"Sun Scoop" tracking solar cooker is working! Almost 1.5 sq meter parabolic solar cooker.

This is a tracking solar cooker with a square dish just under 4 ft by 4 ft. It is made of 8 curved strips cut out of a 1/8 inch thick  4 by 8 sheet of ABS plastic.   When the strips are taped together they form a parabolic curve.   Why use strips? Well, the sticky material for making it reflective is "flat" (can only be curved in one direction or plane) but real parabolic dishes  are curved in 2 directions or planes,   so it is easy to stick them to the strips but not so easy to stick them to a real parabolic dish! You will end up making a lot of extra cuts if you use a true parabolic dish!   It isn't a perfect parabola and  it focuses to a ball of light that is about 6 inches wide.  (good enough for solar cooking).     The reason it is only part of a parabola is so the cooking pot can be independent of the dish.  This allows for easy access,  It's on "equatorial mount so  tracking of the sun is time based,  it goes at 15 degrees per hour and I reset it back to the morning position every evening.   I made a wood frame for it.  An aluminum frame would be perfect, lighter, more compact and more accurate  but I cannot weld anymore due to a medical condition, so wood it is for my proof of concept!
I bought rolls of special aluminum reflective tape from China to cover it and make it reflective. If you can't see your reflection in a material for a parabolic reflector, don't use it, because it has poor directional reflectivity.   Also, most "mylar" lets a lot of light through,  (some is even used on windows  to let you see out but others can't see in).   So, my advice is to get the Chinese rolls because they have thousands of parabolic solar cookers there that have to be resurfaced every year or 2,  so they probably know what they are doing.   So anyway, it works,  it's potentially 4 times as productive as last years attempt and I am happy with it so far, even though the weather has not co-operated.   The solar power is all focused on the bottom of a big pot (I use a 14 liter pot and another pot that is a bit smaller).    The next stage is to make a box cooker for it,  its going to be about 15 inches wide high and deep, and its going to have a tube with a lid on it at the front to soak up the heat from the parabolic.  The inside of the box will be made from  aluminum for flashing or roofing.   never made a box cooker before, so hopefully I can do it.   When I fried, I measured up to 230 centigrade on the bottom of the pot, so it can get plenty hot.  If I can get that in the box, then almost any type of oven cooking is possible. I attached some pictures but don't know how they will be displayed.    

This is great Brian! Well done and thanks for sharing. I've actually got one of those rare (for me) periods where a solar cooker might actually be worth while.....
Can you share more of how your tracking system works? I didn't catch how the water flow is made to change with the sun direction, and quite how that moves the dish.

Nancy Reading wrote:This is great Brian! Well done and thanks for sharing. I've actually got one of those rare (for me) periods where a solar cooker might actually be worth while.....
Can you share more of how your tracking system works? I didn't catch how the water flow is made to change with the sun direction, and quite how that moves the dish.

Oh, hi, Nancy and thank you. My tracking system is a bit strange. It relies on low pressure air gradually increasing.  A Chinese student has offered to help me do the photovoltaic thing to do it by motor.  But, I might see if I can convince him to have the photovoltaics  open and close an air valve instead, then it can turn on and off my waterwheel to move the solar cooker. (I just like the waterwheel because it is so low tech).  I checked the temperature below the cooking pot.  

Thanks for sharing Brian.     I have been attracted to long focal length for the cookers....      

I liked the one in this video ->

Nancy Reading wrote:This is great Brian! Well done and thanks for sharing. I've actually got one of those rare (for me) periods where a solar cooker might actually be worth while.....
Can you share more of how your tracking system works? I didn't catch how the water flow is made to change with the sun direction, and quite how that moves the dish.

Hi, Nancy,  I made the waterwheel winch,  using an old fan as the bearing,  a piece of waste plywood for the wheel,  and 36 plastic cups from the dollar store as the "buckets".   It works like a motor,  you turn it on by turning on the airlift pump,  and it drives the solar cooker forward slowly.     And because some of the buckets have water in them,  the waterwheel winch resists going backwards and acts like a brake if a gust of wind  hits the solar cooker.  (You don't realize any of this until you experiment with the thing).  The video is from last year when the waterwheel winch was running my old solar cooker reflector.  The new solar cooker seems to be more wind resistant even though it is bigger.  

My soil is a heavy clay with not much organic material in it (apart from weed seeds) so, when I was sterilizing it, I usually added lawn mower clippings at the bottom (to leave a space for water to pool) and the turn into plant food later . What actually happened was the water still soaked into the soil, and when the solar cooking got started, the clippings and soil started to burn at the bottom of the pot.  I wasn't planning to make biochar,  so I decided that this was bad.   The main aim is to kill off weed seeds, (I hate weeding!)  so seeds can grow without competition. No need to burn anything.  The answer that I came up with was a little water chamber at the bottom of the cooking pot.   The water boils, it steams the soil,  the soil doesn't get muddy wet, and 80 or 90 Centigrade is achieved all through the soil in the pot.   So far it seems to be working very well.  

Today,  I have been steaming weeds to grow mushrooms in.   I don't know if it will work but it is worth a try.  It takes about 2 hours to steam up a batch.  I pick them,  then run the lawnmower over the weeds a few times and pack them into the 14 liter pot over the water chamber in the pot. On top I put a shovel of soil (because when I started doing it, the weeds at the very top were not getting so well steamed).  The soil seems to trap the steam better.  I guess I could just buy a steamer but that is a lot more expensive that a free pot.  Thermometer in the middle at the top is my guide.  If it is over 98 C, that is steamed enough for me.   I don't know how much energy the solar cooker is transferring to the pot,  but at least as it heats up, it is probably over 500 Watts.  I did a boil test (heating 10 liters of water) prior to setting the pot exactly at the focal area, and that was when I noticed that significant light was missing the pot!  The very best heat up from that test was  just under 600 Watts when the water heated up from 27C to 33 C in 7 minutes.  Then as the pot heated up,  the water and the pot started radiating heat, faster and faster so even though it was probably still 600 watts, the actual amount transferred to the water got lower and lower.  I have mushroom spawn in the soil in the greenhouse and I am also putting some spawn in cooked weeds in an old aquarium and in a half plastic barrel.   I will put pallet wood on the top with little gaps, then turn it on its side and hopefully the mushrooms can fruit between the gaps.  I might do something like that with the aquarium too. (Turn it on its side and let the mushrooms grow out the side).   I will much more heavily inoculate the cooked weeds in the half barrel and in the aquarium. Hopefully that will prevent undesirable fungi from establishing themselves.    But I'm a bit scared that the glass might break in the aquarium if the glass is on its side.   Today I did 4 batches of weeds and it is nearly enough to fill the half barrel (along with some of what I cooked up yesterday).   Tomorrow,  hopefully, it will be another nice day and I will get enough weeds steamed to fill the half barrel.   Anyway, here is a video from yesterday of where I dug mushroom spawn under steamed soil.

This video may be of interest...