I'll probably write again when ideas develop....
This design is interactive - please feel free to either make it yourself or suggest design-changes for us to incorporate (using the 'comments'....)
Sunday, April 22, 2007
Solar cooker build
Once again: Freecycle is brilliant. I put a 'wanted' post up yesterday morning for an old satellite dish, had three responses within a couple of hours, and by the middle of the afternoon we had one to start testing! (Thanks very much to Steve of Kingsway). Here's how we built it:
An old satellite dish, 90cm diameter
Using PVA glue to attach kitchen foil
Using garden canes to position the dish, and to hold the kettle in the focal point
As you can see in this video, it works pretty well! My estimate of twelve and a half minutes to boil half a litre of water was a little out - it took nearly an hour to not-quite-boil! (We did get a nice cuppa though). This is partly because the power available from the sun varies during the day, and 1000W/msq is a peak midday value for a summer day (so a little optimistic for April at 4pm), and partly because the kettle is a reflective aluminium at the moment.
We tried coating the bottom with a little soot from a candle flame, but what we really need to do is paint the bottom black, so that it absorbs more of the sun's focused irradiation. We will leave the sides and top aluminium, as black also radiates heat very effectively (and we don't want to lose the energy!). For more photos see here
Esteban
An old satellite dish, 90cm diameter
Using PVA glue to attach kitchen foil
Using garden canes to position the dish, and to hold the kettle in the focal point
As you can see in this video, it works pretty well! My estimate of twelve and a half minutes to boil half a litre of water was a little out - it took nearly an hour to not-quite-boil! (We did get a nice cuppa though). This is partly because the power available from the sun varies during the day, and 1000W/msq is a peak midday value for a summer day (so a little optimistic for April at 4pm), and partly because the kettle is a reflective aluminium at the moment.
We tried coating the bottom with a little soot from a candle flame, but what we really need to do is paint the bottom black, so that it absorbs more of the sun's focused irradiation. We will leave the sides and top aluminium, as black also radiates heat very effectively (and we don't want to lose the energy!). For more photos see here
Esteban
Solar cooker in action!
The solar cooker reflects and focuses the sun's energy onto a small area. We were moving a seed tray around in front of the cooker to find this focal point, and this is what happened....
Solar cooker size?
What size does our solar cooker need to be?
To answer that we need to work out the energy required to boil our water in a chosen time-period. Here's a section of a parabolic solar cooker, focusing solar energy onto a point, with diameter D:
Solar cooker schematic
Click on the small image below, and a larger version will open up that goes through the maths of sizing a solar cooker based on the diagram above (hold on to your hat, it gets quite exciting):
We find that on a sunny day, an 80cm diameter solar cooker will boil half a litre of water (two cuppa's worth) in about twelve and a half minutes. Tea-tastic!
To answer that we need to work out the energy required to boil our water in a chosen time-period. Here's a section of a parabolic solar cooker, focusing solar energy onto a point, with diameter D:
Solar cooker schematicClick on the small image below, and a larger version will open up that goes through the maths of sizing a solar cooker based on the diagram above (hold on to your hat, it gets quite exciting):
We find that on a sunny day, an 80cm diameter solar cooker will boil half a litre of water (two cuppa's worth) in about twelve and a half minutes. Tea-tastic!
Saturday, April 21, 2007
Solar cooking
Wouldn't it be great to be able to make a cup of tea out on the allotment (or anywhere else for that matter), using renewable energy? YES! So, we're having a look into a couple of different solar cooker designs to make this possible.
Solar cookers and ovens use the radiative heat of the sun to cook your food or boil your water. Solar cookers are used much like the hob of a typical kitchen cooker, and designs are often parabolic in shape (the reason for this is explained beautifully here and on this interactive diagram). Solar ovens are sealed, insulated boxes that are perfect for slow-cooking.
The advantages to (all) solar cookers are:
The DATS cooker design is perhaps easier to make, at the expense of a less efficient design in terms of solar concentration (it will therefore cook more slowly). The parabolic design will cook more effectively, but it is more difficult to produce. The parabolic shape could be achieved by the use of a discarded satellite dish, which has the advantage of strength, ease-of-manufacture, and a close-to-ideal parabola with concentration-spot already identified (the antenna).
We will update when we've made some progress from this decision-making point!
Esteban
N.B. When making a solar cooker you should NEVER STARE DIRECTLY into the cooker once the reflecting material is installed (keep it safe kids).
Solar cookers and ovens use the radiative heat of the sun to cook your food or boil your water. Solar cookers are used much like the hob of a typical kitchen cooker, and designs are often parabolic in shape (the reason for this is explained beautifully here and on this interactive diagram). Solar ovens are sealed, insulated boxes that are perfect for slow-cooking.
The advantages to (all) solar cookers are:
- You can cook in remote locations, without the need for fuel
- They use clean, free, renewable energy
- You can't cook at night! (Not a problem of course for allotment application, as I won't be kicking about up there at night)
The DATS cooker design is perhaps easier to make, at the expense of a less efficient design in terms of solar concentration (it will therefore cook more slowly). The parabolic design will cook more effectively, but it is more difficult to produce. The parabolic shape could be achieved by the use of a discarded satellite dish, which has the advantage of strength, ease-of-manufacture, and a close-to-ideal parabola with concentration-spot already identified (the antenna).
We will update when we've made some progress from this decision-making point!
Esteban
N.B. When making a solar cooker you should NEVER STARE DIRECTLY into the cooker once the reflecting material is installed (keep it safe kids).
Friday, April 20, 2007
Bath event: environmental question time for local elections
Thur 26 Apr - Green Question Time
In advance of the local elections on May 3rd, this will be an opportunity to hear representatives from the four main parties outline their their local environmental policies and take questions from the audience. If you would like to put a question to the panel, please email it in advance to peter@eco-logicbook.com. Organised by Bath FoE, Bath Greenpeace, and Bath Organic Group. 7.00 for 7.30pm at the BRLSI, 16 Queen Square, Bath.
In advance of the local elections on May 3rd, this will be an opportunity to hear representatives from the four main parties outline their their local environmental policies and take questions from the audience. If you would like to put a question to the panel, please email it in advance to peter@eco-logicbook.com. Organised by Bath FoE, Bath Greenpeace, and Bath Organic Group. 7.00 for 7.30pm at the BRLSI, 16 Queen Square, Bath.
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